Fourier-transform THz spectroscopy based on electric-field interferometry using THz-PMT.

We demonstrate a high dynamic range (DR) Fourier-transform-based terahertz (THz) spectrometer by combining a THz photomultiplier tube (PMT) with a metasurface and a conventional Michelson interferometer. Because the THz-PMT response depends on the incident electric-field strength following the Fowler-Nordheim equation, we can directly obtain an electric field interferogram without any synchronized optical probe pulse in contrast to conventional THz-time-domain-spectroscopy (THz-TDS). The DR of the corresponding power spectrum using the proposed method was 4.6 × 105 without the use of a lock-in amplifier. The complex refractive index of a quartz glass plate obtained using the proposed method was in good agreement with the results of conventional THz-TDS.

Measurement of group refractive indices of glass using a color-selective multi-pulse generated with a spatial light modulator.

We demonstrate a method of measuring group refractive indices (ng) by using only a temporal waveform of a color-selective multi-pulse (CSMP) generated with a spatial-light-modulator-based optical pulse shaper. Each pulse of the CSMP is characterized by different spectral components. Thus, ng of a sample can be estimated by calculating the group delay of the spectrally different pulses in the CSMP after passing through the sample. As a proof-of-concept, we measured ng of a glass plate by using a CSMP. We confirmed that the measured ng values were in agreement with those derived from Sellmeier's formula with an accuracy on the order of 10-4.

Generation of arbitrarily chirped and CEP-controlled terahertz pulses for dispersion compensation using an optical pulse shaping technique and a fan-out periodically poled crystal.

We constructed a system that can generate phase-controlled terahertz (THz) pulses using a fan-out periodically poled lithium tantalate crystal and an optical pulse shaper containing a spatial light modulator. The phase of each THz frequency components could be controlled by manipulating the delay time of the corresponding optical pulses. Using the system, we generated arbitrarily group-velocity-dispersion-controlled THz pulses, where the chirp parameter was 2.53 ps2/rad between 0.6 and 1.5 THz. In addition, we generated arbitrarily carrier-envelope-phase-controlled THz pulses in the same system. Phase-controlled THz pulses may be useful for applications such as dispersion compensation.

Widely and continuously tunable terahertz synthesizer traceable to a microwave frequency standard.

We constructed a widely and continuously tunable terahertz frequency synthesizer traceable to a hydrogen maser linked to coordinated universal time. Photomixing of two optical frequency synthesizers, linked to the hydrogen maser via dual optical frequency combs, gave this THz synthesizer frequency uncertainty of 10⁻¹². To demonstrate the potential of wide and continuous tunability in the THz synthesizer, we tuned its output frequency up to 50 GHz discretely and 1.26 GHz continuously in the F-band while maintaining the unprecedented frequency uncertainty by using a uni-traveling-carrier photodiode as a photomixer. This THz synthesizer will be a powerful tool for broadband, high-precision THz spectroscopy and THz frequency metrology.