Dual-Wavelength ${\rm Cr}^{3+}{\colon}{\rm LiCaAlF}_{6}$ Solid-State Laser With Tunable THz Frequency Difference

We present a scheme for dual-wavelength operation of a diode-pumped
${\rm Cr}^{{3+}}{\colon}{\rm LiCaAlF}_{6}$
(Cr:LiCAF) laser with tunable frequency difference suitable for terahertz continuous-wave generation by heterodyne mixing in low-temperature-grown GaAs photomixers or intracavity nonlinear difference-frequency mixing. The laser is based on a double external optical feedback configuration to achieve spectral purity of the laser light through self-injection locking. The wavelength separation reported allows for a fully equalized dual-wavelength source between 0 and 9 THz in the 785-nm region.