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10 Watt DPSS 532 nm Pointer, finally got one (38 pound labby).

Alaskan

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I’m tempted but when I look at all of the dust sparkling in the beam output, I back off of that idea.
 



Buffo

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What a beast! Haven't seen one of the CNI units with the large external driver like that in quite a while...

If you're curious about stray IR in the output, you could always send the beam through a prism and then check the power output right after the beam exits the prism and again at a considerable distance away from the prism. If there is any IR in the output it will be bent away from the visible beam, so in the near field (next to the prism) the power meter head will still capture both the visible and IR portions but in the far field the head will only be able to capture the visible portion. So if you see a large difference between the two readings then you can infer that the difference is IR that is leaking out of the cavity.

As for the difference in apparent brightness between a 10W unit and a 1W unit, the raw beam is already so bright that the human eye's intensity response will likely be close to saturation. If so then any difference will be hard to quantify. You may want to send the beam through a set of scanners (or even just 1 scanner to make a line) and then look at the apparent brightness of the fan (or tunnel) in the air. That will often give you a better idea of the difference.

Regarding the data transmission project: did you up-collimate the source beam at all? I have not done any experiments myself, but I've spoken with people who have used TTL modulation on a low power beam (<500 mw) to get reliable transmissions at a distance of several miles, but they were using a 10" telescope on the receiving end and a big beam expander at the source to blow the beam diameter up to 4" or so...

Adam
 

Alaskan

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I have some hot filters to block the IR, I can use one of those and see how much difference there is going through it, the visible should pass without much loss and I can quantify the amount of loss to VIS with a 520 nm beam to know. I will see.

Good idea on using a scanner head to sweep the beams and then do a comparison, that 10 watt next to 1 watt completely dominates my ability to see much of the 1 watt, sweeping it will reduce the saturation to my eyes (camera as well) and allow me to see the difference, if a wide enough sweep,

I will improve the video soon, maybe just make it over. I have installed a free trial of an Adobe video editor on my old gaming computer (8 years old, old, but i7 with 16GB RAM). I also bought a wireless BlueParrott noise cancelling headset (noise cancelling mic too) truck drivers use to get rid of high ambient noise on ebay, so hope to be able to make a do over in a few weeks to post. I can include the results of the IR hot filter on the output. That would truly disappointment if there is much IR and the 532 nm output is below 10 watts.

I was going to TTL modulate using ASCII, I used to do that with radio transmissions, easy to do, and put a telescope on the far end to gather the light to detect and then demodulate.
 
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Alaskan

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I measured the output through an IR window which appears to have about 12 percent loss to 525 nm, not sure the loss at 532 nm, the wavelength the filter was made for. It appears there is an amount of infrared mixed in with the green, I need to do more checking with other IR filters as well as a pass filter which blocks 532 nm to be sure what I am really measuring.

Edit: Full output of the 10 watt DPSS melted and cracked my IR pass filter :( - I tried it at 1 watt out first and I didn't see too much IR power, but then tried full output which destroyed it.

Anyone know how much percentage the beam can be 808 nm and how much 1064 nm if there is no internal IR filter in a DPSS laser like this? I suppose unless you had information on this specific laser, it would be difficult to know.
 
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Buffo

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Sorry to hear that you cracked your IR filter! :cry: If you decide to try it again you may want to expand the beam diameter before it strikes the filter to spread the power out and prevent a localized hot-spot.

One advantage of using a prism vs an IR filter is that the prism is merely refracting the beam so there is far less internal heating vs a filter that is trying to absorb part of the beam. You're unlikely to damage a prism even at very high power levels.

Another advantage to using a prism is that any attenuation from the optic cancels out between the two measurements (because the loss applies equally to both the visible portion and the IR portion), whereas with the filter you expect near total rejection of the IR but you don't know how much of the visible light you will also lose. Although your idea to calibrate the visible loss with a 520 nm direct diode is a clever one - I agree that the attenuation at 520 should be within a few percent of the attenuation at 532. Assuming you can find a more robust filter that can handle the peak power this approach should work.

Regarding the relative power of 808 and 1064, the rule of thumb is that the KTP doubling stage is 40% efficient. However, as the power density goes up the KTP efficiency increases, and if you have very accurate temperature control on the KTP crystal you can get even better efficiency. I think the high end is around 70% or so. To be safe I would assume at least 50% conversion efficiency, meaning that the intra-cavity IR flux at 1064 nm is probably around 20 watts.

The KTP will have an optical coating on the output face that reflects 1064 and passes 532. Depending on how good that coating is, you may have between 2 and 10 percent of the 1064 leaking through it. So if they did not include a final IR filter at the aperture you could expect to see between 400 mw and 2 watts of 1064 in the output.

The 808 nm pump is more difficult to quantify. Vanadate efficiencies are all over the place and there are many variables to consider. I think it's safe to assume that your 808 nm pump is at least double the power of the 1064 nm output you need, although in practice it could be 4 times as much or more.

But if we go with the most efficient assumption, that means your pump source would need to be at least 40 watts. Similar to the KTP, the output face of the vanadate crystal will also have a coating, except that this one will pass 1064 and reflect 808. So assuming the same efficiency range for the coating means 2 to 10 % of your 808 pump wavelength could be leaking through, giving you something between 800 mw and 4 watts of 808 in the output. Remember that this is on top of the 1064 that leaks through the KTP...

This ignores any 808 losses through the KTP of course, and it also assumes that they did not include a final broad-band IR filter at the aperture. If they did include the filter, then you should see at least an order of magnitude reduction in the above numbers, if not two.

