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Good afternoon.

As far as I know, industry grade UV diodes are still in statu nascendi. A 
"comparatively" cheap UV-laser is the 325nm HeCd-laser (ref. e.g. 
www.kimmon.com), but there are some problems with this as well. Firstly, it 
prefers to lase in TEM 01* mode instead of TEM00, but you can get HeCds in 
TEM00, though at a somewhat reduced output power. Secondly, 325nm is 
comparatively deep in the UV and this might cause problems with your 
microscope optics. Thirdly, the HeCd tubes have to be frequently exchanged 
(see the lifetime specifications). The nitrogen laser, even cheaper, which 
emits light at 337nm, has the disadvantage of a poor mode structure and an 
unsufficiently small repetition rate vs. pulse length (i.e. duty-cycle) 
(ref. e.g. www.ltb.fta-berlin.de) .

The medium size Krypton laser provides lot of wavelengths between 400nm and 
450nm, but it is already of the water cooled class, and I suppose you 
consider it as too bulky and expensive.

Besides that, UV-light in the confocal means trouble, anyway, since you 
need to carefully consider chromatic aberration effects a.s.o. Years ago, 
Zeiss offered the Ultrafluar lenses for the Axio microscopes, 10X, 40X and 
100X dry and/or glyverin immersion (I can't find them at the first glimpse 
on their webpage any more, but might be they are nevertheless still 
available), and even earlier were lenses for the old 160mm microscopes 
10X/0.2, 32X/0.4glyc, 100X/0.85glyc and 100X/1.25glyc. The price you pay 
for chromatic correction from the limits of VUV to the NIR is a strong 
curvature of field. You'll need special coverslips for those (fused silica, 
200um thick). Besides that you'll need a special tubelens for UV, which is 
a fused silica CaF2-doublet instead of the normal BaF3 tube lens (again, if 
I recall this correctly from information I received by Dr. Höcherl at Zeiss 
many years ago, might be all this is outdated by now).  I have never 
applied the more recent Fluar lenses, which according to the specifiations 
on Zeiss' webpage, provide good transmission at lambda > 340nm, but at 
limited correction. Exotic lenses like Ealing's mirror objectives or OfR's 
catadioptric lenses are normally difficult to use on a standard confocal, 
Bausch&Lomb's excellent (sic!) catadioptric lenses are history.

Ref. e.g. Carlsson et al. (1992), Micron and Microscopica Acta 23(4):413-428

Best wishes
Johannes

At 02.57 em 02-06-04 +0200, you wrote:
>Search the CONFOCAL archive at
>http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
>Hi listers,
>
>Has anyone of you some experience with the cheaper UV/blue light diodes to
>excitate e.g. DAPI, instead of using an expensive UV laser in confocal
>microscopy?  We have a Zeiss LSM510 and would like to be able to use blue
>emission-fluorophores too, but a UV laser is just too expensive.
>Thanks in advance for sharing your experiences / findings about it!
>
>Sven Terclavers

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