Time parameters of optimal emission spectrum registration using millisecond laser pulses

Abstract

Subject and Purpose. Emission spectra of copper-silver alloys are examined for various recording durations. The radiation coming to the photodetector of the spectrometer consists of the reflected laser radiation and the line spectra of vapors formed by the test substance and the heated material in condensed phase. As the spectrum recording time increases, the background component builds up substantially. The purpose of the work is to study the interaction conditions of millisecond laser pulses with the metals and determine recording time parameters of the optical radiation signal in an effort to achieve an optimal recording of the emission spectrum in the range 400…800 nm Methods and Methodology. The main problem with emission spectrum recording is a persistent thermal component. The laser pulse shape for the optimal recording of the emission spectrum is theoretically calculated. The purity of the emission spectrum depends on its recording duration. The matter of persistent thermal component minimization in laser emission analysis implies the optimal shaping of the laser pulse and its maintenance during the operation. Empirical guidelines exist that the optimal time of the emission spectrum recording is 1...3 ms at a laser pulse duration of 5 ms. Results. It has been found that the main factors affecting the intensity ratio of the continuous and line spectra are thermophysical properties of the metal and a laser pulse shape, especially the value of its trailing edge steepness. Lasers with quasi-optimal pulse shape enable us to increase a maximum frequency of optimal emission-spectrum recording in laser emission analysis. For a 3 ms duration and a 10 J energy of the pulse, the maximum laser frequency at which the laser emission analysis is still possible can be 70...75 Hz. Conclusion. The process of laser emission analysis optimization consists in optimal laser pulse shaping and its maintenance during the operation.