Comparative photon statistics of several ultraviolet laser systems determined by transient two-photon absorption

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Abstract
The photon statistics of several different laser systems operating at 226 nm are probed by measuring absolutely the fluorescence following two-photon absorption in atomic oxygen. The integrated fluorescence, obtained by scanning the laser frequency through the two-photon resonance, is theoretically shown to be proportional to G(2)(0)σo(2). The second-order intensity-correlation function at time zero, G(2)(0), characterizes the laser, and σo(2)is a fundamental atomic property. Measurement of the integrated fluorescence permits determination of the relative value of G(2)(0) for each laser. The assumption that G(2)(0) = 1 for one of the lasers, a single-frequency source, allows G(2)(0) for the other lasers to be placed on an absolute scale. The values thereby obtained range from 0.8 ± 0.2 to 3.2 ± 0.4. Different values are obtained when the radiation is generated by frequency mixing or Raman shifting of the same frequency-doubled visible dye laser, suggesting that frequency-conversion processes have a significant effect on G(2)(0).