DPSS design for blue/yellow?

[seoguy]

OK, I think I have a basic understanding on how a DPSS "greenie" works. High-power IR diode laser optically pumps Nd:YAG or vandate at 808nm, this excited solid-state laser crystal then lases at IR 1064nm, which is then fed into a frequency-doubling crystal, which produces 532nm (green) laser light.

But what about blue? I have read that it works identically, again using the same (808nm IR) laser diode, which is again used to pump the same (Nd:YAG) laser crystal, which is again fed into a doubler. But instead of green, this time they get blue! Somehow, they magically convince the Nd:YAG crystal to lase in the wrong color! :-? (which is then frequency-doubled to blue instead of green?)

How the heck do they do that? Do they alter the doping %, or use a different crystal structure, or change the angle of the Nd:YAG crystal, or what?

And what about yellow? (It appears this magic trick requires an even higher level of wizardry, as the power output on these is said to be extremely unstable, so it seems whatever they are doing inside those, it apparently is not working very well!) How does that one work?

Are there any other colors we don't know about that this can also be coaxed into creating? (other than doing something insane, like tripling or quadrupling 1064 to output coherent UV! )

 

[GooeyGus]

ND:YAG has more than one lasing line. The primary line is 1064nm, which is doubled through a KTP into 532. Another line is 946nm. 946nm is doubled through LBO, BBO, BiBO or any other number of similar crystals into 473nm light. It also lases at 1342nm. Double 1342nm and you get 671nm red.

Yellow is a bit different. My understanding of yellow is that you pump the lasing medium (I'm not sure if it is nd:yag or vanadate or something else) with 808nm light like most other DPSS lasers, but you get the lasing crystal to lase on two different wavelengths. So you now have two wavelengths coming out of your one laser crystal. Then it goes into the doubling crystal. Again, I'm not really sure what they use for doubling on 593.5nm DPSS. But anyway, the doubling crystal takes one of each of these different wavelength photons and (for lack of a better term) smashes them together to get you the 593.5nm light. Yellow is so unstable because you are trying to get this crystal lase on two different wavelengths, the gain for one of the wavelengths is probably a bit higher than the other, and thus it tries to suppress the lasing of the other wavelength.

there are tons of DPSS colors out now. I'm honestly not sure how most of them work though, but it's basically the same principle for all, they just use different lasing mediums and non-linear optics (doubling crystals)

There is 435nm, 457nm, 491nm, 500nm, 515nm, 523nm, 526nm, 543nm, 556nm, 561nm, 589nm, 671nm and then many into the infrared. Most of those are listed as available on the CNI website.

 

[691175002]

I believe I read somewhere that for yellow you lase at two wavelengths and then sum them or something.

 

[scopeguy20]

I think the "Trick" is in the coatings, the yellow 593.5 nm results from the non-linear KTP getting both 1342 and 1064 nm, true, but the coatings trap the energy until the small fraction of light generated at the yellow wavelength is, ideally), all the coatings allow to escape,  The laser energy is from IR and longer IR. how it is summed up escapes me!    Apparently it works!

 

[AdamR]

Couldn't you double up 808nm to get a very powerful 404nm blu-ray laser ? ;D why hasn't this been done yet

 

[GooeyGus]

You can directly double a diode but it is very hard and impractical. The beam quality going into the crystal must be very very good, And probably would need to be polarized. Coherent made a directly doubled diode laser... I don't know of any others.

Oh and as far as coatings, the trick is always in the coatings, or the mirrors. The output coupler of a yellow laser will be coated for HR 532, 1064, and 1342 and HT for 593.5. This way all the ir wavelengths get reflected back into the nlo to resonate so it can do it's magic

 

[WonHungLow]

ok . i have a good understanding of laser diodes, but the crystals throws me off. i understand that the green use the 808nm IR diode and then it hits a crystal to change the wavelength and the the frequency doubler actually takes the output wavelength and divides it by 2 to get the output on the green lasers.

how do the blue (real blue 473nm) work. do they use the same IR diode and what is the difference in the crystals and how they are arranged in the optical path? wanting to see what it would take to build a 473nm labby.

or find a decent deal on a multi line argon

 

[digital_blue]

The diode is still an 808nm. The Nd:YAG or Nd:YVO4 is probably aligned or polarized differently to get it to lase on it's other lines. A BBO or LBO is used as a doubler since KTP only has a range of +/- a few nm from 532.

 

[DayOfShadows]

From my understanding it always lases 2 lines, they just block 532 to get yellow / blue.

 

[digital_blue]

From my understanding it always lases 2 lines, they just block 532 to get yellow / blue.

If that was the case, all greenies would be slightly "white" due to all the colours mixing

 

[DayOfShadows]

its REALLY feint and the IR filter kills what evers left. and they use HELLA big LD for 5mw of yellow, those LD would make a lot of green and those greens have IR filters in them that kill any other color that come out, and the reflection in the crystals, that arnt coated for yellow or blue, hurt its output too so you can see why theres no white effect. 5mw of green = 0.005 mw of yellow/blue, unnoticeable at any light.

 

[digital_blue]

The YAG crystal in a greenie probably does lase(very weakly) on other lines, but the dominant line is 1064nm. The YAG crystal in a blue or yellow laser is aligned for optimal power at it's respective line.

 

[DayOfShadows]

True, and they got all those coating and filters and what not.
Laser + crystals = confusing mathematics.
Although i would really like a job making lasers and selling them and such. Seems like i would be doing something i love but nowadays no one cares what your good at huh? if you have a degree you get bumped ahead of all the other people.
Good luck on trying to make the laser though.

 

[WonHungLow]

what crystals are used for what colors? what are you talking about different crystals and different lines? just wanting to know a little about different colors besides green, red, and violet.

 

[FrothyChimp]

We all know the primary transition of vanadate is 1064nm. This follows the standard four level lasing profile. It is frequency doubled to 532nm. Blue, on the other hand is a bit different. The upper lasing level for 946nm is the same as 1064nm but the terminal level of the 946nm line is the ground state making it essentially a three level laser. Because ground state is the terminal level the unexcited Nd atoms tend to absorb 946nm. This makes the design a bit tricky. The vanadate has to be pumped pretty hard to overcome the absorption and thus is much less efficient. Furthermore, the crystal length must be carefully designed so that the pump energy does not leave any unexcited regions within the beam waist (active area) of the crystal. Blue lasers have a tendency to just turn on suddenly. You can turn the power up and up on the pump diode and then suddenly, bam, there is blue light as the absorption is overcome. This is even worse with 457nm where the laser is nearly all on or all off around the threshold level.

The coatings on the resonator mirrors determine what wavelengths oscillate in addition to the pump power and pump wavelength. Making the mirror AR to 1064nm will destroy the Q for that wavelength and it never oscillates. You can also walk it off by refraction out of the crystal.

 

[Hemlock_Mike]

Professor Chimp  ;D    

This is the info I like to see here as this is where new ideas form taking this from hobby to something new.  
Use this info to research what he says and try something new.

Mike

FC -- is "Q" the same in optics as in elecrtronics ?