燃烧物理学基础

气体动力学基本原理 A编 气体动力学诸方程

目录

A laser-diode-pumped acoustic-optic Q-switched Nd:YVO4 slab laser with a hybrid resonator

A 32.1 W laser-diode-stack pumped acoustic-optic Q-switched Nd:YVO4 slab laser with hybrid resonator at 1064 nm was demonstrated with the pumping power of 112 W and repetition rate of 40 kHz, the pulse duration was 32.47 ns. The slope efficiency and optical-to-optical efficiency were 37 and 28.7%, respectively. At the repetition rate of 20 kHz and pumping power of 90 W, the average output power and pulse duration were 20.4 W and 20.43 ns, respectively. With the pumping power of 112 W, the beam quality M-2 factors in CW operation were measured to be 1.3 in stable direction and 1.6 in unstable direction.

Ultrafast electronic excitation in CaF2 crystals

A new pump and probe experimental system was developed, the pump pulse duration of which is stretched and is much longer than that of the probe pulse. Using this system, time-resolved electronic excitation processes and damage mechanisms in CaF2 crystals were studied. The measured reflectivity of the probe pulse begins to increase at the peak of the pump pulse and increases rapidly in the latter half of the pump pulse, when the pump pulse duration is stretched to 580fs. Our experimental results indicate that both multiphoton ionization and impact ionization play important roles in the generation of conduction band electrons, at least they do so when the pump pulse durations are equal to or longer than 580fs.

Phase-dependent properties for absorption and dispersion in a closed equispaced three-level ladder system

It is shown that in a closed equispaced three-level ladder system, by controlling the relative phase of two applied coherent fields, the conversion from absorption with inversion to lasing without inversion (LWI) can be realized; a large index of the refraction with zero absorption can be gotten; considerable increasing of the spectrum region and value of the LWI gain can be achieved. Our study also reveals that the incoherent pumping will produce a remarkable effect oil the phase-dependent properties of the system. Modifying value of the incoherent pumping can change the property of the system from absorption to amplification and enhance significantly LWI gain. If the incoherent pumping is absent, we cannot get any gain for any value of the relative phase. (c) 2007 Elsevier GmbH. All rights reserved.

Single sub-100 attosecond pulse generation in a two-colour time-gating laser field

We theoretically propose a method of generating a single sub-100 attosecond (as) pulse with a two-colour time-gating laser field. The field is synthesized by an 8 fs/800 nm (three optical cycles) pulse and a 24 fs/2400 nm (three optical cycles) pulse with an optimal time delay between them. In our simulation, we obtain a supercontinuum with an extremely broad spectrum of 150 eV and generate an isolated attosecond pulse with 96 as pulse duration without any dispersion compensation.

Generation of sub-5 fs pulses through cascade of filamentation and hollow fiber compression

A pulse-compression scheme based on cascade of filamentation and hollow fiber has been demonstrated, Pulses with duration of sub-5 fs and energy of 0.2 mJ near 800 nm have been generated by compressing the similar to 40 fs pulses from a commercial laser system. This method is promising to generate near monocycle high energy pulses. [GRAPHICS] Measured autocorrelation curve of the final compressed pulses with duration of sub-5 fs (black solid) and the simulated autocorrelation curve of 4.6 fs pulse near 800 rim (red dash) (C) 2008 by Astro Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA

Inter-stage line ratio of He- and Li-like Ti emissions for the electron temperature measurement

Under coronal conditions, the steady state rate-equations are used to calculate the inter-stage line ratios between Li-like Is(2)2p(P-2(3/2))-> 1s(2)2s -> ((2) S-1/2) and He-like 1s2p (P-1(1))-> 1s(2) (S-1(0)) transitions for Ti in the electronic temperature ranges from 0.1 keV to 20 keV. The results show that the. temperature sensitivities are higher at the electronic temperature less than 5000 eV and the temperature sensitivities will decrease with the increase of electronic temperature.

Effect of plasma temperature on electrostatic shock generation and ion acceleration by laser

The effect of plasma temperature on electrostatic shock generated by a circularly polarized laser pulse in overdense plasma is studied by particle-in-cell simulation. Ion reflection and transmission in the collisionless electrostatic shock (CES) are investigated analytically. As the initial ion temperature is varied, a distinct transition from the laser-driven piston scenario with all ions being reflected to the CES scenario with partial ion reflection is found. The results show that at low but finite temperatures the ions are much more accelerated than if they were cold.

Study of dynamical behaviour and fermionization of a bosonic gas in funnel potential

This paper presents a funnel external potential model to investigate dynamic properties of ultracold Bose gas. By using variational method, we obtain the ground-state energy and density properties of ultracold Bose atoms. The results show that the ultracold Bose gas confined in a funnel potential experiences the transition from three-dimensional regime to quasi-one-dimensional regime in a small aspect ratio, and undergoes fermionization process as the aspect ratio increases.