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how fast can cheap lasers be pulsed?

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Patrick

Wed Dec 12 2012, 08:38AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

im thinking resistor and mosfet, since it looks like 50mA at 3-5vdc, for 5-20mW output.
so power efficiency may not matter much in my application.

Shrad

Wed Dec 12 2012, 12:56PM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
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if you want better than hundreds of microseconds, you have to bias the diode to just under the lasing treshold, and modulate over it =)

teravolt

Wed Dec 12 2012, 02:37PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

I think that you could get away with 1us if you drive it right. A mosfet driver with a resistor driven by a TTL cir circuit should do the trick. I have not tried this but it should be straight forward

Patrick

Wed Dec 12 2012, 09:00PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

im thinking of using this one:

Industrial 20mw 808nm 810nm Infrared IR Laser Line Diode Module 120Â°mrad

and replacing the 120 degree line lens with a 30 degree line one.

(but what do they mean by "mrad" ? surely not milli-radians and degrees?)

Proud Mary

Wed Dec 12 2012, 10:43PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Patrick wrote ...

im thinking of using this one:

Search for laser diode Beam Parameter Product (BPP) and you'll quickly find the relevant formulae.

Patrick

Thu Dec 13 2012, 04:17AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Proud Mary wrote ...

Search for laser diode Beam Parameter Product (BPP) and you'll quickly find the relevant formulae.

im searching, but still dont have any idea what BPP means in my case, maybe i need to get that "optics for dummies book"

in this page, i see "mrad" too :

this really helps:

Beam divergence measures how much a laser beam expands per meter. For example, a laser with a beam divergence of 1.0mRad will have its beam expanded by 1.0mm per meter.

iJim

Thu Dec 13 2012, 07:59AM

Registered Member #2662 Joined: Fri Jan 29 2010, 10:14AM
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Posts: 36

If you're still looking for info on how to pulse LEDs/lasers then the following link contains some useful info:

I used the same approach to drive a laser for some 'high speed' photography. Worked well!

Proud Mary

Thu Dec 13 2012, 09:35AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Patrick wrote ...

Proud Mary wrote ...

Search for laser diode Beam Parameter Product (BPP) and you'll quickly find the relevant formulae.

im searching, but still dont have any idea what BPP means in my case, maybe i need to get that "optics for dummies book"

in this page, i see "mrad" too :

this really helps:

Beam divergence measures how much a laser beam expands per meter. For example, a laser with a beam divergence of 1.0mRad will have its beam expanded by 1.0mm per meter.

Patrick, I think your ebay seller has missed out a term in the specification. 120Â° is a common angle for the long axis on laser line modules, but "120Â° mrad" is a confusion of terms, so far as I can see, as there are 17.4532925199 milliradians in 1Â°. However, laser line divergence is usually expressed in mrad, and this figure is what I think has been missed out.

I suggest you contact the seller for clarification.

Pinky's Brain

Thu Dec 13 2012, 03:44PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

Shrad wrote ...

if you want better than hundreds of microseconds, you have to bias the diode to just under the lasing treshold, and modulate over it =)

This doesn't increase the rise time of the light intensity so much as it decreases the delay from the electrical signal to optical ... this is important for modulation, because the delay has "memory" for the currents the diode saw before the pulse, but for isolated pulses it doesn't matter as much.

With the pulse widths you can generate with saturated switching with discrete MOSFETs it's almost irrelevant altogether.

Patrick

Thu Dec 13 2012, 06:39PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

i think its a typo.

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