Abstract
Laser analytical methods are usually preferred for supersonic jet spectroscopy since a high photon flux across a narrow spectral region is required for sensitive detection. Lamp sources have been used for fluorescence excitation, but their performance has been poor due to low photon fluxes. The major problems associated with lamp excitation lie not in the radiant output of the lamp but in the ability to transfer the radiation to the experiment. For example, commercial 1000-W xenon arc lamp systems can deliver up to 40 mW/nm in a "collimated" beam. For a 1-cm<sup>−1</sup>-wide region in the visible, this would represent the same photon flux as a pulsed laser system delivering 120 μJ/pulse at 10 Hz. To put this value in perspective, we normally use 20 to 50 μJ/pulse for fluorescence excitation experiments. Clearly, an acceptable photon flux is available from the lamp. Trouble arises, however, when a narrow spectral region must be isolated from the lamp radiation. The conventional approach is to use a monochromator with narrow slits. The poor optical throughput of this method, along with difficulties in transferring the output radiation into the vacuum chamber through a baffle system, results in low photon fluxes through the expansion.
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