Dot Physics

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.

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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.

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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)

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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).

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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.

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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.

Comments

  1. #1 rijkswaanvijand
    May 14, 2010

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

  2. #2 Dave X
    May 14, 2010

    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.

  3. #3 anders
    May 15, 2010

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

  4. #4 N/A
    October 5, 2010

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

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