Demonstration of temporal coherence,spatial coherence,and threshold effects in the molecular xenon laser

Stimulated emission has been observed at 1722 ± 1 Å in high-pressure xenon gas originating from the bound-free continuum of the Xe¹₂ molecule. This emission exhibits strong line narrowing, spatial coherence corresponding to a few times the diffraction limit, a sharp oscillation threshold, and an output time dependence radically different from the spontaneous emission observed without an optical cavity or below threshold. The confluence of all these observations is an explicit and unequivocal demonstration of a coherent stimulated emission process. Specific data detailing the pressure dependence of the stimulated output and results with rare-gas mixtures are given.     

Effect of atmospheric turbulence upon the spatial coherence of laser radiation

The present article is an analysis of the effect of atmospheric turbulence upon the spatial coherence of laser radiation. Young's experiment was used for an experimental study of the coherence of radiation traversing path lengths of 100 and 200 m in the atmosphere.The experimental measurements of the relation between the coherence function of the radiation and the temperature gradient are in strong agreement with the theoretical values. The relation between the coherence function and the distance between the field points considered disagrees with the theoretical values. The discrepancy can be explained by the limitations of the approximation of geometrical optics.     

Second-harmonic conversion of neodymium glass laser radiation with controlled spatial coherence

The experimental results on the second optical harmonic conversion of neodymium glass laser radiation with controlled spatial coherence in a nonlinear KDP crystal are presented. The conversion efficiency is studied depending on the radiation power density on the crystal and the crystal rotation angle in the principal optical plane with respect to the radiation propagation direction. The experiments were performed in the radiation power density range I = 0.2–3 GW/cm² for the number of cavity transverse modes N = 100–1000, radiation divergence 2ч = 0.5–3.5 mrad, spectrum width of 26 Å, and pulse duration of 2.5 ns.     

Competition effects on spatial coherence in a CO2 laser

The degree of spatial coherence between two points separated by 6 mm in a radiation beam is almost unity, when two competing transitions lines which differ below 100 cm^-1 oscillate with a TEM₀₀ mode, while it varies greatly when a single line occurs on competing TEM₀₀ and TEM₁₀ modes.     

激光空间相干性对照明均匀性的影响

研究了激光相干性对照明均匀性的影响,为照明激光器的选择提供了理论参考。其中,部分相干高斯光束分解为模式间相互独立的厄米-高斯光束的迭加。采用相位屏的近似处理方法对激光通过大气湍流的传输进行计算模拟。数值模拟的结果表明：当照明光束的空间相干性降低时,其照明均匀度逐步提高。因此对于照明激光器而言,选择空间相干性较差的激光器对其照明均匀度更加有益。     

激光空间相干性对照明均匀性的影响

 研究了激光相干性对照明均匀性的影响，为照明激光器的选择提供了理论参考。其中，部分相干高斯光束分解为模式间相互独立的厄米-高斯光束的迭加。采用相位屏的近似处理方法对激光通过大气湍流的传输进行计算模拟。数值模拟的结果表明：当照明光束的空间相干性降低时，其照明均匀度逐步提高。因此对于照明激光器而言，选择空间相干性较差的激光器对其照明均匀度更加有益。     

Relationship between temporal coherence and laser parameters in a two-longitudinal-mode HeNe laser

The relationship between the temporal coherenceg ⁽¹⁾ () and laser parameters - the output relative intensity (I ₁/I ₂) and the frequency width _h of the longitudinal mode in a two-longitudinal-mode HeNe laser - is studied experimentally. The experimental results show that both the relative output intensity and the frequency width of the longitudinal mode have a great influence on the temporal coherenceg ⁽¹⁾ (). Moreover, the spectral line-shape function of each longitudinal mode in a two-longitudinal mode HeNe laser is a Lorentzian function, with a frequency width of about 18.2 MHz. A model of the power spectrum with Gaussian amplitude distribution and equal frequency width of the longitudinal mode in a multi-longitudinal-mode gas laser is employed in the theoretical analysis. Good agreement between theory and experiment is obtained.     

Spatial and temporal coherence characterization of a smoothed laser beam

The measurement of the coherence characteristics of the speckles generated by an optically smoothed laser source is investigated. We present a new method that can be used for every kind of smoothing technique. A modified Mach-Zehnder interferometer allows us to measure both the lifetime and the spatial transverse size of the hot spots generated by a broadband and transverse multimode source. Experimental results agree well with theoretical predictions.     

Decoupling of temporal/spatial broadening effects in Doppler wind LiDAR by 2D spectral analysis

Pulse echo accumulation is commonly employed in coherent Doppler wind LiDAR(light detection and ranging)under the assumption of steady wind. Here, the measured spectral data are analyzed in the time dimension and frequency dimension to cope with the temporal wind shear and achieve the optimal accumulation time. A hardware-efficient algorithm combining the interpolation and cross-correlation is used to enhance the wind retrieval accuracy by reducing the frequency sampling interval and then reduce...     

Coherent and incoherent laser spectroscopy of spatial and temporal fluctuations

Information on spatial and temporal fluctuations of the transition frequency is theoretically shown to be obtained from transient four-wave mixing (FWM) at $\text{k}\text{=2}\text{k}{}_1\text{?}\text{k}{}_2$ or $\text{2}\text{k}{}_2\text{?}\text{k}{}_1$ under coherent excitation by two laser pulses with wave vectors k₁ and k₂. The same information is available from the FWM by two CW incoherent laser beams k₁ and k₂ split off from a single source as a function of the relative delay time. In these cases, we can select a specified diagram for the FWM which depends on double sites. This makes it possible to observe the spatial fluctuations in addition to the temporal ones.     

Copper vapor laser with intracavity radiation scanning by a spatial and temporal light modulator based on PLZT ceramics

The results of an experimental study of the output radiation parameters of a copper vapor laser (CVL) with a self-conjugate resonator are presented. TheQ-factor was controlled by diaphragms (slit or circular) and spatial and temporal light modulators (STLM) based on PLZT ceramics.     

Atomic coherence effects in the ion-trap laser

The influence of atomic coherence effects on the statistical and spectral properties of the ion-trap laser is investigated. Various pump configurations are considered for a realistic level scheme using a Ca ion. Compared to previous suggestions, 50% more output is obtained.     

Transformation of spatial characteristics of excimer laser radiation

An optical attachment of an excimer laser beam that enables the transformation and optimization of spatial characteristics of a coherent UV beam was studied in an experimental setting. Experiments revealed that a rectangular 3 × 20 mm laser beam with the a divergence of 2 × 5 mrad attains a square shape of 20 × 20 mm and a divergence of 5 × 5 mrad in orthogonal directions after passing through the beam attachment. It is demonstrated that the application of a beam attachment in installations for material microprocessing simplifies optical layout of the illumination module allows one to obtain optimal homogeneity of sample illumination (under 2%) upon the projection of the image on the processing plane of the sample with submicron precision and to reduce the radiation load on optical elements via the elimination of hot spots.     

Amplitude and polarization effects in self-focusing of laser radiation in media with spatial dispersion of nonlinearity

Moscow State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 31, No. 9, pp. 1042–1052, September, 1988.     

Some measurements of the spatial coherence of a giant pulse laser

A simple Young-type two-point correlation experiment with photographic detection is described. Comparisons are made for the various factors contributing to the spatial coherence. The determining rôle of the number of superimposed transverse modes is confirmed. The importance of the back mirror, the active medium and the short build-up time is found, experimentally.