Short Length Large Diameter ND: YAG Crystal - What for?

[Deleted member 49011]

Re: Short large diameter ND: YAG Crystal with Brewster Angle?

I have no idea, usually an 808nm pumped ND-YAG is frequency doubled with a YV04 to make 532nm, I have not seen Brewster's angle used except in gas lasers such as argon. I have not worked with any ruby lasers. EDIT I meant helium neon, lol.

I assume it was to strip off polarized light using the angle as the output, but that's just a wild guess.
EDIT : I take that back, I think it's pumped through that angle.

YVO4 isn't a SHG crystal , KTP is used to perform the 1064nm to 532nm SHG in most cases or LBO sometimes .

Nd:Yag & Nd:Yvo4 both lase at 1064nm hence why they are both seen in 532nm systems

 

[Alaskan]

Thought I'd add this non related (to this crystal) YT video of a 1064nm to 532nm pulsed YAG tattoo removal machine, only 1500 dollars and up to 10 Hz reputation at 8ns and 2000 mJ, or so claimed. If so, that's many millions of watts of peak power in a 8ns pulse.

http://www.ophiropt.com/laser-measu...-energy-meters/services/peak-power-calculator

 

[RedCowboy]

Re: Short large diameter ND: YAG Crystal with Brewster Angle?

YVO4 isn't a SHG crystal , KTP is used to perform the 1064nm to 532nm SHG in most cases or LBO sometimes .

Nd:Yag & Nd:Yvo4 both lase at 1064nm hence why they are both seen in 532nm systems

Yes, I was up late and not thinking, I knew ND:YV04 and KTP are bonded in many of the little 532nm modules.
Neodymium doped yttrium orthovanadate is pumped by the 808nm diode to emit 1064nm and the KTP doubles that to 532nm.

 

[Alaskan]

Don't need a YV04 with a 1064nm YAG to make 532nm, just a non-linear KTP or LBO crystal, ain't that nice

 

[RedCowboy]

It's very interesting, the real question is how practical is any of it, I know higher powers and better beam quality can be had, albeit temp sensitive and prone to mode hopping.

Also there's portability and power supply, I really would like to work with some pre owned/de commissioned fiber lasers.

There could be undiscovered jewels and I am looking for them, but bigger direct diode sure will make things easier. :beer:

 

[ultimatekaiser]

It's very interesting, the real question is how practical is any of it, I know higher powers and better beam quality can be had, albeit temp sensitive and prone to mode hopping.

Also there's portability and power supply, I really would like to work with some pre owned/de commissioned fiber lasers.

There could be undiscovered jewels and I am looking for them, but bigger direct diode sure will make things easier. :beer:

Ummmmm...

Very practical, used a lot. Though expensive. YAG is not temperature sensitive at all. The lasing medium doesn't care what temperature it is, just that it is kept reasonably cool and constant. If you were doubling it, then yes you need the doubler at the right temp, and held constant too, but so long as that's being held constant it isn't going to be doing any hopping, especially if the cavity is well designed.

As for portability, it's nice, but not generally a requirement for lab lasers... In fact it's often preferred for them to be large on purpose because it makes them easier to work on. Ti:sapphire lasers for example often fill entire tables and work benches. We rarely have to move them so it's not usually a concern except if it were being implemented into something else.

 

[Alaskan]

For us, YAG lasers, as toys, not so practical compared to the portability and higher safety levels of CW laser pointers due to the lower power and constant visible spectrum outputs, but as working lasers that's a different story, very solid technology. For myself, YAG lasers are just another branch of the technology I am interested in, but you won't see me spending that kind of money to convert one of these new units into a hobby machine. I already bought some ND:YAG eye surgery lasers on eBay I want to get to someday with crystals to go with them, although the two I bought are not much different from the well known surplus tank distance ranging SSY1 systems in power or size, using a tiny 3mm X 52.3mm YAG rod.

Coherent Pulsed ND YAG Laser Module Q Switched Rod Lamp Trigger | eBay

 

[ultimatekaiser]

Well yeah, it's not practical in a handheld, it wasn't meant to be.

Yeah I've seen those eye surgery systems for capsulotomy and such. They're just simple little things relatively speaking. Isn't it amazing how something so simple can be so expensive? :tinfoil:

 

[Alaskan]

Got some spare rods for that little eye laser too. Should be able to push these up to at least 300,000 watts peak power/2 mJ without going beyond their working rating, but not much faster than 3 Hz without periods of cool off time.. At 1 Hz, hoping I can do 1,000,000 peak power shots, but I don't know if a rod that small without water cooling, as it was designed for, can be pushed to over 6 mJ to produce that much power. That might be too much but since I have a bunch of spare rods, I can experiment to find out but the passive Q-switch glass might fail first, that would destroy its ability for high peak power short duration pulses, not sure I want to try that without finding replacement glass first.

Since these units are low repetition rate without water cooling, they could be built into a large hand held device and run off of batteries, but what for? No reason other than perhaps flashing across great distances with IR, at 1064nm most cameras are not very sensitive to that long of a wavelength, but then again how sensitive does a camera need to be to pick up a high power pulse, even if at 1.06 um the camera is only 1% as sensitive compared to 500nm, for example, several KW of coherent 1064nm ought to be picked up as a very bright flash, as long as the camera can pick up such a short duration pulse; 6ns.

Edit: Expensive is right, the manufacturer was selling these for outrageous amounts of money, but then, doctors charge that much too so they get their money back. UltimateK, do you happen to know what the relationship of divergence is for YAG rods if they are thin, or fairly large diameter, which way it goes, gets worse or better if a larger diameter rod?

