Old 11-20-2010, 09:49 AM #1
Class 3R Laser
 
Join Date: Sep 2007
Location: California
Posts: 1,142
Rep Power: 1114
ixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond repute
ixfd64 ixfd64 is offline
Class 3R Laser
 
Join Date: Sep 2007
Location: California
Posts: 1,142
Rep Power: 1114
ixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond repute
Default LBO instead of KTP in DPSS green lasers?

I know that KTP is supposedly the most efficient crystal for doubling 1,064 nm light. However, I've noticed that some lasers (such as Coherent's Verdi series) use LBO instead of KTP. Does anyone know what advantages does LBO over KTP have, with respect to green DPSS lasers?


__________________

"5 mW" 405 nm eBay pen
Wicked Lasers Core
Wicked Lasers Executive Series - Advanced
Wicked Lasers 200 mW Spyder I Pro
Lots of generic red laser pointers

Check out my laser media here.
ixfd64 is offline   Reply With Quote


















Old 11-20-2010, 10:17 AM #2
goninanbl00d's Avatar
Class 2M Laser
 
Join Date: Jun 2010
Location: Sydney, AU
Posts: 892
Rep Power: 97
goninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond repute
goninanbl00d goninanbl00d is offline
Class 2M Laser
goninanbl00d's Avatar
 
Join Date: Jun 2010
Location: Sydney, AU
Posts: 892
Rep Power: 97
goninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond repute
Default Re: LBO instead of KTP in DPSS green lasers?

Firstly, you get a +rep for this question. Instead of being able to pull the knowledge off the top of my head, I actually had to go and do some research, and learnt quite a fair bit in the process.

To understand the reasoning behind the decision for the use of LBO (instead of KTP) in the Verdi, you need to understand the properties of both crystals. I've listed them out below for ya.

KTP:
  • Has a relatively high damage threshold
  • Can be non-critically phase matched
  • (Relatively) non-temperature dependant
  • Efficient (even when using a shorter crystal)

LBO:
  • Needs precise temperature
  • Needs to be critically phase-matched
  • Longer crystals are needed for higher efficiency
  • Very little problems with damage threshold

Now, in normal green lasers, it can be apparent that KTP is the better choice. High efficiency, no need for critical phase matching and no need for precision (~1C) temperature stabilization.

As a result, KTP is pretty much seen in every 532nm laser out there.

However, at the power that the Verdi is running at, KTP will no longer suffice. Take note of the last point listed under LBO- very high damage threshold.

The diameter of the KTP needed would mean that the tight beam specs of the Verdi would no longer be achievable if KTP was used- it would not be feasible to maintain the beam diameter after SHG.

As a result, Coherent decided to use LBO, as it did not suffer from the problem with the damage threshold. Although it adds to the complexity of the system (needing precision electronics and alignment), it does mean that the high powers are still achievable while maintaining a very low beam diameter (for that power level).

Other companies such as CNI continue to use KTP in their 5W+ green lasers, however, you will notice that their beam diameters are often much larger (by up to 3 or 4 times) and that they are running in Near TEM00 or Near TEM01 modes.
goninanbl00d is offline   Reply With Quote
Old 11-20-2010, 10:28 AM #3
Prototype's Avatar
Class 3B Laser
 
Join Date: Jun 2009
Posts: 2,712
Rep Power: 3309
Prototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond repute
Prototype Prototype is offline
Class 3B Laser
Prototype's Avatar
 
Join Date: Jun 2009
Posts: 2,712
Rep Power: 3309
Prototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond repute
Default Re: LBO instead of KTP in DPSS green lasers?

Do you happen to know the damage threshold for LBO, gonin? I'd be interested in finding out. I know the threshold for quality 5mm x 5mm x Xmm KTP is 500MW or more, but then you've got to deal with the crystal coatings and what not before anything else. The Verdi are also ring cavity SLM lasers, and as such have an etalon to stabilize the LBO. I do know that KTP is temperature ~1*C at higher powers (think multi-watt CW/QCW monsters) else they'll shatter.

