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Review of Ehgemus' Custom 2X 14500 Skinny Laser Diode Host
I bought one of Ehgemus' skinny little laser hosts and thought enough of it to write this review. The host uses Li-Ion rechargeable AA-sized batteries, has a button contact PCB board with spring already built in with red and black silicone rubber insulated wires inside the head already soldered and ready to hook up to a DTR 12mm diameter Aixiz module, red going to the spring near the head of the laser. If hooking the red wire to the laser diode module's positive lead the batteries go in like a normal flashlight but it appears you can wire it either way, case negative or positive if you wish, depending upon the configuration of your laser diode. The head with its matching threaded cap allows you to vary the focus of the beam using a Aixiz G2 type of threaded M9x0.5 lens holder (which you can get with a DTR module, or 3 element M9x0.5 lens assembly for lower divergence). The on-off push button has a positive action and the feel of a click when pushed all the way in to light the laser and stays pushed in while on as well as recessed enough to help prevent accidentally turning it on. The aluminum housing is very resistant to discoloration from handling, so far mine has none after using it several times and looks as good as new.
Due to the small size and lower capacity batteries this unit uses, this host is better suited to lower powered laser diodes and to get the most bang for your milliwatts when doing so, 520nm green is the color to use due to the heightened sensitivity of our eyes to green compared to blue or red, milliwatt for milliwatt the beam of a 520nm green laser is viewed to be close to 10 times brighter than 445nm blue or 638nm red and the spot intensity near double that at near 20X. With the two 14500 batteries in series (for up to 8 volts when freshly charged) you can use a 120mw 520nm green multimode laser diode in a Aixiz module with plenty of battery capacity which will have a brighter beam than a 1 watt blue or red laser with a longer visible throw than the other colors, to borrow a flashlight term, especially when using a 3 element lens which has higher loss than a single element G2 lens, but will produce a more concentrated spot of light at a distance due to the physics of divergence.
When I received this host, even after viewing the photographs in this thread, I was surprised how small it really is. The price might seem high for a little host, but I wouldn't want to spend the amount of time it takes to make one of these for less than 50 dollars myself, in fact, for that price I wouldn't even do it unless retired and doing this for the love of the work.
Note: I believe this host could be used with much higher power output laser diode modules, but the user must be very mindful of the duty cycle, or how long the laser operates due to how fast the diode can warm up and possibly overheat if such care isn't taken. Although small, the head and body of the laser are cut from one solid piece of aluminum without joints, because of this the body of the host will likely transfer heat away from the diode more efficiently than hosts of similar size which use a separate section for the head.
DTR 120mw 520nm modules: https://sites.google.com/site/dtrlpf/home/diodes/osram-plp520
Datasheet for 120mw 520nm LD: https://drive.google.com/file/d/0B_6-KC5wFXIJRk5MYXQ0M2YzQkk/edit?pli=1
Don't let it's small size fool you, awesome things can be done with such a small host when using single mode diodes!
I'm promoting the idea of using single-mode laser diodes because so few know that at a distance these low power lasers, even with a higher loss three element lens, can outperform their higher power multimode diode brothers with single element G2 lenses. This is because their far lower divergence allows them to catch up and overtake the spot producing brilliance of some lasers which are more than 20 times the power output. Adding a beam expander to a laser which already has low divergence due to using a single-mode diode and three element lens brings you to a whole new level of performance, as expanding the beam further reduces the divergence beyond what a multimode diode laser pointer could do, even if they added the same beam expander.
Here's a link to DTR's single mode 520nm diode module: https://sites.google.com/site/dtrlpf/home/diodes/pl520-520nm-laser-diode and Osram PL520 laser diode datasheet: http://www.semicom.co.uk/get_file.php?part_no=PL-520&file_type=datasheet
Test Results
I am very pleased with the performance of this host with a single mode PL520 single mode diode, it's divergence using a simple acrylic lens is great, to the eye just as good if not better than a DPSS 532nm laser. The other night was able to see a very nice terminus spot on a cloud base which was over 5,000 feet above me. Last night I compared this small 70mw output 520nm single mode diode laser with a 1.9 watt blue multimode 455nm laser and while the higher power laser with G2 lens had a much brighter beam, it could not produce a terminus spot on the cloud base while the lower divergence 520nm laser at 1/27th the power output could. The green spot wasn't bright on a 10,000 foot cloud deck above me but solidly there while the high powered 455nm blue laser was unable to make a spot, its beam spreading out far too much on the end to be able do so at that distance. I then swapped out the acrylic lens to a three element Aixiz type of lens and the power output increased by about 15% and again, a very low divergence beam which would produce a tiny terminus spot on a cloud deck 10,000 feet above me (according to FAA WX), the spot more defined using the three element lens and slightly brighter.
