Do green lasers really vary that much in wavelength?

[Hiemal]

On the listing for my ebay greenie they state the output wavelength can vary +/- 10 nm...

I thought DPSS systems were extremely precise, would it/can it really vary that much?

 

[LesPaul]

If you take a look at CNI, under green lasers they have about 8 different types of green wavelengths, going from 514nm to 561nm.

 

[Sigurthr]

I've only ever once seen a green which had secondary lasing effects at different wavelengths. My understanding is that the doping has to be just right by chance in the Nd crystal to allow multiple lines to come through with enough strength to be doubled by the KTP. Normally the Nd crystal only puts out the 1064nm line with enough power for KTP doubling.

 

[Cyparagon]

Yeah, in >99.9% of pointers, there is 532.05nm. All the time, every time. I think the +/- 10nm is just from label copy paste.

 

[Hiemal]

Sigurthr, what do you mean by doping?

Is it just the coating on it? What happens when you remove the coating?


Would you get a multi-color emission DPSS laser? Or would it just cease to work properly?

Would it be possible to somehow coat the crystal yourself?

 

[Sigurthr]

C'mon quack, you should know about semiconductor doping! It is the injection of certain atoms/ions in to a crystal lattice which changes the physical, electrical, and optical properties of the material. NdYAG is Neodymium doped YAG crystals. It is doping that determines it's bandgap and thus it's emission spectrum along with the electrical characterisitics.

In diodes you have the base material which is doped to change the bandgap and generate their emission spectrum. LEDs chemical/electrical difference from LDs is mostly due to the sloppy doping. The main physical/optical differences are the formation of cleaved cavity mirrors and the substantially reduced size of the active region in LDs.

The coatings form the mirrors needed for lasing. If you removed them you'd get a poorly functioning LED. Multicolor DPSS is how SFG (593.5nm) works, the coatings are generated to work over two frequencies and both are created then combined.

I've heard of people doing coatings but I wouldn't try it, it's pretty complex and sometimes dangerous stuff and it will never come out like the pros.

 

[Hiemal]

C'mon quack, you should know about semiconductor doping!

I know fully well about doping, but I didn't know doping was involved with DPSS crystals, as they're not semiconductors! I wasn't talking about the IR diode itself.

And I know, they were probably silly questions but I was just curious.

 

[Sigurthr]

Hehe, sorry, didn't mean to come off in a mocking tone, just a "D'oh" invoking one.

Aye, it's the same process though. They dope the optical crystals to determine their function and then coat them with wavelength-specific reflective coatings to act as mirrors - instant laser cavity.

 

[geekypyro21]

Wow, that is a really amazing process, I didn't realize how little I knew about DPSS crystals until now, I love it when I learn something new!




(yes I do know its been a few days since the last post on this thread)

 

[Bluefan]

I've only ever once seen a green which had secondary lasing effects at different wavelengths. My understanding is that the doping has to be just right by chance in the Nd crystal to allow multiple lines to come through with enough strength to be doubled by the KTP. Normally the Nd crystal only puts out the 1064nm line with enough power for KTP doubling.

532nm lasers definitely can't lase even 1nm away from their wavelength. The 1064nm line from neodymium embedded in a YAG or YVO4 host material are two very closely spaced lines, close enough to overlap considerably by broadening. The complete gain curve is I think 0.3nm wide. Beyond that you need a different transition which occur at different wavelength and are all less efficient. Doping won't change this, it will only change absorbtion and things like energy transfer upconversion and cross relaxation which aren't occuring significantly anyway.

The nonlinear crystal, usually KTP, is only phasematched at 1064nm/532nm, beyond that the efficiency rapidly drops off with a sinc^2 function. No other Nd transition can be doubled with any efficiency unless picowatts are your thing.

C'mon quack, you should know about semiconductor doping! It is the injection of certain atoms/ions in to a crystal lattice which changes the physical, electrical, and optical properties of the material. NdYAG is Neodymium doped YAG crystals. It is doping that determines it's bandgap and thus it's emission spectrum along with the electrical characterisitics.

No. First: doping a semiconductor and doping a laser crystal are majorly different.

A semiconductor is doped by electron donors or acceptor. These do not change the bandgap of the host semiconductor material, they can only add donor and/or acceptor states close to the conduction or valence band. Electrical properties are determined byt he semiconductor material and doping concentrations. In laser diodes the bandgap is tuned by picking the right semiconductor material and by changing the active layer thickness as this confines the electron states and thus influences the energy difference between the lowest state in the conduction band and the highest state in the valence band.

