Frequency addition source of optical radiation

For other uses, see FASOR (disambiguation).

A 50W FASOR used at the Starfire Optical Range.

FASOR is an acronym for frequency addition source of optical radiation. The name is used for a certain type of guide star laser deployed at US Air Force Research Laboratory facilities SOR and AMOS. Commercialization has been attempted by the company FASORtronics. The laser light is produced in a sum-frequency generation process from two solid-state laser sources that operate at different wavelengths. The frequencies of the sources add directly to a summed frequency. Thus, if the source wavelengths are $\lambda_1$ and $\lambda_2$, the resulting wavelength is

$\lambda = \left(\frac{1}{\lambda_1} + \frac{1}{\lambda_2} \right)^{-1}.$

Application

The FASOR is used for laser guide star experiments. It is tuned to the D2a hyperfine component of the sodium D line and used to excite sodium atoms in the mesospheric upper atmosphere. The FASOR consists of two single-frequency injection-locked Nd:YAG lasers close to 1064 and 1320 nm that are both resonant in a cavity containing a lithium triborate (LBO) crystal, which sums the frequencies yielding 589.158 nm light.