From: Winfield Hill
Subject: Re: laser diode operating range
Date: 19 Nov 2002 17:59:20 -0800
Organization: Rowland Institute
References: <3DD9B41E.A6D85CCB@webaccess.net> <3DDAE478.2FE930EF@webaccess.net>
X-Newsreader: Direct Read News 4.11
>Winfield Hill wrote:
>> Chuck wrote...
>>> There is no particular need for a laser diode if the application
>>> does not require a narrow line source. The major need is in fiber
>>> communication to reduce dispersion and in devices using holograms,
>>> diffraction gratings, Bragg cells, interferometers and the like.
>> An interesting use is fluorescence spectrometry, where the
>> fluorescence emission wavelength may be near the excitation
>> wavelength. Bleaching is a serious issue that dictates power
>> control, but the easy servo-control solution to low power can
>> mean a cessation of lasing. Resulting in line broadening, or
>> a shift to longer wavelengths, interfering with fluorescence
>> detection. One tries to avoid or minimize expensive filters.
>> - Win
> I see what you are worried about. I have not looked at UV lasers
> but for your application, you really want an APC (Automatic Power
> Control). [ snip ]
Thanks, Chuck but we do have APC (my own analog implementation,
which works down to 2% light level if desired, where the laser
first starts putting out light). That's not the issue. Maybe
there is no real "issue;" I was simply commenting on the fact
that once one has APC as you call it, it's tempting to use that
for attenuation instead of neutral-density filters... However,
only a limited current range produces coherent narrow-band light.
One thing missing from my design is a BELOW LASING THRESHOLD