In a lasery cyrstal there is no semiconductor involved. There is a rare earth ion inside a host crystal. There are no electrical properties as the crystals are isolators. The rare earth ions are moderately affected by their surroundings, the 1064nm line in Nd:YAG is 1047nm in Nd:Glass and Nd:YLF is slightly different again. This is purely the effect of the crystal surrounding on the rare earth atom.

In diodes you have the base material which is doped to change the bandgap and generate their emission spectrum. LEDs chemical/electrical difference from LDs is mostly due to the sloppy doping. The main physical/optical differences are the formation of cleaved cavity mirrors and the substantially reduced size of the active region in LDs.

The biggest physical difference is indeed the small active layer. The doping is used to shift energy levels with respect to other layers in a multilayer in case of a laser diode, LED's don't need that. This is done to let the recombination take place in the thin active layer. The bandgap and layer thickness determine the total energy gap and thus the emission spectum.
So it's far more involved than just making is small and cleaving the facets.

The coatings form the mirrors needed for lasing. If you removed them you'd get a poorly functioning LED. Multicolor DPSS is how SFG (593.5nm) works, the coatings are generated to work over two frequencies and both are created then combined.

Laser diodes have no mirrors, the high refractive index and very high gain are sufficient. A cleaved edge in the semiconductor material already has around %30 reflectivity. Coatings can't change the LD's wavelength, only the threshold and efficiency and that kind of things are affected.

DPSS is different. Nd:YAG has multiple transitions, with the right mirrors two can resonate in the same cavity, both in the infrared. A nonlinear crystal then converts the two wavelengths into one shorter wavelength, or sum frequency generation.

I've heard of people doing coatings but I wouldn't try it, it's pretty complex and sometimes dangerous stuff and it will never come out like the pros.

You'd need a well equiped cleanroom to do coatings properly, DIY coatings are slightly impossible unless you're experienced in UHV and stuff like that. And you'd need all that equipment.

 

[Sigurthr]

532nm lasers definitely can't lase even 1nm away from their wavelength. The 1064nm line from neodymium embedded in a YAG or YVO4 host material are two very closely spaced lines, close enough to overlap considerably by broadening. The complete gain curve is I think 0.3nm wide. Beyond that you need a different transition which occur at different wavelength and are all less efficient. Doping won't change this, it will only change absorbtion and things like energy transfer upconversion and cross relaxation which aren't occuring significantly anyway.

The nonlinear crystal, usually KTP, is only phasematched at 1064nm/532nm, beyond that the efficiency rapidly drops off with a sinc^2 function. No other Nd transition can be doubled with any efficiency unless picowatts are your thing.

There is a thread/post on this forum where someone posted to find out why their laser was behaving strangely - when shined through a diffraction grating (linear 1000lines/mm single axis) they were getting too many dots. There were other wavelengths in the photo posted next to 532nm one, which were between the center dot and the repetition of the 532nm. I agree totally about the loss of efficiency, but how else would you explain that photo other than multiple lines being doubled?

About the doping; I thank you for the detailed elaboration! Btw, I didn't mean that it was the -same- as semiconductor doping, just that in both cases, doping helps determine the application and properties.

The coatings form the mirrors needed for lasing. If you removed them you'd get a poorly functioning LED.

I was referring to the earlier question of if you removed the coatings from NdYag in a DPSS system. You'd get a piss-poor 1064nm led, iirc.

 

[lazeristasUVISIR]

Nd:YVO+KTP can indeed lase at several wavelengths without any special coatings. Though, the intensity is very very very low at a side band. SHG and SFG give three lines in the spectrum.

Nevertheless, to write a bandwidth 10 nm for the DPSS Nd:YVO+KTP laser is insane. It is more appropriate for a laser diode.

 

[Super Critical]

I don't have an an LPM but I have a few greens and the one I bought off looks different than Swims. The difference maybe do to things other than the wavelegnth it would be interesting to LPM it though.

 

[TheReddish]

about the doping, the laser I worked on in the army, don't quote me it was years ago, but it was a small very bright greenish light flashlamp and a glass rod coated with ruby powder and very slightly radioactive isotope of neodymium and filled with helium, A really small unit but it was cooled by one of the ac units used to cool the left side FAB they called the coating on the tube its doping. I can't remember much as it did not break much, I know it was a pusle IR laser though and you could not see the beam with FLIR but the computer could using the same optics. What wavelength do you guys think it was?

 

[BShanahan14rulz]

Do a search for SSY-1 to find more info about the ND:YAG targeting laser.

Sam's Laser FAQ - Commercial Solid State Lasers Sam's laser faq link

wavelength is 1064nm infrared.