Two-frequency MOPA laser system generates terahertp waves
In January at Photonics West (San Jose, CA), researchers from the California Institute of Technology and Jet Propulsion Laboratory (CalTech and JPL; Pasadena, CA) described generation of coherent terahertp waves by photomixing in low-temperature-grown gallium arsenide photoconductive antennas, using a tunable, two-frequency, high-power laser-diode system emitting at 850 nm. Three diode lasers generated the difference frequency in the CalTech-JPL device. Two were locked to adjacent modes of an ultrastable Fabry-Perot cavity, and a micro wave source was used to offset-lock the third diode laser to the cavity-locked laser. A master oscillator-power amplifier (MOPA) amplified the difference-frequency signal to 500 mW. The system was calibrated to an accuracy of 107 using molecular lines over 250-1400 GHz.
Remote sensing of the atmosphere using terahertp spectroscopy offers a particularly sensitive measure of the diurnal behavior of stratospheric hydroxyl (OH), and the Microwave Limb Sounder on the Earth Observing System CHEM-1 polar satellite will use heterodyne OH measurement at 2.5 THz. Contact Herbert Pickett at [email protected].