Submillimeter Wave Laser Research Articles

Far infrared spectrum of Methanol-D2 in the lowest torsional state (e0)

The infrared (IR) and far infrared (FIR) absorption spectra have been measured for the Methanol-D1 and D2 species in the wave number range of 20–1200cm−1 at the Justus Liebig Universität in Giessen, Germany using a Brüker Fourier Transform spectrometer at a resolution of 0.002cm−1. The spectra looked very complicated but analyses were possible for the lower lying states. At higher wave number regions spectra of few vibrational fundamental modes were visible. In this communication, the details of the assignments and analyses of the lowest lying internal rotational state (e0) for Methanol-D2 are reported. A catalog of about 900 assigned spectral lines has been prepared and is made available from the author to conserve space. As application of this work, it was possible to assign some optically pumped FIR laser lines to quantum states. The results should be useful for “radio astronomers” and in the field of optically pumped FIR and Sub-millimeter Wave (SMMW) lasers which are used in Tokamaks for plasma diagnostics and as local oscillators in radio detection from space.

EFFECTS OF PUMP SOURCE ON SPECTRA OF OPTICALLY PUMPED SUB-MILLIMETER WAVE LASER

The output power intensity of optically pumped sub-millimeter wave laser(OPSMMWL) increased with increasing of power intensity of pump source, till to its maximum; and decreased with increasing of the frequency off-set of pump source, if frequency off-set reached or exceeded its Raman threshold, no SMMWL could be obtained; the infrared pumping laser with collision broadening was considered in our computing model, which made our theoretical calculations agreed with the practical. Spectra of CO2-9R(16) pumped NH3 90.4 μm laser was used to be a practical case.

Temperature and Mass Factor of Buffer Gas Effect in Optically Pumped Submillimeter Wave Laser

Based on semi-classical density matrix theory and SSH theory, the effect of buffer gas in optically pumped submillimeter wave laser was theoretically studied and the effect of temperature and mass on the effect of buffer gas was analyzed, then the selection rules of buffer gas were achieved. The results could do favor to find high-efficient buffer gas of miniature optically pumped submillimeter wave laser and also had some instruction to its application.

Operating Parameters Optimization of Buffer Gas in Optically Pumped Submillimeter Wave Laser

Based on the basic theory of molecular vibration relaxation and semi-classical density matrix theory, operating parameters optimization of buffer gas in the process of miniature pulsed optically pumped submillimeter wave laser was systemically studied and the theoretical calculated result was tested by experiments. The result would do favor to develop and study high-power and wide-range tunable miniature and high-efficient pulsed optically pumped submillimeter wave laser and also had some instruction to its application.

A Quantum-Mechanical Explanation of Buffer Gas Effect on Submillimeter Wave Laser

Based on the theory of molecular vibration relaxation, the model of buffer gas effect was built up. By theoretically deducing the vibrational lower-level deactivation rate of operating gas molecule with quantum mechanics, the selection rules of high-efficient buffer gas under different working conditions were educed and tested by experiments. The results could be helpful to the study of large-power wide-range efficient tunable miniature pulsed optically pumped submillimeter wave laser and its application.

Multi-Raman Processes and Their Effects in Two-Longitudinal-Mode Optically Pumped Submillimeter Wave Laser

Based on the semi-classical density matrix theory, multi-Raman processes in two-longitudinal-mode optically pumped cavity submillimeter wave laser were studied theoretically. And their effects on submillimeter wave laser spectral characteristics were discussed under different pump powers, operating pressures and laser tube lengths.

Comparison Between Single-Longitudinal-Mode and Two-Longitudinal-Mode Pumping Cavity OPSMMWL

A CO2 infrared laser system with a etalon to be the longitudinal mode select equipment was set up to be the optically pump source, as well as a mini NH3 with 20cm long sample tube to be the sub-millimeter wave laser. CO2-9R(16) line was chose to pump the mini-NH3 SMMW laser, and 90.4um SMMW line was obtained by single-longtudinal-mode or two-longitudinal-mode pumping. Experimental comparison of output power and operating gas pressure between single and two-longitudinal-mode OPSMMWL were studied. It was found that the two-longitudinal-mode OPSMMWL could get higher output power and broader spectrum, existed a lower operating gas pressure and wider range of operating gas pressure. These experimental results verified the theoretical calculations before.

Multi-Raman Effect and Longitudinal-Mode Structure in Optically Pumped Submillimeter Wave Laser

Based on semi-classical density matrix theory, multi-Raman interaction in multi-longitudinal-mode CO2-9R (30) optically pumped NH3 molecules laser was studied theoretically. With different parameters such as pumping power and operating gas pressure, the effect of multi-Raman interaction and the longitudinal-mode structure of submillimeter wave laser were also discussed.

Study on the Spectrum of Miniature Optically Pumped NH 3 Submillimeter-Wave Laser

By means of an iteration method and taking into account the broadening of the infrared pumping laser, the spectrum of a miniature, optically pumped, superradiant NH3 submillimeter-wave(SMMW) gas laser pumped by CO2-10R(8) has been calculated and studied by solving density matrix equations. Experimentally, the interferogram of miniature SMMW laser pumped by a TEA-CO2 laser with 10R(8) line is measured. This is the first time that the theoretical spectrum has been in good agreement with experimental results.

Energy Exchange Process in Two-Longitudinal-Mode Optically Pumped Submillimeter Wave Laser

Based on the semi-classical density matrix equations and numerical iteration calculation, the gain coefficient of nine-energy-level NH3 molecular system was figured out. Energy exchange process in two-longitudinal-mode optically pumped submillimeter wave laser was studied in detail. Laser output intensity was calculated and discussed in case of different operating parameters such as operating gas pressure, length of laser cavity. Finally the optimization rules were concluded.

