Determination of Atomic Temperature and Doppler Broadening in a Gaseous Discharge with Population Inversion

Abstract

The Doppler linewidth of the $5d{{\left[\frac{3}{2}\right]}_1}^0-6p{\left[\frac{3}{2}\right]}_1$ transition of xenon (Racah notation) at 2.026 μ in a helium-xenon discharge has been measured directly. Earlier, this transition has been shown to exhibit large optical amplification. The Doppler linewidth determination has been accomplished by measuring the optical gain in a helium-xenon discharge tube as a function of frequency. A short maser oscillator containing the same gas mixture is used as a tunable source of monochromatic radiation. The tuning has been accomplished by changing the length of the optical cavity and thus sweeping a cavity resonance across the Doppler-broadened gain curve. The source oscillator has been operated on a single longitudinal and transverse mode of the cavity to ensure as monochromatic source signal as possible. The measurements have yielded a Doppler linewidth of (210±10) Mc/sec corresponding to an average atomic temperature of 515°K±10%. It is seen that the actual line shape measured coincides very closely to a pure Doppler broadening with a Doppler width of 210 Mc/sec. This indicates that for the $5d{{\left[\frac{3}{2}\right]}_1}^0-6p{\left[\frac{3}{2}\right]}_1$ transition of xenon, the primary source of broadening is Doppler broadening. From this, an upper limit has been assigned to the line broadening due to finite lifetime and due to isotope shift effects.