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.
