Page 5 of 5 FirstFirst 12345
Results 41 to 44 of 44

Thread: Building DPSS from scratch. Trouble getting YV04 to produce any spontaneous emission

  1. #41
    Join Date
    Jun 2017
    Location
    Seattle, WA
    Posts
    25

    Default

    Quote Originally Posted by kecked View Post
    Try burning the pinhole in place. I do this all the time. I use thin plastic. Just let the IR do the work. Couple pulses is all it takes and the hole exactly matches the power core of the beam. The trick is finding a plastic that doesnít shrink. Capton tape or nylon works but Iím not being very picky. Itís just to clean up diodes.
    Iím running this CW, not Q-switched. Will I still see that kind of build up? Intracavity seems really fragile for me - anything in there seems to kill the beam.

  2. #42
    Join Date
    Nov 2008
    Location
    Cleveland Ohio
    Posts
    2,517

    Default

    Quote Originally Posted by brianpe View Post
    Iím running this CW, not Q-switched. Will I still see that kind of build up? Intracavity seems really fragile for me - anything in there seems to kill the beam.

    true that! I was always using the finished beam so my idea wonít work intracavity.

  3. #43
    Join Date
    Jun 2017
    Location
    Seattle, WA
    Posts
    25

    Default SHG Conversion Update

    So lenses for the telescope arrived (while I did have lenses to build a telescope they were too long a focal length to fit the apparatus inside the resonator). Telescope built and...no lasing. Two lenses in there is almost 16% cavity loss, and I think that's just too much. Also, in order to fit the telescope I needed to stretch the cavity length a bit, and this puts me further down the stability map. If I turn up the power to work past the loss, thermal lensing kicks in.

    The upside is I'm now an ace at aligning this thing.

    I've gone back to the cavity design and I did find an all-mirror design that can get me down to a tight waist in the KTP...and I even have the mirrors here to try it. But alas, I can't get it aligned. The output coupler in my design is at one fold of a Z-fold -- this way when I frequency double I can couple all the green out the end without it making its way back to the vanadate. To get a tight waist into the KTP this mirror needs to be tightly curved: 100mm ROC. Since this mirror is AR coated for 532 and I'm using a 532nm alignment laser, what I have been doing is replacing this mirror with a HR1064/532 Plano mirror, aligning, and then swapping the final OC back in and tweaking until I get light. It works pretty well for large ROC output couplers. But for 100mm, well that's a problem. The mirror is a bounce mirror so it's at an angle, which means when a curved mirror is inserted the intracavity beam is not dead center, and the curve of the mirror will change the alignment pretty drastically. For 100mm, it's so bad the beam is not even hitting the vanadate. It's so far off I need to coarse reposition the mirror to get it onto the crystal. So I don't have a lot of faith that's a great plan and after a bit of time tweaking it I gave up.

    Instead, I looked at re-working the cavity using AOI 45ļ Plano mirrors, with a single concave mirror at the end of the resonator to provide some focus toward the KTP and help with stability. The 45ļ change allows me to shorten the resonator length by 100mm, which does wonders for thermal lens stability. This gets a pretty big waist of 260um into the KTP, which isn't great. If I go on the assumption that intracavity power will increase and balance SHG conversion until it produces the optimal coupling (which is a big assumption....but the energy has to go somewhere), I calculate a circulating power of about 1.3KW if I ran full tilt. I plugged this into a few formulas in MatLab and while this is about 13x the circulating power for just IR, it is still well below the damage thresholds of everything.

    I tried a setup with the mirrors I have that has about the same KTP beam waist and took some power measurements. This setup isn't optimal for thermal lensing but before it sets in I am getting a maximum IR to green conversion rate of almost 40%:

    Pump Power IR Power 532 Power
    6.7W 1.5W 620mW

    Only about 20% efficient generating the fundamental so I'll have to work on that.

    I also tried my hand at starting the second pump to see if I could reduce thermal lensing by pumping both ends with less power at each end and discovered another aspect of beam alignment I'll need to worry about: with only one pump if the beam is a little crooked in the vanadate it's no big deal. But with two pumps if it's not parallel the coupling is off an I get mode hopping or wasted pump power.

    Speaking of pumps, the FAP pump diodes I'm using are eBay specials and are pretty end of life. That 6.7W of pump power above was at 20 amps of current which is way off their spec'd slope. I have better FAPs, but since these are still producing more IR than I can handle with lensing, I might as well burn their hours out first.

    Some things I also noticed: if I tweak the Z of the HR mirror that's reflecting both 1064 and 532, I can eliminate the "green problem" and get more power that looks nice and consistent. This helps get the phase of the second green beam that's doubling back into the KTP in phase with the original I think. This is a little fiddly as adjusting the Z on this mirror throws the X and Y off, so they need to be re-tweaked. But it seems to work OK and a precision translation stage for this is several hundred dollars.

    Thanks for reading!

  4. #44
    Join Date
    Nov 2008
    Location
    Cleveland Ohio
    Posts
    2,517

    Default

    I have a dpss head that takes less than a watt and outputs 500mw 523nm all day and never even gets warm so you should be seeing 2-3W.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •