Nd:YVO4 and KTP

What's to stop someone like me from buying a standard, cheap, $20-dollar, 5mw, green laser, taking it apart (as carefully as possible), and using the Nd:YVO4 and the KTP frequency doubler out of it, and using those with an 808nm diode I find online?  If anything I said doesn't make sense, or was incorrect, or anything like that, please let me know.  I don't want to seem like I think I really know anything about green lasers, especially since I know that I don't know much.  My dad mentioned that IR light doesn't really react to standard glass lenses like visible light does.  Is that true?  If so, how would/does one focus IR light?  For that matter, where could I learn about green and IR lasers, and the properties of IR light, etc.?  Thanks!

EDIT: Along with green and IR lasers, and IR light in general, I'd also like to learn about the crystals used in green lasers, Nd:YVO4, frequency doublers, etc., so I can understand these darned charts about crystals, and what-not; I don't understand doping, or its significance, or anything like that, and thusly whether higher or lower percent is better. Any links to available information would be the BOMB. Thanks!

crystals are built for the power they're expected to run at - if you have the crystal from a 5mW green and try to pump it with like a 2 watt pump diode, you're just gonna burn the crystals

if it was that easy, then you could have like 1 watt greens for only a few hundred dollars

So how/where can I get crystals for higher powers? CNILaser.com seems to have plenty of crystals. But if I had to guess, they probably aren't at all cheap with CNI. So, yeah, where?

CASIX sells hybrid crystals providing up to ~100mW 532nm out with ~1W 808nm in for about $60 (these are really only rated for 50mW out, but they can handle up to 100mW fairly easily). A hybrid crystal is what is used in green pointers, and consists of Nd:YVO4, KTP and mirrors in one tiny crystal. These are by far the easiest crystals to work with, and I would recommend them for medium power green lasers.

As far as doping, Nd:YVO4 stands for Neodymium Doped Yttrium Orthovanadate. In this configuration, the actual lasing medium is the Neodymium. The YVO4 is just a type of crystal that accepts Nd doping very easily due to it's crystal structure. The same applies to Nd:YAG, Nd:Glass and others. Each type of host crystal/glass provides different characteristics in terms of pump absorption and efficiency.

This section of Sam's Laser FAQ should help answer any other questions you have about crystals in general:

http://www.repairfaq.org/sam/laserssl.htm#ssllme

here's a link to CASIX's hybrid crystal page:

http://www.casix.com/product/prod_opt_laser_dpm.html

Hope this helps.

What about 473 or the yellow? Similar process with just different crystals?

K

kristopher said:

What about 473 or the yellow?  Similar process with just different crystals?

K

Click to expand...

Exactly. Basically there are two types of crystals, gain crystals (the Nd:YVO[sub]4[/sub] in my last post)
and nonlinear frequency multipliers (the KTP above). The pump diode pumps the gain crystal, which uses the pump energy to generate it's own light at a different frequency, which when frequency doubled, tripled, summed or otherwise manipulated by the nonlinear crystal becomes colored visible output. With current technology, this is the only way to make small, manageable lasers with these colors with the exception of blue/violet diodes.
Different color lasers use different combinations of pump diodes, gain crystals and nonlinear crystals to obtain the color desired..
CASIXs website has many types of crystals for sale with pretty good info on each type..

ElektroFreak said:

... With current technology, this is the only way to make small, manageable lasers with these colors with the exception of blue/violet diodes...

Click to expand...

Are you referring to the exception of the blue/violet diodes because they would produce double the frequency into the ultraviolet?

Even at that, it would be interesting to double the 405nm to ~200nm or the 532nm to 266nm. If it is possible, what crystal would do this?

:thanks:

jmgallego said:

Are you referring to the exception of the blue/violet diodes because they would produce double the frequency into the ultraviolet?

Even at that, it would be interesting to double the 405nm to ~200nm or the 532nm to 266nm. If it is possible, what crystal would do this?

:thanks:

Click to expand...

I meant that using DPSS is unnecessary for obtaining violet light since we have diodes.

It is possible to double 405nm light to far UV, but doubling diodes directly is very difficult since diodes don't have very good beam quality. Also, UV at that wavelength is carcinogenic.

Usually the cheapest pointer do have some overcapacity on the crystals as those can't be made ultra tiny. I see people sell crystals on ebay claiming things like 75mW with the crystal size of my 5mW pointer (if it ever gave 5mW, I esimate 1~2mW). They are a simple as aligning an 808nm IR diode to the crystal assembly. This means you can get more than 5mW out of the cheapest pointers, but I wouldn't push it too far. I don't know the damage threshold, but I think cheap pointers like 30mW use the same crystals, but I only know my cheapest pointer I hacked up.

ElektroFreak said:

I meant that using DPSS is unnecessary for obtaining violet light since we have diodes.

It is possible to double 405nm light to far UV, but doubling diodes directly is very difficult since diodes don't have very good beam quality. Also, UV at that wavelength is carcinogenic.

Click to expand...

Thanks!!! Got it... I have a nonlinear noob question, I don't understand why it is difficult, what do you mean that it does not have a good beam quality? What would be the requirements of the laser to double the frequency of a 532nm, 405nm or a 635nm diode laser, the common ones in this forum?

Absolutely, at those wavelenght not only eye protection is necessary but also skin protection. Thanks also for the reminder.

Laser diodes do not give a nice gaussian beam profile, it is very assymetric. Also, the light appears to be coming form two locations depending on which axis you choose, so you need to compensate with a cylindrical lens. Also the spectrum of the diode may be a problem, they tend to mode-hop to a different longitudal mode, making phasematching a problem.

But probably the biggest disadvantage of doubling diodes is that is happens outside of the laser cavity. Light only passes the nonlinear crystal once at a low intensity, making a lousy conversion efficiency. Only high power pulsed solid state lasers can double efficiently outside the cavity.
This is why a DPSS method is used. The Nd doped YAG crystal is the lasing medium, and is together with the nonlinear crystal inside the cavity, both are between te mirrors. Now the light is trapped between two mirrors, building up to a high intensity. And that makes a nice conversion. And that's a DPSS with intracavity doubling.

A 532nm laser is actually already a DPSSFD, doubling this green is as easy as changing the mirrors and inserting another crystal. Depending on the laser type this is relatively easy or plain impossible. Doubling 405 or 635 would be very hard, get a trippled yag for that. You'd need custom KTP or LBO for phasematching, control the diode's mode, correct the beamshape and more to get some decent light out of it.

Thanks BlueFan.

AGH! Sounds too complicated. Doing it with 532nm sounds easier, but it would be a matter of finding the the right mirrors. I will think about that one, the others would be more of a headache than the one I just got reading what you said. :wtf: (I'll see if I can find something to read about this subject too)

BIG :thanks:

I'm planning on building DPSS lasers with discrete components instead of the hybrid crystals, but I haven't got much time lately, and it will take a lot. Hybrid crystals (those in pointers, Nd:YAG + KTP + coatings) are really 808nm diode on one side, green on the other side.

See the link in my sig.