Well, if anyone is interested in this laser, i got mine, and tested it extensivelly..
The first thing i noticed was how big the spot is.. Then i noticed, that my beam is splitting in two. This made me very depressed..
I heard about several people getting rid of this problem simply by using Ni-MHs instead of alkalines. So i tried them, but no improovement.
After a while i noticed that the beam is changing in brightness abruptly. I didn't know why at first, but later discovered, that it is related to pressure on the button. By varying the pressure i could actually make it go back to TEM00.
Since the "driver" PCB is soldered directly to the IR LD's leads, pressure on the button moves it, and puts stress on the LD. If it's not mounted strongly enough it can obviously move it slightly, which causes misalignment with the crystals.
To make things worse, there is a spring going up from the board, putting additional force on the PCB, in the same direction as the button.
As a result, the PCB is bent in one direction, causing the battery contact spring not to be in the middle of the enclosure.
So i thought about supporting the PCB from below, since as it is, it is only supported by a piece of foam.. I cut a 2mm thick piece of plastic and put it below the big transistor on the lower side of the PCB. I had to raise the board a little, and after the plastic piece was in position, it pressed against it, and held it in place.
After this, my laser was MUCH more stable, and behaved much better. It stayed in TEM00 for much longer, but again, not long enough.
I really wanted to take it appart, so eventually i did. I was hoping that tightening the IR LD would help with my problem and i also wanted to fix the focus, to make the dot smaller.
Inside, everything is held in place with glue, so after i broke the bond, i had to spend an hour cleaning bits of it out, not to mention brass splinters, left from the manufacturing process.
Unfortunatelly, focusing it didn't really help much. I just couldn't get the spot any smaller.. I don't know why.
Tightening the IR LD made things MUCH worse. The beam lost most of it's brightness, and mode hopping was constant.
After loosening the IR LD nut, i was able to turn the LD around with the power on, to see if i can find the best position for it.
Turning it around actually produced big changes in the brightness and lots of mode hopping.
But i was able to find several positions, where the beam was bright and mode hopping didn't occur.
Right now, it looks like i managed to find an area of the crystals, where there areless imperfections, and i get a nice bright TEM00 beam.
But unfortunatelly, i have a feeling it is not as bright as it was before.
I didn't get all the parts for my LPM yet, so i can't measure the output..
Curiously_Coherent did measure up to 240mW with completelly fresh Energizer alkalines tho.. The laser was put in a chill cell during the test, and peaked at around 240 and later dropped to 180mW, as it warmed up.
On the other hand, i don't know how much of this is in the form of IR..
Also, his laser doesn't have mode hopping problems. He obviously got a good one.
Here's the video of the test:
http://www.youtube.com/watch?v=0aWEnjYW7Lw
Oh, just a
warning about supporting the PCB:
Theoretically, while it worked for me, it could make things worse, if you bend the PCB up, like i did. Simply supporting it, without bending, could prolong it's life on the other hand.
It is something, that should have been done by the manufacturer already. In my oppinion, it's a major design flaw. When i did it, the improovement was incredible. Had it been this way from the start, maybe my laser wouldn't have these problems.