Spikes in raman spectrum of miniature optically pumped NH3 fir laser

In this paper, the semiclassical density matrix equation was solved to calculate the spectral characteristics of V₂:a--sR(0,0) transition in a miniature optically pumped NH₃ far infrared laser (mini-NH₃-OPFIRL), which was pumped by CO₂-10R(6) line. The results of theoretical calculation showed that the spikes in Raman spectrum of V₂:a--sR(0,0) would appear when the operating NH₃ gas pressure was higher than a certain critical value or pumping power density was lower than a certain critical value, which was caused by Raman processes interaction of AC-Stark splitting. In our experiment, 298 µm FIR spetral line of a--sR(0,0) pumped by a TEA-CO₂ laser with 10R(6) line was observed but the spikes could not be observed owing to the limitation of the resolution of the F-P interferometer.     

Power-dependent dispersion in far-off-resonant raman scattering

We investigate the saturation effects of power broadening, Stark shifting, and population transfer on Stokes conversion in stimulated Raman scattering. We do not make the usual rotating wave approximation because the detuning from the next electronic state is assumed to be in the optical regime. Retaining the counter-rotating terms allows an exact determination of the pump and Stokes indexes of refraction. Steady-state solutions for the Stokes intensity and phase are obtained and the effects of making the rotating wave approximation (RWA) are discussed. Finally, we examine the behavior of these solutions for Stokes conversion in hydrogen gas when geometric propagation is appropriate.     

High power FIR NH3 laser using a folded resonator

A compact FIR laser cavity having a couple of folding mirrors was designed. By inserting this FIR cavity into the pump TE CO₂ laser resonator, we observed 19 FIR NH₃ laser lines of which 4 new lines were included. The maximum output power was over 500 W at 90 μm.     

一体化的小型腔式光泵NH3分子远红外激光器

研制了包括泵浦源在内的一体化小型腔式光泵ＮＨ３远红外激光器，实验测量了输出功率、工作气体压强、腔体长度与腔体耦合条件之间的优化规律：发现了小型腔式光泵远红外激光器中普遍存在的特别宽带的激光辐射现象，这将是解决远红外激光频率大范围连续可调谐的一个新途径。     

Theoretical study of multi-mode optically pumped NH3 FIR laser

The two or multi-mode optically pumped NH₃ FIR laser had been studied theoretically. The NH₃ molecular gas was assumed to be a three-level system and obeyed the time-dependent behavior of the density matrix equations. Considering the situation of playing the two or multi-mode optical pumping and the FIR laser field were same polarized. The gain coefficient and the output FIR power of the system could be calculated by using the iteration method. It had been predicted that the two or multiple longitudinal mode optically pumped NH₃ FIR laser could have a greater output power or higher lasing efficiency than single mode pumped FIR laser under suitable selected operating parameters of laser.     

光泵NH3分子远红外激光的一条新谱线

利用反射光栅调谐的脉冲ＴＥＡＣＯ２激光１０Ｒ（６）泵浦０．２ｍ长的小型ＮＨ３分子远红外激光器，当泵浦能量为１．１Ｊ，ＮＨ３分子气压为０．９ｋＰａ时，产生２９８μｍ的新谱线，对应Ｖ２：ａＲ（０，０），受激喇曼跃迁。     

Simultaneous tunable raman and fixed frequency oscillation of a CH3F FIR laser

Experimental observation of simultaneous oscillation at the Raman frequency and a cascade frequency in a broadly tunable¹³CH3F far-infrared laser is reported. Oscillation on both components persists over the full 25 GHz separation between thev_{3}R(36)andR(37)lines. This observation is in marked contrast to the behavior of the tunable¹²CH3F FIR laser which produces only the Raman frequency when it is optically pumped at lowerJvalues in the same branch. A marked qualitative difference in the large-scale emission spectra for the two lasers is also discussed.     

Theoretical study on gain and tuning characteristics of infrared-microwave pumped NH3 FIR laser

Based on the semi-classical density matrix equation theory, the gain and tuning characteristics of infrared-microwave pumped NH₃ FIR laser were studied. It was shown that quasi-continuously tuning could be obtained by the tuning of microwave frequency and the efficiency of the laser could be enhanced by electric dipole transition enhancement effect, but compromise should be made between FIR laser output and frequency tuning range.     

Compact,high power FIR NH3 laser pumped in a three mirror CO2 laser cavity

A compact CO₂?NH₃ FIR laser system where an NH₃ laser cavity was inserted in pump, three mirror CO₂ laser cavity was designed. The total length of this system was about 1.8 m. Output energy of about 1 mJ (⊥10 KW pea power) was obtained at the 152 μm and 90 μm lines in NH₃. Power conversion efficiency of 1.7 percent was obtained at the 90 μm line.     

