Wing profile measurements of the resonance emission lines of Na (5890/96Å) and Sr (4607Å) in flames

The blue and red wing intensity distributions of the Na 5890Åand 5896Åresonance lines were measured in emission in a pre-mixed, laminar, shielded H₂/O₂ flame at 1 atm with Ar or N₂ as diluent gases (T≈2000 K). The wavelength range scanned amounted to about 20Åfrom line center. In addition, we measured the wing intensity distributions of the resonance line of Sr (4607Å) in CO/N₂O flames at 1 atm (T≈2800 K) in a wavelength range of about 10Åfrom line center. The scanning monochromator used in these emission experiments had a spectral bandwidth of 0.30±0.04Å.For the resonance lines of Na and of Sr, the wavelength dependence of each wing was derived from 25 repeated scans and found to differ from theoretical predictions based on binary quasistatic theory.The red wing of the D₁ line of Na was investigated for the occurrence of satellites. We discovered a structure resembling a “smoothed” satellite at about 12Åfrom line centre. A satellite-like structure was also found in the blue wing of the resonance emission line of Sr at about 5Åfrom line center.     

Momentenanalyse derR 2-Nullphononen-Linie in NaF unter einaxialem Druck

The R₂ zero-phonon absorption line 4480 Å in NaF at 4.2 °K and 23 °K is studied under uniaxial stress along 〈100〉 and 〈100〉. According to the F₃ model of theR center the R₂ line is found to be due to a transition between a degenerate ground state (²E) and a nondegenerate excited state (²A) of this center. Instead of a splitting into single components under stress, changes in line shape are observed which are analyzed by means of the method of moments. The zeroth and first moment of the line are calculated as functions of the magnitude of stress and temperature. The theoretical moments are found to be in good agreement with those determined from the experimental data. From a comparison of the measured moments with the theoretical expressions the stress splitting parameters are obtained which describe the removal of both the orientational and the orbital degeneracy of theR center under uniaxial stress. The corresponding strain parameters of the R² line in NaF are compared with those in other alkali halides.     

Single line high efficiency tunable fir generation by resonant four-wave mixing in CH3 pumped by a multiatmosphere tunable CO2 laser

By pumping CH₃F with a high pressure tunable TE-CO₂ laser, the resonant four-wave mixing process (RFWM) generates a very efficient tunable single line FIR emission at the Raman frequency. This result is strictly related to the spectroscopic structure of the CH₃F molecule. By means of this process, a tunable FIR emission on a 0.1 cm^–1 bandwidth 150 kW (8 mJ) single line, is obtained which can be used for many FIR multiphoton applications.     

Evidence for the existence of a complex isoelectronic center in Si : In

The effect of 1 MeV electron irradiation and a 100° annealing stage on the intensity of the U₂ line at 1.1182 eV is presented. Evidence is provided from intensity vs. excitation power measurements that the U₂ radiative recombination involves only a single exciton. Eight models are discussed, with a complex isoelectronic center being favored.     

Absorptions- und Fluoreszenzspektren des Systems KCl:Sm2+ bei tiefen Temperaturen

Sharp emission line spectra of Sm²⁺ in KCl single crystals are observed up to 40 °K. From these it is possible to verify the idea of a substitution of a regular cation by an impurity ion and of a simultaneous association of a cation vacancy in the nearest neighbourhood [1/2 (110)]. This means that the crystal field at the place of the bivalent Samarium has the site symmetryC _2v . A cubic symmetry does not explain the spectra. It is possible to identify the line groups with the transitions, which are permitted by reason of the selection rules, and to set up the energy level diagram of the Sm²⁺ ion in KCl. The separation of the single impurity-vacancy complexes was reached by quenching the crystals from 650 °C to room temperature. The assumption of excitation exchange between neighbouring Samarium ions explains the spectra of the non-quenched crystals. The number of emission lines is determined for two different orientations of two dipole complexes towards one another. An interpretation of the absorption spectra of Sm²⁺ in KCl is proposed.     

