Old 08-06-2012, 01:06 PM #1
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Default Huge power drop on DHOM

Hey all,

It's been 10 months since last I "played" with any laser. Just been so busy with other activities.
I powered up my 1.6W DHOM and was rather disappointed that it peaks @ 900mW. Even after an hour warm up. I powered it on/off several times, but it always settled @ around 900mW.

I bought the laser last year April so it is out of warranty. The laser did about 1637mW in October last year when I last used it. It's been nicely covered up sitting in a dark room ever since. Total usage is <10 hours.

Should I attempt to adjust the pots in the power supply?


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Old 08-06-2012, 02:16 PM #2
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Default Re: Huge power drop on DHOM

I dont think its psu, How does the lens look like?
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Old 08-06-2012, 03:42 PM #3
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Default Re: Huge power drop on DHOM

Quote:
Originally Posted by sinner View Post
I dont think its psu, How does the lens look like?
The external lens? It's good. I cleaned it too, using a professional fibre optic cleaning kit.

Pump diode degraded?
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Old 08-06-2012, 04:06 PM #4
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Default Re: Huge power drop on DHOM

Whenever I hear about lasers degrading while sitting idle I think moisture inside the laser.. not that there is anything you can do about it now that damage might have been done.

If the laser is out of warranty it probably wouldn't hurt to play with the pots, starting with TEC control if you know which pots control them.
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Old 08-12-2012, 05:51 PM #5
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Default Re: Huge power drop on DHOM

Well, today was rather cold in Johannesburg so I though, what better than too try play with the pots of the power supply. Knowing that I could possibly pop the laser, I went ahead anyway.

I've attach 3 LPM images

The first shows the initial output. Second shows the output while adjusting the 6 pots(carefully)

Third image is the result. Thankfully the laser is working OK with an extra 300mW. Still way down from the 1700mW.
I think this is about the max I can do because as I adjusted the pots a little more, the output dropped. I could never get much more than 1300mW.

FYI, the TEC output was never more the 2 volts. The temperature on the optic side of the TEC was 27 degrees Celsius. The hot side 22 degrees. I attached 12V 3A to the TEC directly, chilling the laser but the output stumble to 100mW! The KTP must not have been happy at all.

I still crave those extra 300+mW. Not sure if I should be brave(and stupid) and attempt to crank those pots alot more! ?
Attached Thumbnails
Huge power drop on DHOM-1.jpg   Huge power drop on DHOM-2.jpg   Huge power drop on DHOM-3.jpg  
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Old 08-12-2012, 06:57 PM #6
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Default Re: Huge power drop on DHOM

KTP usually likes to be warmer than room temperature. So the TECs under the KTP are actually "ovens" rather than coolers. Type II phase matching occurs under the proper angle, and happens most efficiently at the right temp. If the enclosure is not properly sealed, and if South Africa is particularly humid, I suppose moisture could be an issue for the optics after a cool-down when condensation occurs and water spots decrease the effectiveness of all optical functions but it would not be from KTP degradation as only BiBo and LBO are the ones that absorb moisture.

It should be safe to have the cover removed long term assuming you can control the amount of moisture on the optics and the dust that may settle. This is a good opportunity to experiment, though please be careful with those pots. 300mws increase is a good sign, but it may be coming at the cost of stressed electrical components, so don't bank on any more reliability along with the power increase. The more measurements you you take (Like, diode current, TEC current) the better. The last thing you should ever need to do (pray that you won't have to) is adjust the optical alignment.

Good luck and have fun! Post your findings here, I would be interested in following your results in progress.

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Old 08-13-2012, 07:05 AM #7
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Default Re: Huge power drop on DHOM

The DHMO, like many other China lasers, has only a single TEC. Both to cool the LD and to warm the KTP ?
All the optics are epoxied! So I am not even able to access, check for moisture or clean them.
Sorry, I forgot to take pictures when I had it in pieces. I'll wait next month for Spring when it is a bit warmer. I'll then strip it open and re check the temps, output etc.

But you may be right regarding the condensation. Strangely, my other 800mW laser also degraded to 400mW over 2 years. We are in a more tropical climate so perhaps DPSS are not ideally suited here.
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1657mW 532nm Lab
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1183mW 650nm
1800mW Watt 445nm (2x900mW through PBS)
510mW 532nm
500mw 635nm (DEAD Apr 2011)
259mw 660nm
2 Watt 808nm
205mw 404nm
YAG 2J Pulse (Still need a PSU)
Countless laser diodes.
Lots of 5-10mw green lasers
3mw He-Ne (My first laser. 1995)
20 high power c-mounts

Last edited by blrock; 08-13-2012 at 07:05 AM.
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