skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Threshold laser power density for regime transition of a laser absorption wave in a reduced-density air atmosphere

Abstract

Shadowgraph visualization experiments provide measurements of the threshold laser power density (S{sub th}) for the regime transition of a laser absorption wave generated using a transversely excited atmospheric CO{sub 2} pulse laser with various pulse shapes. Results revealed a great influence of the plasma expansion in the direction lateral to the wave propagation on the regime transition by showing that the threshold increased proportionally to the inverse of the beam cross-sectional radius at which the transition occurred (r{sub f,tr}): S{sub th}=C{sub th}/r{sub f,tr}. The proportionality constant, C{sub th}, was insensitive to air densities of 0.2-1.3 kg/m{sup 3}.

Authors:
; ;  [1];  [2];  [2]
  1. Institute of Fluid Science, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai, Miyagi (Japan)
  2. (Japan)
Publication Date:
OSTI Identifier:
20778844
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 88; Journal Issue: 12; Other Information: DOI: 10.1063/1.2183812; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ABSORPTION; AIR; ATMOSPHERES; CARBON DIOXIDE; DENSITY; LASERS; LIGHT TRANSMISSION; PLASMA; PLASMA DIAGNOSTICS; PLASMA EXPANSION; PLASMA WAVES; POWER DENSITY; PULSE SHAPERS; PULSES; WAVE PROPAGATION

Citation Formats

Mori, Koichi, Komurasaki, Kimiya, Arakawa, Yoshihiro, Department of Advanced Energy, University of Tokyo, Kashiwanohara 5-1-5, Kashiwa, Chiba, and Department of Aeronautics and Astronautics, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo. Threshold laser power density for regime transition of a laser absorption wave in a reduced-density air atmosphere. United States: N. p., 2006. Web. doi:10.1063/1.2183812.
Mori, Koichi, Komurasaki, Kimiya, Arakawa, Yoshihiro, Department of Advanced Energy, University of Tokyo, Kashiwanohara 5-1-5, Kashiwa, Chiba, & Department of Aeronautics and Astronautics, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo. Threshold laser power density for regime transition of a laser absorption wave in a reduced-density air atmosphere. United States. doi:10.1063/1.2183812.
Mori, Koichi, Komurasaki, Kimiya, Arakawa, Yoshihiro, Department of Advanced Energy, University of Tokyo, Kashiwanohara 5-1-5, Kashiwa, Chiba, and Department of Aeronautics and Astronautics, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo. Mon . "Threshold laser power density for regime transition of a laser absorption wave in a reduced-density air atmosphere". United States. doi:10.1063/1.2183812.
@article{osti_20778844,
title = {Threshold laser power density for regime transition of a laser absorption wave in a reduced-density air atmosphere},
author = {Mori, Koichi and Komurasaki, Kimiya and Arakawa, Yoshihiro and Department of Advanced Energy, University of Tokyo, Kashiwanohara 5-1-5, Kashiwa, Chiba and Department of Aeronautics and Astronautics, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo},
abstractNote = {Shadowgraph visualization experiments provide measurements of the threshold laser power density (S{sub th}) for the regime transition of a laser absorption wave generated using a transversely excited atmospheric CO{sub 2} pulse laser with various pulse shapes. Results revealed a great influence of the plasma expansion in the direction lateral to the wave propagation on the regime transition by showing that the threshold increased proportionally to the inverse of the beam cross-sectional radius at which the transition occurred (r{sub f,tr}): S{sub th}=C{sub th}/r{sub f,tr}. The proportionality constant, C{sub th}, was insensitive to air densities of 0.2-1.3 kg/m{sup 3}.},
doi = {10.1063/1.2183812},
journal = {Applied Physics Letters},
number = 12,
volume = 88,
place = {United States},
year = {Mon Mar 20 00:00:00 EST 2006},
month = {Mon Mar 20 00:00:00 EST 2006}
}
  • Experiments conducted using a 200TW 60 fs laser have demonstrated up to 720 MeV electrons in the self-guided laser wakefield regime using pure Helium gas jet targets. Charge and energy of the accelerated electrons was measured using an electron spectrometer with a 0.5T magnet and charge callibrated image plates. The self-trapped charge in a helium plasma was shown to fall off with decreasing electron density with a threshold at 2.5 x 10{sup 18} (cm{sup -3}) below which no charge is trapped. Self-guiding however is shown to continue below this density limitation over distances of 14 mm with an exit spotmore » size of 25{micro}m. Simulations show that injection of electrons at these densities can be assisted through ionization induced trapping in a mix of Helium with 3% Oxygen.« less
  • Experiments conducted using a 200 TW 60 fs laser have demonstrated up to 720 MeV electrons in the self-guided laser wakefield regime using pure helium gas jet targets. The self-trapped charge in a helium plasma was shown to fall off with decreasing electron density with a threshold at 2.5x10{sup 18} cm{sup -3}, below which no charge is measured above 100 MeV. Self-guiding, however, is shown to continue below this density limitation over distances of 14 mm with an exit spot size of 25 {mu}m. Simulations show that injection of electrons at these densities can be assisted through ionization induced trappingmore » in a mix of helium with 3% oxygen.« less
  • Based on the nonstationary one-dimensional heat conduction equation, taking the efficient heat removal into account, a thermal absorption wave of laser radiation in the core of an optical fibre is studied. The dependence of the wave velocity on the laser radiation intensity is calculated and threshold intensities at which the thermal wave appears are estimated. It is shown that the wave velocity at high intensities is well described by the formula known from the combustion theory and is proportional to the square root of the radiation intensity. Simple expressions are derived which describe the dependence of the threshold intensity onmore » the effective cooling radius and the dependence of the wave velocity on the radiation intensity (including the near-threshold region). The calculated threshold intensities of laser radiation are approximately twice those needed to obtain the equality between the power coupled to the fibre and the effective heat removal power. The calculated dependences of the wave velocity on the radiation intensity and threshold intensities are in agreement with the experimental data available. (optical fibres)« less
  • The feasibility of using high-power CO[sub 2] lasers [1,2] for machining, development of a laser-propelled jet engine, atmosphere sounding, plasma heating, and other applications is the subject of much research into the physics of the interaction of IR laser emission with gases and condensed media. This research was initiated following the observation of low-threshold optical breakdown of gases near solid surface [3-5], and is extensively reviewed, e.g., in [6,7]. Characteristic features of the action of high-power laser pulses on gaseous targets are evaporation and ionization of the target material, gasdynamic expansion of the erosion plasma [8], and entainment of themore » ambient gas in the laser-emission absorption wave [9].« less
  • This paper examines the propagation of focused femtosecond gigawatt laser pulses in air under normal and reduced pressure in the case of Kerr self-focusing and photoionisation of the medium. The influence of gas density on the beam dimensions and power and the electron density in the plasma column in the nonlinear focus zone of the laser beam has been studied experimentally and by numerical simulation. It has been shown that, in rarefied air, the radiation-induced reduction in the rate of plasma formation diminishes the blocking effect of the plasma on the growth of the beam intensity in the case ofmore » tight focusing. This allows higher power densities of ultrashort laser pulses to be reached in the focal waist region in comparison with beam self-focusing under atmospheric pressure.« less