 

[RedCowboy]

I wonder how efficient the flash lamps are and if surrounding the rod with super bright strings of tiny smd led's could do away with the need for a reflective cavity, there would also be less waste heat as the led's are more efficient, the trick will be the peak pulse power, but with many thin strings sharing the workload a high pulse rate could be achieved.
Maybe the surface of the led's could be a pass reflect coating.

Is this video BS?

 

[diachi]

I wonder how efficient the flash lamps are and if surrounding the rod with super bright strings of tiny smd led's could do away with the need for a reflective cavity, there would also be less waste heat as the led's are more efficient, the trick will be the peak pulse power, but with many thin strings sharing the workload a high pulse rate could be achieved.
Maybe the surface of the led's could be a pass reflect coating.

Is this video BS?

Yeah ... wouldn't use LEDs, you won't see good results, even with IR LEDs with center wavelength close to the absorption of Nd:YAG. If you want to go that route then LDs are the way to go - much higher optical powers, much more effiecient as all of that power is in one narrow band, centered around the narrow absorption band of Nd:YAG at ~808nm. LEDs are much much wider and as such most of the already lower output won't be absorbed by the rod.

Flash/arc lamps can produce immense amounts of optical power, of which a major portion is right around 808nm. LEDs while more efficient, can't come close.

Spectral distribution for a 300W xenon arc lamp:

Not sure about your video.

 

[paul1598419]

There's lots of different kinds of ring lasers. All are very complex, and some have very creative construction. I have even seen some that use the crystal itself as the entire cavity, referred to as an NPRO. The crystal is shaped such that it acts like a turnaround prism of sorts and uses the internal surfaces as standing wave forming mirrors, and the forward face as both a focus and the OC and is very interesting. You can use it linearly without worrying about the curve, just use a guide laser to align it. it'll not affect much-your cavity just wont be straight physically. I'd also verify that (likely) both sides are planar. (edit: both are referenced in the article you linked)

The coherence is a measure of how far the photons can travel before having a small but significant change in frequency/wavelength. It's very important for certain applications like holography, where the wavelength cannot change too much or you can't get the required interference. Most people here wouldn't care, because they don't use it, and it wouldn't change enough to be significant to the eye as it travels, but for the sake of scientific purposes, it's a very important concept. Diodes generally have a crap beam quality, not just in terms of divergence, but also coherence. Part of why good lab lasers are so expensive. A cheap 5mW laser might be a few dollars, and a good generic, temp controlled lab laser anywhere from a few hundred to maybe a thousand or so, a good SLM would be a several thousand minimum. by eye they all would look similar, but the SLM one is far more useful in almost every way compared to the former two. you can do dozens more experiments with a coherent compass at 10mW than you can with any number of other greens.

I made this same point in another thread awhile back. It's nice to see it made again, here. The coherence length of lasers used for holography is one of the most important concepts when trying to make a quality reflection hologram. I'm aware of laser with coherence lengths out to 150 meters, but mine are limited to between 20 and 100 cm. Still good enough to make a quality reflection hologram.

 

[RedCowboy]

-----------------------edit-------------------------

This triangle shaped crystal is interesting.
http://www.stellarnet.us/wp-content/uploads/Nd_triangl.pdf

--------------edit-------------

Wait a minute, looking at these other pics, is this thing cylindrical? That 1st pic posted looks different, is it an optical illusion...yes it is, that 1st pic looked like it was cut across the top but it's just the way it's sitting, the other pics show it better, I don't see how that part could be side pumped as it looks semi transparent around the edges unless via flash lamp, not that I have seen, if it's side pumped I would think it would be by flash lamp and not a LD, but I could be completely wrong.

What threw me was not looking at the other pics to start, just that top pic looked like possibly a Brewster's angle cut across the top and had me thinking it could use a LD but it's just how it was sitting in the pic.
The bottom of the original pic looked like the shadow was the side of the crystal with a reflective circular mark on it, but it's just the shadow and the circles top and bottom are reflected room light.
I thought this was some fancy cut gain medium/resonator with a BA cut across the top, my mistake.

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These pics show what it is much better.

Northrop Grumman ND YAG Laser Crystal 12 5mm x 6 1mm x 4 7mm Angled | eBay

p.s. I have some of those surplus rangefinder rods and lamps but they are buried in a mountain of boxes, they were cheap years ago when I got them, I haven't done anything with them, I don't have the mirrors or anything else, but I suppose a portable unit could be fun, however in order to maintain a high pulse rate that could appear CW as the 100W medical behemoth in photonicinductions video, that would likely take a backpack of battery and capacitors. I also would need to build a control, I would almost rather cannibalize something else that's intact.

 

[Alaskan]

I didn't realize you had thought the crystal was some other shape, didn't put more photographs there due to having the link where you could go look, did, after awhile This seller has a lot of these if someone else is interested, but at this point I might have bought something I won't end up using, unless I can learn more about the application a rod of this size and end angle can be used for. Fortunately I didn't spend much, but I was hoping the larger diameter rod, even if short, might provide lower divergence, perhaps it is the opposite. I will be searching the net to see what I can find in regard to typical power outputs vs diameter and length for ND:YAG rods and to understand the divergence of different diameter rods, if anyone here knows, please chime in.

 

[diachi]

I will be searching the net to see what I can find in regard to typical power outputs vs diameter and length for ND:YAG rods and to understand the divergence of different diameter rods, if anyone here knows, please chime in.

Must take into account dopant % too for power.

 

[ultimatekaiser]

There's a lot of variables determining power. As for divergence and profile-that's all lenses and cavity construction.