From: ar3@mrc-lmb.cam.ac.uk
Date: Mon Oct 26 1998 - 06:18:42 EST
>From: Pizzo@nso1.UCHC.EDU (Pizzo,Eugene) >To: Cytometry Mailing List <cytometry@flowcyt.cyto.purdue.edu> >Date: Fri, 23 Oct 1998 09:51:58 -0400 >Subject: Re: COHERENT LASER PROBLEM > > > >Andy, > >Thanks for all that info, I think that about does sum it up. >We have the Innova-90-6 which indeed is supposed to >put out 5W MLV and 400mw UV but in fact we do have >the over pressure problem you mentioned. > >Optics and Brewster windows were cleaned professionally >just last week by Coherent service and the output /front Brewster window >could not be adequately cleaned with Ammonium Bifluorite but they do not >agree with >your 'dying' scenario. They support Peter Lopez's 'UV dropping-out-first' >syndrome in which the fact that I'm getting over-pressure at 4689 >hours suggests I do indeed need a new tube if I'm going to require >reliable UV. > >Coherent tells me that UV is more dependent on correct pressure and >that given the age of the tube that running it at full power in visible for >an >extended period will in fact not correct the pressure problem. And the >inability to adequately clean the Brewster window necessitates a new tube. > >Thanks to you and everyone else that replied, > >Gene/UCONN Health Gene, I talked with a Coherent engineer here in the UK about your problem, because I had experienced a similar thing. In my case it was a faulty rear Brewster window on a new tube. He told me about the way Lasers of this type die, and that the anode or cathode in the tube tend to go first, hence the 'firing up problem'. The very fact that you front Brewster window cannot be cleaned suggests to me that, that is your main problem. You did say that you were getting 100mW of UV from your laser, even though it is over pressure and has a dirty front Brewster. I reckon you would get lots more UV if the Brewster window was clean. That is not to say that the pressure problem is irrelevant, try running your laser hard in visible for a long while (days?) and see if your UV improves. If it does not, then it is your window. Anyway, if you've got the service contract then coherent will replace your tube. Can anyone else clarify the way the Innova 90 class lasers die? Regards, Andy. Andy Riddell PNAC MRC-LMB Hills Road Cambridge UK tel (0) 1223 402218 fax (0) 1223 412178 email ar3@mrc-lmb.cam.ac.uk
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