Effects of Quantum Interference on the Profile of Excitation Spectra in the Atomic Sodium D_1

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The continuous wave electron paramagnetic resonance experiment revisited

When the modulation frequency used in continuous wave electron paramagnetic resonance (cw EPR) spectroscopy exceeds the linewidth, modulation sidebands appear in the spectrum. It is shown theoretically and experimentally that these sidebands are actually multiple photon transitions, sigma(+)+kxpi, where one microwave (mw) sigma(+) photon is absorbed from the mw radiation field and an arbitrary number k of radio frequency (rf) pi photons are absorbed from or emitted to the modulation rf field. Furthermore, it is demonstrated that both the derivative shape of the lines in standard cw EPR spectra and the distortions due to overmodulation are caused by the unresolved sideband pattern of these lines. The single-photon transition does not even give a contribution to the first-harmonic cw EPR signal. Multiple photon transitions are described semiclassically in a toggling frame and their existence is proven using second quantization. With the toggling frame approach and perturbation theory an effective Hamiltonian for an arbitrary sideband transition is derived. Based on the effective Hamiltonians an expression for the steady-state density operator in the singly rotating frame is derived, completely describing all sidebands in all modulation frequency harmonics of the cw EPR signal. The relative intensities of the sidebands are found to depend in a very sensitive way on the actual rf amplitude and the saturation of single sidebands is shown to depend strongly on the effective field amplitude of the multiple photon transitions. By comparison with the analogous solutions for frequency-modulation EPR it is shown that the field-modulation and the frequency-modulation technique are not equivalent. The experimental data fully verify the theoretical predictions with respect to intensities and lineshapes.     

Observing the Stimulated Raman Gain Spectra of Solutions Using an Infrared Pump Pulse with Narrow Linewidth and a Low-Noise CW Probe Laser

Stimulated Raman gain (SRG) spectroscopy using infrared pump pulses with narrow linewidth and a low-noise cw probe infrared laser was proposed. High-resolution Raman spectra of solutions were obtained. The SRG spectra of crystal GaP, benzene, and toluene were measured to confirm the spectral resolution and sensitivity over the terahertz (THz) region. We discuss the polarization dependence of the spectral measurement of carbon tetrachloride. Our system can detect organic molecules in aqueous solutions.     

Single vibronic level fluorescence of CrO2Cl2 excited by a tunable cw dye laser

Fluorescence of gaseous chromyl chloride has been excited using a tunable cw dye laser, and fluorescence spectra have been recorded for excitation in 20 different absorption bands. The vibrational structure of these spectra shows activity of all of the totally symmetric vibrations, but there is no evidence for activity of any non-totally symmetric vibration as previously proposed from absorption spectra. We conclude that the absorption band system near 5800 Å comprises at least two electronic transitions.     

Effects of Quantum Interference on the Profile of Excitation Spectra in the Atomic Sodium D1

In this paper, an experiment in a sodium vapor cell with cw laser pumping is reported. Two dips in the excitation spectrum profile of the sodium \$D1\$ line are observed. Theoretically excitation spectra in the three-level system are calculated in detail and results are identical with experiments. It is demonstrated that the appearance of the two dips in the excitation spectrum is close connected with quantum interference effect.     

Continuous-wave pumping in the anomalous- and normal-dispersion regimes of nonlinear fibers for supercontinuum generation

Supercontinuum (SC) growth in highly nonlinear fibers is compared for cw pumping in the anomalous- and normal-dispersion regimes. For anomalous-dispersion pumping, the combined effects of modulation instability (MI) and stimulated Raman scattering (SRS) contribute to spectral broadening. Furthermore, breakup of the cw light into ultrashort pulses by MI leads to the formation of a Raman pulse that evolves into a soliton, as evidenced by the observation of soliton self-frequency shift. Blueshifted, nonsolitonic radiation associated with the fission of higher-order solitons is also present in the SC spectra. For normal-dispersion pumping, SRS seeds the SC growth by generating several cascaded Stokes orders. When the Stokes orders are shifted into the anomalous-dispersion regime at higher launch powers, MI again causes soliton formation. Broadband continua are generated when the laser is positioned as far away as 191 nm from the zero-dispersion wavelength in normal dispersion.     

Raman scattering in thallium iodide and thallium bromide vapor

Intense Raman spectra of thallium iodide and thallium bromide vapor were excited with a cw Ar⁺-ion laser. Up to 30 anti-Stokes lines and 45 Stokes lines were observed.     

