Luminescence characteristics of new substituted coumarins

Fluorescence spectra at 298 and 77 K and phosphorescence spectra at 77 K have been measured for five new compounds. Fluorescence and phosphorescence quantum yields have been measured by comparison with a standard (8-methoxypsoralen). Phosphorescence lifetimes at 77 K have been found for 2-hydrazyl-3,4-cyclopentyl-14,14-dimethylpryanocoumarin (1.60 msec); 2-hydrazyl-3,4-cyclohexyl-7-methoxycoumarin (1.35); 3,4-phenyl-4′,5′-cyclohexylpsoralen (2.50); 4′-methyl-3,4-cycloheptylpsoralen (1.10); and 4′,5′-dimethyl-3,4-cyclohexylpsoralen (1.25). The basic channel of energy deactivation for 3,4-phenyl-4′,5′-cyclohexylpsoralen; 4′-methyl-3,4-cycloheptylpsoralen; and 4′,5′-dimethyl-3,4-cyclohexylpsoralen is radiative transfer. Energies of the lowest excited triplet states have been calculated using an INDO/S quantum-chemical method.     

Calculation of some characteristics of substituted benzenes

Compounds of the C₆H₅XY₁Y₂ type have been examined, and the dependence of energy and wave functions ona _Y, ß_XY and ß_CX has been studied. Numerical calculations have been carried out and tables compiled.In conclusion the authors would like to thank N. A. Prilezhaev and V. I. Danilov, who helped us daily in carrying out this work.     

Threshold gain characteristics of the asymmetrical distributed bragg-reflector laser

The asymmetrically distributed Bragg-reflector (DBR) laser is analyzed by using the coupling-mode theory. Threshold solution for the required laser gains are presented. Numerical computations show that the asymmetrical geometry of the laser considered here allows for optimization of the laser characteristics such as lowering the threshold gains and providing the unidirectional operation.     

Spectral and laser gain characteristics of solvated species of scopoletin

This paper reports the spectral and small signal laser gain characteristics of various solvated species of scopoletin. The spectra show that a methoxy substituent in the sixth position of 7-hydroxy coumarin precludes the formation of excited state tautomers and leads to a large overlap of the fluorescence bands of various species. This is also reflected in the gain, and the total gain bandwidth of scopoletin is small compared to that obtainable in 4 MU or 7 HC, utilizing the solvation characteristics of these dyes.     

Approximative evaluation of CO2 laser gain switch pulse characteristics

Gain switch laser light pulse profile has usually the multipeak structure. Peak intensities, lengths and delays of pulses are significant characteristics of laser output. An approximative evaluation of the characteristics based on the rate equation analysis is presented. The validity of the approximation is testified via numerical integration of starting equations for several physical parameters.     

Operational characteristics of dual gain single cavity Nd:YVO4 laser

Operational characteristics of a dual gain single cavity Nd:YVO₄ laser have been investigated. With semiconductor diode laser pump power of 2 W, 800 mW output was obtained with a slope efficiency of 49%. Further, by changing the relative orientation of the two crystals the polarization characteristics of the output could be varied. In particular by keeping the two Nd:YVO₄ crystals with their c-axes orthogonal to each other and adjusting the gain of the crystals so that both operate at approximately the same power level, completely unpolarized beams could be obtained.     

Solvent effects on the spectral and gain characteristics of a DAMC dye laser

Small signal gains of a 7-diethylamino 4-methyl coumarin (DAMC) dye laser in a variety of solvent environments have been experimentally determined from the super-radiant emission of these dye solutions. The study suggests that polar, hydrogen-bonding solvents appear to be most suitable for producing high gain in the DAMC dye laser.     

Effect of gain media characteristics on the formation of soliton molecules in fiber laser

Erbium doped fiber and Er³⁺/Yb³⁺ codoped phosphate glass fiber are used as the laser media, respectively, to achieve self-started mode-locking based on nonlinear polarization rotation. It is found that the formation of the soliton molecule is the popular phenomenon in fiber laser. The laser media with high gain coefficient and short length is benefit of the formation of the soliton molecule at fundamental repetition rate and will generate evident soliton molecule pulse profile with strong accompanied structures. The achievement of soliton molecule owes to the partial operation of polarization filter effect in laser cavity due to the weak nonlinear polarization rotation in gain media with high gain coefficient and short length.     

有源耦合腔激光器锁模特性研究

本文在理论上首次发现有源耦合腔激光器的自启动锁模和时域调制特性,并对其进行了全面的分析和计算.对有源耦合腔激光器的自启动锁模机制和时域调制特性给予详尽的数值计算结果和清晰的物理图象解释,提出在有源耦合腔锁模激光器中可用连续泵浦源代替锁模泵浦源,而且有产生更短的光脉冲可能性.     

