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61.
R. Giovanelli 《Il Nuovo Cimento D》1995,17(1):61-83
Summary A direct numerical analysis, based on the Lienard-Wiechert potentials, is performed in the present paper, aiming to describe
the relativistic interaction of the electrons composing a high-intensity beam (in Raman regime) both with each other and with
the fields of an FEL structure and of an external resonant travelling electromagnetic wave. The different accelerations, due
to the various forces acting on the charged particles, are seen to give different contributions to the total radiation field,
which are separately considered here. The angular and frequency distributions of the obtained radiation are compared with
the analytic ones deduced in the particular case of a single charge launched along the FEL structure. The interference effect
between the fields of many bunches is seen to cause the shrinkage of the resulting radiation beam. 相似文献
62.
The use of non-contact laser techniques for the generation of ultrasound has extended the limits of the application of traditional ultrasonic techniques. This paper focusses on the use of one such non-contact laser technique, known as ‘optical fibre array’, to generate shear and surface waves. The shear wave experimental directivity pattern results are presented and compared with the theoretical results of a single source and an array source. The experimental directivity results for the surface wave are also presented, and compared with the theoretical results. The data show that the array enhances signal generation in the forward direction for both shear and surface waves. The array gain is also discussed. The receiver for the directivity measurements was a contact piezoelectric transducer. 相似文献
63.
The present study examines the combined effects of chemical reactions taking place between a gas jet and molten metal, the cooling effect of the jet and the evaporation of metal, during a CO2 laser cutting process. A laminar boundary layer approach was used to develop a theoretical model for the oxygen gas jet laser cutting mechanism. An experiment was carried out to monitor the keyhole formation using a video recorder and detect the light emitted from the entrance and exist surfaces of the workpiece using a fibre-optic probe during the cutting process. The experimental study was extended to employ two different workpiece materials (stainless steel and mild steel) at two thicknesses, and varying oxygen assisting gas pressures. It is found that the theoretical model developed in the present study is valid for a cutting speed of about 30 mm s−1 and all jet velocities up to sonic, since the effect of shock is excluded in the model. 相似文献
64.
Operating characteristics of a Q-switched Nd3+: doped single-mode silica fibre with a mechanical chopper as a Q-switching device are presented. Peak powers as high as 16 W with pulse duration of 146 ns are demonstrated. Self-mode-locking in Nd3+:doped fibre is also reported. An output power of 312 W with a centre pulse duration of 4 ns is observed. 相似文献
65.
M. Dell'erba 《Optics & Laser Technology》1985,17(5):260-261
For the first time it has been possible to laser weld copper sheets up to 3 mm thick with a 2 kW cw CO2 laser. The main questions arising from the process are indicated. 相似文献
66.
Six FIR laser lines from CD3OH pumped by the 10R(36) and the 10R(18) CO2 laser lines are assigned to specific rotational energy levels in the excited C–0 stretch state. It is found that their upper laser levels are shifted by a Fermi resonance between the C–0 stretch vibration and the third and forth harmonics of the torsional mode. The Fermi resonance shifts are +0.332 cm–1 and +2.251 cm–1 for the upper laser levels pumped by the 10R(36) and the 10R(18) CO2 laser lines, respectively. Calculated frequencies of the pump and the laser transitions agree with those of the pump CO2 laser lines and the observed FIR laser lines within estimated accuracy. 相似文献
67.
The conditions for realization of the regime of self-oscillations of the intensity of a continuously pumped solid-state laser have been qualitatively analyzed using a system of kinetic equations. It has been established that, in the case where a thin semiconductor layer absorbing light at frequencies close to the lasing frequency is placed into the cavity of such a laser, self-oscillations of its radiation intensity arise as a result of the amplitude-phase self-modulation of the laser light field.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 136–139, January–February, 2005. 相似文献
68.
Baren RE Parrish ME Shafer KH Harward CN Shi Q Nelson DD McManus JB Zahniser MS 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(14):3437-3447
A compact, fast response, infrared spectrometer using four pulsed quantum cascade (QC) lasers has been applied to the analysis of gases in mainstream (MS) and sidestream (SS) cigarette smoke. QC lasers have many advantages over the traditional lead-salt tunable diode lasers, including near room temperature operation with thermoelectric cooling and single mode operation with improved long-term stability. The new instrument uses two 36 m, 0.3 l multiple pass absorption gas cells to obtain a time response of 0.1s for the MS smoke system and 0.4s for the SS smoke system. The concentrations of ammonia, ethylene, nitric oxide, and carbon dioxide for three different reference cigarettes were measured simultaneously in MS and SS smoke. A data rate of 20Hz provides sufficient resolution to determine the concentration profiles during each 2s puff in the MS smoke. Concentration profiles before, during and after the puffs also have been observed for these smoke constituents in SS smoke. Also, simultaneous measurements of CO(2) from a non-dispersive infrared (NDIR) analyzer are obtained for both MS and SS smoke. In addition, during this work, nitrous oxide was detected in both the MS and SS smoke for all reference cigarettes studied. 相似文献
69.
P.?Bhargava M.?Kumar H.?Kumar P.?Pandit R.?Pandey A.?K.?NathEmail author 《Pramana》2004,62(4):923-932
We have studied about the thrust imparted to targets of different materials by pulsed TEA CO2 laser and chopped CW CO2 laser in air and its dependence on different parameters such as laser intensity and pulse duration. We estimated the impulse-coupling
coefficient and compared it with the published results. The mechanism of generation of thrust by laser incident on targets
in air is, in effect, combination of those involved in laser ablation in vacuum and laser-induced air detonation. 相似文献
70.
L. G. Samsonova T. N. Kopylova A. V. Vasil'ev A. V. Reznichenko I. V. Komlev O. I. Chekmacheva 《Journal of Applied Spectroscopy》2001,68(3):427-431
Spectral manifestations of protolytic forms of 1aza2methyl6aminopyrene in ethanol and aqueous solutions are investigated. The ionization constants of the protolytic forms are determined. The generation properties and photostability of a neutral molecule and a cation in excitation by an excimer XeCl laser are studied. 相似文献