Secondary anti-stokes emission from the bulk of gallium phosphide at 4.2 K

Secondary radiation (photoluminescence and Raman scattering) emitted by gallium phosphide single crystals at helium temperatures is investigated. It is established for the first time that, in the case when the secondary emission spectra are excited by a cw low-power He-Ne laser, whose linewidth lies in the transparency region of GaP, anti-Stokes photoluminescence from the bulk of the sample occurs due to interband and impurity recombination. The results obtained make it possible to carry out a qualitative and quantitative analysis of impurities which are present in the bulk of a semiconductor by recording the bulk anti-Stokes photoluminescence spectra at low temperatures.     

Nonlinear Absorption and Dispersion Response in Optically Dense Media Driven by a Single-Mode Laser

Taking the density-dependent near dipole-dipole （NDD） interaction into consideration, we theoretically investigate the response of nonlinear absorption and dispersion in optically dense media of three-level atoms driven by a single-mode probe laser. The influence of the NDD effects on the absorption and dispersion spectra of the probe field is predicted via numerical calculations. It is shown that the NDD effects reduce gradually to transient absorption and amplification with the increase of the strengths of the NDD interaction, but do not change the steady-state behavior. Due to the presence of the NDD effects, steady-state absorption spectra exhibit asymmetric double-peak structure and overall shifts when a continuous-wave （cw） probe field is applied. However, frequency dispersion spectra are insensitive to them near the zero detuning.     

60-W continuous wave laser diode arrays emitting at a wavelength of 808 nm

Samples of cw laser diode arrays (LDAs) with an output power higher than 60 W emitting in the spectral range of 808 nm are developed and fabricated. Main output parameters, including light–current, current–voltage characteristics, and emission spectra of a lot of 5 LDAs are measured.     

Nonlinear Absorption and Dispersion Response in Optically Dense Media Driven by a Single-Mode Laser

Taking the density-dependent near dipole-dipole (NDD) interaction into consideration, we theoretically investigate the response of nonlinear absorption and dispersion in optically dense media of three-level atoms driven by a single-mode probe laser. The influence of the NDD effects on the absorption and dispersion spectra of the probe field is predicted via numerical calculations. It is shown that the NDD effects reduce gradually to transient absorption and amplification with the increase of the strengths of the NDD interaction, but do not change the steady-state behavior.Due to the presence of the NDD effects, steady-state absorption spectra exhibit asymmetric double-peak structure and overall shifts when a continuous-wave (cw) probe field is applied. However, frequency dispersion spectra are insensitive to them near the zero detuning.     

Continuous-wave cavity-ringdown detection of stimulated Raman gain spectra

Cavity ringdown (CRD) spectroscopy, with its high sensitivity, provides a novel way to perform continuous-wave (cw) stimulated Raman gain (SRG) spectroscopy, rather than by conventional optically detected coherent Raman techniques. Tunable cw laser light at ∼1544 nm is used to probe ringdown decay from a rapidly-swept, high-finesse optical cavity containing a gas-phase sample of interest and itself located inside the cavity of a cw single-longitudinal-mode Nd:YAG ring laser operating at ∼1064.4 nm. This approach is used to measure cw SRG spectra of the ν ₁ fundamental rovibrational Raman band of methane gas at ∼2916.5 cm⁻¹. The resulting SRG-CRD resonances have ringdown times longer than in the off-resonance case, in contrast to the usual shorter ringdown times arising from absorption and other loss processes. Previously reported noise-equivalent sensitivities have been substantially improved, by using a second ringdown cavity to facilitate subtraction of infrared-absorption background signals. Moreover, by employing a ringdown cavity in the form of a ring, the SRG-pump and CRD-detected Stokes beams can co-propagate uni-directionally, which significantly reduces Doppler broadening.     

激光工作模式对苯氰S_1电子态高分辨光谱的影响

本文研究了不同激光工作模式对苯氰分子高分辨光谱的影响,高分辨的激光为Ar~+泵浦的cw环形染料激光经过Nd:YAG激光三步脉冲放大后倍频产生的UV光.实验发现当Nd:YAG激光的振荡级有种子光注入时,光谱呈现转动分辨的谱线,可以很好地标识为苯氰分子S_1←S_0 0_0~0跃迁的转动结构;而当Nd:YAG激光工作于多个模式(无种子光注入)时,光谱则为连续的毫无结构的谱带.由于苯氰分子S_1电子态具有较大的偶极矩,工作于多个模式下激光脉冲的峰值功率的增强产生AC Stark效应,是导致谱线加宽从而无法观测到转动分辨光谱的可能原因.     

