Laser Power

Andrew Beernink ABeernink at
Fri Aug 16 14:46:27 EST 2002

Hi guys & gals-

I'm betting the gurus out there already know this, so for the rest of us:

Here's a little tidbit I just picked up:  tunable wavelength lasers must be
calibrated to display and output at the indicated power, for each

I have a Coherent I70 Spectrum, which was probably set for 488 or 514 when
it was installed.  Having recently purchased a LaserCheck power meter, I (of
course) started measuring everything that shined.  To my dismay, I found
that 100 mW of 647, as indicated on the remote, gave ~200 mW on the power
meter.  I had heard that these small power meters were pretty inaccurate...

When I called our FSE, he told me that there is a small prism near the
output coupler, which directs a "tiny bit" of emitted light to a small
sensor.  As the sensor does not recognize wavelength, but heat (I think I
got that right!), there will be variation at different wavelengths.  On top
of this, it turns out that said sensor is much less accurate than the
handheld power meter; so, calibrating the output based on the reading on the
power meter is (allegedly) a step in the right direction.

This was not a criticism of the Coherent laser!  I love the thing, and now
that I can more accurately determine power output, I'll have more time to
spend on experiments utilizing its many available output lines!

Novasite Pharmaceuticals

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