poor laser power - too soon?

SIMON MONARD smonard at staffmail.ed.ac.uk
Wed Sep 10 05:46:50 EDT 2008


Hi Ray

Yup most folk use the uv multiline optics with no mirror, you can get  
300mw out of a good I90. Are yo sure its the actual laser power  
changing and not the measurement? Do you have one of those dinky laser	
power meters Coherent sell? As I remember the front brewster faces  
upwards and is prone to dust falling off the cover onto the window if  
you knock  it. A quick wipe may well restore your power.  Also I think	
if the brewster window covers are not in place the power will decline,	
again maybe dust settling on the window. Phil at evergreen lasers was  
always my guru for laser problems.
All the best

Simon

   Quoting Ray Hester <rhester at jaguar1.usouthal.edu>:

> Hi,
>
> We have a Coherent 5-watt I 90 that we use primarily for UV for cell
> cycle analysis with Hoechst stained samples on a FACSVantage.  It was
> purchased in August 2004 and has around 1,500 hours on the tube, which
> is the original one.
>
> We have been using it at somewhere around 365 nm in single-line
> operation (which we have recently learned from a Coherent service rep
> is unusual, with most labs having this laser on a FACS  using the
> multi-line configuration for UV and getting around 150 to 200 mW of UV
> power, or more!)
>
> The max power we had been getting out of that laser in single-line UV
> had pretty much remained stable at around 100 mW for a long time - the
> last several years at least.	Then about six months ago that changed.
> It would show 100 mW when we first started it but during the day the
> power would decrease, leveling out at around 35 mW.  We had a Coherent
> service rep come in about a month ago and he was able through cleaning
> with ABF to get the max back to 100 mW.  Soon after he left, we once
> again begin experencing this decline in power and now the the max we
> can now get is around 40 mW - when first turned on it's at 40 mW and
> pretty much remains there throughout the day. We haven't cleaned the
> windows or mirrors, since it's been such a short period of time since
> the rep was here and he did all of that as part of his routine.
>
> Does anyone ahve any idea what might be the cause of this decline,
> especially so soon after the service rep had it back up around 120 mW
> just two  months ago?
>
> Also, taking into account the above, are we likely to return to the 100
> mW power level if we switch from single line (i.e., with prism) to the
> multiline high reflector mirror?  We are going to switch to the
> multiline and see with what results, but just thought we would ask what
> the consensus is.
>
> Thanks for any help.
>
> Ray Hester
> Univ. of South Alabama
> 251 460-6029
>
> .....................
>
> From 'Description of Work Done' on the service report (7/16/08):
>
> "Cleaned and peaked, unit is used exclusively in the UV 363 nm so I
> went back to ALVS and found that anode window needed ABF'd [ammonium
> bifluoride] that helped the power.  Also the beam is very close to the
> top of the anode window, but service did not bend stem since tube is
> out of warranty.  Obtained 7.6w ALVS. 120 mw 363 nm. unit runs fine"



Simon Monard
FACS Facility Manager
Institute for Stem Cell Research
University of Edinburgh
Roger Land Building
West Mains Road
Edinburgh
EH9 3JQ

Tel. Lab 0131 6505876
Tel Office 0131 6517265

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