Optical Density, the base-10 logarithm of the inverse of transmission, so OD 3 passes one thousandth of the light and OD 7 one ten-millionth. Laser safety eyewear and filters are labeled with OD per wavelength range, and the required OD is calculated from the laser's power or energy against the maximum permissible exposure. Neutral density filters for attenuating beams are graded the same way.
Goggles say OD 7 from 1000 to 1100 but only OD 2 at 532, so they're useless once the doubler is in.
Also heard as
- optical density
- OD rating
Related terms
Goggles
Lab shorthand for laser safety eyewear, the filtering glasses or goggles rated by optical density at specific wavelengths.
Class 4
The highest laser hazard class, for beams that can injure eyes and skin even by diffuse reflection and can start fires.
Bleed-through
Residual unwanted wavelength, such as leftover infrared pump, leaking past filters into the useful beam.