Laser sources based on laser diodes are available in wavelengths from 375 nm in the near UV to over 2300 nm in the infrared. Most laser diodes are Fabry Perot laser diodes. The center wavelength is specified by the diode manufacturer and can vary up to 5%. For most inspection systems, the usable wavelengths are limited by the sensitivity of the camera to the visual spectrum range 400-700 nm plus the shorter end of the near infrared (up to about 1000 nm). Within the visual range the wavelength is further limited to the wavelengths available as laser diodes.
There are still some gaps in the spectrum:
On the market are violet (375 - 410 nm), blue (415 - 488 nm), green (505 - 520 nm), red (633 –- 690 nm) and infrared (705 - 1550 nm) laser diodes.
Violet or blue are often used when very thin lines or small spots are required, and depth of focus is not important. Most other applications still often work with red lasers.