Laser

Physical Benefits

jhalper — Sun, 13 Oct 2013 03:47:35 +0000

Physical Benefits

Of the four new articles online on our website, three happen, purely by accident, to be on physics research. The three are very different, and yet each is an illustration of the ways that basic physics research changes our world – in small and large, practical and enlightening ways. And each is situated at a different intersection between the technological and the theoretical – a technological breakthrough that resulted from a successful attempt to provide proof for a theoretical construct, new inventions based on elementary physical principles of light, and a theory substantiated through a large array of advanced particle detectors.

Take the work of Dr. Shahal Ilani. Ilani and his research team created something that had been predicted back in 1934 by Eugene Wigner: an electron crystal. In an electron, or Wigner crystal, individual electrons are held in a fixed configuration by mutual repulsion. Clearly, there are no practical uses, yet, for electron crystals (Ilani’s first, proof-of-concept, crystal consisted of two electrons). One creates them for their own sake – to prove the prediction, and thus a fundamental precept of quantum physics.

The challenge was to produce a system so inert that the electrons would only interact with one another; not with any other part of the system. And that has led to a very practical invention. Ilani and his team managed to create their original tiny electron crystals in ultrapure carbon nanotubes. But scaling up the nanotubes to make larger electron crystals was problematic: Adding length increased the probability that electron-attracting defects would be introduced. So Ilani and his team developed a whole new method for producing flawless carbon nanotubes; these are likely to have a number of immediate applications.

A system for creating ultrapure nanotubes. Image: Dr. Shahal Ilani

Dr. Dan Oron’s research, in contrast, is eminently practical: He, too, builds nanocrystals, but these are tiny rod-shaped crystals about 50 nanometers long that can absorb two low-energy photons and emit a high-energy one in their place. This neat trick may enable the design of solar collectors that could make use of a much broader range of the light spectrum.

Oron’s research has also led him into biological imaging: A microscopy method he developed uses femtosecond (a millionth of a billionth of a second) laser pulses that start out long and shorten as they penetrate living tissue. He and his colleagues then used these pulses to image excited neurons within mouse brains.

But if you look closely at Oron’s work, the advanced technology also illuminates some basic light physics. For example, the nanorods make use of the dual nature of light. They absorb light as individual photons, but are tuned to the wavelength of the light: The radius of each rod is set to a particular wavelength (color). The microscopy, as well, depends, among other things, on a precise understanding of the way that light scatters from a surface.

Nanocrystals seen under an electron microscope. Image: Dr. Dan Oron

The third article concerns a phenomenon that has no foreseeable practical application: high-energy neutrinos that come from the far reaches of space, passing straight through the earth on their way. Prof. Eli Waxman is a theoretical physicist who, together with the late Prof. John Bahcall, had developed a theory proposing that such cosmic neutrinos originate near certain young black holes, as well as suggesting an upper limit to the number of particles that could be detected. That number is very small because, even though billions of them are passing through at any one instant, only rarely do they interact with matter. Though it did not take 80 years (as it did with the Wigner crystal) for technology to catch up to the theory, several decades did intervene between the original idea and the detection of neutrinos that appear to support Waxman and Bahcall’s model.

That technology is quite impressive – not least in size and scope. This is the IceCube experiment, based on some 5,000 detectors buried in a several-kilometer cubic array under the Antarctic ice. It takes an array that large (and isolated from other sources of radiation) to detect a mere handful of neutrinos.

Because these neutrinos have traveled straight from their source to the earth, they carry information about how they were produced – a sort of telescope that can peek into the insides of stars. They can thus give us clues as to the very workings of the universe – in other words, basic physics at its finest.

IceCube detector array

jhalper Sat, 10/12/2013 - 23:47

Why observatories shoot lasers at the Universe

esiegel — Wed, 24 Jul 2013 15:38:43 +0000

Why observatories shoot lasers at the Universe

"But certainly the laser proved to be what I realized it was going to be. At that moment in my life I was too ignorant in business law to be able to do it right, and if I did it over again probably the same damn thing would happen." -Gordon Gould, inventor of the laser

You're used to the iconic image of an observatory's dome surrounded by a dark sky. From within, a telescope peers up at the heavens. And with a huge amount of light-gathering power that dwarfs a fully dilated human eye, we can use this tremendous tool to peek into the dark depths of the Universe.

Image credit: Fort Lewis College Observatory, via http://www.fortlewis.edu/.

Size is a big deal in astronomy: if you double the diameter of your telescope, you quadruple your light gathering power. Still, size isn't everything. Nearly a century ago, Edwin Hubble was using the famed 100-inch Hooker telescope on Mt. Wilson. Along with the latest in photographic techniques, he was taking images like this one, in which he discovered that Andromeda -- the galaxy in the picture -- lay far beyond our Milky Way. That was back in 1923.

Image credit: Carnegie Observatories, via http://obs.carnegiescience.edu/.

But size isn't everything. Nearly a century later, the largest optical telescopes are only about four times the diameter of the telescope Hubble was using a century ago, and there are only a handful that large. Even the Hubble Space Telescope -- the greatest telescope of our generation -- is smaller than that 100-inch relic! Yet, when the Hubble telescope takes a look at a galaxy nearly 100 times as distant as Andromeda, it can make it out in far greater detail than Edwin Hubble could ever see looking at any galaxy, and in fact was able to resolve individual stars in there.

Image credit: Jeffrey Newman (Univ. of California at Berkeley) and NASA/ESA.

That's because of two reasons: first off, there have been huge advances in optical systems. Photographic plates have been replaced with charge-coupled devices (CCDs), analog equipment has been replaced by digital, and photons can be counted one-at-a-time. In short, a hobbyist today -- for just a few thousand dollars -- can do better science than the most advanced professionals could -- with equipment ten times the size -- a century ago. But the second reason the Hubble Space Telescope is so fantastic is its location: it's in space!

Image credit: NASA / International Space Station.

For astronomy, this is a huge, huge advantage. Here on Earth, the simplest way to tell a planet from a star in the night sky is to look at it for a while, and watch and see whether it twinkles or not. If it doesn't twinkle, it's probably a planet; only stars twinkle in the night sky.

Image credit: retrieved from Astro Bob of http://astrobob.areavoices.com/.

The first humans to see a star (other than the Sun) not twinkle in the sky were the first humans to travel to outer space: from the vantage point of anyone -- human or telescope -- it's only the effects of the atmosphere that cause that twinkling. In reality, that star is fixed in the sky, and it shouldn't matter whether you're on the surface of the Earth or hundreds of miles (or kilometers) above it. But our atmosphere is a turbulent entity, with gases rising and falling, and swooping past rapidly, from any point of view, in stratified layers.

Image credit: Wikimedia Commons user Kelvinsong.

But if you've ever seen a photo like this -- of an observatory shooting a yellow-orange laser into the night sky -- this is our attempt to compensate for the atmosphere. What we're actually doing is nothing short of brilliant.

Image credit: Gemini Observatories, NSF / AURA, CONICYT.

