Optical emission from laser-produced chromium

and magnesium plasma under the effect of two

sequential laser pulses

V N RAI¹, F Y YUEH² and J P SINGH²

¹Laser Plasma Division, Centre for Advanced Technology, Indore 452 013, India

²Diagnostic Instrumentation and Analysis Laboratory, Mississippi

State University, 205 Research Boulevard, Starkville, MS 39759, USA

E-mail: vnrai@cat.ernet.in

Abstract. Parametric study of optical emission from two successive

laser pulses produced chromium and magnesium plasma is presented. The

line emission from chromium and magnesium plasma showed an increase

by more than six times for double laser pulse excitation than for

single-pulse excitation. An optimum increase in emission intensity

was noted for inter-pulse delay of $\sim$2--3 $\mu$s for all the

elements. The experimental observations were qualitatively explained

on the basis of absorption of second laser pulse in the pre-formed

(by first laser) coronal plasma by inverse Bremsstrahlung process,

which were found responsible for the excitation of more ions and

atoms in the plasma. This process starts as the plasma scale length

becomes greater than the laser wavelength. This study further

indicated the suitability of this technique in the field of elemental

analysis.

Keywords. Laser--plasma interaction; laser-induced breakdown

spectroscopy; plasma heating; visible emission.

PACS Nos 52.38.-r; 42.62.Fi; 52.50.Jm; 32.30.Jc