Laser Local Oscillators for Heterodyne Receivers beyond 2 Terahertz

Abstract

The design and performance of a local oscillator (LO) for an airborne terahertz heterodyne receiver is reported. The LO is based on a THz gas laser, which is transversely excited by radiation from a CO₂ pump laser. Frequency stabilization is achieved by cascaded locking loop. where the frequency of the CO₂ laser is stabilized to a Fabry-Perot interferometer, which in turn is stabilized to a HeNe laser. The LO is compact and mechanically rugged in order to comply with the harsh environment on board of an aircraft. It also fulfills all physical requirements with respect to output power, beam profile and frequency stability. A THzquantum cascade laser (QCL) is a potential alternative to a gas laser LO. We report on the performance of a 2.5-THz QCL with respect to beam profile, frequency tuning behaviour and width of its emission line. The QCL has been used as LO to pump a hot electron bolometric mixer at 2.5 THz.