Question: what is nm on laser?
Answer: An 'nm' is a nanometer (1.0 x 10^-9) and it determines the wavelength of the laser, 650nm is red, 532nm is green (and near the peak of human eye-sensitivity), 473nm is blue, 405nm is a violet shade. Green lasers cost more because they're DPSS, as are blue lasers, but are far less inefficient.