Knowledge Bank

Continuously tunable laser sidebands have been generated by mixing radiation from an optically pumped far infrared (FIR) molecular laser beyond 3000 GHz with that from millimeterwave klystrons in a Schottky-barrier diode. An enhancement in conversion efficiency over similar systems reported previously is obtained by using a Michelson interferometer to separate the sidebands from the carrier and by placing the Schottky diode in an open structure corner cube mount. With 4 mW of laser power at 693 and 762 GHz the sideband power was measured to be $10\mu $W. This is at least an order of magnitude better than the previously reported results. At higher frequencies, 22 mW of 1627 GHz laser power produced about $7.5\mu W$ of sideband output while 3mW of 1839 GHz laser power generated about 200 nW of sideband radiation. The lower efficiency at the higher frequencies is due primarily to the mismatch between the laser radiation and the fixed-length diode antenna. Spectral lines have been observed up to 3200 GHz. The molecular absorbtion signals are easily seen using either video or lock-in detection techniques. The combination of various lines from FIR lasers, the continuous tunability of klystrons, and the high efficiency of this system promises nearly complete coverage of the entire submillimeter and far-infrared regime, and provides a powerful tool for spectroscopic measurements. Some of these recent measurements to provide frequency calibration throughout the region will be described.