Theoretical Study on the Gain and Tuning Characteristics of Miniature Optically Pumped NH3 Submillimeter Laser

The gain and the tuning characteristics of miniature optically pumped super-radiant NH3 submillimeter-wave gas laser have been studied theoretically based on the quantum density matrix equations. The density matrix equations of three-level quantum system have been solved, and the gain and the output density versus different frequency detuning of submillimeter laser and infrared pumping laser have been calculated respectively by means of iteration method. The characteristic curves corresponding to ideal monochromatic IR pumping model and broadened IR pumping model have been obtained. Meanwhile, the tuning and the nonlinear properties of the system have been revealed.

The Optimum Operation of an Unified Mini-Optically Pumped NH 3 Submillimeter Wave Laser

An unified miniature optically pumped NH3 submillimeter wave laser (OPSMMWL), including a mini TEA-CO2 pump laser, was developed. It lased successfully with coherent emission at 67.2μm, 90.4μm and 151.5μm. The optimum operation of the unified mini-OPSMMWL was studied experimentally and the relations among SMMW laser output power, operating gas pressure, length and coupling condition of the cavity were measured. It has been found that buffer gas N2 has significant effect on 67.2μm and 151.5μm emissions and very wide band SMMW laser emission was a common feature of the mini-OPSMMW cavity laser.

Design of SMMW Laser Resonators with On-Axis Signal and Pump Beam Guiding in a Mirror Ring

A ring resonator design for optically pumped submillimeter wave (SMMW) lasers using the same set of four mirrors (including one focussing mirror) for pump beam and SMMW beam guiding is introduced.

Operating Parameters Optimization of Miniature Optically Pumped Cavity NH3 Submillimeter Wave Laser

By means of the iteration method, the output power density of the miniature optically pumped NH3 submillimeter wave (SMMW) laser was calculated based on the density matrix equations of a quantum system. Optimization of operating parameters including operating gas pressure, reflection coefficients of input and output meshes of the laser were studied systematically. In the paper, the concepts of the average activated length and the synthetical optimum value were defined, and some rules of the optimization were explained successfully. Experimentally, a cavity NH3 SMMW laser that was composed of a pair of inductive metallic meshes and pumped by TEA-CO2 10R(8) line was used. The experimental results were in good agreement with our theoretical calculations.

Effect of Submillimeter-Wave Low-Intensity Laser Radiation on the Regeneration of Bone Tissue

Effect of Submillimeter-Wave Low-Intensity Laser Radiation on the Regeneration of Bone Tissue

Gaussian optical design of a submillimeter-wave and far-infrared laser sideband heterodyne spectrometer

A submillimeter-wave/far-infrared (SMM/FIR) laser sideband heterodyne spectrometer has been built for molecular rotational spectroscopy application in the frequency range of 600–3000 GHz. Based on Gaussian optics, optical system of the spectrometer is designed to be quasi-achromatic and low losses. In this article the optical design and the performance of the spectrometer are presented.

Design of a 2.5 THz submillimeter wave laser with optical pump beam guiding

A ring resonator design using the same set of mirrors for pump beam and submillimeter wave (SMMW) beam guiding is introduced. Optimal design is discussed on the example of a 2.5 THz methanol laser. It turns out that due to refocussing of the pump beam on the pinhole certain focal lengths of the focussing mirror, which mainly is responsible for the beam guiding, should be avoided. Diffraction losses and pinhole losses determine optimal g-parameters for which the pump beam guiding losses of the resonator are minimum, and optimal pump beam waist radii. The setup of an experimental laser with the optimized resonator and the experimental setup to measure laser performance are described, and results concerning laser output power, beam quality and efficiency are discussed.

Reflectivity measurements of graphite in the infrared and submillimeter wave regions

This paper presents first experimental results of the power reflectivity of graphite in the synchrotron radiation regime for the future fusion experiment. The reflectivities are measured for the C/C composite materials (CC-312 and PCC-2S) and carbon materials (PD-330S and B 4C/PD-330S) used in the present JT-60U experiment. The submillimeter (SMM) wave laser and CO 2 laser sources were used to measure the wavelength and angular dependencies of reflectivity in the wavelength region from 10 to 790 μm. Theoretical analysis considerably agreed with experimental result.

Experimental verification of the theory on the inverse Smith–Purcell effect at a submillimeter wavelength

The inverse Smith–Purcell effect is a candidate for laser-driven linacs utilizing the interaction between laser light and an electron beam traveling just in front of a metallic grating. We have performed experiments to study electron energy spread as a function of electron beam position above the grating. A submillimeter wave laser (CH3F, 496 μm) is used as a driving source. It is found that the energy spread characteristics show exponential decay of the interaction strength (field intensity) in the direction perpendicular to the grating surface, as a classical theory on the effect predicts.

Precision submillimeter wave laser reflection measurements of high-temperature superconductors

Submillimeter wave laser reflection measurements of surface resistance can provide improved capability in the combination of sensitivity, spatial resolution, and frequency range. We have made reflectivity measurements on metals at 1630 GHz with an uncertainty of less than 0.3%. This sensitivity corresponds to a measurement sensitivity for surface resistance of 0.3 Ω. Assuming anf2 frequency scaling of high-temperature superconductor surface resistance from the microwave to the terahertz frequency range, this sensitivity corresponds to about 1 ×10−5 Ω at 10 GHz. Capability for 10−7 Ω sensitivity could eventually be possible. Preliminary submillimeter wave reflection measurements of a YBCO thin film have been made with a sensitivity of 1%. Submillimeter wave reflectometry can make it possible to determine the spatial dependence of surface resistance in a wide range of material sizes and shapes. The spatial resolution could be on the order of 0.3–0.5 mm.