Unveiling spectral purity and tunability of terahertz quantum cascade laser sources based on intra-cavity difference frequency generation

Abstract

Terahertz sources based on intra-cavity difference-frequency generation in mid-infrared quantum cascade lasers (THz DFG-QCLs) have recently emerged as the first monolithic electrically-pumped semiconductor sources capable of operating at room-temperature (RT) across the 1-6 THz range. Despite tremendous progress in power output, that now exceeds 1mW in pulsed and 10 μW in continuous-wave regime at room-temperature, knowledge of the major figure of merits of these devices for high precision spectroscopy, such as spectral purity and absolute frequency tunability, is still lacking. Here, by exploiting a metrological grade system comprising a terahertz frequency comb synthesizer, we measure, for the first time, the free-running emission linewidth (LW), the tuning characteristics, and the absolute frequency of individual emission lines of these sources with an uncertainty of 4 x 10-10. The unveiled emission LW (400 kHz at 1ms integration time) indicates that DFG-QCLs are well suited to operate as local oscillators and to be used for a variety of metrological, spectroscopic, communication, and imaging applications requiring narrow-linewidth THz sources.

References in corpus (1)

• Observing the intrinsic linewidth of a quantum-cascade laser: beyond the Schawlow-Townes limit

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• High dynamic range, heterogeneous, terahertz quantum cascade lasers featuring thermally-tunable frequency comb operation over a broad current range
• Room-Temperature Continuous-Wave Frequency-Referenced Spectrometer up to 7.5 THz
• Direct observation of terahertz frequency comb generationin difference-frequency quantum cascade lasers
• High-purity microwave generation using a dual-frequency hybrid integrated semiconductor-dielectric waveguide laser
• Terahertz Spin Transfer Torque Oscillator Based on a Synthetic Antiferromagnet