Question(s) about the 593.5/589nm process

[crazyspaz]

so i have been looking up some of the more exotic DPSS wavelengths-exotic being really anything that isnt 532nm (although it seems 473nm will be as affordable as 532nm is in the not too distant future). I really, REALLY like the color of 589...who doesnt, honestly.

in my searched, i quickly found out that 808nm is pumped into ND:YVO4 (or some other crystal? first question which lases 2 lines- 1,064 and 1,319 nm for 589, and 1,064 nm and 1,342 nm for 593.5. these 2 lines are then combined (second question) and passed through the KTP, frequency doubling (third question) to produce 589 and 593.5nm respectively.

so to my questions.

1) im fairly sure its ND:YVO4, as it seems to me to be one of the most commonly used pump crystals in solid state lasers, and this is what my gooooogling has showed to be true of the two yellows. but, how does this crystal produce two lines? is it a different coating, different angle, what?

2) the two lines are then combined-a few sources say "paralleled". this leads into question 3, because no matter which way i look at it, i dont get 589 from 1064 and 1319.

3) if the two lines are combined-say 1,064 and 1,319 (for 589), then doubled, how the heck does that come out to 589? cant think of any math that makes that check out. if those two beams are added, then tripled, that gets close, but last time i checked, close to 589 wasnt 589 (comes out to be 595.75).



so either a) the sources i have looked at are wrong, b) i dont know what im on about c) i cant brain today or d) all of the above


anyway, sorry for rambling on, and :thanks: for reading!

 

[hwang21]

Welcome to laser physics... I can't answer all of your questions (I have to do some googling myself ) but I believe that's Sum Frequency Generation, SFG for short. Basically, 1/1319+1/1064=1/589

 

[crazyspaz]

ok, that makes sense. but still...how does that happen through a crystal? haha, googling comes up with this great definition of SFG (wikipedia for the win/loss) :

Sum-frequency generation - Wikipedia, the free encyclopedia

notice the definition: .... annihilation of two input photons at angular frequencies (1) and (2) while, simultaneously, one photon at frequency (3) is generated.

not quite the best definition ever....but it works i guess

 

[ZRaffleticket]

I thought it was more absorption than annihilation. But yeah thats what happens in there.

473nm is about as cheap as it'll ever be at this point. It hasn't changed prices much the past two years.

589nm is commonly Nd:YAG
593.5nm is Nd:YVO4

It's all in the coatings. The 589nm coating is pretty faulty, I'm also seeing 588nm and 585nm.

1/((1/WL1)+(1/WL2))=WL3

Check out my DPSS wavelength chart

 

[crazyspaz]

nice chart

now if someone knows the answers to those other questions...

 

[ZRaffleticket]

1) im fairly sure its ND:YVO4, as it seems to me to be one of the most commonly used pump crystals in solid state lasers, and this is what my gooooogling has showed to be true of the two yellows. but, how does this crystal produce two lines? is it a different coating, different angle, what?

Nd:YAG for 589nm, Nd:YVO4 for 593.5nm

2) the two lines are then combined-a few sources say "paralleled". this leads into question 3, because no matter which way i look at it, i dont get 589 from 1064 and 1319.

I thought 589nm came from a single coating rather than two paralleled to eachother. Though... that would account for the 30/70 ratio that I read about... anyway, two different wavelengths are produced at the same time by Nd:YAG, through that formula 1/((1/1064)+(1/1319))=589

3) if the two lines are combined-say 1,064 and 1,319 (for 589), then doubled, how the heck does that come out to 589? cant think of any math that makes that check out. if those two beams are added, then tripled, that gets close, but last time i checked, close to 589 wasnt 589 (comes out to be 595.75).

They're not both doubled. They're going through Second Harmonic Generation. Frequency doubling is the phenomena of WL1=WL2. Technically 532nm lasers are going through SFG.

once again, that formula roughly solves it (unless you take temperature, more exact measurements, medium and etc into account)

 

[crazyspaz]

We now see why the 80mW 589 from cni costs an arm, leg, and first born child.


and, ZRaffleticket, Second harmonic generation IS frequency doubling...just a typo, maybe?

 

[bloompyle]

DPSS God

I've actually wondered this myself. I was able to figure out 532nm DPSS by using an image like this:

However, I was not able to find a similar diagram for the yellows.

So, after passing through the ND:YAG, what is it that sums the two frequencies? Is it just a natural phenomena for them to interact that way? Or is there a second optic that does this?

