ftpam1@acad3.fai.alaska.edu (MUNTS PHILLIP A) (07/22/90)
In article <5350@milton.u.washington.edu>, whit@milton.u.washington.edu (John Whitmore) writes... >In article <1990Jul21.023806.12927@hayes.fai.alaska.edu> ftpam1@acad3.fai.alaska.edu writes: >>In article <14380@venera.isi.edu>, sllu@jenny.isi.edu (Shih-Lien Lu) writes... >>>will detect UV light only (200nm to 400 nm wave length)? >>>If not, is there any device that will detect light down to 200 nm wave >>>length? >> >> Photomultiplier tubes (possibly with optic filtering). > > Or perhaps simple photocells. The bias voltage on a >photomultiplier (PMT) tube's first cathode can be deliberately >degraded (run low) so that only energetic photons (UV) generate >electrons... this is the 'photoelectric effect' that Einstein >got his Nobel for explaining. Photocells, while having MUCH >lower currents, are easier to bias. Look up 'stopping potential' >in any discussion of photoelectricity. > > John Whitmore Hmmm... an interesting idea that I wouldn't have thought of. There are some problems, however. First ordinary glass doesn't pass UV. Second you need a photocathode designed for high quantum efficiency at UV. I am afraid you can only satisfy these with a PMT or photocell specifically designed for UV. Still, I wonder if anyone still makes non-PMT phototubes? It's worth a test. Anyway, I just found a blurb in the August 1990 "Modern Electronics" that lists a G3614 UV (260 to 400 nm) detector (solid state GaAs) from Hamamatsu Corp, 360 Foothill Road, POB 6910, Bridgewater NJ 08807. (Note that I left out a "ma" from the name before.) Philip Munts N7AHL NRA Extremist, etc. University of Alaska, Fairbanks
heskett@titan.tsd.arlut.utexas.edu (Donald Heskett) (07/22/90)
The Hamamatsu Photomultiplier Tube catalog seems to show that most classes of photocatode material used in their PMTs have significant UV response. The 200K and 250M classes, in particular show wide responses, from roughly 120nm to roughly 300nm. The photocathode material in both cases is Cs-Te and the window material in both cases is synthetic silica. Hamamatsu devotes one of their catalogs to non-PMT phototubes (a.k.a., "phototubes"!). The R1187 phototube, with Cs-I photocathode and MgF2 window, shows the best short-end response, down to slightly below 120nm, though extending "redward" only to about 200nm. As I remember, Hamamatsu responds with their catalogs quite quickly. Also, college physics and astronomy departments are almost certain to have them on hand.