Here is a diagram from Sam's FAQ on the layout of a Coherent Verdi for any interested:
Click HERE

And an actual picture of the inside of one of these wonders of laser engineering:
Click HERE

Last edited by Prototype; 11-20-2010 at 10:31 AM.
Prototype is offline   Reply With Quote
Old 11-20-2010, 10:39 AM #4
goninanbl00d's Avatar
Class 2M Laser
 
Join Date: Jun 2010
Location: Sydney, AU
Posts: 892
Rep Power: 97
goninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond repute
goninanbl00d goninanbl00d is offline
Class 2M Laser
goninanbl00d's Avatar
 
Join Date: Jun 2010
Location: Sydney, AU
Posts: 892
Rep Power: 97
goninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond repute
Default Re: LBO instead of KTP in DPSS green lasers?

Quote:
Originally Posted by Prototype View Post
Do you happen to know the damage threshold for LBO, gonin? I'd be interested in finding out. I know the threshold for quality 5mm x 5mm x Xmm KTP is 500MW or more, but then you've got to deal with the crystal coatings and what not before anything else. The Verdi are also ring cavity SLM lasers, and as such have an etalon to stabilize the LBO. I do know that KTP is temperature ~1*C at higher powers (think multi-watt CW/QCW monsters) else they'll shatter.

Here is a diagram from Sam's FAQ on the layout of a Coherent Verdi for any interested:
Click HERE

And an actual picture of the inside of one of these wonders of laser engineering:
Click HERE


Sorry, I have no idea. The FAQ didn't give any number and RP-Photonics was possibly just as vague.

But the FAQ did say that LBO did not have any of the gray tracking issues of KTP, and that LBO didn't have any of the issues with power density.

Quote:
For a laser like the Coherent Verdi, with an output between 5 and 10 W CW. To keep that below 10 kW/cm2, the beam area has to be at least 1/1000 cm2 or 0.1 mm2. That is roughly a beam diameter of 1/3 mm, not very small for a laser where you want to focus tighter to get good conversion. And that's operating at the limit. I would guess that Coherent would prefer to have some margin there. LBO doesn't have such a problem - you can focus as tight as you wish. The coatings are going to be a problem, if you go too tight, but not damage to the crystal (at least not anywhere near this value).

Last edited by goninanbl00d; 11-20-2010 at 10:46 AM.
goninanbl00d is offline   Reply With Quote
Old 11-20-2010, 10:45 AM #5
Prototype's Avatar
Class 3B Laser
 
Join Date: Jun 2009
Posts: 2,712
Rep Power: 3309
Prototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond repute
Prototype Prototype is offline
Class 3B Laser
Prototype's Avatar
 
Join Date: Jun 2009
Posts: 2,712
Rep Power: 3309
Prototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond reputePrototype has a reputation beyond repute
Default Re: LBO instead of KTP in DPSS green lasers?

I wasn't disagreeing that the LBO was better suited to the task than KTP, just that KTP has an extraordinary damage threshold as well.
Prototype is offline   Reply With Quote
Old 11-20-2010, 10:48 AM #6
goninanbl00d's Avatar
Class 2M Laser
 
Join Date: Jun 2010
Location: Sydney, AU
Posts: 892
Rep Power: 97
goninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond repute
goninanbl00d goninanbl00d is offline
Class 2M Laser
goninanbl00d's Avatar
 
Join Date: Jun 2010
Location: Sydney, AU
Posts: 892
Rep Power: 97
goninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond repute
Default Re: LBO instead of KTP in DPSS green lasers?

Yeah, in theory, they could have used KTP, but that would mean they would have a greater beam diameter at the aperture.

AFAIK CNI uses KTP in their big greens as well, and as a result, they've got a much larger beam diameter at the aperture as the beam has to be expanded before it hits the KTP.
goninanbl00d is offline   Reply With Quote
Old 11-20-2010, 11:01 AM #7
Class 3R Laser
 
Join Date: Sep 2007
Location: California
Posts: 1,142
Rep Power: 1114
ixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond repute
ixfd64 ixfd64 is offline
Class 3R Laser
 
Join Date: Sep 2007
Location: California
Posts: 1,142
Rep Power: 1114
ixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond repute
Default Re: LBO instead of KTP in DPSS green lasers?

