Line width of green DPSS laser Could someone suggest what is the line width/mode stability/coherence length of generic cheapo green (532nm) DPSS laser?
I've found lots of nice info here: http://redlum.xohp.pagesperso-orange.fr/laser/modeanalysis.html but there are no any DPSS lasers.
 A: For questions like this I always recommend finding the relevant article on Sam's Laser FAQ, which is an incredible practical resource. However,The short answer is that they are much better than standard diode lasers on all three points.
The emitted beam from an Nd:YAG or Nd:YVO crystal is very pure 1064 nm light and the nonlinear crystal, typically potassium titanyl phosphate (or KTP for short), doubles  it precisely to 532 nm ($\pm1$ nm I'd guess). You can find several diagrams of the internals of green laser pointers in the link above. My guess is that main effect of variations in the performance of the 808 nm pump diode would be to reduce the coupling efficiency and thus the output power, but I believe that Nd:YVO is relatively tolerant to such variations. 
Hazarding a wild guess based on your question, I'd say that you might be interested in doing some holography experiments with a green laser pointer. This paper details how to do professional quality holography with a green laser pointer as the source.
Apologies for not providing quantitative answers to your question, but hopefully I've provided the practical info that you need.
A: You may build an interferometer as you split it through a mirror and your optical pathlengths differ < 1 cm and you want to do no serious science. However cheap green laser pointers are not ideal:


*

*It is no single-mode light. 

*Extensive mode hopping and power modulation drifting with temperature

*awfull beam profile, you need a tiny hole in a foil to get an acceptable profile and be able  to focus it with optics (the rest is lost)

*the infrared light is allways a risk to your eye if it is not correctly filterd out


I suggest using a HeNe laser tube (ebay 20€) instead of a chinese laser pointer (ebay 30€?)
