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Enhanced terahertz-to-infrared(THz-to-IR)emission from gas-surrounded nanostructured metal films as a result of femtosecond laser irradiation is systematically investigated using selected gases. The dependencies of the THz-to-IR power on the gas species, gas pressure, and pump optical power are studied for Ar, N2, Ne, and He. The experimental results reveal that the power of the THz-to-IR emission...
Large gain of optically pumped gas (ammonia) was obtained at 1.073 and 1.068 THz. Tunable quantum cascade laser allows to excite sharp mid-infrared transitions of ammonia close to 967 cm−1. Obtained population inversion of umbrella modes near 1 THz is not accessible by any other pumping methods. Exceptionally high gain demonstrated can be used for future terahertz applications. The proposed method...
Quasi-continuous terahertz laser plasma discharge in inert gases on the Novosibirsk free-electron laser exists in form periodical self-oscillations at sound frequencies caused by plasma screening of its focal area. Full suppression of the self-oscillations has been obtained by a negative optical feedback.
We demonstrate a low-threshold, compact, continuous-wave molecular laser optically pumped by a mid-infrared quantum cascade laser. NH3 molecules are pumped around 10.3 μm and de-excite by stimulated emission on pure inversion transitions. We demonstrate CW generation of ten lasers lines around 1 THz. At 1.07 THz a power of 34 μW is obtained with a low threshold of 2 mW and a high differential efficiency...
We present in situ measurements of the relative phase shift induced by Gouy phase shift near the focus in two-color field. The good agreement between the measurement and the theoretical prediction shows that the optimal phase of THz is robust enough as an useful tool to measure the relative phase change.
We experimentally demonstrated that the circularly polarized two-color femtosecond pulses with the same helicity can effectively enhance terahertz intensity by a factor of 5 in comparison with the linearly polarized counterparts. The quantum mechanical simulations confirm this enhancement based on the analysis of residual current calculated by time-dependent Schrödinger equation in three dimensions...
A laser system emitting within the IR wavelength range from 12 to 16.6 micron is discussed. The hybrid laser system consists of molecular gas lasers with a frequency conversion in a nonlinear crystal. One gas laser is a carbon monoxide laser operating in multi-line or single-line mode. Another one is a carbon dioxide laser operating in multi-line mode. These lasers operate in a Q-switched mode. Spectrum...
PTB applied a novel thin-film pyroelectric detector in an international pilot comparison on THz power measurement below 1 THz. Due to its spectrally flat response, this detector is suitable for accurate absolute TDS power measurements and as reference material for TDS transmission and reflection measurements as well.
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...
Laser induced terahertz (THz) waves generation from metals is a result of thermal nonlinear effects in the electron gas near the surface. We describe the mechanism of THz response and discuss the possibility of electron scattering investigation with a help of nondestructive optical-to-THz conversion on the surface. It is also shown that array of anisotropic metallic particles irradiated by fs laser...
The present work looks at the properties of powerful THz and X-ray radiation generated in gas nanocluster targets. Combining in one experiment the generation of pulsed THz and X-ray radiation using multifrequency femtosecond radiation has made it possible to carry out the study of temporal dynamics of ionization and electron movement in gas clusters. The same experimental approach was used to study...
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