Thanks for the information, goninanbl00d. I'd +rep you too, except the forum won't let me. :-(

By the way, would it be possible to shrink the beam back after it has been frequency-doubled?
__________________

"5 mW" 405 nm eBay pen
Wicked Lasers Core
Wicked Lasers Executive Series - Advanced
Wicked Lasers 200 mW Spyder I Pro
Lots of generic red laser pointers

Check out my laser media here.

Last edited by ixfd64; 11-20-2010 at 11:10 AM.
ixfd64 is offline   Reply With Quote
Old 11-20-2010, 11:23 AM #8
HIMNL9's Avatar
Class 4 Laser
 
Join Date: May 2009
Location: Lost somewhere in the EU mess ;)
Posts: 5,416
Rep Power: 1478
HIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond repute
HIMNL9 HIMNL9 is offline
Class 4 Laser
HIMNL9's Avatar
 
Join Date: May 2009
Location: Lost somewhere in the EU mess ;)
Posts: 5,416
Rep Power: 1478
HIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond reputeHIMNL9 has a reputation beyond repute
Default Re: LBO instead of KTP in DPSS green lasers?

Technically is possible to "shrink" back the beam with a pair of plano-convex lenses, but remember that, more the beam is thin at start, more high is usually the divergence, and this for long distance cause bigger spots .....

EDIT: also with a positive and a negative lens ..... same principles of the beam expanders, used in reverse.
__________________
High Impulse Multipath Neutron Laser (mark 9 ) (LOL)
Dare mo mita koto no nai, kaze, kumo, suna, umi ..... Kokoro no hate no doko ka eien ga kagayaku.

Last edited by HIMNL9; 11-20-2010 at 11:39 AM.
HIMNL9 is offline   Reply With Quote
Old 11-20-2010, 11:33 AM #9
goninanbl00d's Avatar
Class 2M Laser
 
Join Date: Jun 2010
Location: Sydney, AU
Posts: 892
Rep Power: 97
goninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond repute
goninanbl00d goninanbl00d is offline
Class 2M Laser
goninanbl00d's Avatar
 
Join Date: Jun 2010
Location: Sydney, AU
Posts: 892
Rep Power: 97
goninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond reputegoninanbl00d has a reputation beyond repute
Default Re: LBO instead of KTP in DPSS green lasers?

Yes, as HIMNL9 said, it is possible.

However, beam diameter is inversely proportional to beam divergence. Bring one down, and the other goes up accordingly.

If they had expanded the beam inside the cavity, bringing the beam diameter down would have resulted in a massive increase in divergence. Halve the beam diameter, and double the divergence.

It made better sense, then, to use a crystal where the exit beam would be in-spec, as opposed to using external optics and having to sacrifice either divergence or beam diameter.
goninanbl00d is offline   Reply With Quote
Old 11-20-2010, 12:01 PM #10
Class 3R Laser
 
Join Date: Sep 2007
Location: California
Posts: 1,142
Rep Power: 1114
ixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond repute
ixfd64 ixfd64 is offline
Class 3R Laser
 
Join Date: Sep 2007
Location: California
Posts: 1,142
Rep Power: 1114
ixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond repute
Default Re: LBO instead of KTP in DPSS green lasers?

Quote:
Originally Posted by goninanbl00d View Post
However, beam diameter is inversely proportional to beam divergence. Bring one down, and the other goes up accordingly.

If they had expanded the beam inside the cavity, bringing the beam diameter down would have resulted in a massive increase in divergence. Halve the beam diameter, and double the divergence.
Yeah, I'm aware of that. However, I thought that the specs of a beam exiting the crystal was independent of that of the beam that pumps the crystal, which is why DPSS lasers have good beam specs even when pump diode has horrible specs.