The laser used here on these observatories takes advantage of a special property of our atmosphere: certain elements are segregated from others at specific altitudes. One of the elements that's very rare is sodium, which happens to be concentrated in a thin layer about 100 km (60 miles) up. If you fire a sodium laser into the air, it will excite those sodium atoms found at that particular altitude, which then spontaneously de-excite, creating an artificial light source to be used as a guide star.

Image credit: Gemini Observatory.

The light from this artificial star then travels back to the telescope through that 100 km of atmosphere, and gets distorted by that same turbulent air column that all the other light coming to your telescope must pass through. Only this time, we know for absolute certain that this should be a single, point source of a particular wavelength at a particular location. So no matter what the light that we actually get back from that artificial star looks like, we know what it should look like: that single point source.

So what do we do? We adapt.

Image credit: Wikimedia Commons user Rnt20; unadapted on the left, AO on the right.

We can compute exactly what the shape of a mirror would need to be -- at any instant -- to undo the turbulent effects of the atmosphere, and return our artificial guide star to simply being a single point of light at the correct location. What we then do is we delay the light from all the other sources coming into the telescope, and actually mechanically adapt a mirror along the light path to be the exact shape it needs to be to undo the effect of the atmosphere, which we then pass the delayed light through.

Image credit: Gemin Observatory - Adaptive Optics - Laser Guide Star, annotation by me.

We update the shape of this mirror on a continuous basis, and this allows us to obtain -- to the best of our ability -- an image that undoes all the negative effects of the atmosphere. This entire setup is the most advanced technique in the field known as adaptive optics, and it's perhaps the most spectacular, revolutionary advance in ground-based astronomy since the invention of photography. Here's a lovely video from Gemini Observatory, detailing how the entire process works.

Adaptive optics, in general, has allowed us to resolve binary stars in a system that, without it, would look only like noisy speckles.

As of last year, for the first time, we've used this advanced version of adaptive optics to obtain a cleaner, higher-resolution image than even the space-based Hubble Telescope could obtain!

Image credit: Gemini Observatory / NSF / AURA / CONICYT / GeMS/GSAOI.

Click on the above image for a comparison, or the one below to see the same region of the sky -- side-by-side -- with Hubble's data on the left and Gemini's (with the new adaptive optics) on the right.

Images credit: NASA / ESA / Hubble (L); Gemini Observatory / NSF / AURA / CONICYT / GeMS/GSAOI (R).

That was a view of the interior of globular cluster NGC 288, but adaptive optics system on the Keck, Gemini and Lick observatories now routinely performs comparably to telescopes like Hubble that don't even have to contend with the atmosphere! It's allowed us, for example, to look inside the Orion Nebula like never before.

Image credit: M. Robberto/STScI and NOAO/AURA/NSF/Gemini Observatory.

So the next time you see an observatory (or even an image of one) shooting a laser up at the Universe, there's no need to pretend we're fighting aliens, attacking a distant civilization, or beaming energy to a distant location.

Image credit: Adam Contos (Ball Aerospace).

As is often the case with science, we're actually doing something much more spectacular: we're using our best technology, to the best of our abilities, to get the resolution of a space-based observatory, all without leaving the Earth!

esiegel Wed, 07/24/2013 - 11:38

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Mona Laser

cevans — Sun, 20 Jan 2013 09:35:12 +0000

Mona Laser

The cultural critic Walter Benjamin, in his seminal 1936 essay The Work of Art in the Age of Mechanical Reproduction, argued that the "aura" of a work of art, that sense of special awe and reverence we feel, being in its presence, isn't inherent to art itself. Rather, it's a side-effect of its exclusivity, restricted exhibition, authenticity, or perceived value. With the age of "mechanical reproduction" (i.e. printed copies, films, and photographs), that aura disappeared, freeing art from its ties to the bourgeoisie and allowing mass audiences to, in a sense, "own" the work too. Take the Mona Lisa, for example, an image so completely burned into the collective retina that the experience of seeing it in real life is rarely more meaningful than a frantic photo-op. Why bother to stand around and look at the Mona Lisa when visiting the Louvre? You've already seen it a million times. What even is the Mona Lisa, at this point, other than an image retained in the minds of millions of people?

The average Louvre visitor generally spends about 15 seconds viewing the Mona Lisa. There are countless other images–ideas too–that share this aura-smashing cultural ubiquity. Who could give an unbiased critique of the Venus de Milo, or the Last Supper? Even the iconic "Earthrise" image of the whole Earth taken from space, which changed the world when it was first seen, is now little more than a bumper sticker. We always seek the new, in the arts, precisely because an overly familiar image conceals as much as it reveals; we become blind to the everyday. And the Mona Lisa trumps them all: by some unspoken consensus, it has always been the image with which the West represents its cultural legacy. It is easily the best known, quantifiably the most visited, and probably the most parodied work of art in the world. Now it holds the auspicious status of being the first piece of art beamed to the moon via laser.

The smiling Gioconda traveled nearly 240,000 miles in digital form from the Next Generation Satellite Laser Ranging (NGSLR) station at NASA's Goddard Space Flight Center in Greenbelt, Md., to the Lunar Reconnaissance Orbiter, a robotic spacecraft currently in low orbit around the moon. By transmitting the image piggybacked on laser pulses routinely sent to track the craft's position, the team achieved simultaneous laser communication and tracking–a first for one-way laser communication at planetary distances.

It seems we're due for an update of Benjamin's oft-cited essay. Perhaps The Work of Art in the Age of Optical Teleportation? Of course, the notion of flattening the complexity and totally specific context of a piece of art–in this case, 16th-century Florence–in order to transmit it, efficiently, across minds and generations like a winsome smiling cultural totem: well, it's not that different from using compression to reduce a painting to its simplest numerical essence.

In order to make the cosmic transmission, the Mona Lisa had to be converted from a 500-year-old oil painting into a teensy 152 x 200 pixel array, each pixel of which was converted into a shade of gray, represented by a number between zero and 4,095 (the first fifty, presumably, were especially exciting). Each pixel was transmitted by a laser pulse, with the pulse being fired in one of 4,096 possible time slots during a brief time window allotted for laser tracking. The result: a data rate of about 300 bits per second. Not great for an internet connection, but then again, we're talking about metamorphosing a priceless emblem of Western art into incorporeal units of measurement, destined to be launched on a river of light to a spacecraft hanging around the moon, so, not bad.

The glitches and errors caused by Earth's atmosphere were tidied up with Reed-Solomon correction, which is the same compression coding we use for CDs and DVDs. Conceptually, this is nothing new. After all, the Mona Lisa currently pulses around the planet in digital form, bandied about on vast fiber-optic lattices under the sea and across the globe, all day every day. You've loaded her image just now, decoding my low-resolution desktop file from your home computer. Presumably, in the future, moon colonists and astronauts will be able to perform similar feats from desktops linked to the near-space laser Internet.

Walter Benjamin argues that the purpose of art can change over the years. An ancient sculpture or idol can begin its career as a cult object, central to a specific ritual use, and then grow to be appreciated aesthetically, historically, or forgotten entirely by different societies throughout time. "The uniqueness of a work of art is inseparable from its being imbedded in the fabric of tradition," he writes, "This tradition itself is thoroughly alive and extremely changeable." The purpose of the Mona Lisa, in 1503, was simple: it was a sign of wealth, of patronage, and had a practical function, as a portrait of the wife of a middle-class silk merchant. Later, after the vagaries of history displaced it from Italy to pre-revolutionary France, it served to represent monarchical power; it wasn't until the 20th century–after a highly-publicized theft and rediscovery, and lots of speculation–that it became the most famous painting in the world. That it started to belong to everyone. And, in suit, became a unit of communication itself.

