2-05
Heinz-Wilhelm Hübers
DLR-Institute of Optical Sensor Systems and Humboldt University Berlin
Phase Locking of 3.5- and 4.7-THz Quantum-Cascade Lasers for Local-Oscillator Applications
Terahertz (THz) quantum-cascade lasers (QCLs) are of great importance as local oscillators (LOs) in high-resolution heterodyne spectrometers such as upGREAT on SOFIA. The frequency resolution of such a spectrometer depends on the frequency stability of the QCL LO. Typically, the linewidth of QCL LOs of the upGREAT heterodyne spectrometer is a few MHz. This is sufficient for most astronomical targets. However, some targets such as planetary atmospheres require a spectral resolution of about 100 kHz or even below. A powerful method for frequency stabilization is phase locking to a reference source. We report on a phase-locked loop (PLL) for QCLs operating at 3.5 and 4.7 THz. These are two important frequencies in atmospheric science and astronomy because of transitions of the hydroxyl radical at 3.5 THz and atomic oxygen at 4.7 THz. The PLL is based on a multiplier source serving as a reference oscillator and a Schottky diode harmonic mixer.
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