The red laser pointers you see are laser diodes, wavelength not particularly well characterised, it varies with operating temperature, ~0.25 nm / deg. I would recommend a green laser, these are normally diode pumped solid state lasers. Wavelength always 532nm, determined by energy levels in Neodymium rather than band gaps in a semiconductor. Blue lasers are diode lasers as well so again wavelength not well characterised. An old style red gas laser would be good, these are Helium Neon lasers, wavelength always 632.8nm.
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