Can a green laser pointer be used to create pulses about 10 microseconds wide?
ElectricAye
Posts: 4,561
I was considering using banks of LEDs to create bright pulses of light, each pulse lasting about 10 microseconds, but then I found out that many green laser pointers emit a wavelength (532nm) close enough for what I need. So I would like to know if such cheap laser pointers can be kluged to emit pulses that fast - or even faster.
Also, is there any way to vary the intensity of those pulses or do laser pointers always emit the same intensity no matter how short the pulse?
I know nothing about laser diodes so any suggestions would be greatly appreciated.
Thanks!
Also, is there any way to vary the intensity of those pulses or do laser pointers always emit the same intensity no matter how short the pulse?
I know nothing about laser diodes so any suggestions would be greatly appreciated.
Thanks!
Comments
Sorry, I can't answer your other questions.
I've read that green lasers (at least the ones in laser pointers) actually use an IR laser that travels through some sort of crystal to shift its frequency. I believe there is still a lot of IR left in cheap green laser pointers' light.
how are you communicating with green led??
Laser diode intensity changes by varying the current to the diode. The diode will vary in brightness as long as the current is above the lasing threshold and below the current which will kill the diode (see the diode's spec sheet). However, most of the drivers boards I've seen don't expose that to external control. There's a soldered on trim pot used to control the current and the resulting brightness.
Finally, there are no green laser diodes. They use an IR diode with a frequency doubling crystal and an IR filter. Green laser modules are twitchy as a result and shouldn't be opened.
This guy uses a RED (not green) laser pointer on his targeting system. And the Hamamatsu chip is modulating the red laser at ~1.25 Khz, much slower than the 10uS pulse width you seek, but there may be some info there you can use. http://www.junun.org/MarkIII/datasheets/S6809.pdf
If nothing else, check out the target acquiring, missile launching video in the last link.
Thanks for the heads up about the residual IR. I didn't know about that and that would have definitely messed up everything I'm trying to do.
I'm not using this for communications. It's for pulsing a photosynthetic complex in bacteria to see how it behaves.
Thanks, Martin, for your advice. I'll poke around and see what I can find. I first thought about the laser pointer because it sounded like a cheap place to start, but maybe just going with a module might save me money in the longer run.
Thanks erco. You're right about this system being too slow for my application. Looks like fun, though.
There is no question that a laser diode can be driven to produce 10 µs pulses. Whether or not a laser pointer can be driven to do it depends on the circuit in the pointer. Some of them are barely more than a resistor in series with the laser diode, but others use a feedback circuit that monitors a photodiode that is co-housed in the laser package. Those would be more expensive, and slower.
Tracy, thanks for the link to Sam's! And for word about laser diodes. I'm out of my league with this but without your help, I'd be lost.
The best way to modulate laser light is with an acoustic modulator. You don't want to have to buy one, as they are very expensive. The modulator works by shifting the beam pattern ever so slightly. Modulation speeds of 400 MHz and above are not uncommon. You need to match the modulator with the wavelength of the light. A modulator for an argon laser should work, as the mainlines are close.
Whether or not you need an acoustic modulator depends on the precision required by your application. The fact that the module may not be operating in true laser mode may not matter to you, in which case you can try toggling the power supply with a MOSFET. Then the only problem will be finding an affordable high speed detector for that wavelength...
-- Gordon
Thanks, Gordon, you brought up an important point. I don't really need the light to be coherent. This is all about pumping as much ~530nm light as possible into a small tube. The high speed detector situation is also a good point, as I found out last night.
The light intensity from a penlight laser isn't necessarily more than a couple of cheap ultrabright LEDs, though. It just seems brighter because it's collimated and coherent. If you're not looking for spatial or temporal coherency, rethink using some LEDs. A 1 watt LED will pump out much more light than a penlight laser, is the same price or less, and if properly collimated (think telescope in reverse), will more than flood whatever you're trying to illuminate.
Something along these lines, for example, assuming the wavelength is what you need:
http://www.allelectronics.com/make-a-store/item/LED-111/1-WATT-GREEN-ULTRA-ULTRA-BRIGHT-LED//1.html
or this one, which could cause eye injury if you looked directly at it:
http://www.niktronixonline.com/10_Watt_High_Power_LED_Green_700_LM_p/10wattledgreen.htm
Thanks again, Gordon.
I'm marking this thread as SOLVED since you wonderful people have given me plenty to chew on for the next week or so.
Have a great weekend, everybody!
:-)
That's not true anymore... the Microvision laser projecter, for example, is actually using the new generation of lasers which do produce a 523nm output without the need for an IR doide pump. There are several companies now moving to this new native green technology.
Bill
http://www.nytimes.com/2011/06/14/science/14oblaser.html
http://www.nature.com/nphoton/index.html
http://www.nature.com/nphoton/journal/vaop/ncurrent/full/nphoton.2011.99.html
Main line is at 516 nm.
Yes, I saw that. Turning living things into lasers, how crazy is that. How long will it be before we're all beaming with happiness?
Lend new meaning to flashing a smile?
After realizing how difficult it is to work at 532nm, I think I might try working at one of the other action points in the spectrum, around 880nm. It looks like cheap LEDs at that wavelength can work really bright and fast. Also, detectors at that wavelength are cheap and easy to use. That green part of the spectrum turned out to be an expensive nightmare. The only drawback I can "see" with 880 nm is that its transmission through water isn't very good.
Thanks for your help on this. I'm glad I didn't wander too far into the green zone with this. The infrared district seems more suitable to my budget. :-)
This is over my head...!!
Hey, it's way over my head, too, but that's never stopped me!
Most people I've worked with never knew what they were doing, either. :-)
Also, if it's of any value, for laser- related stuff, there's two places I can always rely on to get both excellent info, and fantastic hardware:
[url]Http://www.photonlexicon.com/[/url]
[url]Http://www.laserpointerforums.com/[/url]
Both places have some rough edges around various personalities, but there's quality people on both who are amazingly knowledgable and willing to help, and the fourms are a treasure-trove of schematics and detailed project descriptions. I'm currently building a 445nm 1 watt device... it actually cuts stuff! I could have never built it without the information on these two forums. In short, if you need truly massive quantities of almost any given wavelength or combination thereof, pumped into a tiny space, you will find info there.
BTW, if it isn't proprietary, I'd love to know more about the photosynthetic compound you're playing with... sounds quite intriguing.
Dave
I'm not associated with the guys to which I've linked below, but this is related to the kind of stuff I work on. Nature's capability to capture sunlight is far better than anything humans can do, so it's worth figuring out how these 3 billion year old complexes do their thing.
http://www.ks.uiuc.edu/Highlights/?section=2007&highlight=2007-10a
Dave