Seeking highest power output 780-850nm pulse laser diode available

[Alaskan]

I wanted to use the camera to see if I could see bright pulses at a great distance and thought there could be a way to couple it to pull data somehow, but the more I thought about it the more I understood that was completely unworkable, photo diode it is.

 

[diachi]

I wanted to use the camera to see if I could see bright pulses at a great distance and thought there could be a way to couple it to pull data somehow, but the more I thought about it the more I understood that was completely unworkable, photo diode it is.

Yep, and a narrow pass filter/telescope if you need it ... not sure what distances you're using, how much ambient light there is etc. But you're a radio guy ... you know how all that works.

 

[bloompyle]

Can't tell in that video whether it's functioning as you think it is.

If you think about it this way. The cycle of the shutter versus the cycle of the pulsing. If the pulsing speed is of a rep rate that it's up time is longer than the down time of the camera's shutter, then you're more or less ok.

The shutter rate on a camera IS NOT nanoseconds. I don't even thing it's microseconds. Which means the downside of the camera shutter will miss dozens or hundreds of pulses in sequence.

Think of it like your eye blinking while watching a blinking light. It the light stays on for a longer period of time than your eye is closed, you'll never miss all of a single pulse. If the opposite occurs, every time you blink, you will miss pulses.

In this case, photodiode is the optimal option. You can aim the laser at the wall of the detection facility. Then, route a photodiode that is covered on all sides, but would let in extreme light from under it. This prevents false positives from non-target laser sources by blocking any light from above it. Also keeps you from beaming it directly. They don't typically like that very much.

Once your IR source illuminates the wall, the photodiode will detect target light from under its enclosure, and ping whatever is observing for a signal.

Now here's the tricky part. Finding a a photo-reactive component that also has ns up/down times so it can detect the peaks and troughs of light. This is something that means high dollar signs.

Also, and I should've brought this up a long time ago, you will not get nanosecond pulses from one of these drivers. You just can't. We can't modulate light that fast without electro-optical devices, see Pockel's Cell.

An acousto-optic modulator (AOM) wouldn't be a bad idea, a couple hundred bucks versus a couple thousand. That'll get you in the microsecond domain for sure. This also cheapens the photo-reactive side of things.

 

[paul1598419]

A very good camera should have a frame repetition rate of maybe tenths on a millisecond. I think that's the best you can hope for.

 

[RedCowboy]

What laser do they bounce off the moon mirrors and what detectors do they use?
I have read it is done, I don't think the bandwidth is much, but the distance is impressive.

 

[Alaskan]

At this point I'm interested in how well a camera might pick up the short pulses from one of these laser diodes to know how bright the IR might be viewed by the camera, but so far I can't find photographs of the output produced by a laser range finder which uses one of these diodes. I'm guessing although the frame rate, or sample rate of a CCD camera is slow compared to the pulse, when taking a still photograph a lot of pulses might be photographed by the camera, not as individual pulses, but all of the pulses together adding to the displayed brilliance, assuming the camera can pick up the IR. I'm guessing this is what would happen, even though the pulse widths are much shorter than the shutter speed.

Here's a photo I found tonight showing the output of a SPL LL85 14W 850nm pulsed laser diode on a curved piece of paper:

I found more about these diodes on Sam's Laser FAQ:

And Those High Power Pulsed Laser Diodes?

You may have seen offers of IR laser diodes with 9 W or 14 W or much higher too-good-to-be-true power ratings from various surplus companies. These are pulsed ratings and the power rating is peak. Such laser diodes have been available surplus as part of the laser rangefinder from the Chieftain tank. Since they are actually not that expensive to buy new as these things go (maybe $20 to $100). Unfortunately, while they have nice peak power ratings, the average power ratings are typically only a few mW as they must be run at a very low duty cycle - typically 0.1 percent (1 part in 1,000) or less. Furthermore, the most common wavelengths are between 850 and 910 nm and these aren't much use for most laser projects (though wavelengths from 780 to 980 nm are available). There isn't any realistic possibility of efficiently frequency doubling these to visible (though a few blue photons might be possible if focused into a KTP crystal at a funny angle) and the wavelength isn't useful for pumping common solid state laser crystals. However, they would be suitable for rangefinder or similar applications.

These laser diodes come in plastic packages that look much like LEDs and thus there is no real possibility of decent cooling. Therefore, power dissipation is one of the major limiting factors. It may be possible to use a lower peak current with a longer pulse width than what's specified in the datasheet as long as the average power dissipation rating isn't exceeded. However, with the high threshold current, this probably doesn't provide much benefit. And, no guarantees of any kind with laser diodes!

There is some info on driver circuits for pulsed laser diodes in the section: http://www.repairfaq.org/sam/laserdps.htm#dpspld

The following assumes a device rated at 16 W peak power, 100 ns max pulse width, 0.1% max duty cycle:

(From: Roithner Lasertechnik" (office@roithner-laser.com).)

The absolute limit is the heat stress of the LD chip inside. Under normal conditions, the laser will emit a pulse of the rated 16 W, 100 ns at 10 kHz (200 ns at 5 kHz is the absolute limit) - which is highly recommended for an expected long lifetime of several khours with usual chip degradation. Take this integrated V x I (voltage x current) thermal heat stress as a final constant. If you run with a higher frequency than the rated, but with a shorter pulse width, still never go higher than this constant. If you go higher, the laser pulse power will go down rapidly due to overheating of the LD chip (still reversible, LD is not yet blown) but overall lifetime is shortened. Keep in mind, that the rise and fall time of this LD is typically 1 ns, so you will get the next limit soon.