Benjamin writes that "the instant the criterion of authenticity ceases to be applicable to artistic production, the total function of art is reversed. Instead of being based on ritual, it begins to be based on another practice–politics." Why did NASA choose the Mona Lisa to beam up to space? It's no simpler, technically, than any other image. The very specific and pointed choice of something so neutrally iconic is a political one: or, rather, a canny public relations move. Whether or not it intended to, NASA used the Mona Lisa as cultural shorthand. Even if you only read the headline of this story, the essential is communicated: we stand at the temporal zenith of an unbroken legacy of intellectual adventuring, we can draw lines of inquiry–after all, DaVinci was a consummate doodler of flying machines–through time, across boundaries, and into the bleeding edge of the present all while honoring those who came before us.

cevans Sun, 01/20/2013 - 04:35

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Your Friday Dose of Woo: Can somebody get me some frickin' laser beams with my Reiki?

oracknows — Fri, 15 Oct 2010 05:15:00 +0000

Your Friday Dose of Woo: Can somebody get me some frickin' laser beams with my Reiki?

Every so often, real life intrudes on blogging, preventing the creation of fresh Insolence, at least Insolence of the quality that you've come to expect. This is one of those times. I happen to be sitting here in Palm Beach, Florida, but I'm not chilling at the beach or pool. Rather, I'm attending "leadership training." Yes, be very, very afraid! In any case, I never saw the point of having these sorts of training seminars at beautiful oceanfront locations if they're going to pack the entire day with, you know, actual training! Worse (for purposes of blogging), I really have to fine tune my talk for Monday. Well, more like a major overhaul. So enjoy this bit of Classic Insolence from three years ago. Remember, if you've been reading less than three years, this will be new to you, and, even if you have been reading more than three years, it's fun to see how posts like this have aged.

Regular readers of this blog are probably aware of my general opinion about Reiki and other "energy healing" modalities. In short, they're woo, pure and simple. Consequently, one might reasonably ask why I've never featured the woo that is Reiki in Your Friday Dose of Woo. There's a simple reason for that.

Basic Reiki is boring.

Really, I mean it. In and of itself, it just doesn't reach the level of sheer ecstatic nuttiness that I like to feature every week. Oh, sure, there's lots of handwaving about "channeling the universal energy" through the healer to augment the life force of the person being healed. Certainly there's lots of serious woo about being able to heal people at a distance or through laying on of hands. (And you thought Jesus was main guy known for this.) But, in its basic form, Reiki lacks something to put it truly over the top. I wasn't sure what it was, but I found out.

It's missing laser beams. No, really. We're talking about Laser Reiki, which provides this promise:

If you loved the movie The Matrix, then you will love healing your life and changing your reality with Laser Reiki.

Now we're talking! Personally, I did like The Matrix. I even liked The Matrix Reloaded. The Matrix Revolutions kind of sucked, though. Is Laser Reiki like The Matrix, or is it like The Matrix Revolutions? You be the judge!

Of course, the question that I have is: Where did this fabulous woo come from? How was it discovered? Who thought of combining lasers and Reiki? Follow me, Grasshopper, on a journey of discovery:

Now, Reiki Masters, Taylore Vance and Roi Halse both of Chehalis, Washington have introduced new healing concepts that take Reiki a quantum leap into the future.

"In 1994 we discovered additional levels of Reiki healing beyond Masters." Taylore explains, "I call Level 4 -- Laser Reiki (LR) and Level 5 -- Cosmic Energetic Healing (CEH). They are light years ahead of basic Reiki." LR & CEH as defined and taught by Roi and Taylore heals at the atomic, sub-atomic, quantum and original creation level. Its impact can in many cases cause the body to instantly heal itself, and the mind and spirit as well.

In the traditional 3 levels of Reiki you are flowing the god force energy as it flows from the 4th dimension to heal the physical. In other words, you are flowing energy to mass. It works, but it may take several weeks or more to permanently bring wellness to an individual.

Perhaps I should have treated Reiki before. After all, if Lionel Milgrom can graft a misbegotten distortion of quantum theory onto homeopathy to create a Frankenstein monster of woo, then why couldn't the someone else fart something similar out and graft it onto Reiki? And, of course, why should Reiki limit itself to a paltry four dimensions? In the world of woo, that's pathetic. Heck, even the DNA activation guy claims twelve dimensions! Given that Reiki is perhaps the most popular energy woo out there, that's pathetic. Fortunately, Vance and Halse are there to crank up the dimensionality of Reiki to a more respectably woo-ful level:

With the use of Laser Reiki and Cosmic Energetic Healing the energy flows directly from the 6th or higher dimensions directly into the patient's energy body where it first aligns the energy body with a hologram of perfection. Next, the healing flows naturally into the physical body. In other words, the transfer of healing flows from energy to energy. This is hundreds of times more efficient. Instant healings can and do happen! (Many times, but not every time because there are other factors involved.)

"But not every time"? One can't help but marvel at the built in excuse. Of course, believe it or not, it's all about the...science:

Science seems to have proven that we are even born with tendencies for disease and problems. These show up imprinted within the cells in three ways: 1) energy blockages from unresolved problems from the past, 2) genetic tendencies from our biological lineage, and 3) those astrological tendencies caused by the birth/conception date. These are very similar to abandoned software still operating behind the scenes in a computer. Each disruptive program causes little disturbances in the overall well being of an individual.

A clearer indication of the mindset behind this woo would be hard to find. Consider: "energy blockages" and "astrological tendencies" are treated as equivalent to genetic tendencies from our biological lineage. Science, superstition, woo, to them it's all the same. They take this risible connection even further in another section of their website, where a Dr. Gutierrez, who is represented as a research physicist and engineer. He assures us that all of this Laser Reiki and Cosmic Energetic Healing are really and truly science:

Our small scientific group, UTC Research Group (UTCRG), has found that latest research in brain neurophysiology, cognitive sciences, information theory, quantum physics, Theory of Relativity and astrophysics can explain many of these "bizarre" symptoms/conditions, for now it is known that CONSCIOUSNESS is not the product of the highly organized/complex brain; but that the brain is a mere transducer/computer of Consciousness, Thought & Subtle Energies that are extrinsic to the Mind-Body Complex, the result of which is EMOTIONS, FEELINGS & ATTITUDES. And, it is these last byproducts of the human psyche -- the ones responsible for triggering psychosomatic conditions in the physical body, organically, psychologically or sensorially. Modern eminent medical authorities in the Quantum Healing Paradigm, such as Dr. Deepak Chopra, Dr. Caroline Myss, Dr. Norman Shealy, Dr. Richard Gerbee, Dr. Bernie Segal, and others, have written extensively on the relationships of Mind, Spirit, Body & Health.

