Scattering of CO2 laser beam by a plasma of air breakdown at pressures of 1–300 torr

Results from experiments with a TEA CO₂ laser with an unstable cavity and a power of 10⁷ W are presented. Laser radiation was focused by a lens with a focal length of 100 or 150 mm in air free of dust (grains larger than 0.1 μm were filtered out). The power and energy of radiation scattered within a central cone of an annular laser beam was recorded. The dependences of the threshold (for scattering) laser power and the scattered power on pressure were determined. The angular divergence of the collimated scattered beam was found to be 3.9 mrad, which was close to the divergence of the laser beam (2.5 mrad). The amplification of the scattered radiation pulse was performed.     

Non-linear effects in the spectrum of 90° scattered laser light from gas breakdown plasmas

Laser radiation scattered at 90° from gas breakdown plasmas induced by focussed 10 nsec, 1.06 μm wavelength laser pulses was simultaneously spatially and spectrally analysed. The scattered spectra showed non-linear, side band generation, smearing out of spectral structure and Doppler shifts. The side bands are attributed to a non-linear refractive index n₂ = 0.6 × 10^-12 e.s.u. which causes phase modulation when a weak side band frequency beats with a strong centre frequency. The observations suggest a fast response non-linearity such as would arise from the near resonant non-linear polarizability of excited atoms.     

Expressions for the computer-evaluation of the four kernel functions for line formation with Doppler and Lorentz profiles

Rational approximations for the kernel functions K₁(τ), K₂(τ), M₁(τ) and M₂(τ) that describe the transfer of radiation scattered with complete redistribution over Doppler and Lorentz profiles have been obtained from their series and asymptotic expressions by the techniques of Padé approximants with a maximum relative error of less than 10^-4.     

Level-crossing under nearly monochromatic excitation by a narrow-band cw dye laser

The shape of level-crossing signals under excitation by a narrow-band tunable dye laser has been investigated. The light of the laser was scattered on a highly collimated atomic beam of Na. The laser radiation (bandwidth about 3 MHz) was fairly monochromatic compared with the natural line-width of the 3 ²P_{$\text{3}\text{2}$} state (10 MHz). The form of the zero-field level-crossing signal of this state depends strongly on the frequency of the exciting radiation. The experimental results agree well with calculated signal shapes.     

The energy dispersive scheme of X‐ray fluorescence analysis with a crystal polarizer and polycapillary optics

The efficiency of the polarization scheme based on polycapillary optics and a diamond crystal polarizer was demonstrated. The scheme provides suppression of the background of scattered radiation in measuring X‐ray fluorescence spectra. A quasi‐parallel X‐ray beam with an angular divergence of 4.2 mrad was formed by a microfocus source with a copper anode and polycapillary half‐lens. Simultaneous polarization and monochromatization of radiation was obtained with a crystal of natural diamond, which was set at the diffraction reflection (113). The degree of polarization of CuK_α1 spectral line and the maximum radiation flux were respectively equal to 99.86% and 5 · 10⁶ photon/s. In the direction orthogonal to the plane of diffraction, the maximum attenuation of the background was up to 19 dB.     

Determination of hyperfine parameters using quantum beats

We have observed the delayed time spectra of the coherently scattered radiation following nuclear Bragg diffraction of incident synchrotron radiation pulses. The measurements were carried out using single crystals of⁵⁷Fe-YIG and⁵⁷FeBO₃ by conventional coincidence techniques. Although the intention of these measurements was only to show effects like speed-up and quantum beats, the spectra also provide the possibility of a sensitive direct measure of the hyperfine interaction parameters. It is demonstrated that even with a counting rate of only 1 Hz it was possible to obtain within 1–2 hours (in the case of⁵⁷FeBO₃) spectra of sufficient statistics to derive precise hyperfine parameters.     