Absolute time-resolved x-ray laser gain measurement

We present the first direct measurement of the time evolution of the gain of a soft x-ray laser amplifier. The measurement is based on the injection of a seed pulse, obtained by high-order harmonic generation, into an x-ray laser medium. Strong amplification occurs when the seed pulse is synchronized with the gain period. By precisely varying the delay between the x-ray laser plasma creation and the seed pulse injection, the actual temporal evolution of the soft x-ray amplifier gain is obtained with a subpicosecond resolution.     

The impact of nonequilibrium gain in a spectral laser diode model

We describe the inclusion of nonequilibrium gain into a self-consistent 2.5D CW spectral laser diode model and report on the use of this model to investigate the origin of gain compression in a 975 nm high-brightness tapered QW laser diode. Nonequilibrium gain is calculated using a dynamic gain model, which simulates the dynamic relaxation of the quantum well carrier energy distributions under the influence of steady-state electrical and optical excitation. Calculated gain and spontaneous emission spectra are included in the laser model via parameterised look up tables. Both simulated and experimentally measured intracavity spontaneous emission spectra show an increased carrier density and a blue-shift of the gain maximum with increasing bias caused by carrier heating and spectral hole burning. The accurate incorporation of nonequilibrium gain compression is therefore vital for the accurate prediction of the operating characteristics of these devices and for the experimental determination of the active region temperature.     

高功率激光光束特性对激光加工的影响

决定光与物质相互作用的激光束的波长、入射角、偏振特性以及时间和空间特性是激光材料加工的主要光束特性。激光束的光束质量是其空间特性的量化反映。通过对两种不同激光加工系统输出激光光束质量进行测量和计算,根据多模激光束的聚焦理论,以及对激光深熔焊接实验结果的分析,研究了光束质量对深熔焊接焊缝成形的影响。结果表明,光束质量对聚焦光束的焦斑、聚焦角和焦深的影响不仅体现了激光源的可聚焦性,而且也标志了激光源的可加工能力,这是聚焦系统和焦点位置在选择过程中应该考虑的重要因素。     

Flashlamp-pumped high gain laser dye amplifiers

Flashlamp-pumped organic dyes (e.g. Rhodamine 6G) are considered as an amplifying medium. Calculations have been made for optimising the small signal gain and the concentration of the active molecules for given dye cell dimensions. Under the assumption of weak pumping the maximum useful gain is only dependent on the geometrical dimensions of the cell. An optimum concentration could be derived resulting from the compromise of uniform gain distribution over the cylindrical cross section of the medium and maximum absorption of pump power. It is shown that the near uv-radiation of the flashlamp is very efficient in achieving the desired inversion. Some experiments supporting the theoretical results are given.     

Multiplasmon laser gain in low-dimensional systems

The light absorption and laser gain in quantum wells are calculated using the cumulant expansion method and the fluctuation-dissipation theorem with allowance made for the strong Coulomb interaction of charge carriers. It is shown that the multiplasmon transitions result in a smoothening of the absorption spectrum and a shift in the absorption edge toward the long-wavelength range. The theoretical laser gain spectra are in agreement with the available experimental data. For In_0.05Ga_0.95As quantum wells, the laser gain g = 50 cm^?1 is reached at an electron density nd₀ = 1.64 × 10¹² cm^?2.     

Experimental investigations on energy-transfer characteristics and performance of some laser dye mixtures

Energy transfer from both Coumarin 120 (C120) and p-Bis(o-methylstyryl)-benzene (Bis-MSB), energy donors, to coumarin 7(C7) (acceptor) individually has been studied by steady-state emission measurements in methanol. The dye laser characteristics of the above-mentioned dyes have also been studied with respect to the energy transfer mechanism in the same solvent using a pulsed nitrogen laser as a pumping source. The large values of the critical transfer distances, R₀, indicate that the dominant mechanism responsible for energy transfer is due to long-range dipole–dipole interaction between the excited donor and ground state acceptor molecule. Both photophysical and photochemical stability of the donors has been examined under the effect of N₂ laser pumping.     

Automatic gain control of semiconductor laser amplifiers

A new approach to automatic gain control has been demonstrated and a signal polarization independent operation over a 35-nm wavelength range at a gain level of 17 dB has been obtained.     

Automatic gain control of semiconductor laser amplifiers

A new approach to automatic gain control has been demonstrated and a signal polarization independent operation over a 35-nm wavelength range at a gain level of 17 dB has been obtained.     

Output mode characteristics of an in-phase locked gain waveguide array CO2 laser

In this paper,experimental and theoretical studies of the output mode characteristics of an in-phase locked gain waveguide array CO 2 laser are reported.The experimental results of the optical oscillation mode frequency,the far-field intensity distribution and the burnt pattern of the sliced waveguide array laser are obtained.A revised mode expression of the rectangle waveguide,which is suited for this waveguide array CO 2 laser,is proposed.The theoretical simulation results based on the revised mode expression are shown to be in good agreement with the experimental results.