What Do You Need to Make Cold Atoms? Appendix: "No-Laser" Methods

Last week's series of posts on the hardware needed for laser cooling and trapping experiments dealt specifically with laser-cooling type experiments. It's possible, though, to make cold atoms without using laser cooling, using a number of techniques I described in two posts back in January. Those didn't go into the hardware required, though, so what's different about those techniques in terms of the gear?

Less than you might think. In fact, most of the labs that do these experiments use exactly the same sorts of equipment that laser coolers do. Including some lasers.

It's not all of them, but lasers are a great tool for probing the states of atoms and molecules. You can use laser spectroscopy to completely characterize the state of your cold atoms. You learn about the internal states from what frequencies they absorb, and you learn about their temperature from the width of the absorption features in the spectrum-- the Doppler shift due to their thermal motion is usually one of the dominant contributions to the spectrum. You'd be hard pressed to find an atomic physics lab these days that doesn't use at least one laser in the course of the experiment.

Lasers even turn up in the atom source end of things-- the buffer-gas cooling method used by John Doyle's group (among others) often involves a laser ablation source, where a chunk of the substance they want to cool and trap inside the vacuum system, where it is then blasted with a high-power laser, vaporizing part of the solid. The atoms in the produced by the laser pulse interact with a background gas of helium atoms at cryogenic temperatures, cooling them to the point where they can be trapped and cooled further. And then studied by laser spectroscopy.

Other than the lasers, most of the hardware is the same. Vacuum systems tend to be stainless steel ConFlat, the pumps they use are similar (though many of these techniques require really high flux, so they tend to use whopping huge pumps), and so on. In some experiments, the whole thing takes place inside a dilution refrigerator to hold the temperature down within a few degrees of absolute zero, which requires a little care with the materials used (everything other than helium is a solid at those temperatures, so it's tricky to make moving parts like valves that open and close) but the major techniques are at least similar.

On the test and measurement end, there are some specialized detection techniques that don't necessarily turn up in laser-cooling experiments, things like "hot wire" detectors (which use a heated piece of wire to ionize atoms colliding with it, after which the ions are collected and counted; scanning the wire across an atomic beam can give you the beam profile) and ion mass spectrometers (atoms entering the detector are ionized, and then accelerated into an ion detector; the time required to reach the detector tells you the mass of the ion) turn up a lot. The outputs of these devices tend to be monitored with the same oscilloscopes and computers we use in laser cooling.

All of my training has been in cold-atom experiments, so I'm not familiar in detail with the hardware used for non-laser-cooling cold-atom experiments, and might be leaving something out. As a general matter, though, if you know how to use the tools and techniques in one area of cold AMO physics, it's not generally a huge jump to a different area.

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