On the mechanism of photon emission from thin film tunnel structures

The light emission from Al−Al₂O₃−M planar tunnel diodes was investigated where M=Ag, Au or Cu. Experiments on smooth and periodically corrugated (holographic grating) substrates showed that the emitted light originates from surface plasmons scattered by the surface roughness and, probably, from the bremsstrahlung of tunneling electrons. All the three noble metals show qualitatively similar behaviour and their light emission can be described as the superposition of three independent sources. The quantum efficiency of radiation was found to be ≈10⁻⁵ photon/electron, close to the theoretical limit.

     

Influence of 60Co gamma radiation on fluorine plasma treated enhancement-mode high- electron-mobility transistor

AlGaN/GaN depletion-mode high-electron-mobility transistor(D-HEMT) and fluorine(F) plasma treated enhancement-mode high-electron-mobility transistor(E-HEMT) are exposed to 60Co gamma radiation with a dose of 1.6 Mrad(Si).No degradation is observed in the performance of D-HEMT.However,the maximum transconductance of E-HEMT is increased after radiation.The 2DEG density and the mobility are calculated from the results of capacitance-voltage measurement.The electron mobility decreases after fluorine plasma treatment and recovers after radiation.Conductance measurements in a frequency range from 10 kHz to 1 MHz are used to characterize the trapping effects in the devices.A new type of trap is observed in the F plasma treated E-HEMT compared with the D-HEMT,but the density of the trap decreases by radiation.Fitting of G p /ω data yields the trap densities D T =(1-3) × 10 12 cm-2 · eV-1 and D T =(0.2 0.8) × 10 12 cm-2 ·eV-1 before and after radiation,respectively.The time constant is 0.5 ms-6 ms.With F plasma treatment,the trap is introduced by etch damage and degrades the electronic mobility.After 60Co gamma radiation,the etch damage decreases and the electron mobility is improved.The gamma radiation can recover the etch damage caused by F plasma treatment.     

Rayleigh scattering of Mössbauer radiation on a myoglobin single crystal

The RSMR technique was used to determine the fraction of radiation which is scattered elastically and inelastically, respectively, into Bragg reflections of a metmyoglobin single crystal. From this measurement 〈x² _1c〉=0.027±0.008 A² has been determined which is due to long range correlated motions in analogy to acoustic and optic modes in solids.     

回火金属玻璃小角X射线散射强度的背底校正

提出校正回火金属玻璃（非晶合金）小角ｘ射线散射强度的背底误差的方法：将淬火态非晶合金的小角Ｘ射线散射强度作为在相同的实验条件下得到的回火非晶合金小角Ｘ射线散射强度的背底而予以扣除。并将这样扣除背底和用通常方法扣除背底得到的结果相比较，由前者得到的散射强度遵从Ｐｏｒｏｄ律，并进而得到Ｐｏｒｏｄ常数Ｋ_p＝４．６×１０^-2（ｎｍ^-3），积分不变量Q_s＝１．６３（ｎｍ^-2），比内表面Ｓ_p＝８４ｍ²／ｃｍ³，Ｐｏｒｏｄ半径Ｒ_p＝４．４ｎｍ用通常方法扣除背底后的散射强度不满足Ｐｏｒｏｄ规律。 关键词：     

Effect of the pump absorption on generation of infrared stimulated electronic Raman scattering in alkali-metal vapors

The main properties of infrared stimulated electronic Raman scattering (SERS) at the 6² S _1/2-7² S _{1/2, 3/2} transitions in cesium atoms are studied theoretically and experimentally as functions of the atomic concentration, which was varied from 10¹¹ to 10¹⁶ cm^?3. It is found that the efficiency of generation of Stokes radiation strongly depends on one-photon absorption of the pump radiation tuned near frequencies of the 6² S _1/2-7² P _{1/2, 3/2} transitions. By using the equation for the density matrix, which describes the evolution of a three-level system, the theory of resonance excitation of IR radiation upon one-photon absorption at an adjacent transition is developed. The theory describes well the main features of IR SERS in alkali-metal vapors.     