A couple years ago I saw a video of a laser used with the retroreflector left on the moon, it was huge and high power. When searching the web tonight I can't find that video, but I found this information:

http://www.lpi.usra.edu/lunar/missions/apollo/apollo_11/experiments/lrr

Ten years ago I had a hobby where I would use the moon as a reflector of 144 MHz radio waves, I built a very large RF amplifier which would put out enough power into a big 16 phased Yagi antenna array that I was transmitting over 4.5 milliion watts of EIRP equivalent power and could hear my own voice coming back from the moon about 2.5 seconds delayed, it sure was fun!

 

[diachi]

What laser do they bounce off the moon mirrors and what detectors do they use?
I have read it is done, I don't think the bandwidth is much, but the distance is impressive.

Big pulsed (Q-switched maybe?) DPSS or LPSS laser as far as I remember. Can't remember if output is fed through a telescope or if that's just for the return - something like a couple photons they get back for each pulse. It's a long distance and the mirror isn't huge.

Edit: Think they use a Q-switched 532nm laser now. First tests were with ruby/Q-switched ruby as far as I can see.

The first successful tests were carried out in 1962 when a team from the Massachusetts Institute of Technology succeeded in observing laser pulses reflected from moon's surface using a laser with a millisecond pulse length.[2] Similar measurements were obtained later the same year by a Soviet team at the Crimean Astrophysical Observatory using a Q-switched ruby laser.[3]

I was a grad student on the APOLLO (Apache Point Observatory Lunar Laser Ranging Operation) project that was shown on Mythbusters. The short answer is no way. You need laser that can shoot enough photons in a short pulse that you'll get some back in the return pulse (shoot 1017 green 532 nm photons per pulse). You need sensitive detectors because, even if you shoot 1017 photons up, you're only going to get about 1 photon back (we used avalanche photodiodes). You need fancy filters and timing electronics, because, when you are only getting 1 photon back, you need to turn the detectors on in as little a time as possible to minimize false detections from background light. You need a big telescope to maximize the number of photons you get (we used the 3.5 meter telescope at Apache Point). And you need to set this all up in a place with minimal background light and minimal atmospheric distortion (seeing). http://physics.ucsd.edu/~tmurphy/apollo/apparatus.html I guess you could do all these things on your own, but you would need about $1 million and a couple years of time to set it up.

 

[Alaskan]

Any members here have a laser range finder?

 

[ultimatekaiser]

I don't have a rangefinder per se, but I have a long distance ruby range pole, which is basically the same thing, but vertical. Probably the only portable ruby ever... most stuff like that are YAG now of some kind.

 

[Alaskan]

I remember seeing photographs of that beauty and its ability to run off of batteries

I'm asking because if I can find someone who has one, I'd sure love to see a photograph or video taken of the output shooting straight into a camera 100 feet away to see how bright the camera picks it up, even if it has a IR filter in it. Supposedly, at 15 feet away the short pulse and wide divergence of one of these 14 watt 850nm laser diodes is safe for a camera 15 feet away. If they say that, then 100 feet away ought to be safe for any camera with some room to spare, but better if I could see how bright it might be pointing at a camera 1000 feet away. If I can't find someone who has a LRF with a high power pulse diode in it, I might have to buy one myself, their prices are coming down but I think they have all moved to 905nm and no longer available at 850nm where the SPL LL85 diode I'm interested in operates at. Regardless, if I could see how bright the pulse is to a camera at 905nm, I'm still interested, maybe CCD sensitivity doesn't drop off very fast for 55nm longer wavelength?

 

[ultimatekaiser]

Well the SSY1s are a yag rangefinder and are pretty strong, 10-50mJ typically over 100ms lamp pulses and sometimes more IIRC.

I need to realign my ruby, but it was doing 200mJ over 35ns with the q-switch, which is visible by mechanical means over huge distances. Many many miles- in watts that's about 5-6MW...no diode can easily compete with that.

 

[Alaskan]

SSY1 sounds interesting, but not finding them on ebay anymore, I bought the parts to put one together last year, didn't start on it, should have. I just saved my search on ebay for ssy1, should have bought two of those.

 

[diachi]

Well the SSY1s are a yag rangefinder and are pretty strong, 10-50mJ typically over 100ms lamp pulses and sometimes more IIRC.

I need to realign my ruby, but it was doing 200mJ over 35ns with the q-switch, which is visible by mechanical means over huge distances. Many many miles- in watts that's about 5-6MW...no diode can easily compete with that.

Didn't the SSY1s also have a mechanical Q-Switch option?

SSY1 sounds interesting, but not finding them on ebay anymore, I bought the parts to put one together last year, didn't start on it, should have. I just saved my search on ebay for ssy1, should have bought two of those.

Meredith Instruments may still have some? Saying that - no good if you're looking to transmit data, way too slow.

 

[Alaskan]

Just went over there, they have some pieces, but I don't see complete SSY-1 heads anymore. I wouldn't use that for anything but a big IR flash

 

[diachi]

Just went over there, they have some pieces, but I don't see complete SSY-1 heads anymore. I wouldn't use that for anything but a big IR flash

They have all the parts you'd need to put one together listed (Lamp, YAG rod, flash cavity and PFN) - but they are all (or mostly at least) marked "Out of Stock" at the moment.

 

[Alaskan]

Since they are out and being an old surplus item I was thinking they wouldn't be able to source more. These do pop up on ebay from time to time, I will just keep my eyes open for another but I have at least one to work with when I get back home.