高次谐波辐射光子的能量-激光相位关系研究

原子在强激光电场中高次谐波辐射的理论与实验研究是当今科学前沿之一.利用量子力学理论和鞍点方法,细致地研究了高次谐波辐射光子的能量与激光相位的关系.对于时间宽度无限长激光,在一个激光周期内特定相位处产生的高阶辐射(X射线)有特定的能量.能量分布在7180°处成峰,有高斯形函数的对称形状.给出了这种分布的参数化公式.对于不同宽度的飞秒激光,能量分布的成峰位置、最大值和带宽等参数会发生变化.计算表明,三个振荡周期(半高宽)的飞秒激光,当载波-包络相位为175°和105°时,可以分别得到纯净的阿秒单脉冲和双脉 关键词： 超短脉冲激光 高次谐波产生 鞍点方法 能量相位关系     

Band-edge photoluminescence of PbI2

Photoluminescence spectra of the hexagonal layered semiconductor PbI₂ have been measured at 4.2°K on various single crystalline specimens. They are interpreted in relation with the anisotropic polariton model. The emitted radiation is assumed to originate from free and bound exciton recombination, with and without phonon emission. A peak polarized E ∥ c about 4 meV above the excitonic line is related to the extraordinary polariton mode.     

Spectroscopy and lasing of cryogenically cooled Yb, Na:CaF2

Absorption, photoluminescence and cw-lasing properties of a novel Na⁺-codoped Yb³⁺:CaF₂ laser crystal are investigated in the temperature range from 10 K to 290 K. Cryogenic cooling leads to the disappearance of the ground-state absorption in the spectral region above 1000 nm and a substantial increase of emission and absorption cross-sections. A particular advantage of the Yb³⁺, Na⁺-codoped CaF₂ crystal lies in the possibility of a direct pumping in the vicinity of the zero phonon line while nearly perfectly avoiding an overlap with the stimulated emission. Further advantages of the low-temperature operation are demonstrated by achieving a close to the theoretical limit slope efficiency of 92% in a cw-laser operation with an output coupler of 28%. By seeding stretched pulses from a femtosecond Yb fiber oscillator into a cryogenically cooled DPSS Yb³⁺,?Na⁺:CaF₂ regenerative amplifier, we obtain >3-mJ pulses at a 1-kHz repetition rate with a spectral bandwidth exceeding 12 nm. The pulses are compressed with a single grating compressor to 173 fs as verified by SHG FROG. Shaping of the spectral amplitude of the seed and active control of the higher-order phase is shown to be crucial for obtaining sub-200-fs pulses at multi-mJ energies.     

Radiation emission coefficients for sulfur hexafluoride arc plasmas

Calculations are made of the total spectral absorptivities of plasmas of sulfur hexafluoride for wavelengths of 100 to 15,500 Å. Both line and continuum radiation are considered. For the contributions from line radiation, we have calculated the strengths, widths and shifts of both neutral, singly and doubly ionized atoms of S and F, except that we used experimental line strengths where they are available. The theory used was that of Griem, which assumes LS coupling. Curves are given for the emission coefficient of radiation appropriate to the arc center for isothermal cylindrical plasmas of various radii for pressures of 1 and 10 atm and temperatures from 5000 to 35,000°K. It is found that at 1 atm line radiation can be an order of magnitude higher than continuum radiation and radiation >2000 Å is less than 10% of the total radiation for temperatures greater than 15,000°K. Predictions are given of volt-ampere characteristics and central temperatures for arcs of various radii in SF₆ at pressures at 1 and 10 atm.     

High resolution emission spectra of laser-excited molecular iodine as the excitation frequency is tuned through and away from resonance

We have studied the ΔJ = 2 rotationally shifted emission lines in the region of the strong absorption of molecular iodine which occurs within the 5145 Å argon ion laser line. We used an etalon tuned, single frequency argon ion laser with a linewidth of 20 MHz to excite the iodine emission and recorded the spectra of the rotational lines with Fabry-Perot spectrometers having resolutions up to 70 MHz (0.0023 cm^-1). To overcome Doppler linewidth limitations we took spectra of the emission at small angles to the exciting beam and found the lines to have widths less than our instrumental resolution and frequencies which accurately tuned with the incident laser frequency. We recorded the emission lines for laser frequencies in the absorption line center and out into the absorption wing. Our spectra show that the intensity of the emission lines follows the absorption line profile while the frequency of the emission lines is determined by the laser frequency; the intensity is maximum at the absorption line center, falling by 10⁴ as the laser frequency is moved off the line center, while the line position maintains a constant frequency shift from the laser frequency.     