Is the 1319nm from the 808nm, or is that a second line normally produced by ND:YAG? I only knew of ND:YAG lasing at 1064 with your normal SSY flash pumped solid-state laser. I think you know what I am talking about.

 

[crazyspaz]

So, after passing through the ND:YAG, what is it that sums the two frequencies? Is it just a natural phenomena for them to interact that way? Or is there a second optic that does this?

Is the 1319nm from the 808nm, or is that a second line normally produced by ND:YAG? I only knew of ND:YAG lasing at 1064 with your normal SSY flash pumped solid-state laser. I think you know what I am talking about.

precisely what i want to know. as far as i know, its just gypsy magic. gypsy magic that eats infrared laser beams, then does some magical magicness, then "blargh, laser", and you get yellow.

 

[ZRaffleticket]

From how I understand it, SFG and frequency doubling are both the same peculiarity that SHG causes.

There are more types of SHG than frequency doubling or SFG. It just so happens, in our laser world that's what it does.

Besides, 1/((1/1064)+(1/1064)) is the same as 1064/2.

 

[bloompyle]

Second Harmonic Generation means nothing to me, but I also need sleep. Will google it tomorrow.

So what is it that causes the two lines to interact and undergo SFG, and output 589?

I know very little about DPSS...

 

[hwang21]

I think it's a phenomenon that deals with the absorption of the crystal and the doping. Obviously I could be wrong, I didn't have time to thoroughly look into this, but I believe it's like non-linear optical effects: the two energies of the incoming photons are precisely the energy required for the crystal to drop to a lower energy state, releasing the third photon at 589nm of energy equivalent. I believe both photons have to hit the same atom or electron I guess to provide enough energy for the electron to jump back down to base and release that 589nm photon

Could be totally wrong but that makes sense to me

 

[ultimatekaiser]

here I'll take a crack at this and attempt to explain it in english. this is complex laser physics, and I admit I don't know everything myself...but i'll explain what I can.

808nm pumps a Nd:YAG vanadate crystal with a specific dopant level causing it to lase at two different lines. 1064 and 1319. now the vanadates have different opacities when they lase different lines, the YAG is famous for being efficient at 1064 and being mostly transparent, however it when done under specific conditions also lases these other smaller more rare lines. the 1319 line is smaller, and the vanadate is much more opaque to that light, resulting in much lower output. After a correct setup these two lasing lines are then coupled using a special dichroic optic so that they are combined as a single beam at the sum of these two frequencies at 1178nm. this is then doubled with a special crystalline non linear optic (NLO) called a ppKTP. (a periodically poled potassium titanyl phosphate) or sometimes other periodically poled NLOs which doubles the combined beams (your second harmonics) into the 589 raw output, which is then collimated etc. These crystals must be maintained at a specific range of temperatures or they won't react properly and you lose your lasing process.

Alternately they will create two seperate lasers and combine them, then pass them through the crystal if higher power is needed, but this requires more space and energy consumption and heatsinking, making the cost go up a lot more.

there's also the possibility of direct doubling a rare diode to it too, but I've never personally seen this done.

some other interesting references and info:
http://www.brl.ntt.co.jp/people/nisikawa/589nm.html

http://www.opticsinfobase.org/view_...13331.pdf?da=1&id=201810&seq=0&mobile=no&org=

http://www.phys.ens.fr/~dalibard/publications/2008_yellow_laser.pdf

How'd I do? *rests fingers*

 

[hwang21]

Wait the two lines are combined and then doubled? I thought the two lines were directly summed into 589nm... :thinking:

 

[ZRaffleticket]

Well for 589nm it's my unsderstanding that Nd:YAG is used in our handhelds. I'll prove whatever it is whenever the friggin physics department lets me use their spectrometer.

Both lines still need to be absorbed to react and lase 589nm as I understand it. They're still being summed, just both lines need to be present. I would imagine that the cavity lasing two lines simultaneously would do the combining from the get-go

 

[ultimatekaiser]

Well for 589nm it's my unsderstanding that Nd:YAG is used in our handhelds. I'll prove whatever it is whenever the friggin physics department lets me use their spectrometer.

Both lines still need to be absorbed to react and lase 589nm as I understand it. They're still being summed, just both lines need to be present. I would imagine that the cavity lasing two lines simultaneously would do the combining from the get-go

Yes and for 589 I think you can use either a yag or a yvo4. For the 593.5 process it has to be the yag I think but I'm not positive. One of the two doesn't have the other spectral line necessary. I forget which I'd have to check, I just did most of that from memory