By the way, would BiBO be a better option than LBO? From what I've heard, BiBO is much more efficient than LBO (at least for doubling 946 nm); it also has a similar damage threshold as LBO but without the disadvantage of being hygroscopic. BiBO is relatively new, though, so I haven't been able to obtain too much information about it.
__________________

"5 mW" 405 nm eBay pen
Wicked Lasers Core
Wicked Lasers Executive Series - Advanced
Wicked Lasers 200 mW Spyder I Pro
Lots of generic red laser pointers

Check out my laser media here.
ixfd64 is offline   Reply With Quote
Old 11-20-2010, 01:22 PM #11
Benm's Avatar
Class 4 Laser
 
Join Date: Aug 2007
Location: Netherlands
Posts: 7,623
Rep Power: 210024
Benm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond repute
Benm Benm is offline
Class 4 Laser
Benm's Avatar
 
Join Date: Aug 2007
Location: Netherlands
Posts: 7,623
Rep Power: 210024
Benm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond repute
Default Re: LBO instead of KTP in DPSS green lasers?

Quote:
Originally Posted by ixfd64 View Post
Yeah, I'm aware of that. However, I thought that the specs of a beam exiting the crystal was independent of that of the beam that pumps the crystal, which is why DPSS lasers have good beam specs even when pump diode has horrible specs.
In a way it is. The beam quality of the pump is not important, as long as you can focus it such that all of th pump light enters the solid state laser.

The quality of the 1064nm solid state laser is important for the output specifications. Even though the frequency doubling is an additional step, a bad/big beam that enters the doubler will produce an equally bad output beam at 532.

I suppose that in this case the 1064nm laser isnt a problem, it can produce a beam of the desired power density... but that would damage the KTP. They could also have chosen to make the 1064nm laser wider to get a lower power density, and use KTP for doubling. To get the same diameter/divergence ratio they would have to use a much larger 1064nm laser though - not to be able to handle the power, but to get a beam of lower divergence.
Benm is offline   Reply With Quote
Old 11-21-2010, 03:33 AM #12
Class 3R Laser
 
Join Date: Sep 2007
Location: California
Posts: 1,142
Rep Power: 1114
ixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond repute
ixfd64 ixfd64 is offline
Class 3R Laser
 
Join Date: Sep 2007
Location: California
Posts: 1,142
Rep Power: 1114
ixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond reputeixfd64 has a reputation beyond repute
Default Re: LBO instead of KTP in DPSS green lasers?

Quote:
Originally Posted by Benm View Post
The quality of the 1064nm solid state laser is important for the output specifications. Even though the frequency doubling is an additional step, a bad/big beam that enters the doubler will produce an equally bad output beam at 532.
That explains things. I'm assuming that the specs of the input and output beams would only be independent for the actual lasing medium, not the NLO crystal, though I could be wrong.
__________________

"5 mW" 405 nm eBay pen
Wicked Lasers Core
Wicked Lasers Executive Series - Advanced
Wicked Lasers 200 mW Spyder I Pro
Lots of generic red laser pointers

Check out my laser media here.

Last edited by ixfd64; 11-21-2010 at 03:38 AM.
ixfd64 is offline   Reply With Quote
Old 11-21-2010, 12:09 PM #13
X FLY's Avatar
Class 2 Laser
 
Join Date: Aug 2009
Location: Finland
Posts: 338
Rep Power: 13
X FLY is just really niceX FLY is just really niceX FLY is just really niceX FLY is just really nice
X FLY X FLY is offline
Class 2 Laser
X FLY's Avatar
 
Join Date: Aug 2009
Location: Finland
Posts: 338
Rep Power: 13
X FLY is just really niceX FLY is just really niceX FLY is just really niceX FLY is just really nice
Default Re: LBO instead of KTP in DPSS green lasers?