Line shape and excitation strength of the first excited state in9Be

The line shape and the excitation strength of the very weak first excited J ^π =1/2⁺ state at E_x=1.684 MeV in Zeitschrift für Physik Zeitschrift für Physik⁹Be has been investigated with high-resolution inelastic electron scattering at E₀=45 and 49 MeV and scattering angles θ=105°, 117°, 129° and 165°, and with high-resolution inelastic proton scattering at E₀=13MeV and θ=15° and 18°. Due to lying just above the neutron threshold the level has a strongly asymmetric line shape which in both experiments can be described consistently with a Breit-Wigner expression modified on the low energy side by the threshold behaviour of the cross section. The resonance energy is E_R=1.684 ± 0.007 MeV and the width T=217± 10 keV in thec.m. system. A single particle potential model calculation reproduces the line shape and the resonance parameters fairly well. In addition, the inelastic electron scattering form factor has been measured. In the range of momentum transfersq =0.24-0.46 fm^?1 it is dominated by a 0p_3/2→ 1s_1/2 particle-hole transition. The transition is mainly longitudinal and of isoscalar nature with a strength of B (E1)↑ =0.027 + 0.002 e² fm², but a small M2 contribution ofB(M2)↑=8.8 ±1.5 μ _N ² fm² has also been detected.     

Line emission of SrBe2Si2O7:Eu2+ and BaBe2Si2O7:Eu2+

The compounds SrBe₂Si₂O₇ and BaBe₂Si₂O₇ both have the barylite structure. With 254 nm excitation, the Eu²⁺-activated compounds give UV emission peaking at 360 nm (Sr) and at 375 nm (Ba). Maximum quantum efficiencies of 40% (Sr) and 65% (Ba) were measured. The emission consists of a 5d-4f band emission as well as 4f-4f line emission, in contrast to many other Eu²⁺-activated oxides which generally show only 5d-4f band emission. At 77°K, both compounds show only the 4f-4f line emission peaking at 360 nm. At higher temperatures, 5d-4f band emission shows up at the cost of the line emission. A thermal equilibrium is assumed between the lowest excited 5d and 4f levels. The energy difference between these levels, calculated from the variation in the line-band intensity ratio with temperature, was computed to be 0.15 eV (Sr) and 0.09 eV (Ba). The occurrence of the line emission in the barylites is correlated with the weakness of the crystal field at the Eu²⁺ ions and with the high quenching temperature of the 5d-4f band emission.     

EPR of cadmium ferric voltaite above the ferrimagnetic transition

A single isotropic EPR line of Fe³⁺ in synthetic cadmium ferric voltaite, (NH₄)₂Cd₅Fe₃Al(SO₄)₁₂ · 18H₂O, was observed in a wide temperature range from 295 to 1.57°K. The ferrimagnetic transition temperature of CdFe voltaite was determined to be ～ 0.7°K using the temperature dependence of the g-factor and the line width. The cubic crystal field parameter, a, for Fe³⁺ in CdFe voltaite is extracted from the EPR line width measurement using the exchange-narrowed line width model of Anderson and Weiss. The parameter a for Fe³⁺ in CdFe voltaite at 4.2°K is 157 × 10^-4cm^-1 which is consistent with the corresponding values for Fe³⁺ in other cubic structures.     

Photoluminescence of mercurous halides

Mercurous halides show strong orange luminescence at 77°K when excited at energies above the fundamental absorption edge. At room temperature this luminescence is strong only in the chloride and bromide. Spectral features, including band maxima and half widths of both excitation and emission spectra are also temperature dependent. At 77°K a strong green luminescence was observed from the Hg₂Cl₂. Both Hg₂F₂ and Hg₂I₂ exhibited weak green emission, while no luminescence was observed from Hg₂Br₂ in this spectral region. The common orange luminescence is tentatively attributed to structural defects unique to mercurous salts, while the green emission is ascribed to an unspecified impurity center.     

Long-term ozone trend and its effect on night airglow intensity of Li 6708 ? at Ahmedabad (23°N, 72.5°E), India and Halley Bay (76°S, 27°W), British Antarctic Service Station

A critical analysis has been made of the long-term yearly and seasonal variations of ozone concentration at Ahmedabad (23°N, 72.5°E), India and Halley Bay (76°S, 27°W), a British Antarctic Service Station. The effect of O3 depletion on night airglow emission of Li 6708 ? line at Ahmedabad and Halley Bay has been studied. Calculations based on chemical kinetics show that the airglow intensity of Li 6708 ? line has also been affected due to the depletion of O₃ concentration. The nature of yearly variation and seasonal variation of intensity of Li 6708 ? line for the above two stations have been shown and compared. It has been shown that the rate of decrease of intensity of Li 6708 ? line was comparatively higher at Halley Bay due to dramatic decrease of Antarctic O₃ concentration.     