Wavelength-modulation spectroscopy using a frequency-doubled current-modulated diode laser

We have studied atomic absorption in an argon discharge by wavelength-modulation spectroscopy with a frequency-doubled diode laser. The tunable wavelength-modulated radiation at 430 nm was generated by frequency doubling a current-modulated 860-nm diode laser in a KNbO₃ crystal. 2f-, 4f- and 6f-harmonic spectra as a function of diode laser modulation depth were measured on a Doppler-broadened sample of excited argon atoms produced in a capacitively coupled plasma chamber. Characterisation of the harmonic signals was accomplished. Minimum detectable absorbances of 7.7×10^-5 and 1.9×10^-4 based on a 3σ criterion (σ being the standard deviation of the noise) were estimated for 2f- and 4f-harmonic detection of the frequency-doubled radiation with a time constant of 0.1 s. The concentrations of argon in the 1s₄ state were found to be in the range of 3×10⁸ to 1.2×10¹¹ cm^-3 for the experimental conditions studied. Received: 25 February 2002 / Revised version: 4 April 2002 / Published online: 14 May 2002     

High temperature diamond anvil cell with the laser heating

Abstract

Focusing laser radiation in the center of a diamond anvil cell (DAC) allows investigations up to P?100 GPa with the pulsed' and sustained heating to 5000 K^2,3. The use of laser radiation permits the exclusion of a heater if the sample itself strongly absorbs the radiation. Many materials are transparent for 1.06 μm YAG-laser radiation usually used for the heating. Therefore it is necessary to mix absorbing radiation powders, for example, graphite, platinum²³. The use of the powerful C0₂-laser for the heating considerably extends the scope of the materials under investigation, as the wavelength radiation Λ= 10 μm is in the range of the strong lattice absorption (absorption coefficient～ 10³-10⁴ cm-^l) of many oxides, nitrides and so on.     

Resonance absorption and fluorescence in argon

Absorption cross sections of argon for argon resonance radiation have been measured by several techniques. The apparent cross sections are small (0·1 to 1·6 × 10^-18 cm²) for resonance absorption and the values depend on the technique used for measurement. These observations are interpreted in terms of extensive reversal and broadening in the source. The excitation and quenching of resonance fluorescence was studied to provide information about the rates of the processes

The rate constants were estimated relative to k _r, the rate constant for radiation. Radiation imprisonment leads to a reduction of k _r from its natural value and observations of the decay of resonance fluorescence suggest that k _r ～ 1·5 × 10⁵ s^-1 in our system at [Ar] = 2 × 10¹⁷ atom cm^-3. Combining this value with the relative values for the quenching rate constants gives k ₁ < 1·5 × 10^-13, k ₁′(M = N₂) ～ 6 × 10^-12, k ₁′(M = NO) ～ 4 × 10^-10, in units of cm³ s^-1 molecule^-1.     

199Hg+光频标的黑体辐射频移

光学频率标准会受到环境温度的黑体辐射影响发生频移,进而影响其准确度. 本文估算了¹⁹⁹Hg⁺的超精细能级5d¹⁰6s²S_1/2 (F=0)和5d⁹6s^{2 2}D_5/2 (F=2)的极化率,得到了室温(300 K)下黑体辐射引起的相对频移为-5.4×10^-17, 最后讨论了低温环境下黑体辐射对¹⁹⁹Hg⁺光频标的影响.     

Loss of electrons by fast H− ions in gases

The characteristic angles and cross sections for a (\mathop 1^- 0) + (\mathop 1^- 1)(\mathop 1\limits^ - 0) + (\mathop 1\limits^ - 1) reaction in which H⁻ atoms with an energy of 0.1–10 000 MeV lose electrons when scattered on C, N, or O atoms were calculated for the relativistic case of the Bethe scattering theory. The cross sections for N₂, O₂, and CO₂ molecular targets were obtained using the additivity rule. The results presented are compared with known experimental and theoretical data.     