Egads! it sounds like an unholy fusion of Deepak Chopra and Michael Egnor! Of course, when you see a paragraph like the above, you know that there's only one way the woo must be going. Yes, it's going quantum:

Notice the above definition regards the human body, not as a Newtonian-Cartesian machine, but as Quantum-Relativistic Consciousness/Vital Energy Transducer, a Wholistic Entity, in which ENERGY (Vital-Cosmic) in-forms/governs the BODY (Matter), not vice-versa. This is precisely the Quantum Mechanics view of Consciousness, Energy & Matter -- hence the New Quantum Healing Paradigm proposed by Prof. David Bohm (Implicate Order Physics), Prof. Karl Pribram (Holographic Brain/Body) & Dr. Deepak Chopra (Healing is a Quantum Process).

Since Prof. David Bohm's Quantum Physics postulation included Super Quantum Potential and an Implicate Order in the Universal Chaos, it needed non-local space-time relativistic interactions. Being a "protTgT" of Einstein while at Princeton, he was highly influenced by Einstein's Relativity Theory, and later formulated his famous Hidden Variables Theory, which in simple terms means that not all forces/energies may be "measurable/detected", yet they still affect matter. In other words, Subtle Energies do indeed exist! But can't always be measured or detected, and that is the premise that LASER REIKI - COSMIC ENERGETIC HEALING uses in dealing with subtle energies that are beyond the conventional concepts of CHI/PRANA, yet, being more rarefied and subtle, they approach, our concepts of SPIRIT/SOUL and the "dreaded" G-word: "GOD"!

In simple terms, all the above means that LASER REIKI Ã» COSMIC ENERGETIC HEALING takes into account in their healing modalities the various energetic factors that do not follow LINEAR TIME FLOWS, but Quantum-Relativistic non-linear "jumps" in space-time. This could be simultaneous/parallel realities (lives), or factors from previous incarnations(reverse time flow) or potential situations/conditions created in the future(by Consciousness/Attitudes/Emotions)that may be influencing the NOW!

Sounds bizarre or crazy? Why, this is standard stuff with Quantum-Relativistic Physicists! What was considered "science-fiction" 30 years ago has become "standard" scientific fact today in the strange, but wonderful world of the Quantum-Relativistic View of Nature! Isn't physics great!

Yes, physics is indeed wonderful. What's not so wonderful is to see physics abused in such a manner. In fact, it's ugly indeed to see so many seemingly legitimate-sounding terms from physics mixed with the most potent woo in a witches' brew. Most amusing to me is the part where the existence of "subtle energy" is postulated; yet it is also said with a straight face that this energy "can't always be measured or detected." Even funnier is that these undetectable "subtle energies" are at the heart of Laser Reiki. Does this mean that the effects of Laser Reiki can't be detected either? If that's the case, then what good is it?

Before I can finish my "loving treatment" of this most wondrous woo that I have discovered, one question remains. Indeed, it is a question that nagged at me as soon as I saw the website and started reading its amazing contents. It's a critical question that goes right to the very heart of Laser Reiki in an absolutely undeniable way. In fact, it's the same question Doctor Evil asked of his henchmen in Austin Powers: International Man of Mystery: Where are the laser beams? Just as Doctor Evil wanted laser beams attached to the heads of his sharks, I want frickin' laser beams attached to my Reiki in Laser Reiki! Otherwise, again, what good is it?

So where are the laser beams? Just like Dr. Evil, sadly I'm to be seriously disappointed:

Anyway, some folks wondered why the term "Laser Reiki" was used. Well, when consciousness is focused and willfully directed by a powerful pulse of breath, as in Oriental martial Arts, It delivers a powerful burst of energy -- laser-like indeed! In fact, the specialized type of breath used in LASER REIKI - COSMIC ENERGETIC HEALING together with a precise hand motion is reminiscent of Oriental Martial Arts/Japanese-style Katas (Formal Exercises), or more precisely, the Cobra Breathing of Tantrik Yoga's Fire Breath (Kapalabhati)with hand Mudra/Gesture. It delivers a very powerful burst of concentrated CHI/PRANA, with the intensity of a Laser Beam, hence the name -- Laser Reiki.

Whaaaat? No lasers? You mean the use of the term "Laser Reiki" is nothing more than a metaphor? I mean, I had one simple request, and that is to have Reiki with frickin' laser beams attached to it! Now evidently my woo-meister colleague informs me that that cannot be done, that the term "Laser Reiki" is nothing but a metaphor! Would Dr. Gutierrez remind me what I would be paying Taylore Vance and Roi Halse for, honestly? Throw me a bone here! What do we have?

Laser Reiki without real lasers?

That's like having to settle for mutated sea bass instead of real sharks.

oracknows Fri, 10/15/2010 - 01:15

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complementary and alternative medicine

complementary and alternative medicine

humor

medicine

religion

Orac, have you had time to study the apparently wildly exaggerated claims that cancer is (almost) purely man-made? http://www.physorg.com/news/2010-10-scientists-cancer-purely-man-made.h…
The more I check it out, the less credible it seems.

(But sharks with lasers still looks like a cool idea)

Oprah should read more.

Oprah... she should read, more.

That's like having to settle for mutated sea bass instead of real sharks

Are they ill-tempered?

"In the traditional 3 levels of Reiki you are flowing the god force energy as it flows from the 4th dimension to heal the physical. In other words, you are flowing energy to mass."

This is just painful to read. I literally winced as my brain rebelled at the notion that these words could be put together in that order and intended to impart such utter nonsense.

Energy flowing from the 4th dimension? That's like saying that there's a mysterious power flowing out of width and you can channel it into height to heal the woes of those residing in the height plane. All dimensions do is measure the properties of an object. That's it. And as for imparting energy to mass, that's just radiation plain and simple. So these woo-meisters will summon mystical energy from an abstract, arbitrary measurement of time to irradiate you, somehow instantly healing you of all that ails you?

The stupid, it literally burns. Or should I say irradiates?

@Birger Johansson

Steve Novella has a post up about that over at Neurologica.

Quantum? Aha! How just one word can cure all ills.

Orac sounds in need of a laugh! Wednesday, while I was in the midst of tedious business calls and readying myself for an appointment, I caught a snippet of the Noontime Radio Woo-fest where the host, guests, and office minions were discussing "Quackbusters"(sic)**; it appears that while "Barrett has now been *totally* discredited", *new* stars are emerging through the drecky, mist-enshrouded Woo-esphere : doctors from Yale and other "big universities" have a website called "Science Based Medicine", Randi is also a factor , and ...... someone ( or something) wrote a post entitled,( quoted verbatim) ".... Blaxill....irony meter...". No names other than Randi's were mentioned, nor was RI. ** ( "Quackbusters"- in contradistinction to Barrettt's "Quackwatch"-is Bolen's site). Laughter is a good thing.

At least your not working on an NIH grant application to suck money away from the American taxpayer in order to conduct some useless science experiment

I don't think I've seen this here, but I crossed it on Fark today and it's great.

http://3.bp.blogspot.com/_RQjQvxtmK8A/TLYv7qkUodI/AAAAAAAADVg/gbx_qcAB5…

Flowchart to determine which "Alternate Medicine" is for you.