High power ns FIR Raman pulses in NH3 pumped by a short pulse tail-free CO2 oscillator

By using a short pulse CO₂, tail free, broadband laser it is possible to produce a compressed, high power FIR pulse in a pure Raman system when a suitable pressure and Raman cell length are used. In this way we have obtained 4ns (70KW) emission around the sR(3,0) NH₃ line pumped by 130 mJ (23ns) 9P20 CO₂ line. More resonant transitions can be also compressed at a suitable high pressure also if they show a large optical pumping and cascade processes at low pressure.     

Synchronisation in data networks

Synchronisation is of fundamental importance to the performance of digital networks, but the effects of poor network timing on the information being transported are often largely ignored. This paper provides an introduction to the subject of synchronisation, discusses the current BT network synchronisation arrangements and describes the platform being deployed to address both the current network requirements and the needs of future telecommunications technologies.     

Photoluminescence and raman scattering from superlattices made by phase-locked epitaxy

The precision of layering of crystals grown by the Phase-Locked Epitaxy (PLE) method, which controls the molecular beam by monitoring the reflection high energy electron diffraction (RHEED) intensity, is investigated by photoluminescence from quantum-well structures and Raman scattering from superlattice structures. Peak energies and peak widths in the photoluminescence spectra show that the quantum-well widths are precisely controlled to one monolayer.     

Distributed temperature sensor system based on raman scattering using correlation-codes

A distributed sensor system employing spontaneous Raman scattering with use of correlation-coding techniques and a single-detector scheme is discussed and experimentally characterised. A sensing distance of up to 8 km is achieved with high spatial and temperature resolutions; use of correlation-coding significantly reduces measurement time and allows use of low-power laser sources.     

Temperature measurement in a silicon carbide light emitting diode by raman scattering

Raman spectra of the transverse-optic phonon mode from a light-emitting layer of a SiC diode have been measured. The phonon peak broadens and shifts to lower frequency with the rise of temperature when the injected current is increased. The frequency shift was compared with a result for bulk reference measured separately at various temperatures. We found that the temperature of the light-emitting layer reached 350°C at a current density of ∼200 A/cm².     

Depolarised broadband source generated by hybrid effects of Raman scattering, parametric process and erbium-doped superfluorescent

A depolarised high power (200 mW) broadband source (1520-1620 nm) with high polarisation stability is obtained using a single pump based on the hybrid effects of dual-order Raman scattering, parametric process in highly nonlinear fibre and erbium-doped superfluorescent.     

Time-resolved raman scattering measurement of electron-optical phonon intersubband relaxation in GaAs quantum wells

We have measured the lifetime of electronic intersubband excitations by emission of longitudinal optical phonons in GaAs---AlGaAs quantum wells using time-resolved anti-Stokes Raman scattering. We find the lifetime of electrons in the N = 2 level of a 146Å well to be 1ps which is in excellent agreement with theoretical calculations of two-dimensional electron-photon interactions.     

Resonant raman scattering and dispersion of polar optical and acoustic phonons in hexagonal inn

It is shown that a study of the dependence of impurity-related resonant first-order Raman scattering on the frequency of excitation light makes it possible to observe the dispersion of polar optical and acoustic branches of vibrational spectrum in hexagonal InN within a wide range of wave vectors. It is established that the wave vectors of excited phonons are uniquely related to the energy of excitation photon. Frequencies of longitudinal optical phonons E₁(LO) and A₁(LO) in hexagonal InN were measured in the range of excitation-photon energies from 2.81 to 1.17 eV and the frequencies of longitudinal acoustic phonons were measured in the range 2.81–1.83 eV of excitation-photon energies. The obtained dependences made it possible to extrapolate the dispersion of phonons A₁(LO) and E₁(LO) to as far as the point Γ in the Brillouin zone and estimate the center-band energies of these phonons (these energies have not been uniquely determined so far).     

A physical scattering model for MIMO macrocellular broadband wireless channels

This paper presents a physical scattering model that predicts multiple-input multiple-output (MIMO) channel characteristics conforming well to experimental observations in macrocells. Our approach is to start with a given single-input single-output power-delay profile (defined for specific range, bandwidth and antenna parameters) and fit a scattering model that characterizes the MIMO channel. From the derived scattering model and antenna array configurations, the MIMO channel is computed using a ray-based method. Simulations of several MIMO channels are shown to exhibit experimentally observed channel correlations, antenna beamwidth effect, range dependency, and frequency selectivity.     

Enhancement of photoluminescence and raman scattering in one-dimensional photonic crystals based on porous silicon

In porous-silicon-based multilayered structures that exhibit the properties of one-dimensional photonic crystals, an increase in the photoluminescence and Raman scattering intensities is observed upon optical excitation at the wavelength 1.064 μm. When the excitation wavelength falls within the edge of the photonic band gap of the structures, a multiple increase (by a factor larger than 400) in the efficiency of Raman scattering is detected. The effect is attributed to partial localization of excitation light and, correspondingly, to the much longer time of interaction of light with the material in the structures.