High brightness, ultra-narrow linewidth Hg source for diagnostics

Recent work has shown that imaging Rayleigh scattering through atomic and molecular filters provides a very attractive method for flow field diagnostics, including the imaging of temperature, density, and in some cases, velocity fields. The extension of atomic filter technologies to imaging Raman scattering is also of interest. Both Rayleigh and Raman scattering are dramatically stronger in the ultraviolet due to both resonance enhancement and to the frequency to the fourth scaling of the cross section. The development of a high-power, narrow linewidth source in the ultraviolet is, therefore, of significant interest. Mercury absorption cells operating at 254 nm are well suited for these diagnostics. This paper demonstrates that a short pulse-driven, high efficiency mercury lamp can be used to generate ultra-narrow linewidth radiation at 254 nm. The lamp is driven at 9 kHz with high voltage (30 kV), 2 nsec pulses and the spectrum of the radiation seen after several hundred nsec is almost purely the 254 nm line. The linewidth of this mercury lamp is narrow enough so it can be used in conjunction with the mercury vapor filter for both Rayleigh and Raman diagnostics.