This is really neat. I just finished building an acoustic guitar, I'd love to see it's acoustic profile as compared to some others... Hmm, another project idea to investigate (although I'll prob have to settle for the old fashioned method).
Laser interferometry is not beyond the scope of an amateur. You just need a laser :-) A true one not a handheld pointer. Then you'd need some optics and a darkroom.
What's wrong with a pointer? Not coherent enough? It seems like a real laser when you shine it on a CD, at least (ghetto diffraction grating).
Yeah, coherence, altough I'm sure you can test for that. Some cheap pointers use nothing more that collimated LEDs.