Rotational relaxation of the 0001 level of CO2 including radiative transfer in the 4.3-μm band of planetary atmospheres

Accurate numerical solutions have been obtained for a model problem of rotational relaxation within the 00⁰1 vibrational level of C¹²O₂¹⁶ accounting for the transfer of radiation in the lines of the fundamental transition 00⁰1-00⁰0 of the 4.3-μm band. Intramolecular exchange of vibrational energy with the reservoir of v₂ quanta and absorption of solar radiation in the 00⁰1- 00⁰0 band are accounted for. A plane-parallel isothermal atmosphere of pure CO₂ with the barometric pressure distribution and solar illumination is assumed. The line opacity is represented by nonoverlapping Voigt profiles depending on temperature and pressure. The transfer problem, which is equivalent to that of a multiplet with a large number of lines with a common lower level, was solved by a generalization of the Rybicki method. We find significant deviations from ratational LTE (local thermodynamic equilibrium) in regions in which the harmonic average of the optical depth over the band is of order 10³-10⁴. Absorption of solar radiation can affect significantly the source functions of lines at the centers of the P and R branches. Deviations from rotational LTE are shown to influence the intensity and shape of the 4.3-μm band of CO₂ in the spectra of Mars and Venus, and should be taken into account in the interpretation of the observations in which the rotational structure is resolved, especially in limb measurements, where these effects are particularly apparent.     

Mid-infrared generation and spectroscopy with a PPLN ridge waveguide

We have utilised a periodically poled LiNbO₃ crystal with a waveguide structure to produce up to 146 μW of mid-IR radiation around 2976 cm^-1 by difference frequency mixing of 1064 nm pump radiation with 1558 nm signal radiation. A conversion efficiency of 45% W^-1 is achieved within a crystal of length 50 mm, and temperature tuning curves are reported. The resultant idler radiation is exploited for high resolution absorption studies of both methane and methanethiol. The absorption cross-sections for methanethiol in the region of 2979 cm^-1 are measured and found to be ∼10^-19 cm², the relevance of these results to breath and headspace analysis of clinical samples containing volatile sulphur compounds is briefly discussed. PACS 42.62.Fi; 42.65.Ky     

Measurements of the upper and lower level lifetime in He-Se lasers

The lifetimes τ₂ and τ₁ of the upper and lower levels of the 5227 Å (5p ⁴D_{$\text{7}\text{2}$}→5s ⁴P_5/2) laser transition in He-Se were measured. The obtained values are: τ₂=(18.5±1.85) × 10^-9 sec; τ₁=(2±0.4) × 10^-9 sec. The value of τ₂ was determined by measuring the time constant of the transient in the fluorescent emission consecutive to a sudden interruption of the laser oscillation inside the cavity.The value of τ₁ was determined by measuring the change induced by one laser transition on the unsaturated gain of another laser transition sharing the same lower level. Finally the “radiation trapping” factor is evaluated, thus ruling out the possibility that radiation trapping might be responsible for saturation in the laser output versus discharge current.     

Statistical estimates of the contribution of multiply scattered radiation to the intensity of acoustic radiation transmitted through a lower 500-m atmospheric layer

The problem of acoustic radiation propagation through a lower 500-m plane-stratified turbulent atmospheric layer has been solved by the Monte Carlo method. Statistical estimates of the contribution of multiply scattered radiation to the transmitted acoustic radiation intensity are obtained. A point omnidirectional source of monochromatic acoustic radiation was placed at a height of 35 m above the absorbing Earths surface. Statistical estimates of the contribution of multiply scattered radiation to the transmitted radiation intensity have shown that it does not exceed 15% for the outer scale of atmospheric turbulence L₀ = 10 m and sound frequency F = 1700 Hz, reaches 30% for L₀ = 20 m, and increases to 90% for L₀ = 80 m. A comparison of the calculated results with the available experimental data demonstrates their satisfactory agreement.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 72–79, December, 2004.