Dear Mark,
I generally use MgF2 windows from Casix and I can measure the transmission, using a VUV PMT with interference filter, and the transmission is ~ 80%. I have used Thorlabs MgF2 lens and I can say that the transmission is good but I cannot quantify it as it focuses the light towards the PMT, so direct comparison with the windows is not legitimate. I suspect this might be the problem for Thorlabs. My feeling is that the Thorlabs lens' transmission is probably at least 50%, based on the fact that I have never bought a MgF2 window any worse than this. It is ~ 115 nm where things start absorbing badly and where the quality of the MgF2 would more come into play. If you want a lens of an exact radius of curvature then you might need to approach an specialist company. In the UK I have used Crystran for
MgF2 lenses, http://www.crystran.co.uk/, and I had no problems with their quality.
In general, I do not use MgF2 lens to direct 118 nm as it has more of a potential to damage optics and cause spurious signals on the mass spectrometer. I use waveguides to take the light from a frequency tripling cell toward the ionization region of the mass spectrometer. This is an efficient way to direct VUV light and it is never focused, so no drilled optics.
Thanks,
Mark
Mark Blitz
School of Chemistry,
University of Leeds,
Woodhouse Lane,
Leeds LS2 9JT. U.K.
Tel 0113 343 6594
Email: [log in to unmask]
-----Original Message-----
From: Molecular dynamics and chemical physics community [mailto:[log in to unmask]] On Behalf Of Mark Sulkes
Sent: 21 October 2013 22:56
To: [log in to unmask]
Subject: MgF2 lenses for VUV (~118 nm)
Dear All,
This is a recurring question. I posed it several years ago and was told that ISPoptics made MgF2 lenses, nominally for the IR, that also worked well in the 118-121 nm range. From experience, this was true, but a graduate student has just drilled our lens and I found that ISPoptics no longer sells MgF2 lenses. Can anyone suggest a current cost effect option here--with the important requirement that transmission is decent at 118 nm? I want particularly to ask about the now available Thorlabs MgF2 lenses. The prices are very low (under $300 for all focal lengths at d = 1"). However, on calling them they said they couldn't provide any transmission data below 200 nm. Can anyone comment on whether their lenses work well for VUV applications? If not, what are the most cost effective alternatives?
Thanks
Mark Sulkes
Tulane University
New Orleans, LA USA
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