Lightwave Halfnote Green Laser Questions

[hologeek]

Ben,

Nice details, I'll talk to you later!

-George

[Showlaser.dk]

Do you have a picture of the units in your projector? Also, how much power are you putting into your TEC to keep it cool? I am putting nearly 10A in this one just to get it to temp so I think the TEC is dead, 120W to move ~15W of heat

Yes, i am working on some pictures of the whole project.. just have to extract them from my iphone, my camera and various places on several pc's

I think 12V 8-10A to the TEC sounds about right.. The diode dissipates a little less than 60W at full power (1.7V up to 30 amps), and the large screws between the heatsink and the laser itself moves a lot of heat back to the laser.. + the TEC is nowhere near 100% efficient.. So i dont think that sounds unusual..

Additionally, did you figure out what the thermistor values for the oven and head temps are? I moved the sensor inside the head for the diode temp to right next to the diode instead of the other side of the cavity. It provides faster response on the controller, but with the TEC damages, it still stays at a high temp.

IIRC the ktp sensor is a 100Kohm thermistor, and the base plate sensor is a 10K sensor.. There is a lot of difference to what the optimum temperature is for the KTP.. i have one that works best at 52 deg. C, and another that needs to be at 83 deg. to be efficient..

I am going to clean the optics on the cavity this week when I get a chance and see what kind of power increase I can get from it. The appear to be clean, but after learning to clean optics the correct way, I think I am going to try again.

Why fix something that isnt broken ?

Aligning this was not very difficult. I used a Coherent Sapphire and got it set up to go collinear with the Nd: YAG rod then readjusted every mirror from scratch to place the reflected beam right on the centers of the next mirror. I didn't count on any of the mirrors being aligned, so I just did all of them. I also repositioned the KTP to an area where the beam was not as focused so there is less chance of damage, and increased power. Once I got all of the other optics aligned, the final end mirror behind the Nd: YAG rod was tweaked with the diode running. I got a bright flash of green, and then slowly got it into a place where i could tighten the screws a tiny bit and just barely treak the mirror. I think now it is still a tiny ways from optomized, but it's way better then not working at all .

I did find that any change to the end mirror made an enourmous change in the divergence and output beam shape. It was actually easy to tweak for optimal power by running the laser and chaning the position until the beam on the wall several meters away was as small as possible.

Every bit of alignment was done without a stage or any precision instrument besides my fingers.

I actually found it was WAY easier to align this laser then to align the SP Millinneas we have at work. They are a pain in the ass, and they even have adjustable kinematic mounts inside the cavity! I have one putting out a tiny bit of green and the other missing one mirror which should be easy to replace once we get a replacement.

Yes, mellinias are a Bi... to align.. been there.. gave up

It is good practise to align doubled lasers at low diode power at first and then only crank up the power when you have beam out and only need to do tiny adjustments.. When the cavity isnt lasing, the power will build up in the yag crystal (its a bit like a capacitor), then when the mirrors hit alignment all this power will be released in one very powerfull pulse, that can damage the other optics and ktp..

Also it is a good thing to have a beam focus spot inside the ktp crystal.. not on the faces but inside..

Regards, Simon

[Showlaser.dk]

Pictures of the halfnote-based laser movinghead build posted:

http://www.photonlexicon.com/forums/...ead.php?t=8251


Regards, Simon

[Laser Ben]

Dude, Simon, that is amazing! Very nice work integrating all of that into something that small

What controller did you use for the current? I notice you posted a link earlier regarding it. Did you use a direct unit from them?

[Showlaser.dk]

Dude, Simon, that is amazing! Very nice work integrating all of that into something that small

What controller did you use for the current? I notice you posted a link earlier regarding it. Did you use a direct unit from them?

Thanks
yes, the current controller is the DSD-500 from OEC, that i posted the link to, and then a Vicor 5V flatpac module for the power.. The DSD is a bit overkill for this laser, but i wanted to be able to modulate the diode current, and i wasnt comfortable designing something like that myself due to the sensitive nature of those laser diodes.. You can see the dsd on some of the pictures.. it is just a square pcb with a heatsink on the back side, and 4 screw terminals at one side.. It is a rather expensive solution, i think the DSDs cost me around $1200 a peice..

I have been thinking a bit about how to build a cheap psu for these lasers.. i have just asked Kevin if he has more of them.. if he has loads but no psus, i will buy a couple (if they are cheap) and design a cheap psu solution for them based on an ATX PC power supply.. then i can post the schematics and pcb layout here, so everybody can build one :-) - it will be without diode modulation though - so blanking will have to be done with an AOM or actuator..

Regards, Simon

[Laser Ben]

We just had lunch with Kevin on Wednesday to discuss a business proposal. I don't think he had any more systems last I talked to him before Wednesday. I have been looking at running the laser off a modified Flex Drive system in parallel to provide for the current demands. According to Drlava, it can be done. I will see if we have any old HTC1500 or HTC3000 controllers at work I can use. We just got one set up this week running a Spectra Physics MG532 heater for the LBO. The main problem was the low value of the thermistor in the heater which made the reading of the temperature so sensitive it made it hard for the controller to keep track of it.

I am really interested in that power board and controller you have. I don't think it is worth a working head, but that's up to you.

I am going to replace this TEC and put the head on a smaller heatsink making it into a lab style laser with a nice power supply. It really should be dissapating only ~40W or so from the diode and very little from the heater so a very large TEC run at low current should work ideal, it's too bad this thing has alignment pins on the underside.

[Showlaser.dk]

Hello Ben

I am sure we can make a deal on the PSU/controller. I have no use for it anyway.. drop me a PM or email - maybe we can trade with some other goodies, or if you are willing to part with one of the heads, maybe i can throw something extra in, to make it a fair deal for you ..

The alignment pins on the underside can be removed.. just hit them with a bit of freeze spray, and you can pull them out with a set of pliers.. they can be stuck pretty well, but it can be done.. worked for me.. be carefull not to cool the whole head too much.. never below dew point..

Regards, Simon

[Laser Ben]

I just spent a bunch of time with the controller I got from George. I think I have profiled what every pin does on it so it can easily be constructed. Let me know if you find anything else out Simon or George.

I attached the list

[Laser Ben]

Crap, I just realized I forgot to post the document. I will do so later when I get home.

[smogthemog]

Ben,

Just build an astable square wave generator using the 555 ic. You don't have to be too concerned about optimal component values. Just use a couple potentiometers for R1 and R2, and while observing the output on that nice scope of yours, adjust both resistors for the desired output. R2 was about 140K and R1 about 14K C1 is 0.01uF and pick C2 to be 100nF. I did it and it worked fine.

http://www.csgnetwork.com/ne555timer2calc.html

Presuming that C1 is the cap marked 0.01uF already in the picture within the link, C1 @ 100nF, R1 @ 14K and R2 @ 140K that dosent calculate too near 500Hz according to the calculator anyway

100nF is 0.0000001F (104)

So if you input:
0.0000001 in the first box
14000 in the second box
140000 in the third box you get:

52% duty cycle
49.082 Hz
0.010s low
0.011s high

Surely C1 should be 10nF (103)?

This would give 490Hz.

If R1 & 2 are then tweeked to 15.5K and 136K repectivly then this would give a nice close 501.9Hz signal with the correct 1ms on/off times