I was playing with the Tank gun device which as some of you may remember was supposed to combine 2 NUBM06 and 2 NUBM08 (all LDs with Ball-lenses in place). But for the reason that the beam of 08 passes through Blue-Blue dichro at low currents (less than 3A) I replaced both 08s by 07s (having Ball lenses as well) to adjust optics at low power. Now all looked fine, even divergence was similar (lines of similar length at 5m, two up are from 07s) but measuring power I just noticed that the output of one of 07 became ridiculously low - 0.99W at 2.3A. Of course the LPM was after all of the optics (WP, PBS, mirror and Dichro), but 2nd 07 gave output of 1.76W and both 06s 2.83 & 2.81W.
So, I checked what happened and noticed a small oval spot in the center of one of 2 wave plates which were installed in the very thin space between Ball-lenses and PBS. Interesting that the WP at the issue of 06 was not damaged. Half of the beam passing through this matt spot is scattered. Not sure if 08 could have done this before I replaced it by 07 but most probably not. Maybe it would not have happened with G-2, maybe the reason is that some of G-ball lenses focus the beam at 5-6mm but it looks that polarising optics does not support high light intensities.
And now I understand why many old members suggested to expand the beams prior to combining. To do this I will have to redesign the whole setup
Maybe most of you knew this but anyway I want to warn those of you who would like to start combining high power LDs.
So, I checked what happened and noticed a small oval spot in the center of one of 2 wave plates which were installed in the very thin space between Ball-lenses and PBS. Interesting that the WP at the issue of 06 was not damaged. Half of the beam passing through this matt spot is scattered. Not sure if 08 could have done this before I replaced it by 07 but most probably not. Maybe it would not have happened with G-2, maybe the reason is that some of G-ball lenses focus the beam at 5-6mm but it looks that polarising optics does not support high light intensities.
And now I understand why many old members suggested to expand the beams prior to combining. To do this I will have to redesign the whole setup
Maybe most of you knew this but anyway I want to warn those of you who would like to start combining high power LDs.