The beam of this little 50mw rated laser diode being pushed to 70-80mw output certainly isn't very bright compared to my 1.9 watt 455nm blue laser, but it will do what that laser can't do with more than 25 times the power; produce a small spot on some very high clouds. I doubt a 520nm 1 watt output multimode diode would be able to produce a terminus spot on a 10,000 foot high cloud deck either, based on my multimode blue laser diode which has close to the same divergence. The beam on these high power diodes fan out far too much at that distance to be able to do so without the use of a beam expander to reduce their divergence, but when doing so this comes at the price of added optics as well as increased beam diameter; ten times wider when using a 10X expander. Knowing that, I still want to buy a MM 1 watt 520nm laser diode, when I get it I will make a comparison to let you know.
LPF member clansley reviewed another host which uses a single mode 520nm diode: http://laserpointerforums.com/f52/lasterbtb-520nm-50mw-hl520-50b-single-mode-review-91206.html and measured the laser to have a full angle divergence of about 0.71mRad which I can believe, the beam output of this diode is exceptionally tight, from the looks of it even tighter than my 1.5 mRad Laserglow 532nm laser, I can believe as much as half of that amount. When I paired this laser with a 10X beam expander the divergence was reduced so much that the terminus spot on the cloud was hard to see because the beam itself kept getting in the way, now that's a tight spot.
Here's a photo showing how small the PL520 laser beam was at 25 feet from the pointer (left) shot through safety glasses with a U.S. penny taped on the wall just above the mm tape measure. The beam was focused at distance to produce the smallest point I could and it ended up being about 1mm wide at the center of the radiance, 4mm wide if you count the blooming around the hot spot as picked up by my camera and safety goggle combination, but that isn't the beam itself, just light reflecting off of the terminus spot on the wall, the beam focused to only 1 mm wide at 25 feet. The penny is 19mm wide itself, now you can see how this low power laser can put a spot on a cloud 2 miles above while the high power multimode diodes can't, at least, not without a considerable beam expansion telescope to reduce their notoriously wide divergence, as viewed on the right from a G2 lens collimated M140 445nm multimode blue laser diode at the same distance with its uncorrected rectangular shape which measured about 25mm wide, a beam-width which keeps on getting wider at a much faster rate for distance than the single mode does. Understand that the whole rectangular spot on the right is the laser beam, not light reflecting around the spot, compare that to the tiny bright spot in the middle of the radiance bloom on the left produced by the single mode laser diode, still a rectangle, but very small due to its extremely low divergence.
Note: The color appears yellow-green for both the 520nm and 455nm lasers due to the shade of the goggles I took the photo's through. Although, some blue did sneak through from reflections in the room getting around to the back side of the goggles, as can be seen in the photo on the right. Notice how although the area I am calling center of radiance is very close to the penny the surrounding bloom is not on top of the penny? That is because the beam isn't that wide, it is actually only as wide as that 1 mm spot in the middle, incredible from 25 feet away.
Note of caution:
While I don't recommend running any laser diode without a current regulator, I've been doing so with this tiny laser diode and it's working for me, perhaps shortening the life of the diode, but I've used it a lot to quite warm and without failure. The diode without a regulated output and freshly charged batteries is putting out from 70 to 80mw (depending on the lens) so the two Li-Ion batteries in series producing 8 volts seem well suited to the diode without a regulator, however if the diode is on too long at some point it will eventually reach too high of a temperature, draw too much current and fail. I plan on installing a constant current regulator soon.
Here's an untouched photograph of the beam using my iPhone, the cloud deck was too high to show a terminus spot tonight but the beam shows well for 80mw without fog.
Below, zoomed in and cropped but otherwise unaltered photo showing a terminus spot on a 6,500 foot cloud base, clearer when viewed for yourself.
02-19-2015 midnight: No constant current regulator and still working great! Ran it for five minutes straight tonight outside at 26 F., I don't think I could keep it lit that long in the summer though without warming too much. Maybe these single mode diodes, being low power, can take more abuse (no regulator) than the higher power laser diodes.
Try running a regular 532nm DPSS laser at this temperature, it either won't run or is very dim compared to running at room temperature where they need to be to operate efficiently, 520nm laser diodes like it cool.
While they last, if you want one of these little hosts here's a link: http://laserpointerforums.com/f39/fs-custom-2x14500-hosts-skinny-body-look-92614.html#post1348440
Ehgemus produces lasers out of a love of the work and is very creative, I just asked him to build a host to hold three DTR laser modules in the head for RGB giving him free artistic license to make it look however he wants, hope to be reporting on that before my next two week out of town job.
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