Sounds bizarre or crazy? Why, this is standard stuff with Quantum-Relativistic Physicists!

A while back a friend of a friend challenged me in a coffee shop: she was a reiki practitioner, and she was sure she could convince me (in front of everyone) that the evidence for reiki was so strong and reliable that it was now an accepted part of mainstream science. It was "standard stuff" and I simply wasn't up to the current scientific consensus. Reiki. Right. I accepted that challenge: it seemed an easy win.

Which, technically, it was. As I recall, her major pieces of evidence were quantum physics, Dr. Emoto's experiments with water and the effect of "loving words" on crystal formation, and -- as the conclusive bit -- the fact that some big nursing association had apparently put its full scientific weight behind the truth and existence of TT, reiki, and "healing energy." I spent what I thought was a patient and tactful 20 minutes or so in rebuttal -- and then got to witness an interesting about-face.

She went from claiming that science was on her side and reiki was "standard stuff" to telling me that science wasn't everything, experience was - and scientists were all a bunch of closed-minded poopyheads -- but they weren't as close-minded a poopyhead as I was. Or something like that. That's a 180.

Which, I expect, has since flipped back to its original state. This reiki master probably continues to tell all her clients that the evidence for reiki is so strong and reliable that it is now an accepted part of mainstream science -- with no sense of irony, or cognitive dissonance. "Sciences" are evidently kind of like faiths: there are different sects or denominations, and the only bad ones are the ones who insist that the others are wrong.

Still, it was fun.

@Sastra - so the friend of your friend (friend^.5) managed to demonstrate quantum entanglement by being able to hold two contradictory positions at once until the wave equation collapsed?

Mephistopheles O'Brien #12 wrote:

so the friend of your friend (friend^.5) managed to demonstrate quantum entanglement by being able to hold two contradictory positions at once until the wave equation collapsed?

Yup -- accepting contradictions is not only cosmically holistic, it's non-judgmental. It requires being an "accepting" sort of person, and one who can contain multitudes.

@ Greg Fish

Energy flowing from the 4th dimension?...All dimensions do is measure the properties of an object.

They are using 'dimension' with the meaning of 'alternate universe' or 'extra plane of reality'. I'm afraid it's part of SciFi/Fantasy culture. Tesseract, anyone?
A number of RPGs are full of extra-dimensional pockets.
In the 70-80's in France, the title of the show 'Twilight Zone' was translated into 'La Quatrieme Dimension' ('The 4th Dimension').
And when in late 80's, our newly-born 5th private TV channel ('La Cinq') decided to run a remake of the Twilight Zone, they named it... La Cinquieme Dimension ('The 5th Dimension').
I'm not sure if our 6th TV channel is running a '6th dimension' TV series, as the joke is getting lame.

Channeling energy from the 4th dimension will not surprise any French SciFi fan. I dunno about other countries. Taking into account this Reiki-laser act, I feel like that 'dimension=extra universe' is a common misconception born of the clash of the quantum theory and the idea of the existence of parallel universes.

Liquidity Acquisition by Superficial Extension of Reiki?

Pablo: Absolutely.

Poked around a bit by googling scientific words + reiki and found:

http://www.thirdeyereiki.com/Reiki_and_science.html

A sample:

Reiki works on multiple dimensions similar to that of the Superstrings. It makes healing happen by restructuring and organising the inconsistancies in the pattern of the superstring that leads to various dis-ease. Reiki has inate intelligence that makes this possible. Thus establishing health and harmony by working at the level of the Super Strings that exist at higher dimensions (ten dimensions - according to the Superstring Theory).

Quantum Optics from the Opposite Direction: QED Limits on Laser Intensities

drorzel — Wed, 18 Aug 2010 07:47:29 +0000

Quantum Optics from the Opposite Direction: QED Limits on Laser Intensities

Most of the time, when we talk about seeing quantum effects from light, we talk about extremely weak beams-- looking at intensities where one photon more or less represents a significant change in the intensity of the light. Last week, though, Physics Buzz wrote up a paper that goes in the other direction: they suggest a limit on the maximum strength of a laser pulse due to quantum effects, specifically the creation of particle-antiparticle pairs.

This is a little unusual, in that most of the time when people talk about really intense lasers, they end up discussing them as an oscillating electromagnetic field, in a very classical sense. The idea is that once you have a large enough intensity, the effect of adding or subtracting one photon from the beam is completely negligible, so you can talk about it as a more-or-less classical field. And, in fact, the paper in question takes this approach for looking at the effects of the laser field after the pair creation. But it's a useful reminder that quantum effects become important not just when you look at really small amounts of energy, but also when you try to pack a large amount of energy into a really small space.

The paper itself is kind of difficult to read-- English is almost certainly not the first language of anybody involved in the writing-- but the basic idea is that an ultra-intense laser pulse, or the "collision" of two pulses, can lead to the production of electron-positron pairs out of the vacuum, converting a small amount of the light energy into mass. (This builds on earlier experiments at SLAC which collided intense laser pulses with high-energy electrons to create a similar effect; this new paper, as I understand it, involves the creation of the electron-positron pairs from light alone.)

Once a single pair has been created, they look at its behavior in the large electric field of the original laser pulse. This will tend to accelerate the electron and positron in opposite directions, and for sufficient laser intensity, the acceleration can be rather dramatic. We know from Maxwell's equations, though, that an accelerating charged particle gives rise to radiation. If the laser field is strong enough, the accelerating electron and positron will emit radiation themselves, and the light produced from their motion can, in turn, produce more electron-positron pairs, which are then accelerated, and so on.

Every one of these steps chips away at the energy of the initial laser pulse. The energy to create the initial pair has to come from the laser, and the energy gained by the accelerating particles also comes from the laser. At high enough initial pulse energy, the creation of a single pair triggers a "cascade," an exponentially growing collection of particles begetting other particles, all of them stealing energy from the initial pulse, until it's gone, or at least down below the threshold intensity needed to start making pairs that make other pairs. This would place a hard limit on the maximum intensity of a laser pulse.

This isn't really a quantum optical effect in the usual sense of requiring a quantum model for the behavior of the light pulse-- as I said, their calculation just uses an oscillating electric field to produce the effects-- but it does involve both light and quantum effects, so it's not too big a cheat to call this a quantum optical effect. And while this is very much a theoretical paper, the pulse intensities where they expect these effects to start showing up should be attainable by some ultra-high-power lasers that are currently under development, so it may soon be possible to see quantum effects using nothing but bright light and empty space. Which is pretty cool, no matter what you call it.

drorzel Wed, 08/18/2010 - 03:47

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When they say the effect will be seen at upcoming laser facilities, I guess the point is that the new generation of lasers is below the critical field strength, but not too far below, so that pair-creation is rare, but happens enough to be studied? Surely no one would have planned to build a laser that actually reaches Schwinger-strength electric fields....

I think the key claim is that the level where this should start to appear is lower than previously believed. Thus, the laser systems under development might be able to trigger these cascades at intensities that are lower than expected. So the development may have begun thinking this wouldn't be attainable.

The paper is very preliminary, though-- it's pretty much a toy model, needing further development.

