Laser noise

[GregS]

I was trying to attempt to measure noise on a 6 watt laser. The main problem
is trying to focus on something without it melting or catching fire.
I was trying to look at the reflective light withg a photodiode.
I guess there migh be some fancy expensive device ??

greg

 

[William Sommerwerck]

What about using a lens to spread the light?

 

[William Sommerwerck]

What about using a lens to spread the light?

Wouldn't that affect or distort the noise or influence
the reading otherwise?

Well, at the least it would reduce the absolute value of noise read. But if
the light were spread evenly, and you knew the area ratio of spread to
direct light...

 

[GregS]

Well, at the least it would reduce the absolute value of noise read. But if
the light were spread evenly, and you knew the area ratio of spread to
direct light...

Spreading would be fine, as long as it does not spread to my eyes.
But thats a good idea.

greg

 

[William Sommerwerck]

Three front-surface reflections from window glass, plus an ordinary

photodiode. Make sure the multiple reflections miss each other.

So you'd have 4% of 4% of 4%, or about .000064 of the original energy,
right?

 

[tm]

I was trying to attempt to measure noise on a 6 watt laser. The main
problem
is trying to focus on something without it melting or catching fire.
I was trying to look at the reflective light withg a photodiode.
I guess there migh be some fancy expensive device ??

greg

Use a clear optical glass beam splitter. Pick the incident angle to
get as much or less as you want. Terminate the beam into a beam stop
(brick?).

T

 

[Samuel M. Goldwasser]

I was trying to attempt to measure noise on a 6 watt laser. The main problem
is trying to focus on something without it melting or catching fire.
I was trying to look at the reflective light with a photodiode.
I guess there migh be some fancy expensive device ??

All sorts of ways of reducing the power density including lenses to spread it
(as someone else mentioned), or a simple beam sampler using a glass plate to
pick up 8 or 10 percent. A couple times and you get down to reasonable power
levels. Or get a proper beamsplitter that can be obtained to reflect
a very low percentage of the beam power. An optical filter or even a mirror
that reflects most of the beam and transmits a small percentage can also be
used, but probably only after the lens to reduce the power density so as not
to damage it.

Then any photodiode will be fine.

Those expensive devices have some means of reducing the power to acceptable
levels for their sensors.

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[Samuel M. Goldwasser]

Wouldn't that effect or distort the noise or influence the reading
otherwise?

Not as long as the noise relative to the total power into the sensor
is what's measured.

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[GregS]

..

Pre-apologize for the naive question:
Are you measuring amplitude noise and/or spectral noise?
Are these valid questions?

I'm mostly concerned with power supply noise or whatever is predominant.

greg

 

[Samuel M. Goldwasser]

I'm mostly concerned with power supply noise or whatever is predominant.

What type of laser are you using (sorry if I forgot!)?

If it's a diode laser, looking at an electrical signal from the power supply
that corresponds to the laser diode current may be nearly as good as looking
at the laser's output and doesn't require a sensor.

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[GregS]

I'm mostly concerned with power supply noise or whatever is predominant.

What type of laser are you using (sorry if I forgot!)?

If it's a diode laser, looking at an electrical signal from the power supply
that corresponds to the laser diode current may be nearly as good as looking
at the laser's output and doesn't require a sensor.
[/QUOTE]

Right, but getting to the right point is somewhat of a risk. I don't want to send anymore lasers back to China.

Greg

 

[Samuel M. Goldwasser]

Right, but getting to the right point is somewhat of a risk. I don't want to send anymore lasers back to China.

Maybe best to just leave them there in the first place.

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