Some question about DPSS crystals

zraffleticket said:

With our "common" yellows, it uses SFG to make these colors. SFG stands for Sum Frequency Generation. This is pretty much the process of combining two wavelengths and generating a new wavelength from these. The formula for this is 1/((1/WL1)+(1/WL2)).(commonly used, there may be more accurate but on our hobby level we don't need anything really more than 1nm off, and this formula shoule be less than .01nm off).

For 593.5nm lasers, you can take either Nd:YAG or Nd:YVO4 (used more commonly in yellows) crystals and generate 1064nm and 1342nm. Using the formula above, WL3 = 1/((1/1064)+(1/1342)). Plug that into your calculator, and it will yield 593.47. 593.47 is VERY close to 593.5, plus take into account it's not exactly 1064nm on the mark. it's just close enough for rounding to do it's job.

589nm works very similarly, except Nd:YVO4 is the only option to generate the needed wavelengths: 1064nm and 1319nm. Plug these into the formula, and you should yield 588.93nm. Nd:YAG cannot generate 1319nm, while it can generate 1342nm.

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Le Quack said:

Basically, it depends on what the coating is on the crystals...

Depending on what coating there is it will output a different color of light. You can technically get any color you wish with DPSS, however, it may become more or less efficient depending on what crystal type you're using. Not every crystal is efficient at certain wavelengths...

KTP happens to work very well at doubling 1064 nm into 532 nm.

ND:YAG works okay for everything if I remember correctly. Not the best. I think it's used primarily for turning 808 nm into 1064 nm.

LBO happens to work very well at doubling 946 nm into 473 nm.

ND: YVO4 works great for turning 808 nm into 1064 nm light.

KDP works okay for doubling 1064 nm into 532 nm. You can actually grow your own KDP crystals... problem is getting coatings.

To get Yellow, you have to do frequency summation, I think, which is a lot more complicated (and thus more expensive) than just simple frequency doubling.

You can actually use the same crystal type for doubling any wavelength, there's just the problems of efficiencies.

As for the IR pump diode, all DPSS lasers use 808 nm IR to begin with, no matter what. If you swap it out with a higher powered one, yes, you will get more light out, but the crystal set can only take so much before it starts to become damaged. You DO have to realign it correctly otherwise you won't get anything out; which is probably why most don't attempt to do it.

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Le Quack said:

You can actually use the same crystal type for doubling any wavelength, there's just the problems of efficiencies.

Click to expand...

Le Quack said:

Basically, it depends on what the coating is on the crystals...

Depending on what coating there is it will output a different color of light. You can technically get any color you wish with DPSS, however, it may become more or less efficient depending on what crystal type you're using. Not every crystal is efficient at certain wavelengths...

KTP happens to work very well at doubling 1064 nm into 532 nm.

That's about all it does, and it does it incredibly well. That's why we use KTP for the 1064-532nm conversion.

ND:YAG works okay for everything if I remember correctly. Not the best. I think it's used primarily for turning 808 nm into 1064 nm.

It has a lot of lines, yes, but it's a bitch to pump correctly. Very picky about pump wavelength (has to be dead-on 808). These days it's only DPSSed for 473nm blue (because Nd:YVO4 lacks a usable 946nm line).

LBO happens to work very well at doubling 946 nm into 473 nm.

Yep. There's also BBO and some other material which isn't sensitive to moisture (which I can't remember).

ND: YVO4 works great for turning 808 nm into 1064 nm light.

Nd:YVO4 is a gain medium, not a doubler. It's used because it's not very picky about pump wavelength and also because it's less of a PITA to work with than YAG.

KDP works okay for doubling 1064 nm into 532 nm. You can actually grow your own KDP crystals... problem is getting coatings.

For low-powered lasers, KTP is more efficient, but for higher-powered (megawatt range) pulse devices, it's a lot harder to damage.

To get Yellow, you have to do frequency summation, I think, which is a lot more complicated (and thus more expensive) than just simple frequency doubling.

You can actually use the same crystal type for doubling any wavelength, there's just the problems of efficiencies.

Nope. KTP doesn't double below 500nm, which is why we're still on LBO for 473nm blue.

As for the IR pump diode, all DPSS lasers use 808 nm IR to begin with, no matter what. If you swap it out with a higher powered one, yes, you will get more light out, but the crystal set can only take so much before it starts to become damaged. You DO have to realign it correctly otherwise you won't get anything out; which is probably why most don't attempt to do it.

Crystal sets do have power limits. Proper cooling and heating can help offset this.

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