The paper gives ~10^25 W/cm^2 as the critical intensity. We're still pretty far from that in the optical regime. I wouldn't hold my breath about seeing pair production any time soon, at least with light of UV wavelengths and longer.

Question: How does this conserve rest mass? In a laser, all the light is going in (roughly) the same direction, so it has no rest mass. If an electron/positron pair is produced, the pair has rest mass.

Question: How does this conserve rest mass?

It doesn't, because rest mass is not a conserved quantity. Energy and momentum are conserved (yes, photons do have momentum), but E = mc^2, so if you have mc^2 of energy lying around, you can convert it to mass m, or you can liberate it by conversion from mass m.

No, I'm pretty sure rest mass is a conserved quantity. The key word is *rest* mass, which is the total mass-energy in the center of mass frame. In a closed system, the center of mass frame is an inertial frame and mass-energy is conserved.

You can't cause two photons going in the same direction to undergo pair production. If it were possible, then the reverse reaction would also be possible. That is, you could have an electron/positron pair produce two photons which go in the same direction. This obviously doesn't conserve momentum. There exists some reference frame where the electron/positron pair has net zero momentum. There does not exist a reference frame where the photons have zero momentum.

What you're talking about is what most people would call "energy conservation", miller; calling the invariant mass of a two-photon system its "rest mass" is a little nonstandard.

You're right that two photons moving in the same direction are kinematically incapable of annihilating. But the initial pair creation event here isn't something you can understand perturbatively in terms of scattering any small number of photons. It happens even in a completely uniform homogeneous electric field. It's a nonperturbative effect that can be understood as a semiclassical tunneling process.

miller: It's conservation of momentum and energy that's at issue here, and were it true that

In a laser, all the light is going in (roughly) the same direction, so it has no rest mass.

then pair production would indeed violate conservation of momentum, energy or both.

However, while the light in a laser beam travels in one direction, the light in the laser cavity itself travels in two opposite directions, so pair production is possible.

http://en.wikipedia.org/wiki/Laser

What Do You Need to Make Cold Atoms? Part 2: Lasers and Optics

drorzel — Thu, 12 Aug 2010 09:23:49 +0000

What Do You Need to Make Cold Atoms? Part 2: Lasers and Optics

Following on yesterday's discussion of the vacuum hardware needed for cooling atoms, let's talk about the other main component of the apparatus: the optical system. The primary technique used for making cold atoms is laser cooling, and I'm sure it will come as no surprise that this requires lasers, and where there are lasers, there must also be optics.

There are lots of different types of lasers used for laser cooling experiments, but they all need to have certain properties: tunability, stability, and adequate power. Tunability is important because laser cooling requires light at exactly the right frequency to be absorbed by the atoms you're trying to cool; stability is important because you need the laser to stay at the right frequency once you get it there; and power is important because you need a decent amount of light, and would prefer not to have to use multiple independent laser systems.

The particular lasers I use are diode lasers, like the ones found in CD and DVD players, or laser pointers:

(The cylindrical black thing on the foil is a collimation tube, which holds a lens in front of the laser to bend the widely diverging output of the diode laser into a more or less constant width beam. the battery is for scale.)

Diode lasers are mass produced for optical data storage purposes, so they're relatively cheap-- the ones shown here are something like $100-200-- and they produce a decent amount of power, around 150 mW per laser. They're tunable over a wide range, as such things go-- the lasers I buy ordinarily put out light with a wavelength of about 808 nm, but I run them at 811 nm by controlling the temperature and current.

The disadvantage of diode lasers is that they can be a little unstable, and also fragile. Static electricity can kill them completely (the ones in the picture are all dead), so you need to be careful to ground yourself to something else before touching the laser system, and they're prone to "mode-hopping," moving to a different wavelength a small fraction of a nanometer away, out of the range where laser cooling will work.

You can improve the stability and provide some fine tuning by putting the laser in an "external cavity," typically involving a diffraction grating that selects light of a particular wavelength and sends it back into the laser cavity. The external cavity laser I use for my main light source is shown at right. The laser itself is inside a collimation tube that is mounted inside the aluminum block-- you can see the power leads going into the block at the top of the picture. The black anodized alumninum mount bolted to the near side of the block holds a diffraction grating mounted on a piezoelectric stack (the little green thing that's just visible in the center), a material that expands or contracts when you apply a voltage across it. The mount lets us tune the wavelength that is sent back into the laser in a very coarse way (you can see an allen wrench coming out the back-- the smallest turn you can reproducibly make with the wrench shifts the wavelength by around 0.1 nm), and we can make very fine adjustments by controlling the voltage sent to the piezo. The light from the laser exits the aluminum block heading up and to the left in the picture, and passes out through a hole cut in the outer aluminum block (which is covered by a microscope slide).

This whole assembly sits in an aluminum box, as you can see, that it usually kept closed when things are working well. The wavelength of the laser is highly sensitive to temperature (there are thermoelectric coolers sandwiched between the aluminum block and the copper baseplate to control the temperature of the block to with a small fraction of a degree), and closing it in a box helps avoid air currents that might upset the temperature. It also reduces sensitivity to sound that might cause the laser wavelength to jump slightly due to vibrations of the grating.

The biggest hassle with these, as you might imagine, is getting the grating aligned just right to send light back into the laser. The laser itself is something like 100 microns in size-- about the thickness of a human hair-- so this is a really fiddly process. It's sensitive enough to the alignment that after making a big change in the tilt of the grating, the tiny change in angle caused by relaxation of the metal "spring" holding the mount in place will make the laser drift off the desired wavelength over a period of days or weeks. The second-biggest hassle is getting the temperature tuning just right, because anything involving thermal processes is sloooow, and something that looks right a minute or two after making a change can settle to a new equilibrium an hour later that doesn't work at all. Once you get everything working, you tend to leave these on 24-7, because they're more stable that way.

There are two other major technologies used for laser-cooling lasers, those being solid-state lasers like the Ti:Sapph laser I used in grad school, which uses atoms in a crystal as the laser medium, and dye lasers which use organic molecules in a jet of liquid as the laser medium. Both of these offer wide tunability-- tens to hundreds of nm-- using the fact that molecules and solids have broad emission and absorption bands rather than narrow lines. They require external pump lasers, though-- typically either an argon ion laser at 514 nm or a diode-pumped doubled YAG laser at 532 nm--
and are extremely expensive. Dye lasers are also messy, and often use toxic chemicals, which are great reasons to avoid the damn things.

Once you have a laser at the right wavelength, you need optics. Lots and lots of optics. This is a slightly outdated picture showing a part of the optical system for my lab, with the beam lines traced out:

A more complete explanation of what the different colors mean can be found in this old post explaining the importance of cosmetics to laser cooling. The master laser shown above is in the grey box at the top of the picture. The cardboard box toward the bottom contains a "slave" laser whose frequency is locked to that of the master laser by feeding a small amount of light into it (the orange beam line). This is only about half of the optics layout I use (the rest is on a different table), and this is a relatively simple system by current standards.

