Abstract

Commercial diode lasers have emission wavelengths that overlap some absorption xenon lines. They have a complex structure, since natural xenon consists of several isotopes, amongst which Xe(129) (26% of relative abundance) and Xe(131) (21%) with a nuclear spin of 1/2 and 3/2 respectively. The investigated lines are 6s[3/2]₂°–6p[3/2]₂ at 823.16 nm, 6s[3/2]₁°–6p[3/2]° at 828.01 nm, 6s[1/2]₁°–6p[3/2]₂ at 834.68 nm and 6s[1/2]₀°–6p[1/2], at 820.63 nm (Racah notation). The lines at 823 and at 820 nm start from the two metastable levels and are especially suitable for plasma diagnostic. The laser was a Sharp LTO15MDO. The working temperature was controlled by a Peltier module in a +15–30°C range, in order to achieve the right wavelength. A continuous tuning of the laser frequency was obtained by sweeping the injection current. The experimental setup is shown in Fig. 1. A saturating beam, of the order of 1 mW over 10 mm², is chopped at about 1 kHz and sent into a xenon glow discharge. The analysis beam is sent in the opposite direction and is detected by a synchronous phase-sensitive amplifier. The cell was filled with 0.1 torr of natural xenon, and the current in the glow discharge was adjusted in the range 1–10 mA. A small fraction of laser power, extracted by a beam splitter, is sent into a confocal Fabry-Perot with FRS of 300 MHz in order to calibrate the frequency sweep.

© 1994 IEEE