Dear Clemente,

        About two years ago we switched from 3mm thick BaF2 windows (50mm
dia) to 6mm thick windows.  Our 25W CO2 laser delivers about 17W to the
sample chamber (after all of the turning mirrors, beam expanders and
focusing lenses.  We have done more than 7000 silicate analyses during that
time and had only one window break.

        From talking with colleagues about this all too common phenomena, I
wonder how other parameters factor into this, for example:

Distance from the bottom of the window to the sample (associated heating of
window, spattering on window).

Power density of the laser as it passes through the window (our beam
diameter is about 5mm as it passes through the BaF2).

High stress regions introduced to the window by clamping mechanisms.

BaF2 crystal quality (I am told there are at least two grades of BaF2, a
lower one for windows, a higher quality used primarily for lenses).

Hope this helps,

Michael J. Spicuzza
Dept. of Geology & Geophysics
University of Wisconsin
Madison, WI 53706

(608) 262-9498 phone
(608) 262-0693 fax
[log in to unmask]