激光工作模式对苯氰S1电子态高分辨光谱的影响

本文研究了不同激光工作模式对苯氰分子高分辨光谱的影响,高分辨的激光为Ar+泵浦的cw环形染料激光经过Nd：YAG激光三步脉冲放大后倍频产生的UV光. 实验发现当Nd：YAG激光的振荡级有种子光注入时,光谱呈现转动分辨的谱线,可以很好地标识为苯氰分子S1←S0 跃迁的转动结构;而当Nd：YAG激光工作于多个模式（无种子光注入）时,光谱则为连续的毫无结构的谱带.由于苯氰分子S1电子态具有较大的偶极矩,工作于多个模式下激光脉冲的峰值功率的增强产生AC Stark效应,是导致谱线加宽从而无法观测到转动分辨光谱的可能原因.     

Spectral characteristics of a high-current pulsed discharge in xenon

The radiation characteristics of a pulsed discharge xenon lamp are experimentally and theoretically studied. The data on radiation spectra are obtained for various compositions and pressures of working medium, energies and time profiles of excitation pulse, discharge gap configurations, etc. Electron temperature and mean spectroscopic symbol of emitting ions are estimated. It is demonstrated that cw radiation (continuum) results from the photorecombination transitions.     

单斜结构的Yb:KLu(WO4)2晶体光谱和激光性质的各向异性

研究了Yb:KLu(WO₄)₂晶体对非偏振抽运光的吸收以及连续波激光振荡性质. 晶体结构的低对称性导致晶体光谱呈强烈各向异性,最强的吸收和发射都发生在平行于N_m主轴的偏振方向上. N_g切向晶体具有最高的非偏振抽运光吸收效率和最大的激光功率产生潜力,2 mm长的晶体产生的最高连续波输出功率为11 W,相对于吸收抽运功率,光—光转换效率为68%,而斜率效率则达80%. 关键词： 吸收谱 发射谱 激光振荡 各向异性     

Coherent Raman beats associated with superhyperfine structure in ruby

Coherent Raman beats associated with superhyperfine structure (shfs) due to Cr-Al interaction were observed in ruby. The rf modulated Stark field was used to create coherences between shfs sublevels under the irradiation with a cw ruby laser. From the beat frequencies high resolution spectra of shfs with width (HWHM) of about 10 kHz were obtained in the frequency range from about 4.5 to 6.5 MHz. The utility of phase sensitive detection technique combined with rf Stark modulation was demonstrated. The observed spectra were compared with the theoretical ones.     

Stimulated emission and laser action of Pr3+-doped YA1O3

Groundstate absorption, fluorescence, excited-state absorption, and stimulated emission of Pr:YA1O₃ were measured in dependence on the polarization. The results reflect the anisotropy of the host lattice. Especially the polarized spectra of the stimulated emission fit very well with the laser data of this material. Seven cw laser transitions in the visible spectral range obtained so far in Pr:YA1O₃ with argon-ion laser pumping were identified in the spectra of the stimulated emission. In addition, two infrared cw laser transitions were realized. The best results were achieved for the³ P ₀³ F ₄ laser transition at 746.9 nm with a maximum slope efficiency of 24.6%, a maximum output power of 49.6 mW, and a laser threshold of 25 mW.     

Laser output power over 5 W at 1.06 μm for Nd:GdVO4 single crystal

In this paper, we report the polarization absorption spectra from 400 to 850 nm, polarization emission spectra from 1050 to 1100 nm and laser properties of an Nd:GdVO₄ crystal. An output power of up to 5.29 W at 1.06 μm has been achieved with a 3×3×3 mm Nd:GdVO₄ crystal sample when it is pumped by a cw laser diode.     

Affinement d'une raie de fluorescence de Pr3+: LaAlO3 par excitation laser

A cw dye laser has been used for fluorescence line narrowing experiments by resonant excitation on Pr³⁺ ions in LaAlO₃. Scanning the excitation radiation through the absorption line width corresponding to the transition ³H₄ (0 cm^-1) → ¹D₂ (16 694 cm^-1) while fluorescence was observed, has put into evidence a deformation of the symmetry around Pr³⁺ ions, different for every site.This experiment shows the power of cw dye laser spectroscopy for investigating optical spectra in crystals.