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Calibration Laser weekend project


Well-known member
Sep 20, 2008
Thank you. I was waiting for someone to mention it.

I would be assert to say that it would be better to start with a good optical feedback loop which can regulate output without any temperature regulation. A good error amp would be able to do so without issue. Temperature should just be a side note for the sake of diode lifetime or wavelength control.
There is a small problem with that...

We all know that a 445nm LD will drop optical power as
it heats up at the same initial current.

If we ONLY regulate the Optical output by increasing the
drive current I can see a Thermal runaway situation if
there is no temperature regulation.

1) you increase current to bring the output back up
2) the LD heats up more due to higher dr5ive current
3) the LD output drops more due to the higher Current
producing more heat.
4) go to #1

With temperature regulation the temperature of the diode
and it's optical output would not change as drastically.

Once it is Temperature stabilized I would then use Optical
feedback to fine tune and hold the output stable.

BTW... with my FAP the optical feedback at the present
time is me watching the output on the LPM and adjusting
the FAP's TEC current manually until I find the sweet spot..

A side note... The OPHIR heads are calibrated at 1064nm
and are accurate at all the visible wavelengths. If you
have a good linear broadband coating the small variations
of the coating at different visible wavelengths will not make
a big difference for the uses on the Forum or for hobbyists
in general.

If you need a wavelength compensated LPM then all
you need to do is spend the big bucks...


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