IR laser illumination for covert night time viewing of targets

[lzrppl]

I am starting this thread to discuss mounting and using IR laser diodes to illuminate night time targets and viewing these targets with IR viewing scopes or goggles. My employer designs and builds high tech scopes for rifles. Basically, these scopes are video camera / computer devices that can tag and track targets up to 10mph. Once the target is tagged, one would bring the crosshairs to the tagged dot and when they are overlapped the shot is taken. This setup has proven repeatable accuracy up to 1200 yards. Also, most all image sensors or CCDs can “see” in the near IR. Lately, we have been interested in night time hunting of wild boar that seem to be taking over my state.

The problem…getting close enough and seeing what you are shooting at. Since March I have been experimenting with different laser diodes and driving circuits. The task was to create basically a handheld IR laser that can be mounted to a rifle. Being that almost all IR diodes are case positive, this presented a few problems. The choices are to either isolate the diode from the host or use a continuous positive driver like the BlitzLinear and put the batteries in reverse causing the host case to carry the positive charge. The latter is easiest if you have determined what current level you need to run at.

I actually prefer diodes that have beam characteristics that have a fast and slow axis instead of a “dot”. This type of beam profile projects a rectangular beam that is great for illumination. The beam is never focused to a point, but rather defocused and adjusted to control the divergence or size of the illumination “window”. I have also discovered that when using IR viewers, the intensity required to illuminate favorably would be different for various Gen1 through Gen3 devices. This introduced the need for varying intensity output instead of 4 or 5 different illuminators. Go out in the field, test and adjust to what intensity works best for your device. Then take a power reading and build a fixed current illuminator for that particular viewer.

How would someone build a laser illuminator with dynamic intensity control that can be changed on the fly in the field? I attacked this problem using LED drivers. In particular, I used the LuxDrive Buck Puck with onboard trim and external pot. This is nice because the onboard trim can be the current range you want from 40% to 110% of the rated drive and the external pot is used to adjust from 0 to 100% of that range. We are not talking PWM, but actual smooth current adjust. These drives come as 350, 500, 700 and 1000ma drives. $17 for the drive and $5 for the wiring harness including the pot from LED Supply. Now this is larger than any drivers that fit in most hosts, so the first prototype looks Frankensteinish. I had to actually glue the drive to the exterior of the host and run wires through a milled slot I created in the host. I also glued the pot to the host for easy access. In the near future, I will probably tuck this drive up into the bored out backside of a Heatsink and install the pot through the host wall. The diode I used for the prototype was a reject 1/2W 808nm which ended up being 675mw at 803nm. So, this one prototype can adjust its intensity from 0mW to 675mW. Now, this is really handy for visible lasers that are too bright to align properly. LuxDrive also make a device called a BuckBlock which comes in 1000, 1400 and 2100mA range. These are too big for portable hosts, but are great for benchtop projects with full dimming capabilities and are only $18.

Right now, my prototype is out in the field, but when I get it back I will take some photos and figure out how to post them. I want to keep this thread open so I can continue to add relevant info as I progress.

 

[lzrppl]

I know it has been awhile, but I have been very busy. Not only am I trying to create a new product but the whole company is moving across town to a new facility. I did get my hands back on my original prototype and took a few photos.
I like to use Solarforce flashlight parts for my hosts. They are inexpensive and easily modified on a lathe. As mentioned before, the prototype is monstrous in it's appearance but quite functional. These photos show the "business end" of the laser. Machined heatsink and electrode along with machined delrin for isolation...all designed around Solarforce parts. The last photo is of the whole mountable laser with it's battery compartment for two 18650 batteries.

Next Post:
Sharper looking hosts
How am I going to make this safe?
What am I going to do about the Feds?
How am I going to comply?

 

[The Lightning Stalker]

Looks like a nice build. FWIW, you can make any adjustable driver dimmable. (and some fixed ones as well) All you have to do is remove the original trimmer and wire your two pots in series. Optionally, you
can replace the one with a resistor when the optimal value is determined.

 

[lzrppl]

Oh yeah...I will try that next. That sounds nice and easy.

Thanks

 

[BShanahan14rulz]

Might see if a 501B heatsink will fit the solarforce host as-is. A few members here sell these heatsinks for somewhere around the $20-25 range. Then, can use the same mini or 17mm drivers and 12mm "aixiz" modules that we use here on LPF :wave:

Use of a 17mm round and you might could get away with flashlight drivers, which would be mode-selectable in some cases. Also, flashlight drivers are cheap @ a buck or two each, and are often low drop-out linears (but often are on the ground side, using the amc7135)

"ahorton" 27mm aspheric lens would be interesting to try too, but wouldn't be focusable. But would be safer because of larger beam at aperture, and the lesser quality of molded vs ground lens.

Just throwing ideas at you. I make no claims as to how good any of these ideas are; the are merely ideas.

 

[davidmikky]

These photos show the "business end" of the laser. Machined heatsink and electrode along with machined delrin for isolation...all designed around Solarforce parts. The last photo is of the whole mountable laser with it's battery compartment for two 18650 batteries.

 

[Hemlock_Mike]

Remember -- In a BAD situation, the illuminator marks
your position to another "scope".
HMike