A new class of saturable absorbers at 10.6 µm based on doped alkali halides

A new class of saturable absorbers for 10.6 μm, CO
2
laser wavelengths, uses alkali halides doped with the perrhenate (ReO
4
) ion. Here the ν
3
vibrational transition saturates like an ideal two-level system owing to a large anharmonic interaction with the crystalline system. Fourier transform and saturation spectroscopy indicate a phonon scattering interaction and homogeneous line broadening at temperatures above 80 K. Multiline saturable absorption at various laser wavelengths can be obtained by either crystal heating or by double doping. Laser applications include pulse compression and passive mode locking.