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Help! Li saturation absorption spectroscopy!

  1. Dec 23, 2011 #1
    Dear PF,

    I'm a graduate student working in an ultracold atomic phys lab. We're trying to build a new machine with Li6 as one of the components, but in order to cool it we need to do saturation absorption spectroscopy on a separate stand-alone cell in order to tell our lasers what frequencies they need to be.

    To get a high enough vapor density of atoms we have to heat the lithium to about 350 - 400 centigrade, so we put the lithium inside of a stainless steel tube (solid Li chunk just sits on the inside of the tube) with windows on each end (for optical access) and heat the tube with fiberglass heater tape. The thermocouple that gives us out temperature reading is just sitting underneath the tape (on the outside of the cell), which gives us a measurement of the temperature between the tape and the cell.

    Note that Li has a melting point of about 180 centigrade. Additionally, the cell has a background pressure of about 10 mTorr (Argon) to prevent adsorption of the Li on the cell windows.

    Here's my question:

    A few months ago I turned the heater tape up to about 400 centigrade, but the Li remained solid! In fact, the shape of the chunk doesnt appear to change at all! Why doesn't it melt? Shouldnt the temperature of the inside of the cell (at least the surface) be the same as the outside of the cell?

    The literature mentions that some groups initially bake their lithium up to 500 degrees to "break oxidation", but even at those temperatures the Li didnt appear to melt either!

    Any ideas would be appreciated.
  2. jcsd
  3. Jul 5, 2012 #2
    Ihave the same question
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