Old 06-10-2011, 05:25 AM #1
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Default Laser pointer "oscillation" frequency

Hi all.

I am designing a photodetector array for a high speed data acquisition system. In order to test the device I used commercially available red and green laser pointers, and I found out to my surprise that the laser light was switching on and off at ~150kHz (red) and ~450kHz (green). I thought that such a switching at a high frequency could help saving power, but I am quite skeptical.

Is this kind of switching common with laser pointers? Or should I go back and check my sensor for problems?

Thanks in advance.


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Old 06-10-2011, 12:59 PM #2
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Default Re: Laser pointer "oscillation" frequency

I have heard of some manufacturers using pulsed drivers
for their laser pointers... but that is NOT common...

I would recheck the sensor.... You can test it with an LED on
a pure DC source..

You can turn on your laser and scan it across the room from
extreme left to extreme right quite quickly...
If the Laser is pulsed you should see the beam broken and
not solid...


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Last edited by lasersbee; 06-10-2011 at 01:01 PM. Reason: Spelling errors
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Old 06-10-2011, 03:19 PM #3
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Default Re: Laser pointer "oscillation" frequency

What are you using for sensors? Photodiodes, LEDs, or recievers? Photoreciever modules may be your problem. Try re-design with a phototransistor array (bridge) feeding a low gain op-amp (or, you could use low biased LEDs feeding a moderate to high gain op-amp as your reciever).
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Old 06-10-2011, 05:37 PM #4
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Default Re: Laser pointer "oscillation" frequency

Only some blue DPSS and some OLD green pointers are pulsed.

Quote:
Originally Posted by lasersbee View Post
If the Laser is pulsed you should see the beam broken and
not solid...
Not at 450KHz you wouldn't.
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Old 06-10-2011, 07:20 PM #5
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Default Re: Laser pointer "oscillation" frequency

Mr paragon,

A un, or poorly, filtered switching supply?? Just guessing...
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Old 06-14-2011, 02:19 AM #6
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Default Re: Laser pointer "oscillation" frequency

Did you properly reverse bias your photodetector array? If not, the photo cells are operating in photovoltic mode and with stray capacitance and a high impedance meter/scope you may be getting false readings.
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