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Second-order nonlinear coefficients (X2)) and refractive indices (n(2)) of crystals were measured at THz frequencies at the FELIX free-electron laser facility. Maker Fringes were used to obtain χ(2) and Z-scan to obtain n(2). The results wer found to differ from the published values measured in the visible and near-IR.
In this work, we explore a room-temperature measurement of photon correlations in the THz range based on electro-optic sampling. We apply this technique to a THz quantum cascade laser and measure below and above threshold first- and second-order degree of coherence with a subcycle temporal resolution of 146 fs.
We report on a detector-free on-chip dual frequency comb setup based on terahertz quantum cascade lasers. The presented dual-comb covers a bandwidth of 630 GHz with a centre frequency of 2.5 THz. Instead of a fast detector one of the lasers has been used as a fast detector itself. The frequency comb spacing was analysed using frequency counting techniques revealing an accuracy down to δfrep/fcarrier...
The gain recovery time of a bound-to-continuum terahertz frequency quantum cascade laser, operating at 1.98 THz, has been measured using broadband terahertz-pump-terahertz-probe spectroscopy. The recovery time is found to reduce as a function of current density, reaching a value of 18 ps as the laser is brought close to threshold. We attribute this reduction to improved coupling efficiency between...
Broadband THz detection technique is required for high precision molecular gas spectroscopy, wireless communications, and so on. In this work, Sensitivities of electrooptic (EO) sampling method for the frequency measurement of continuous-wave terahertz (THz) sources were compared from 0.1 to 3.1 THz. By using a femtosecond fiber laser to gate the EO sampling, we observed beat signals between the harmonics...
We report on a monolithic extracting structure for terahertz quantum cascade laser based frequency combs. For a spectral bandwidth of more than 600 GHz at a center frequency of 2.5 THz a frequency comb with well-defined farfield pattern could be achieved. In addition the dynamic range of the frequency comb has been significantly improved.
We present a demonstration system for gas analysis based on cw-terahertz absorption spectroscopy. The setup combines tunable 1.5 μm distributed-feedback (DFB) lasers, InGaAs photomixers and a multipass absorption cell into a high-resolution spectrometer. At gas pressures of 1 mbar, we achieved detection limits in the range of approx. 20 ppm for ammonia (NH3) and 100 ppm for sulfur dioxide (SO2). Absorption...
Frequency measurement based on dual THz frequency combs of photocarrier (dual PC-THz combs) is a promising method for the real-time measurement of the absolute frequency in CW-THz radiation without the need for cryogenic cooling. However, use of dual femtosecond lasers hinders the practicability of this method. In this paper, we generated dual PC-THz combs using a free-running, dual-wavelength mode-locked...
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