Real time measurement of the electron density of a laser generated plasma using a RC circuit

Abstract A Nd:YAG laser pulse was focused, in air or on a Cu target, between the plates of a planar charged capacitor. The plasma generates a transient redistribution of the electrical charges on the plates that can be easily measured as a voltage drop across a resistor connected to the ground plate. At the same time, the Stark broadening of the Hα spectral line (656.3 nm) obtained from the optical emission spectrum of the plasma was measured. In this work, we show that the peak of electrical signal measured on the resistor is, in the energy range of our laser (30 mJ to 220 mJ) and at time delays typical of Laser-Induced Breakdown Spectroscopy applications (500–5000 ns), univocally related to the temporal evolution of the Stark broadening of the Hα line. Therefore, after a proper calibration depending on the material and the experimental geometry, the peak of the electrical signal can be used to predict the temporal evolution of the electron density of the generated plasma.

[1]  Measurement of the electrical size of a laser-induced plasma in a uniform field , 2005 .

[2]  Marco A. Gigosos,et al.  New plasma diagnosis tables of hydrogen Stark broadening including ion dynamics , 1996 .

[3]  A. Srećković,et al.  The first measured Mn II and Mn III Stark broadening parameters , 2006 .

[4]  J. A. Aguilera,et al.  Application of laser-induced plasma spectroscopy to the measurement of Stark broadening parameters , 2006 .

[5]  R. Russo,et al.  Invited paper Observation of plasma shielding by measuring transmitted and reflected laser pulse temporal profiles , 1996 .

[6]  M. Dimitrijević,et al.  The electron impact broadening parameters in hot star atmospheres: Mn II, Mn III, Ga III, Ge III and Ge IV lines , 1998 .

[7]  G. Cristoforetti,et al.  Evaluation of self-absorption coefficients of aluminum emission lines in laser-induced breakdown spectroscopy measurements , 2005 .

[8]  Jagdish P. Singh,et al.  Laser-induced breakdown spectroscopy , 2007 .

[9]  Takao Kobayashi,et al.  Characteristics of Induced Current Due to Laser Plasma and Its Application to Laser Processing Monitoring , 2004 .

[10]  Mayo Villagrán-Muniz,et al.  Characterization of pulsed laser generated plasma through its perturbation in an electric field , 2002 .

[11]  Stefano Legnaioli,et al.  Evaluation of self-absorption of manganese emission lines in Laser Induced Breakdown Spectroscopy measurements , 2006 .

[12]  T. M. E. Sherbini,et al.  Measurement of electron density utilizing the Hα-line from laser produced plasma in air , 2006 .

[13]  Martin A. Uman,et al.  Electron-Density Measurement in Lightning from Stark-Broadening of Hα , 1964 .

[14]  H. Griem.  Principles of Plasma Spectroscopy , 1997 .

[15]  M. Hong,et al.  Plasma diagnostics at early stage of laser ablation , 1999 .

[16]  William L. Barr,et al.  Spectral Line Broadening by Plasmas , 1975, IEEE Transactions on Plasma Science.