Theoretical and experimental study for shortening laser pulse width by pinhole plasma shutter

¹ Institute of Optics and Laser, Malek Ashtar University of Technology, Shahin Shahr 83145/115, Iran
² Institute of Bahonar, Technical and Vocational University, Tehran, Iran
³ Department of Physics, Faculty of Science, University of Isfahan, Hezar Jerib St., Isfahan 81764-73441, Iran

^a e-mail: jaafari39@yahoo.com

Received: 24 December 2014
Revised: 31 January 2015
Accepted: 13 April 2015
Published online: 21 May 2015

Abstract

In this article, a theoretical model is presented to calculate the laser clipped pulse temporal width by the pinhole plasma shutter, and then the model results are compared with the experimental results of CO₂ laser clipped pulses by aluminum and copper pinhole plasma shutters. In this model, it is assumed that the laser clipped pulse width is approximately equal to the sum of the plasma formation time and the plasma propagation time in order to reach from pinhole edges to the pinhole center. Furthermore, we assume that the plasma formation time is approximately equal to the time for the surface temperature of pinhole metal plate to reach the boiling point by absorbing the laser pulse energy. Heat conduction equation is used to calculate the time of plasma formation, and Taylor-Sedov’s model is used to calculate the plasma propagation time to reach the pinhole center. By these assumptions, a relationship has been established between the laser clipped pulse width on the one hand, and thermo-dynamical and optical parameters of plasma shutter and the involved laser optical parameters on the other. Results of this model are in good agreement with experimental results.