Regarding TTL transmission via laser, yeah, sounds like you're on a similar track to the folks I spoke with. Basically it's "Packet Radio", but with light instead of RF. Telescope on the receiving end is a must, but beam expansion at the sending end is equally important to improve divergence. Also, aggressive filtering of any interfering ambient light really helps. (Combination of band-pass filters and a long tube in front of the receiving telescope to block sunlight.)

Final thought: if you are looking for a free video editor, you can still download Microsoft's Movie Maker and the GoPro Studio software, even though they are no longer officially supported. Both will run under Windows 10 just fine. I've also just started playing around with VideoPad from NCH, and so far it's pretty powerful... (VideoPad is free for non-commercial home use.)

Adam
 

Alaskan

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Thanks for the info, I've been reading up on DPSS over a few years, not intensely, but here and there. I was assuming an 808 nm pump of about 40 watts output to make 10 at 532 nm. I'd love to see what is inside this unit, just don't want to risk causing problems to see.

I did more testing with another filter which blocks visible and passes IR, didn't run the power up as far, but I did go to 5 watts out. I am guessing the filter might be about 85 percent efficient to the IR (as many of these cheap Chinese IR pass filters are), if it is, then combining the filter loss to measured IR would make the infrared component of the beam to be about 6.5 percent of the total beam power. To check if the IR component was a linear ratio of the output power, I ran the beam output at 1 watt, then 2 watts and last 5 watts where the filter began to smoke a bit. During this test the increase of the IR component was at a consistent ratio all of the way up, so my assumption is there is a linear ratio of infrared to green output.

As I am measuring from 10.5 to 10.7 watts out, depending upon which watt meter I use, it might be possible this unit indeed does produce 10 watts of green output and 6.5 or so percent IR mixed in with it. I have more filters coming in about ten days, the next one blocks IR and passes 532 nm, I will see what results I get with that filter. If the IR pass filter I was using today has more loss than 15 percent, then this laser isn't producing 10 watts of 532 nm output. I tried to characterize this filter using a 1064 nm pointer but found the longer wavelength was not passing through it without huge losses, my assumption was this pass filter was fairly linear between 800-1064 nm, but I was loosing 65 percent of the 1064 through it.

Daytime beam shot

 
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RedCowboy

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Chris, how about using a Q-switch to get higher energy pulses, I have seen some used stuff of flebay.
 
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Alaskan

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I have some small Q switches for 1064 nm, have been wanting to build a cavity to insert them into for high pulsed power.
 

RedCowboy

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I was reading that there are active and passive as well as various methods, I believe you can use one in your beam path without modifying your laser and they are also made for 532nm however I am just now starting to learn about Q-switching and it looks like fun, I have always wanted a viscous sounding pulsed laser that sounds like paper tearing as it burns into materials........bbbbbuuuurrrriiiipppppp :D

I tested one of those PBS cubes again tonight and they seem to work very well, as you set the cube you will find the correct sides and the correct rotation of your beams ( polarization ) as if it's wrong the beam wont pass through, I check this at low power to not hurt the cube, I didn't use the wave plate I rotated one laser 90 and I adjusted the fine alignment in the lens barrel slack, the output looks clean, very little leak through, I'm wanting to build that 2 x 44 c-lens corrected with 3XBE soon......I may have a new host made and I would love to find a 5X BE with wider optics.

 
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Alaskan

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Very nice, good combined output, what was the total input? I've never seen a Q-switch function outside of a cavity, only inside it to allow the energy to build up inside a solid state rod.
 

RedCowboy

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2 X 44's with G2's and they tested @ 7.8W and 7.4W so 15.2 in and 13.6W out, that's looking pretty good, I can also tweak my rotation as I literally just set that test up, those are the cubes we got from Hak, what's normal for losses ?

Now I need to correct each beam either before or after and then knife edge two cubed pairs for 28W and that will squeeze through a 3XBE as long as I line it up just right although I would like a bigger BE........I also might cube 2 x 7A75's as I have some doing right @ 6W @ 4.0A and the divergence is better........anyway I'm itching to do something.

The Q-switch I saw was mounted in the beam path and used pockel cells as it's medium to hold and release higher energy pulses.....I'm still learning about Q-switches so I really don't know but IINM you can mount the pockel cell type in the beam path without altering your laser.
 
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Alaskan

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Nice work on your cube, I haven't played with the ones Hak sent yet, he thought they would take the power, did some tests to confirm it himself. They are not likely optically contacted, so I am very interested in how well they do over time. concerned the middle area might be slowly damaged at these power levels. The Pockel only either allows light through, or blocks it, that's all, but it does so with a very fast transition between the two states. If there was a way to put a Q-Switch externally I'd be very happy, but without a solid state medium in a cavity to build up higher states of energy, I don't think there is a way to do that. Prove me wrong, please, I want to be wrong.
 

RedCowboy

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I know virtually nothing about them and am just now learning myself, I have seen them mounted in the beam path and with AR windows in and out plus cooling lines or connections, also there's the acoustic type.

I started here but need to go over it again and chase down some questions, it says passive use a resonator and can be used with microchip lasers.........I'm still learning so......

 

Alaskan

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I suppose you could mount them in the beam path outside of the cavity, but that would just pulse the beam, not allow more energy. If you find where it can somehow be used with something else to increase the peak pulse energy, I'd be happy to see it. I've never built a cavity, willing to learn though!
 




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