I wonder what kind of replies a thread like this would get at lasercommunity.com
__________________
532nm ● WickedLasers Core 5mW
532nm ● 2x Cheap "5mW" pointers bought from Greece
(one is about 30-50mW and the other about 15-20mW)
532nm ● WickedLasers E2 Series Fusion <100mW - ORDERED 13.10.2010, SHIPPED 11.02.2011, ARRIVED 16.02.2011
447nm ● DragonLasers 1W Spartan - review with A LOT of pics

2x 190-548nm Safety Goggles from DragonLasers

X FLY is offline   Reply With Quote
Old 11-21-2010, 04:18 PM #14
Benm's Avatar
Class 4 Laser
 
Join Date: Aug 2007
Location: Netherlands
Posts: 7,623
Rep Power: 210024
Benm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond repute
Benm Benm is offline
Class 4 Laser
Benm's Avatar
 
Join Date: Aug 2007
Location: Netherlands
Posts: 7,623
Rep Power: 210024
Benm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond reputeBenm has a reputation beyond repute
Default Re: LBO instead of KTP in DPSS green lasers?

Quote:
Originally Posted by ixfd64 View Post
That explains things. I'm assuming that the specs of the input and output beams would only be independent for the actual lasing medium, not the NLO crystal, though I could be wrong.
Afaik the beam specs for the doubled light are identical to that of the solid state laser.

The non linear crystal takes 2 photons, and comines them into one new photon. The only thing that changes is the polarization of the light (the doubled photon has a 90 degree rotated polarization compared to the solid state laser output).

Other than that, the doubling crystal does not change the trajectory of the photons its combining, so it should, in theory, not change the beam specs at all.

There is however one aspect that might: Frequency doubling works better with higher power densities. If the incoming beam has a gaussian profile, the output beam would have an even stronger profile, since doubling efficiency is best in the center of the beam, and impossible below a certain power density.
Benm is offline   Reply With Quote
Old 09-11-2014, 03:51 PM #15
mh3 mh3 is offline
Junior Member
 
Join Date: Sep 2014
Posts: 1
Rep Power: 0
mh3 is on a distinguished road
mh3 mh3 is offline
Junior Member
 
Join Date: Sep 2014
Posts: 1
Rep Power: 0
mh3 is on a distinguished road
Default Re: LBO instead of KTP in DPSS green lasers?

LBO:

Needs precise temperature
Needs to be critically phase-matched
Longer crystals are needed for higher efficiency
Very little problems with damage threshold
LBO crystals used in high-power cw lasers such as Coherent Verdi are non-critically phase-matched by heating them to 150 degrees Celsius. As such they are relatively insensitive to misalignment or changes in beam divergence.

Pure KTP crystals are critically phase-matched so their angles have to be carefully oriented. Since KTP's non-linear coefficients are much larger w.r.t. LBO, green light can be produced at high efficiencies from even lower-power 1064-nm cw lasers. At higher powers, flux-grown KTP crystals exhibit "gray-streaking" over time, which causes them to eventually burn. Newer growth methods exist which partially circumvent this problem but they can be extremely expensive.

BIBO has high non-linear coefficient values which would make them very efficient in principle, and they are especially attractive in the blue region. In practice it is probably fair to say that the quality and reproducibility of commercially-available crystals are still inferior to those of LBO or KTP.

Damage threshold values vary on the publication, but numbers such as a few GW/cm^2 for KTP and 20-30 GW/cm^2 for LBO are often quoted. This strongly depends on the quality of the crystal. Poor anti-reflection coating on the crystals can burn before the crystal does.

The beam quality for the fundamental and SHG beams generally differ, since only that part of the fundamental light which lies within the angular acceptance of the crystal gets converted. The divergence and diameter of the SHG light is therefore slightly reduced compared to the fundamental, at a cost of lower conversion efficiency. Hot spots in the fundamental beam can get more pronounced in the second harmonic beam. For high-power pulsed lasers where crystal damage can become an issue, "top hat" type profiles are often selected instead of pure TEM00 Gaussian modes.
mh3 is offline   Reply With Quote
Reply





Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



























Privacy Policy | Advertising Disclaimer | Terms of Use


 


All times are GMT. The time now is 01:57 AM.


Powered by: vBulletin
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO
Privacy Policy | Advertising Disclaimer | Terms of Use
Copyright (C) 2017 Laser Pointer Forums, LLC