External cavity quantum cascade lasers with ultra rapid acousto-optic tuning.

We report operation of tunable external cavity quantum cascade lasers with emission wavelength controlled by an acousto-optic modulator (AOM). A long-wave infrared quantum cascade laser wavelength tuned from ~8.5 µm to ~9.8 µm when the AOM frequency was changed from ~41MHz to ~49 MHz. The laser delivered over 350 mW of average power at the center of the tuning curve in a linewidth of ~4.7 cm-1. Measured wavelength switching time between any two wavelengths within the tuning range of the QCL was less than 1 µs. Spectral measurements of infrared absorption features of Freon demonstrated a capability of obtaining complete spectral data in less than 20 µs. [ABSTRACT FROM AUTHOR]