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




RedCowboy

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

The angle is used for polarization. NDYAG converts 808nm to 1064nm

Beware the surface could be damaged.



 
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Alaskan

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

Thank you, minimum reflection at the Brewster angle, but trying to understand how this thing was pumped and what the application might have been in such a short configuration. My guess on the Brewster angle is that would be the output side and angled to allow the crystal to be used at several wavelength lines, rather than AR coated. Wondering if this is a end pumped crystal.
 

RedCowboy

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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.
 
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Alaskan

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

I really think this was used as a pumped YAG crystal, but being so short I am guessing end pumped. I have seen photo's of doped glass rods with Brewster angles on them to reduce reflection, I am guessing, but that is all so far.
 

RedCowboy

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

I have seen that angle at the output of helium neon and on an iodine laser but I have a lot to learn about that, I have seen the beam exit from that angle before.

In this pic it has a mirror and oc mirror but uses the angle to polarize it appears, I think it can be used in amplifiers





Here's BA used in ND plates as amplifiers. This was the big power method before fiber lasers. https://lasers.llnl.gov/about/how-nif-works/beamline/amplifiers
 
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RedCowboy

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

It could be part of a train and amplified through that angle, I can see a round imprint on the end, almost like an etching. The center looks very reflective.

You can see the room light reflection off the top side lighting up the paper in a oval from the angle of the room light to the surface.

 

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Alaskan

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

Interesting clues, I didn't notice those reflections before Mr. Eagle eyes. ND YAG rods can also be used to produce just 1064nm, or with the right mirrors which suppress 1064nm and are highly reflective to other wavelengths, can output close to 1.2~ um too, but at lower levels as another line output, as they call it, to KTP double the frequency (halve the wavelength) to make other colors closer to yellow. So much to learn, just picking up on some of this lately.
 
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diachi

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RCB - Nd:YAG crystals/rods can come with faces at brewsters angle, works just the same way it does in gas lasers. I believe however that the angle is higher than on Alaskan's crystal, at least assuming the beam is perpendicular to the flat face of the crystal.

Not sure what this is for or how it was used.
 

Alaskan

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Where is Cyparagon when I need him?
 

lazeristasUVISIR

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First it would be good to know a type of coatings on both faces.

imho, the angle is not Brewster, and it used to eliminate parasitic resonators.

Speculations: it might have been pumped with a big laser diode bar filling all volume of the crystal.
 

Alaskan

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The seller had this to say:

I havent been able to find out anything at all. All I know is that Lumenis had about 100 of them that they didnt want. No one will tell me what they were for.
 

ultimatekaiser

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Actually it's not at brewster's angle. it was probably used in a wide diameter ring cavity, or as an amplifier. The slope is an offset to reduce the number of optics required. it is a patented technique-the name of which escapes me at present. The angle would still yield polarization however, just not work quite the same. Brewster's angle for YAG crystals is about 61.3 deg. The slope on that crystal is probably closer to 10-15 degrees, and much more shallow. It's more likely an offset for the beam path as well as to give it an polarization preference, as the YAG will also rotate it slightly with each pass due to the Faraday effect. This help keep the power steady as well as to eliminate internal reflections, and a ring cavity yields greater coherence control inherently simply from its construction principles. Most high power scientific lasers like the coherent Verdi, and the old DPSS-C-532s use this tecnique on a smaller scale and have coherence lengths longer than a football field! My D3 uses a bowtie ring cavity and has a coherence measured in tens of meters when it is working right. the C532 has a spec'd coherence of 150m+! I have several of this crystal, but a bit thicker. Probably for some medical laser of sorts.
 
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Alaskan

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Thank you UltimateK, I will research ring cavities and see what I can pull together on a possible use for this little YAG, it was so thick, for a YAG, I thought it might produce a good beam. I don't understand what you mean when you wrote about the beam maintaining coherence for a great distance, do you mean the beam had low divergence or did not diverge for a great distance?

Edit: Found this, but it isn't for a YAG

https://www.rp-photonics.com/ring_lasers.html
 
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ultimatekaiser

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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.
 
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Alaskan

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Appreciate the update, rep next time I can, I used them all up for this 24 hour period already.
 




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