The main optical elements involved are:

Mirrors: most of the elements you see in these pictures are mirrors used to direct the beam to where it needs to be. These are mounted in sturdy aluminum mounts with two tilt screws to control the horizontal and vertical tilt of the mirror. A good and stable mount will let you adjust the position of a spot a few meters away by a millimeter or so. I have dozens and dozens of these, and am always scrounging more.
Lenses: sometimes you want a beam to be a little bigger than it is (to provide a large trapping volume, say), and sometimes a little smaller (to get it through some narrow opening). We use a whole bunch of different lenses for this.
Optical Fibers: You can direct light all over the place with mirrors, but the problem with this is that a small shift in the tilt of one mirror early in the chain can produce an enormous change a few meters downstream. This problem can be reduced by coupling the light into optical fibers, whose ends will always be fixed. Of course, getting light through the fiber is a hassle, and you generally lose half of it, so this is to be used sparingly. For some things, though, like the alignment of the injection lock of the slave laser, it's absolutely critical.
Waveplates: The polarization of the light is critical for laser cooling, and we use devices called waveplates to control that polarization. These come in two types: "quarter-wave," which turn linear polarization into circular polarization and vice versa, and "half-wave," which rotate linear polarization from horizontal to vertical, or any angle in between.
Beamsplitters: These are partially reflecting elements that split a beam into two parts, typically mounted in glass cubes. These also come in two types, polarizing and non-polarizing. A non-polarizing beamsplitter gives you a fixed ratio of intensities (typically close to 50/50) between the output beams, while a polarizing beamsplitter sends horizontally polarized light in one direction, and vertically polarized light in another. A half-wave plate followed by a polarizing beamsplitter gives you a variable intensity ratio between the output beams, which is extremely useful. If you only want a small amout of light in one beam, you can use a glass microscope slide as a cheap beamsplitter, and this is done in several places for beam diagnostics.
Optical Isolators: This is a crystal of special material mounted inside a strong magnet, sandwiched between two polarizers. This combination lets light pass in only one direction, and is important to protect the diode lasers from reflected light that might screw up the wavelength. These are pricey, but essential-- they're the two clunky gold things visible in the picture with the beam lines, one for each laser.
Acousto-Optic Modulators: An AOM is a block of glass with a small speaker mounted to it. The speaker vibrates at very high frequency-- typically 80 MHz-- setting up a sound wave in the glass. This sound wave acts like a diffraction grating, and shifts both the direction and the frequency of the diffracted light. These are used for fine control of the laser frequency, and fast switching of the frequency for various experiments. We've got two in my lab; other labs with bigger budgets use half a dozen or more.

All of this stuff is expensive-- I've probably dropped over $50,000 on miscellaneous optical elements over the years, and I could always use more.

All of these elements are arranged in very particular ways to get the beams where they need to go. Of course, this is incredibly sensitive to small changes in the position of the optical elements, which is why everything is bolted to the surface of an optical table. These tables are large, heavy tables designed to minimize vibrations, and with steel tops having 1/4"-20 holes drilled in a 1" grid over the whole surface. The mounts holding the mirrors and lenses and so forth are bolted to the table, so they're fixed in position unless you do something really stupid to knock them out of place.

(One of the standard horror stories in this business involves cleaning or maintenance workers who come into research labs to do something, and climb on top of the optical tables, kicking mounts in the process. This is why our labs at NIST had big signs saying "DO NOT CLEAN" on the door.)

So that's the quick guide to the toys used in getting light to where it's needed for using lasers to cool atoms. Questions, comments, things I left out?

drorzel Thu, 08/12/2010 - 05:23

Tags

Not sure if this was deliberate, but you don't mention any of the various monitoring systems that allow you to check whether your lasers are behaving - photodiodes, power meters, spectrometers, etc.

Thank you for posting these - they're what I wanted. A friend of mine does stuff with optical things so I've heard a fair bit of complaining about alignment and so on. I've heard her call optical isolators Faraday isolators instead which is much cooler name. It makes it more Back to the Future-y.

How long does it take to plan out and implement a system like this? Is it very similar to the setups you've had elsewhere? I'm curious how much of this stuff is 'standardised' now it's been around a few years.

These posts about the lab are awesome! Thanks for sharing.

I too am curious how much of your equipment is standarized and how much is home-brew kind of stuff? Of the things you and your student build, how much is that a function of cost versus "one-off" kind of things?

ugh. right now 2.75" viewports are on my list of evil lab items. we have one we use for an optical temperature measurement of our wafers. it developed a spider webbing of cracks.

It's not pinin,' it's passed on! This viewport is no more! It has ceased to be! It's expired and gone to meet its maker! This is a late viewport! It's a stiff! Bereft of life, it rests in peace! If we hadn't bolted it to the port it would be pushing up the daisies! Its structural processes are of interest only to crystallographers! It's hopped the vacuum chamber! It's shuffled off this mortal coil! It's run down the curtain and joined the choir invisible! This.... is an EX-VIEWPORT!

however, it is a plucky little viewport. it is only leaking about 10^6 Torr, rather than imploding and shooting silicate shrapnel into our chamber, shredding everything in it's path.

replacing it will take 5 minutes, but then pumping down and baking the chamber will take days and days and days.

sad face.

The one laser experiment I did involved taking a 100 mW green diode laser. Clamping it in a testtube claw and aiming it by eye at the crystal in the cryostat.

Small miracle that I 1) didn't lose an eye, 2) got a pretty structure.

Blue laser awesomeness

rallain — Thu, 13 May 2010 16:38:13 +0000

Blue laser awesomeness

Yes, green laser pointers are cool. Especially when you use them to make stuff fluoresce. Ok, what about a blue laser pointer? They are getting surprisingly cheap (Amazon has a 10 mW for pretty cheap). Still not cheap enough for me. But, you know what? Some of the physics majors here at Southeastern Louisiana University purchased a couple of these. Physics major Daniel let me borrow his.

First, they don't look too bright. This is probably because our eyes are not too sensitive to this wavelength. The blue 10 mW does not look anywhere near as bright as the 5 mW green that I used in the previous demo. Test number 1 - is the blue laser just one wavelength? (essentially) The laser lists the wavelength at 405 nm. Shining it through my spectral glasses produces a series of blue dots. If it had been multiple wavelengths, you would see different colored dots.

Ok, but what if I shine the dot on anything else and look at the spectrum of the reflected light? Here is what the dot look like when I look through the spectral glasses.

This is not what a red or green laser dot does (well usually not the green). If you can not remember, here is what the green laser looks like when the same thing is done (looking through the spectral glasses - oh, preemptive don't whine about my cheap old spectral glasses)

The green laser reflects as green. UNLESS you shine it at something pink or orange-ish (or some of the pink and orange things do this).

This is an example of flourescence. Basically, the laser excites the electrons in the material to a higher energy level. The electron can then take multiple transitions back to the ground state. Oh, I know it is really more complicated than that - but I want to keep this brief. So, the green does this on some stuff, but the blue does this on just about everything. If you shine the blue on the same stuff that the green makes fluoresce, you get slightly different colors.

Here is a video showing this same thing - but some people like moving pictures better than plain pictures.

Yes, I know that is cool. This is even cooler. What if you take the blue laser and shine it at some glow in the dark stuff? This is a glow-in-the-dark dodge ball (or is it a kick-ball)?

