Atoms and Molecules

Category archives for Atoms and Molecules

Fun With Simulated Scattering

Two chapters of the book-in-progress will be devoted to the development of the modern understanding of the atom. One of these is about the Bohr model, which turned 100 this year, but Bohr’s model would not have been possible without an earlier experiment. The actual experiment was done by Ernest Marsden and Hans Geiger, but…

Laser-Cooled Atoms: Cesium

Element: Cesium (Cs) Atomic Number: 55 Mass: One stable isotope, mass 133 amu. Laser cooling wavelength: 854nm, but see below. Doppler cooling limit: 125 μK. Chemical classification: Yet another alkali metal, column I of the periodic table. This one isn’t greyish, though! It’s kind of gold color. Still explodes violently in water, though. Other properties…

Laser-Cooled Atoms: Chromium

Element: Chromium (Cr) Atomic Number: 24 Mass: Four “stable” isotopes between 50 and 54 amu. Chromium-50 is technically radioactive, with a half-life considerably longer than the age of the universe, so… Laser cooling wavelength: 425nm, but see below. Doppler cooling limit: 120 μK. Chemical classification: Transition metal, smack in the middle of the periodic table.…

Laser-Cooled Atoms: Lithium

Element: Lithium (Li) Atomic Number: 3 Mass: Two stable isotopes, masses 6 and 7 amu Laser cooling wavelength: 671 nm Doppler cooling limit: 140 μK. Chemical classification: Alkali metal, column I in the periodic table. Yet another greyish metal. We’re almost done with alkalis, I promise. Less reactive than any of the others, so the…

Laser-Cooled Atoms: Francium

Element: Francium (Fr) Atomic Number: 87 Mass: Numerous isotopes ranging in mass from 199 amu to 232 amu, none of them stable. The only ones laser cooled are the five between 208 amu and 212 amu, plus the one at 221 amu. Laser cooling wavelength: 718 nm Doppler cooling limit: 182 μK. Chemical classification: Alkali…

Laser-Cooled Atoms: Strontium

Element: Strontium (Sr) Atomic Number: 38 Mass: Four stable isotopes, ranging from 84 to 88 amu Laser cooling wavelength: Two different transitions are used in the laser cooling of strontium: a blue line at 461 nm that’s an ordinary sort of transition, and an exceptionally narrow “intercombination” line at 689 nm. Doppler cooling limit: 770…

Spooky Action at What Distance?

When I wrote up the giant interferometer experiment at Stanford, I noted that they’ve managed to create a situation where the wavefunction of the atoms passing through their interferometer contains two peaks separated by almost a centimeter and a half. This isn’t two clouds of atoms each definitely in a particular position, mind, this is…

Laser-Cooled Atoms: Xenon

Element: Xenon (Xe) Atomic Number: 54 Mass: nine “stable” isotopes, masses from 124 to 136 amu. Xenon-136 is technically radioactive, but with a half-life of a hundred billion billion years, so, you know, it’s pretty much stable. Laser cooling wavelength: 882 nm Doppler cooling limit: 120 μK Chemical classification: Noble gas, part of column VIII…

Laser-Cooled Atoms: Helium

Element: Helium (He) Atomic Number: 2 Mass: two stable isotopes, 3 and 4 amu. Laser cooling wavelength: 1083 nm Doppler cooling limit: 38 μK (It should be noted, though, that despite the low temperature, laser-cooled helium has a relatively high velocity– that Doppler limit corresponds to an average velocity that’s just about the same as…

A little over a year ago, I visited Mark Kasevich’s labs at Stanford, and wrote up a paper proposing to use a 10-m atom interferometer to test general relativity. Now, that sounds crazy, but I saw the actual tower when I visited, so it wasn’t complete nonsense. And this week, they have a new paper…