Physics:Frequency addition source of optical radiation

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. 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 [math]\displaystyle{ \lambda_1 }[/math] and [math]\displaystyle{ \lambda_2 }[/math], the resulting wavelength is

[math]\displaystyle{ \lambda = \left(\frac{1}{\lambda_1} + \frac{1}{\lambda_2} \right)^{-1}. }[/math]

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 1319 nm that are both resonant in a cavity containing a lithium triborate (LBO) crystal, which sums the frequencies yielding 589.159 nm light.