Abstract
Terahertz quantum cascade lasers have been investigated with respect to their performance as a local oscillator in a heterodyne receiver. The beam profile has been measured and transformed in to a close to Gaussian profile resulting in a good matching between the field patterns of the quantum cascade laser and the antenna of a superconducting hot electron bolometric mixer. Noise temperature measurements with the hot electron bolometer and a 2.5 THz quantum cascade laser yielded the same result as with a gas laser as local oscillator.
Highlights
High resolution heterodyne spectroscopy of molecular rotational lines and fine structure lines of atoms or ions is a powerful tool for exploring the interstellar medium as well as planetary atmospheres including Earth
Terahertz quantum cascade lasers have been investigated with respect to their performance as a local oscillator in a heterodyne receiver
The beam profile has been measured and transformed in to a close to Gaussian profile resulting in a good matching between the field patterns of the quantum cascade laser and the antenna of a superconducting hot electron bolometric mixer
Summary
While for single pixel receivers the coupling efficiency between QCL and mixer does not need to be very high, an array receiver will require a very well shaped LO beam, normally a Gaussian beam profile. Coupling by a diplexer might reduce this to several 100 μW Another issue is the distribution of power from a single LO to all mixers in the array. This can be done in an elegant way by using reflective phase gratings (Fourier gratings), which allow splitting a single beam into multiple ones [15]. These gratings require well shaped beams in order to achieve optimum output. Noise temperature measurements of a HEB mixer with a QCL LO and a gas laser LO will be presented
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