Topic Measurement

A helium-neon laser oscillates on an atomic transition, so its wavelength is fixed by physics rather than by temperature and drive current. For alignment, interferometry and anything calibrated against a known wavelength, that stability is worth more than the convenience of a diode.

Silicon detectors work to about 1000 nm and are inexpensive; InGaAs covers roughly 900 to 1700 nm and costs more. The choice is decided by where your sample has features. Colour and fluorescence live in the visible; water, fats and polymer overtones live in the near infrared.