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604nm DPSS Laser






Nexgen said:
I found this on a Thorlabs.

This is 1208nm 3W laser diode, it has a reasonable price.

Link: https://www.thorlabs.de/thorproduct.cfm?partnumber=BAL1112CM

Is it possible to frequency double 1208nm? Would give decent orange beam if possible.

What do you think?

Searching forums didn’t gave any success about this topic.

Sorry if double thread.
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Apparently you did not search the LPF data base--there is a discussion of the same thing see post #4 of May 2011. which also comes up if you search LPF orgoogle so....see here: https://laserpointerforums.com/f40/why-can-t-we-frequency-double-1208nm-63234.html

"As I've said before about KTP and 'throwing photons KTP with a diode for them to shit out a stream of photons out the other end', it isn't a very straightforward process. Finding the correct wavelength is only the start of it.

First off, due to a property inherent to KTP, it cannot double well below 500nm, and not all in the blue, as it cannot be phase-matched for those wavelengths. This same property allows it to double 1064nm with such brutal efficiency.

KTP is also used in the SHG of 1319 and 1342 for 660 and 671nm respectively (both are Nd:YAG/YVO4 lines). It's also used in SFG (sum frequency generation) for both 589 and 594.5nm.

The second issue that comes to mind is power density- and although it may seem easy to get plenty of power (5W in a C-mount 808 is easy to get), cramming that power into something that is usable is not nearly as easy.

First off, although 3W (like in the diode you linked) may seem like a lot of power, bear a few things in mind:

1. Being a multimode, multi-emitter device, the output beam will be very messy, not to mention extremely astigmatic.
2. There'll be no easy way to focus that down to the spot size needed for effective SHG.

To put things into perspective, your dinky little 5mW green pen laser has watts of power circulating through the cavity at any given time. Only a small percentage ever makes it out as 532nm, of course, and most of that power remains in the cavity.

The other thing about said dinky pen laser is that the intracavity 1064nm beam is often micrometers wide. Without a FAC, the intracavity beam is usually slightly smaller than diode's active emitting area, while with a FAC, the intracavity 1064 is often narrower.

So, you have many watts of power in a tiny spot. SHG, being a non-linear process, works better almost exponentially as power levels rise.

Put those two together, and you'll see that sending a single diode for a pass through a doubling crystal won't work.

Case-in-point: An SSY-1 (flashlamp-pumped pulsed Nd:YAG laser with a nominal peak power of 200mJ) has trouble achieving green output when it is shot through a KTP crystal. The same laser with a passive Q-switch (which serves to increase the peak power) has no problem with extracavity doubling. Without the Q-switch, the power is on the order of kW, while with the Q-switch, it rises to hundreds of kW (or even into the MW range if pumped correctly).

Of course, with the diode being multimode and multi-emitter, getting it to the point size necessary is extremely difficult. And even if you do manage to break a handful of the laws of physics and pull it off, it'll be an even bigger challenge to contain it within the doubling crystal.

On top of that, the diode has to be phase-matched with the doubler crystal. Due to the beam profile and astigmatism involved often this can't be done with a diode.

When you have seen a directly-doubled diode (such as the Novalux Protera 488 series), they use a special external-cavity VESCEL diode. The VESCEL diode design eliminates the astigmatism and poor beam profile inherent to normal diodes, while the external-cavity design means that the doubling optic is also part of the cavity, giving the power densities needed. Phase-matching can then be achieved, and a TEC is used to stabilise the doubling crystal and the diode to ensure temperature fluctuations do not result in an un-phase-matching of the setup."
 
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Nexgen said:
Thanks Encap, information you gave is really interesting. :topic:
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My pleasure.
Is something interesting and not clearly understood--the practical real world aspects by most--so is a good thread to have up.

Point is KTP is absolutely brutally efficient at 1064nm so 532nm is relatively easy to achieve

See also post #3 in this thread --is interesting: https://laserpointerforums.com/f45/ktp-dpss-70974-2.html

"The actual frequency doubling process, the point at which 1064 becomes 532, requires a VERY narrow bandwidth to work. If your KTP was meant to double 1064, and you gave it 1065, it wouldn't work.
- When 1064 comes out of a crystal being pumped by 808, that 1064 is basically rock solid at 1064, even if the pump wasn't quite 808 (maybe it was 811, or 807, etc)
- This is important, because it means that you can use something like a diode laser, that fluctuates in wavelength a LOT (with heat, and tolerances from diode to diode), yet still get the very narrow bandwidth 1064nm needed for frequency doubling.

This is why "directly doubled" 1064nm diode to 532nm setups are fairly difficult to achieve. They're out there (like the Corning G-1000s), but it's MUCH more difficult to keep a 1064nm diode locked on 1064nm (tightly enough) than it is to get that 1064nm from a crystal, pumped by an 808nm diode that can wander wherever the hell it wants within a few nm +/- of 808."
 
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Nice thing about using a YVO4 with an 808 nm laser diode is you don't need to be exactly on wavelength, can be off a couple of nm or so, a bit more actually, and will still get enough 1064nm out to make plenty of green with those cheap "5 mw" ebay greenies which really produce 30-75 mw, occasionally more with some IR mixed in, of course, cheap ones don't have the IR filter. I've measured 60 mw out when driven with about a quarter watt of 808 nm, they are sometimes very efficient.
 
It should be worth mentioning that the 604nm DPSS offered by CNI and a few other companies is using 445nm to pump Pr:YLF or Pr:PAYAC (607nm out instesad) to directly lase at these wavelengths without the need for ktp or some other doubler.

And with that, you still get all the fun complications that comes packaged with DPSS... There's a reason 604nm is very expensive :(
 
Regarding that spreadsheet, if anyone wants to have edit access just send me a PM with your gmail address. I haven't touched it in a long, long time.
 
I've looked at that before, Zach. Seemed to be fairly comprehensive, though I can't vouch for all the values listed. Seems like you would have done your homework before posting it, though.
 
Encap said:
If your KTP was meant to double 1064, and you gave it 1065, it wouldn't work.
Click to expand...

I used to believe that as well, but now I'm not so sure it holds. If it did would we see as much wavelength variation/multiline lasing from the cheap 532nm pointers? They're not all 532nm and many produce multiple lines.
 
All the multi-line lasers around 532nm are very close to that primary wavelength. I have a couple that give 4 lines and 6 lines, but they are all green and not far from 532nm. I believe it is due to poor coatings on the crystals as they were never made to give more than one line.
 
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