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Influence of THz waves resonant to molecular vibrations to coherent Raman signal is studied by using THz time-domain coherent Raman spectroscopy. Enhancement of coherent Raman signal in THz region is observed depending on the intensity and polarization of irradiated THz waves.
We have demonstrated a new approach to realize a continuous wave room temperature THz laser source: a low-pressure molecular gas is optically pumped by a solid-state mid-infrared source. A tunable quantum cascade laser allows to have access to transitions that are not accessible to CO2 lasers. Here we present our last results concerning NH3: pure inversion transitions allows emission around 1 THz...
We present a novel photoconductive terahertz source that can generate high power and broadband terahertz radiation with high optical-to-terahertz conversion efficiency. The high optical-to-terahertz conversion efficiency is achieved by confining the optical pump photons very tightly around the radiating elements of the photoconductive source. A distributed Bragg reflector and plasmonic nanostructures...
Molecular gases like ammonia (NH3) and deuterium oxide (D2O) can be used as active media for optically pumped terahertz lasers (OPTL). In this paper we present spectroscopic measurement of chosen NH3 and D2O lasing lines near 1 THz. Rotational-vibrational transitions are pumped by mid infrared quantum cascade laser (MIR QCL) which offers more precise tunability in MIR spectral range than standard...
We present a new technique for generating frequency combs in the mid-IR with potential extension to the THz spectral range, based on division of the frequency of a pump laser in a subharmonic optical parametric oscillator (OPO). Almost two-octaves-wide, 3–10 μm (30–90 THz) frequency comb with high spectral purity was demonstrated and applied to dual-comb coherent molecular spectroscopy.
We study low-temperature-grown GaAs (LT-GaAs) based ultrafast Fabry-Pérot cavity photoconductors, designed for THz optoelectronics applications using 1550 nm pulsed lasers. We present here, as a proof of concept, the under-sampling of continuous RF waves up to 67 GHz.
We applied terahertz (THz) time-domain spectroscopy (THz-TDS) to reveal the mechanism of the relativistic Doppler reflection of THz light from a photo-induced plasma front in a silicon wafer. The frequency up-shift caused by the Doppler reflection was identified by measurement of the reflected THz waveforms and compared to the calculated results obtained using the one-dimensional finite-difference...
Plasmonic contact electrodes are very effective for enhancing the radiation power of photoconductive terahertz sources. Au is a preferred metal for plasmonic contact electrodes due to the high plasmonic enhancement factors it offers in the near-infrared regime. However, Au requires an adhesion layer to stick well to photoconductive substrates. We investigate the impact of the Au adhesion layer on...
We discuss the possibilities of microring resonator based frequency comb sources for applications to THz-wave generation. Numerical simulations were performed using the Lugiato-Lefever model, combined with fully vectorial modal analyses, to investigate how the cavity design impacts the coherence properties of the combs and to quantitatively estimate the power conversion efficiency from the pump to...
Fundamental kinetics of carriers in chalcogenide materials remains controversial, and active debate continues over the mechanism responsible for carrier relaxation. In this study, we used optical-pump terahertz-probe spectroscopy, which permits the relationship between structural phase transition and optical property transitions to be examined, to investigate the ultrafast carrier dynamics in a multilayered...
We experimentally demonstrate linear frequency conversion on time-variant terahertz (THz) metasurface. The proposed metasurface is originally designed to have two resonances, and with optical pumping, the resonances are merged into one. When a THz pulse passes through the metasurface during this merging process, a frequency component corresponding to the merged mode is generated.
Transient-type stimulated emission in the terahertz frequency range has been achieved from silicon crystals doped by phosphorus and bismuth donors under optical excitation by a few picosecond-long pulses generated by the infrared free electron lasers, FELIX and CLIO. The lasing emission occurs due to a population inversion based mechanism for different interpulse intervals (40 ns, 20 ns, 16 ns, 1...
We present THz surface emission by difference frequency generation in nonlinear quantum cascade lasers operating at room temperature. The device comprises two separate, transversely superimposed gratings, one for selective feedback of the mid-infrared modes and one for surface emission of the generated THz radiation. The mid-infrared grating is realized as a higher order, loss-coupled distributed...
Based on multiple quantum wells, we design a pumping-detection quantum cascade structure for the detection of terahertz (THz) radiation. In the structure, electrons are pumped by a mid-infrared (MIR) laser to an excited state, and then extracted by longitudinal optical (LO) phonon stairs. Within the stairs, THz absorption wells are designed. The LO-phonon stair extractor make electrons transport between...
Terahertz light-matter interactions within a semiconductor-filled waveguide can be tuned in space and time via photoexcited regions created on ultrafast time scales and sub-THz wavelength length scales by a patterned optical pulse. These light-induced metal-dielectric structures can be used to dynamically modify the photonic band structure of THz light within the waveguide, controlling the amplitude,...
We synthesized an ultrathin, nonlinear, optical OH1 crystal structure suitable for prism-coupled Cherenkov phase-matching terahertz (THz) wave generation. Physical vapor deposition was used to grow the crystal to a few micrometers thick. We observed THz wave generation from the thin-film crystal and characterized the crystal structure.
The optical excitation effect on the transmission of a terahertz pulse through aligned silver nanowires on a silicon substrate was studied. Terahertz pulses almost pass through the silver nanowires without optical excitation. However, the optically excited sample significantly reduces the transmittance, comparing with the excited silicon substrate only.
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