Spectroscopic investigation of laser-initiated low-pressure plasmas in atmospheric gases.
Laser-initiated breakdown of N2, O2, and Ar has been investigated at sub-atmospheric pressures using a pulsed (10-nsec) Nd:yttrium aluminum garnet (Nd:YAG) laser at 1.06 μm. Breakdown thresholds have been determined from 3 to 760 Torr, and spectral analysis of the plasma emission has been carried out at 10 and 125 Torr over the 300–600-nm range. Sharp spectral features arising from highly excited singly and multiply charged ions are reported as well as an underlying continuum at intermediate pressure. Time-resolved measurements indicate a complex kinetic dynamic optical behavior.
Pulsed-laser-generated rare-gas plasma as a light source in the vacuum ultraviolet.
The plasma generated by focusing a 20-Hz, 330-mJ, Nd:YAG laser pulse in a rare gas at pressures from 1 to 6 bars is proposed as a source of a VUV continuum giving as many as 10(9) photons nm(-1) sec(-1) near 170 nm. Its stability makes it suited to VUV spectrophotometry. The pulse duration, ranging from 20 nsec for Ne to 40 nsec for Kr, should also permit its use in time-resolved spectroscopy.
Spectroscopic Studies of a Laser‐Produced Plasma in Helium
A highly ionized plasma was produced by laser‐induced breakdown in helium at a pressure of 360 Torr. Line and continuum emission from the plasma were studied as a function of time and of position along the axis of the laser beam. Plasma parameters were then deduced from Stark widths, line‐to‐continuum, and line‐to‐line intensity ratios. The applicability of the various methods used to the case of a rapidly decaying laser‐produced plasma is discussed. The decay of the plasma is analyzed and the observed decay coefficients are compared with theoretical calculations.