When looking at this video and the guy using lasers to cool instead of heat a substance, is my assumption that he uses extreme short laser pulses to counter the vibration from said substance true ? Or is it more like the laser having the light frequency that exactly counters the frequency of the substance vibration (so the beam is continuous) ? In any case, does this guys experiment suggest that there's a universal frequency for all atom types ? (a frequency so high it can actually resonate or interfere at the exact same frequency of all atom types ?) Umm I put the link in the description....sorry... Also, does the frequency increase while the amplitude lowers ? (this would explain why the lasers aren't able to cool it any further once the frequency needed to counter the vibration increases beyond the point where the laser emitters can't increase their frequency any more...)
THANX !! That's a process I actually never heard of.. (I get exited when learning something like this..) I have one question.. Let's say the matter is vibrating at 100 Mhz (just for example, not an actual frequency I think) is it like they use 100Mhz - 1Hz to cool it ? I read about that Zeeman cooler, that increases the speed of matter stream to compensate for the lower velocity of the atoms from their vibration, thus once again having the speed the neccesary to apply the Doppler cooling again.. Well my question is: Is it neccesary to use just that frequency, or can it be like a multiple of that frequency ? (like 200Mhz - 1hz, or 300 Mhz -1 hz, etc) (and that off course assuming what I said is actually right..)
I only just now noticed this thread, but good questions! Laser cooling is fascinating. Please Register or Log in to view the hidden image! In your most recent post, it sounds like you're getting the frequency of the cooling laser confused with the vibrational frequency of the atoms. The laser frequency is chosen based not on the atoms' motions, but on their absorption/emission spectra. Every element has a distinctive set of energy levels, or orbitals, that its electrons can occupy. Since the energy in a laser depends on its frequency, we can choose a frequency that corresponds to the energy difference between the lowest-energy "ground" orbital and some higher-energy "excited" orbital. When we shine this frequency of light (or a frequency very close to it) on our atoms, their electrons will tend to absorb the light and jump up to the excited orbital. This is called an "absorption band", because it defines a narrow band of frequencies that are much more strongly absorbed than the ones around them. For cold atoms, the absorption band frequencies are much, much higher than the atoms' vibrational frequencies. For example, in the lab I work with, the atoms vibrate at a few hundred kHz, but the absorption bands are in the hundreds of THz. This means that we take a laser on resonance for absorption and "detune" its frequency down by a few vibrations' worth of energy, it will still be pretty close to the absorption band. (Going back to the lab example, we would tune the laser to its hundreds-of-THz resonance, then lower the frequency by maybe a MHz.) In this situation, the atoms will still absorb the light strongly, but since the laser energy is no longer high enough to drive an excitation on its own, the atoms need to "borrow" some of their vibrational energy to make up the difference. origin's link does a good job explaining this effect more rigorously, via the Doppler effect. Eventually, the excited atom will spontaneously emit a photon and fall back to the ground state, leaving it back where it started minus the kinetic energy it borrowed. Over many cycles of absorption and emission, the atom will steadily lose kinetic energy, until its thermal velocity is no larger than the recoil associated with spontaneous photon emission. Any further details are just tricks scientists use to jump-start the borrowing cycle in various conditions, like if the atoms are moving very fast to start or could be moving in any direction. Hope that helps!