悬浮区域熔炼法制备LaB6单晶体与发射性能研究

采用区域熔炼法成功制备出了高质量,高纯度,大尺寸的LaB₆单晶体. 系统分析了制备过程中每个参数对LaB₆单晶生长的影响,确定了晶体生长最佳工艺为:样品转速为30 r/min,生长速度为8-10 mm/h. 分析了单晶LaB₆ (100) 晶面的热电子发射性能,结果表明,当阴极温度为1873 K时,最大热发射电流密度为44.36 A/cm²;利用 Richardson 直线法求出了绝对零度逸出功和有效逸出功分别为1.99和2.59 eV. 场发射测试结果表明,单晶LaB₆场发射单尖最大场发射电流密度达到4.9×10⁶ A/cm²,场发射因子为41500 cm^-1,表现出良好的场发射性能. 因此单晶LaB₆作为热阴极和冷阴极都具有很广阔的应用前景. 关键词： 区域熔炼法 6')" href="#">单晶LaB₆ 热发射性能 场发射性能     

Transmittance Characteristics of Buckled Fabry--Perot Tunable Filter with Membrane Structure

A wavelength tunable thermo-optic filter has been designed and fabricated for 1550 nm transmission. It has a Fabry--Perot resonator at the center with two sets of distributed Bragg reflector mirrors at both ends. The filter is fabricated as a free-standing membrane of alternating poly-Si and SiO₂ films surrounded by a thick silicon frame. The membrane is buckled due to the residual stress. Because of the buckling effect, high tuning efficiency of more than 0.17 nm/°C is observed. When the filter has a buckled surface, the incident light normal to the filter should have a range of non-zero angle of incidence to the membrane, which is dependent on the degree of buckling that depends again on the temperature. The transmittance calculations which integrate each incoming ray from a different incident angle show good qualitative agreement with the temperature dependence of the center wavelength and bandwidth.     

Edge emission in AgGaS2 single crystals

This paper reports on a study of the luminescence of single crystals of silver thiogallate (AgGaS₂). Cathodoluminescence measurements were made between liquid helium temperature and 250°K at two voltages, 25 kV and 10 kV and for 6 and ⊥ polarizations at the c axis. The cathodo-excitation technique used revealed the self-absorption phenomena, which are considerable near the bandgap.It is shown that the excitonic emission observed at liquid helium temperature remains up to 150°K and at higher temperatures there is band to band transition. In addition, a free to bound type of luminescence is indicated. This transition would appear to involve a level at 75 meV of the transport band.     

Nitrogen implantation in GaAs1−xPx (x=0.4; 0.65)

Nitrogen ions were implanted in GaAs_1−xP_x (x=0.4; 0.65) at room temperature at various doses from 5×10¹² cm⁻² to 5×10¹⁵ cm⁻² and annealed at temperatures from 600°C up to 950°C using a sputtered SiO₂ encapsulation to investigate the possibility of creating isoelectronic traps by ion implantation. Photoluminescence and channeling measurements were performed to characterize implanted layers. The effects of damage induced by optically inactive neon ion implantation on photoluminescence spectrum were also investigated. By channeling measurements it was found that damage induced by nitrogen implantation is removed by annealing at 800°C. A nitrogen induced emission intensity comparable to the intensity of band gap emission for unimplanted material was observed for implanted GaAs_0.6P_0.4 after annealing at 850°C, while an enhancement of the emission intensity by a factor of 180 as compared with an unimplanted material was observed for implanted GaAs_0.35P_0.65 after annealing at 950°C. An anomalous diffusion of nitrogen atoms was found for implanted GaAs_0.6P_0.4 after annealing at and above 900°C.     

Numerical data and experimental proof of the unified theory of electron emission (Christov)

In order to check the unified theory of electron emission (Christov), the temperature dependence of the electron emission from the (013), (001) and (112) single crystal faces of tungsten is measured between 300 °K and 1500 °K at relatively low fields yielding low current densities (10^?1 to 10^?7 A/cm²). Experiments are performed in a field electron microscope using a probe hole technique with an electron multiplier. The experimental results are in a fairly good agreement with Christov's theory. Tables of numerical data of Christov's formulae are presented. Using these tables, typical results of the theory are described.