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Nd:YAG vs. Nd:YVO4?

ixfd64

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I know that most green DPSS lasers use either an Nd:YAG or Nd:YVO4 crystal to convert the 808 nm light to 1,064 nm. It seems that most "hobbyist" lasers use Nd:YVO4.

If my research is correct, Nd:YAG is better at handling high output powers. However, does anyone know what other differences there are? For example, which is more efficient? Also, why Nd:YVO4 is used more often? I'm guessing it's because it's cheaper, but I'm probably wrong.
 



ElektroFreak

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Nd:YVO4 is both more efficient and much more forgiving in terms of pump spectrum and temperature stability.

Nd:YAG requires that the pump diode be held at a much more stable wavelength than Nd:YVO4, and it's more susceptible to temperature changes within the crystal itself, which change the crystal's efficiency.

There are, however, certain colors that can only be obtained using Nd:YAG, such as 473nm blue. Of course this wavelength can be produced with diodes and OPSL these days, but for DPSS 473nm blue, only Nd:YAG will work. The 946nm line that gets doubled to produce 473nm is only found in Nd:YAG at powers high enough for the doubling process to be effective. For 457nm DPSS, only Nd:YVO4 will work, for the same reasons. The superior efficiency and inherent stability of Nd:YVO4 is why 457nm DPSS can be found at much higher powers than 473nm.
 

HIMNL9

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It depend ..... from the relatively cheap ones that you can find on ebay, to the insanely high cost ones that you can order from pro manufacturers ..... ;)

And they never say these high prices in public, if you don't send them a personalized inquiry form .....
 

ixfd64

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So it seems that Nd:YVO4 is better than Nd:YAG when it comes to "hobbyist" green lasers, then. However, Wikipedia lists several other crystals that lase at 1,064 nm, such as Nd:Ce:YAG and Nd:Cr:YAG. Does anyone know how they compare?
 

goninanbl00d

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So it seems that Nd:YVO4 is better than Nd:YAG when it comes to "hobbyist" green lasers, then. However, Wikipedia lists several other crystals that lase at 1,064 nm, such as Nd:Ce:YAG and Nd:Cr:YAG. Does anyone know how they compare?

Although these crystals do lase at 1064nm, they are not suitable for a variety of reasons, in most cases thermal reasons.

Effects of thermal changes include thermal lensing and thermal stress.

Thermal lensing causes optical properties of a crystal to change as it it's temperature changes.

Thermal stress causes the crystal to dislocate/fracture upon a sudden temperature change.

Nd:YVO4, for example, expands very little when heated. On the other hand, Nd:YLF often requires flexible mounts to facilitate for the expansion of the crystal.

Also, these mediums may not be suitable for CW DPSS pumping. Ruby, for example, can be flashlamp pumped easily, but cannot be pumped in CW.
 

BShanahan14rulz

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Which one results in a polarized output beam after doubling?

Edit:
Ok, if you want to know what the lasing medium in your green DPSS laser is, look at the polarization. Nd:YAG medium's output is not polarized, while Nd:YVO4 medium's output is polarized. My 30mW O-like pen uses Nd:YAG. Too scared to shine my 140mW green at my sunglasses just yet. Maybe I can dig up some filters from some old LCDs or something. Anyways, just wanted to follow up on my findings.
 
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BShanahan14rulz

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alright, now I'm confused. So perhaps YVO4 creates polarized beam and YAG creates a dually polarized beam 90 degrees between the two? I don't need anything, I'm really just curious. I like to know how stuff works.
 

goninanbl00d

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The output after SHG is always polarised, without it the SHG process wouldn't work.

However, the polarisation orientation may or may not be random.

In the case of Nd:YVO4, the output beam is polarised, and this polarisation is rotated 90 degrees after it passes through the SHG crystal.

Nd:YAG requires either an external polariser (such as intracavity Brewster plates) or Brewster-cut ends. This is essential for achieving optimal efficiency.

However, at high enough power densities, polarisation does not matter (such as when a Q-Switched Nd:YAG laser is extracavity doubled). This has been done with the SSY-1 Nd:YAG laser.
 

Bluefan

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There is (edit) difference in the polarisation behaviour between Nd:YAG and Nd:YVO. All doubled YAG lasers are linearly polarised (considering the greem output), phase matching uses the birefringence of the nonlinear crystal, so only one orientation works. The SSY-1 will have a conversion efficiency <50% if it is randomly polarized.

lasers that aren't frequency doubled (or tripled etc) will be randomly polarized, a polarising element in the cavity will make them polarized, something like a brewster angle plate will work. There is (edit) difference between Nd:YVO4 and Nd:YAG here.

Edit: YVO4 is anisotropic, so not the same in all directions, and thus has a polarisation dependent gain. Thanks to goninanbl00d for correcting me.
 
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goninanbl00d

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There is absolutely no difference in the polarisation behaviour between Nd:YAG and Nd:YVO. All doubled YAG lasers are linearly polarised (considering teh greem output), phase matching uses the birefringence of the nonlinear crystal, so only one orientation works. The SSY-1 will have a conversion efficiency <50% if it is randomly polarized.

lasers that aren't frequency doubled (or tripled etc) will be randomly polarized, a polarising element in the cavity will make them polarized, something like a brewster angle plate will work. There is no difference between Nd:YVO4 and Nd:YAG here.

Nd:YAG output is randomly polarised, Nd:YVO4 output is polarised.

Encyclopedia of Laser Physics and Technology - polarization of laser emission, polarized output, birefringence
 

Grix

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HIMNL9

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Yes, but then you need also the KTP, and the one that o-like sell is rated for less than 200mW lasers.

It depend all from the use you need to do ..... for cheap units, glued sets are better, where instead for high power units, you need something more "professional" ..... also, remember that if you buy bare crystals, you need to build your own holders.
 




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