Re: laser with 4 dot pattern
From: Sam Goldwasser (sam_at_saul.cis.upenn.edu)
Date: 06/13/04
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Date: 13 Jun 2004 08:34:57 -0400
miso@sushi.com (miso) writes:
> I picked up a melles griot 05-lhp-991 laser at a local swap meet.
I show:
Minimum e/2 c/2L Supply Nominal
Output Beam Diver- Mode Opr/Strt Tube Tube Size Model
Power Diam gence Spacing (Rb=75K) Current Diam/Lgth 05-LHx-
-----------------------------------------------------------------------------
10 mW .65 mm 1.24 mR 341 MHz 2.64/10 kV 6.5 mA 37/440 mm 991
This should be a single TEM00 beam. There is usually no way to get multiple
mode spots from these lasers even with misalignment.
> Yeah, it fires up just fine, but I get 4 distinct "dots", each of
> descending intensity. Any chance this can be caused by something
> simple, like perhaps dust or a particle in the tube housing.
You mean in a row? This is caused by multiple reflections off the output
mirror front and rear surfaces. Usually, just cleaning will help unless
the antireflection coating was damaged. These are called ghost beams
and sometimes there is no way to eliminate them entirely. On some laser
heads, there is also a protective glass plate in addition which could
be dirty or damaged.
Clean the output surface(s) with alcohol and some lens tissue
> My supply is 2450V at 6.5ma, a bit weak for the tube.
Not by much if it's a -991.
If it runs without sputtering or flickering, the power supply is running
it OK, though the power supply may be overloaded and fail prematurely if
the voltage spec is too low.
--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
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