Have you considered using CVD diamond for a CO2 laser window? It is the
perfect solution (other than price) for laser fluorination as diamond is
obviously very tough, transparent to a wide range of wavelengths (>70% at
10.6 micron), thermally highly conductive (hence immune from laser damage),
and totally inert to fluorine or BrF5.
We have used a 30mm diameter window (c. 0.5mm thick) now for nearly five
years and the window requires only an occasional wipe or rinse for cleaning
between runs. The downside is that diamond is elastomer-philic and sticks
like .... , well it forms a very good vacuum seal!
Our experience with BaF2, like others, was a story of continual laser damage
and frosting over between runs, requiring repeated repolishing or
replacement. After switching to CVDD, blanks diminished, pumpout times were
faster and the window remains clear for an entire run.
Oh, and the cost I hear you ask... Prices have fallen dramatically as CVD
production technology improves but you are looking at a four figure sum.
The all round improvement to performance is nevertheless worth considering.
Reader in Isotope Geology
Director of the University of London Stable Isotope Facility
Department of Geology,
Royal Holloway University of London
Egham Hill, Egham,
Surrey TW20 0EX
07780 697564 (Mob)
01784 443687 (Office)
01784 443582 (Dept Secretary)
On 29/11/01 3:42 am, "Kevin Faure" <[log in to unmask]> wrote:
> Dear Listmembers
> I am tossing-up the idea whether to buy ZnSe or BaF2 windows for our
> CO2 laser-BrF5 extraction system. It is apparent that ZnSe has
> several advantages over BaF2, but a little more costly. However,
> scanning the Isogeochem archives I note that Torsten Venneman
> commented that the ZnSe should be coated. Is this coating for
> reflectivity or for chemical resistance to the BrF5? If anyone has
> experience with this I would appreciate comments on what type of
> coating is needed.
> Thank you.
> Dr Kevin Faure
> Institute of Geological & Nuclear Sciences
> Rafter Laboratory
> PO Box 31-312
> Lower Hutt
> New Zealand
> Tel direct: +64-4-5704638
> Fax: +64-4-5704657