This is an example of phosphorescence. In short (super-short), the difference between fluorescence and phosphorescence is time. In fluorescence, the electron transitions back to the ground state essentially right away. In phosphorescence, this transition can take quite some time (that is why glow in the dark stuff stays "on" for some time). With normal white light, only some of the frequencies are enough to excite the electrons. A green laser will not do it. The blue has the right frequency and is super bright, that is why you get that trail.

Someone should give me a commission on any blue lasers Amazon sells. Though really this stuff sells itself. It was probably made by Germans, you know the Germans make great stuff.

rallain Thu, 05/13/2010 - 12:38

Tags

yeah, they also make a lot of stuff disappear; all of my great-grandfathers cows for instance

The traces on the glow-in-the-dark ball reminds me of a CAD system (IDIIOM? IDADS?) I worked on in the 80s. It used high-persistence phosphor as the graphic-screen memory and you had to hit a degauss-like button to clear the screen.

dealextreme has had the 405nm ones for a long time - dirt cheap.

that stuff is boring i know how to do that and way cooler things with lasers

How do color filters work?

rallain — Tue, 04 May 2010 09:01:57 +0000

How do color filters work?

So you have seen these color filters (or gels as they are also called). When you look through a red filter, everything looks red. What do they do to the light? I am not going to tell you the answer. However, I will show you some examples so that you can figure out the answer yourself.

In this video, I am going to use a red and a green laser pointer. The nice thing about laser pointers is that they essentially create only one color of light.

rallain Tue, 05/04/2010 - 05:01

Tags

When I read the above-the-cut paragraph, I assumed you were going to do something hand-wavey which relied on approximately unimodal filters. But good use of lasers.

It's been a while since I took physics, but from what I recall... those gels each absorb certain wavelengths of light. Sometimes that can be a very narrow band (such as with the red and green gels) or it could be a wider range of wavelengths (magenta).

If the gel doesn't absorb the photons, then the light passes through. The red gel allows the reddish wavelengths through, so that's all get we can see through it. Green light is different enough in length that it can't pass through.

As for how the gel can be so selective... I'm not sure, but I'd be interested in a more detailed description as to what's going on at the atomic level!

Lots of additional questions for you...

So a red gel passes red light, easy. But why does a red gel appear red? Is that all from light passing through it? What is the surface color?

On the molecular level, do you happen to know what atoms or bonds are responsible for the absorption in these materials? Do they re-radiate and/or reflect? Is all the re-radiation infra/heat, or are there say, blue filters which radiate red when illuminated with green light?

@travc

Why does a red gel appear red? Good questions - I guess it also reflects some red light and when it is back light, only red light passes through it.

I am not certain exactly of the atomic-level mechanism that makes this work.

"But why does a red gel appear red? Is that all from light passing through it? What is the surface color?"

I'll take a shot at answering these. A red gel appears red only because light passes through it. If you were to place one on a surface where no light passed through, such as a black piece of paper, it would just appear black.

The red gel appears red since it is absorbing other wavelengths in the visible spectrum (except red), where the red wavelength is scattered and reflected back to the viewer's eye. The green gel is the same way. The blue gel is absorbing all but the high energy wavelengths (blue-ultraviolet), thus neither the red nor the green laser will pass through.

The gel is probably scattering a portion of the laser light and absorbing the rest of it, returning to ground state non-radiatively. Cool demo, I wish I had this when TAing Gen Chem.

what do coulor filters do to colors?

what do color filters do to colours because me and my best friend are doing a science experiment

The critical concept here is not absorption, as someone before tried to explain, but transmittance and interference ;)

I thought this was really good!

please ans me how interference is used in colour filters

When the red light passes through the green filter no light comes out i see. but what im wondering is why? why does o light come out?

i'm really confused

Hug a Laser

rallain — Tue, 04 May 2010 08:29:58 +0000

Hug a Laser

It is my duty as a blogger to mention lasers in this time of international laser celebration. This May is the 50^th anniversary of the first lasers. Everyone knows a laser that they love, right? We all use them. So, instead of talking about lasers, I am going to post some great links to other laser stuff (including some of my stuff).

the history of the first lasers (AIP)

The above is the American Institute of Physics's presentation of the history of the laser. Really, this does a great job of giving all the details you would want. I highly recommend it.

Uncertain Principle's Laser applications

Chad gives the result of his laser smack down poll for most amazing applications of lasers (voter based). I guess I can tell you that the winner of voting is Laser cooling.

Laser Recoil discussion

The Virtuosi and Built on Facts have some nice posts about lasers and recoil (for laser guns).

Some of my stuff

Honestly, I have not done that much stuff with lasers. Really most of my laser stuff just uses lasers for something else.

Fluorescence with a green laser pointer

Ruff Ruffman tries to measure temperature with a laser

Lizards like green laser pointers too.

rallain Tue, 05/04/2010 - 04:29

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I definitely have lasers I want to hug, but more often than not, I have lasers I want to kick. It's too bad these lasers cost more money than I'm likely to make in my lifetime otherwise I would kick 'em! Stupid lasers.

The AIP exhibit certainly looks interesting, but the link gives me a 404...

@Rafael,

Thanks for pointing that out. I fixed the link.

The Most Amazing Laser Application of All Time Is...

drorzel — Mon, 03 May 2010 08:27:39 +0000

The Most Amazing Laser Application of All Time Is...

Voting has closed on the Laser Smackdown poll, with 772 people recording their opinion on the most amazing of the many things that have been done with lasers in the fifty years since the invention of the first working laser (see the Laserfest web site for more on the history and applications of lasers). The candidates in the traditional suspense-building reverse order:

Lunar laser ranging 22 votes
Cat toy/ dog toy/ laser light show 41 votes
Laser guide stars/ adaptive optics 46 votes
Holography 47 votes
Laser eye surgery 53 votes
Optical storage media (CD/DVD/Blu-Ray) 60 votes
Laser frequency comb/ spectroscopy 65 votes
LIGO 68 votes
Optical tweezers 74 votes
Telecommunications 91 votes
Laser ignited fusion 95 votes

That means that the winner, and The Most amazing Laser Application of All Time is:

Laser cooling/ BEC 110 votes

And there you have it. The people have spoken, and it doesn't get any more amazing than laser cooling, which is hereby awarded bragging rights over all other fields of laser-related physics.

Thanks to everyone who voted. And even if you missed your chance to vote, I hope you'll take a little time to look over the posts explaining the various applications, and appreciate the many amazing things being done with lasers today.

drorzel Mon, 05/03/2010 - 04:27

and now they are making rain clouds with laser:

http://www.engadget.com/2010/05/03/swiss-scientists-create-dark-clouds-…

Weird outcome, likely has more to do with the fact that Chad does ultracold physics then with anything else (people here are not representative).

By far the most amazing application is telecom, without it there would be no internet as we know it and no poll, second is optical storage, the impact of those two technologies is hard to overestimate.

Telecom did lead the poll for a long time though the results changed significantly near the end (link ended up somewhere?).

BEC/cooling is nice but still a fringe application with more hype then useful results.

Oh. You wanted aMAZing. I read aMUSing, which is why I voted for "cat toy". Lula holding a claw somewhere tender had NO effect on my vote.