Re: photodiode for 500mw laser
- From: Phil Hobbs <pcdhSpamMeSenseless@xxxxxxxxxxxxxxxxxx>
- Date: Fri, 26 Dec 2008 08:50:40 -0500
Helpful person wrote:
On Dec 24, 1:24 pm, Phil Hobbs
<pcdhSpamMeSensel...@xxxxxxxxxxxxxxxxxx> wrote:
Louis Boyd wrote:Sam Goldwasser wrote:My favourite method for this is to use first-surface reflections off a"fz.ghazavi" <fz.ghaz...@xxxxxxxxx> writes: Hello friends,I'd expect damage to the diode. The damage would be purely thermal
I have a 500mw laser diode and want a photodiode for measuring the
power of this laser diode.if any photodiode is appropriate or some
charachteristics are necessary that i must consider? my laser diode
is
ADL-80V01NL and photodiode that i have chosen SFH203PFA
is it possible that this power burn the photodiode?
effects. You picked a 1mm square diode and are trying to dump a half
watt at 808nm. It might survive a while with active cooling. If you're
just trying to measure average power you could use a simple lens to
spread the power a bit unless you really need the high speed
characteristics of that diode. If the beam spread to an inch diameter it
will have about the energy density of sunshine and any silicon diode
will handle it. With a 1cm spot size I'd want a heat sink to run it
continuously, but should be ok if you do the power test in a second or
less.
Sam Suggested a filter. Inconel on quartz beam splitters (ND filters)
are available for around $75 with 1% or 0.1% (and many
other)transmission values which would do the job with the diode you
chose. I'd go that route if I needed high speed measurements. I
wouldn't use an absorptive glass filter as it would likely break.
piece of black glass. Near normal incidence, Fresnel reflections are
better calibrated than your average Inconel-coated filter, and you can
get rid of any polarization effects by using two reflections with the
same incidence angle in the p and s planes.
Cheers,
Phil Hobbs- Hide quoted text -
- Show quoted text -
I've often used reflection off microscope slides (for uncalibrated,
simple measurements) however, I like the black glass method a lot
more.
Interestingly index matching substances such as black glass (fused or
cemented to lens and prism edges) can be used very effectively in
cutting down stray light in optical systems where low noise is
critical. I find it strange that this method is not widely adopted
(or known?).
I've used that method also. For one highish power system I had problems with the thermal expansion of the black glass causing defocusing of the reflected beam, so I UV-epoxied it to the back of a thick BK-7 window. That way I got the first-surface reflection minus the defocusing.
Ordinary hardware store flat black paint (Krylon Ultra-Flat Black) uses an acrylic binder that is an excellent index match to fused silica in the visible. A fused quartz/Krylon interface has a reflectance of about 10**-4 at room temperature, which is pretty good--about as good as each of the glass/cement interfaces in a glued sandwich. Paint doesn't have the power handling capacity of black glass, of course.
Cheers,
Phil Hobbs
.
- References:
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- From: fz.ghazavi
- Re: photodiode for 500mw laser
- From: Sam Goldwasser
- Re: photodiode for 500mw laser
- From: Louis Boyd
- Re: photodiode for 500mw laser
- From: Phil Hobbs
- Re: photodiode for 500mw laser
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