High-power 20-channel neodymium glass laser and combined laser and beam heating of a plasma

A high-power 20-channel neodymium-glass laser is described (energy i kJ, pulse duration 2 nsec). It is part of the Flora facility intended for combined simultaneous heating of a plasma by powerful laser radiation (PLR) and by a relativistic electron beam (REB) produced in a facility of the plasma focus type. The paper deals theoretically with the processes of combined interaction of PLR and REB with a current plasma and a solid target.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Vol. 103, pp. 202–230, 1978.     

钕玻璃宽带激光放大能量提取效率研究

基于钕玻璃宽带脉冲激光放大模型,采用数值模拟的方法,研究了钕玻璃放大器对不同输入光通量、不同脉宽以及不同带宽(或波长分布)脉冲激光放大的能量提取效率。计算结果表明,钕玻璃宽带放大能量提取效率随着输入光通量的增加而提高,并最终趋于某一定值。对于以均匀加宽为主的介质,随着带宽的增加,能量提取效率逐渐下降;对于以非均匀加宽为主的介质,随着带宽的增加,能量提取效率先逐渐升高,达到最大值后开始下降。对于均匀加宽与非均匀加宽线宽比为0.1的混合加宽介质,在饱和通量输入条件下,使用宽带激光能够带来大约80%的效率提升。     

Non-destructive collimation technique for measuring glass constants using a Ronchi grating shearing interferometer

A non-destructive liquid immersion collimation technique in combination with a Ronchi grating shearing interferometer has been used for determining the constants of a transparent glass material, especially when it is in the form of a lens. Due to its simplicity and the fact that it will work equally well at any wavelength, the technique is superior to existing methods for determining the various glass constants (refractive index, Abbe number or v-value, partial dispersion factor etc).The shearing fringes appearing inside a Ronchi-gram are adequate to locate the exact position of the point source which has been treated as the target in the present communication. The fringe-free space in the overlapping region between the two laterally displaced spherical wavefronts indicates the sharply focused position of the target which corresponds to zero defocusing. In this way the target displacements with different liquids are determined.     

Optimization of pumping of active elements of neodymium glass of different composition by light of pulsed Xenon lamps

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 2, pp. 223–228, February, 1991.     

Experimental study on tellurite laser glass doped with neodymium

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 52, No. 5, pp. 781–785, May, 1990.     

Second-harmonic conversion of partially coherent radiation of neodymium glass laser

The experimental results on the conversion of multimode radiation of a neodymium glass laser with controlled spatial and temporal coherence to the second optical harmonic in nonlinear KDP crystal during the oee interaction implementation are presented. The dependence of the efficiency of the conversion to the second harmonic on the fundamental radiation power density on the crystal in the range I = 0.2 ? 5 GW/cm² is studied at the number of transverse modes in the cavity N = 1000; the radiation divergence φ = 3.5, 4.7, and 5 mrad; the emission spectral width δλ = 5and 42 Å; and the pulse duration of 2.5 ns. The breakdown power density of the KDP crystal is determined, the interference properties of the converted radiation of the second harmonic are studied.     

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.     

Determination of the parameters of a neodymium laser

A method is proposed for determining the internal loss coefficient, the probability of absorption of pumping radiation, and the initial gain from measurements of the delay time for induced emission. A comparison of the data obtained with the results of measurements by other authors shows good agreement.In conclusion, the authors express their sincere thanks to B. I. Stepanov for his constant attention to the work and useful advice and to N. S. Efimov and G. A. Kolosovskii for their help in conducting the experimental measurements.     

Reabsorption in a neodymium fibre laser

Resonance absorption, the reabsorption of laser light by the laser transition of the dopant material itself, is found to be the limiting factor for fibre lasers when extremely long fibres are used. We report on measurements of the temperature dependence of the losses in a 8.5 m long commercial Nd³⁺ doped fibre (York, ND 95020/E). To determine the reabsorption losses, the threshold power has been measured as a function of temperature between 243 K and 413 K. The results are compared with theory assuming a ⁴l level energy of 2110 cm^-1 and an absorption cross-section of δ = 1.15 x 10^-20cm². The comparison shows that reabsorption from the thermally populated ⁴l level is the dominant contribution to the measured losses.     

Dynamics of inversion dumping when nanosecond pulses are amplified in the active medium of a neodymium laser

Results are reported of investigations of the properties of inversion-dumping dynamics in the 10.6-m working transition of the active medium of a neodymium laser amplifying nanosecond pulses. The procedure used to record the population of the lower laser level⁴F_3/2 ⁴I_11/2 by determining the selective absorption from it has made it possible to estimate the relaxation times of a number of neodymium glasses for the⁴I_11/2 transition. A numerical model of the amplification, in which account is taken of the inhomogeneous broadening and of the Stark splitting of Nd³⁺ ion levels in glasses, has yielded the gains and the saturation energies of the active medium as functions of the paameters of the amplified pulses, and permitted a comparison with the experimental data. The question of the maximum effectiveness of inversion extraction in neodymium lasers is considered, and it is shown that when nanosecond pulses are amplified the energy extracted can reach 80%.Translated from Preprint No. 85 of the Lebedev Physics Institute, Academy of Sciences of the USSR, Moscow, 1989.     

Formation of the spectra of multiply charged ions from the plasma of Nd-doped glass irradiated with a neodymium laser

The effect of neodymium ions on laser-induced glass destruction and the formation of the spectra of laser plasma ions is studied by the mass-spectrometric and optical-microscopy methods. As the Nd ion concentration increases, the degree of laser-induced damage in silicate glass increases, the threshold intensity for the glass destruction decreases, the maximum ion charge number Z_max and the maximum ion energy E_max decrease, and the energy spectra of target ions change. All this is related to both the coincidence between the lasing lines and the absorption bands of Nd ions and the intensifi cation of recombination processes in the multicomponent laser plasma.