photosensor for use with laser

tay · Jan 20, 2009

Hey folks,

For a project I'm working on, I want to use a laser with photosensors to detect if the beam has been interrupted. I was figuring to just use a ~1mW red laser because I don't want it to cause any damage to whatever interrupts the beam.

I've used Cadmium-sulfide photosensors before, but never in conjunction with a laser. It's a round disk a little smaller than a dime. I was thinking to get a 2" piece of pipe the same diameter as the photosensor, paint the inside with flat black nonreflective paint, and mount the photosensor at the end, to block all ambient light.

Will a CdS photosensor work well with ~650nm red 1mW laser?

PhotonWrangler · Jan 20, 2009

tay said:
Hey folks,

For a project I'm working on, I want to use a laser with photosensors to detect if the beam has been interrupted. I was figuring to just use a ~1mW red laser because I don't want it to cause any damage to whatever interrupts the beam.

I've used Cadmium-sulfide photosensors before, but never in conjunction with a laser. It's a round disk a little smaller than a dime. I was thinking to get a 2" piece of pipe the same diameter as the photosensor, paint the inside with flat black nonreflective paint, and mount the photosensor at the end, to block all ambient light.

Will a CdS photosensor work well with ~650nm red 1mW laser?

Both cadmium-sulfide photoresistive and silicon photovoltaic cells work well at the red end of the spectrum. CdS cells can degrade if moisture gets inside; this is not a problem with silicon cells. On the other hand, silicon cells are MUCH more fragile.

tay · Jan 21, 2009

Does one have an advantage in terms of response time, i.e. will detect the absence of the laser faster, or will detect it if the laser is blocked and quickly unblocked.

PhotonWrangler · Jan 21, 2009

tay said:
Does one have an advantage in terms of response time, i.e. will detect the absence of the laser faster, or will detect it if the laser is blocked and quickly unblocked.

The silicon cell will have much faster response time, although we're only talking a few hundred milliseconds of a difference between the two. If you're going to use a modulated beam though, you definitely need silicon.

tay · Jan 22, 2009

No, wasn't planning on pulsing the laser. I just wanted a beam with a touch sensor that if I wave my hand through it quickly, it is able to detect the change.

PhotonWrangler · Jan 22, 2009

tay said:
No, wasn't planning on pulsing the laser. I just wanted a beam with a touch sensor that if I wave my hand through it quickly, it is able to detect the change.

A CdS cell is plenty quick enough for that.

LLCoolBeans · Jan 22, 2009

This sounds like fun. Are you building a security system to protect against jewel thieves in ninja uniforms?

tay · Jan 23, 2009

laser guitar :rock:

PhotonWrangler · Jan 23, 2009

Is this the same principle as the laser harp?

Ggiant85 · Jan 25, 2012

Hi there, found this site through google and have a related question, hopefully this isnt taken as thread jacking, but i was wondering if you could use these same photosensors to complete a circuit when the laser comes into contact with the sensor, if so, will the green variety of lasers react the same, and are these readily available, radio shack or something similar?

FRITZHID · Jan 25, 2012

in my practice all photo sensors react well to lasers, beit green, red, blue and even IR. i've used all of these to turn off street lights, setting alarm and auto door setups and a few other "booby traps" and even had made a rudimentary "laser harp" as a collage laser science project. the laser beam itself provides plenty of photons to react any of the sensors available. just make sure your alignment is right.

PhotonWrangler · Jan 25, 2012

It doesn't make much difference whether the laser is red or green; I believe both silicon and CdS photosensors have sensitivity across the visible spectrum.

Ggiant85 · Jan 25, 2012

my intention for all of this is geocaching, if anyone has heard of it, i would love to be able to bounce the entire idea off someone that is familiar.

bshanahan14rulz · Jan 26, 2012

I know that PhotonWrangler's laserharp post was made in 2009, but for anybody else searching for laser harp, one of our members here sells a circuit that you integrate with a laser and a scanning galvo. It's at illumination supply, google it.

FRITZHID · Jan 27, 2012

PhotonWrangler said:
It doesn't make much difference whether the laser is red or green; I believe both silicon and CdS photosensors have sensitivity across the visible spectrum.

the CdS cell will also activate quite nicely with IR, but UV has proven not to be as effective, perhaps the Silicon cell would be more receptive?

PhotonWrangler · Jan 27, 2012

FRITZHID said:
the CdS cell will also activate quite nicely with IR, but UV has proven not to be as effective, perhaps the Silicon cell would be more receptive?

I believe that silicon photocells have a little more sensitivity to the blue end of the spectrum than cadmium-sulfide photoresistors. If higher overall sensitivity is needed then a phototransistor or photodarlington might be a good choice.

FRITZHID · Jan 28, 2012

PhotonWrangler said:
I believe that silicon photocells have a little more sensitivity to the blue end of the spectrum than cadmium-sulfide photoresistors. If higher overall sensitivity is needed then a phototransistor or photodarlington might be a good choice.

game & match! phototransistors react to damn near anything including the 10,000nm (heat) range IR. lol

photosensor for use with laser

tay

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tay

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tay

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