Microwave reflections from a VUV laser produced plasma sheet

Summary form only given. A Vacuum Ultra-Violet (VUV) laser pulse is used to create a plasma sheet in a low-ionization-energy organic gas. Microwaves from a highly directive X-band horn antenna impinge on the sheet where they are reflected. A bi-static antenna system is used for transmitting and receiving the microwave radiation. Both heterodyne and homodyne detection systems are investigated for maximum sensitivity. Reflected signals are measured for amplitude and phase analysis. Comparable amplitude and phase shifts are noted when compared to an aluminum conducting sheet placed in the same position as the plasma. The working gas is tetrakis(dimethylamino)ethylene (TMAE) with an ionization energy of 5.36 eV. The ionizing source is a VUV excimer laser operating at 193 nanometers (6.4 eV). The laser and plasma properties are diagnosed by an optical detection system and by Langmuir probes. The laser beam is transformed into a sheet using VUV coated Suprasil lenses (96% transmission efficiency). A plasma sheet with a peak density of 2.5/spl times/10/sup 13/ cm/sup -3/ and T/sub e/=0.8 eV is formed. Additional measurements of transmitted signals are utilized to determine plasma density and collision frequency. A computer model of the microwave transmission and reflection levels has been developed to optimize reflected signal levels as a function of density and thickness and to interpret experimental results. Comparison between the experimental results and the model show that this system is attractive for use as a microwave reflector.