A delayed-coincidence technique has been used to measure the lifetime of the
5d6p1F3 state of atomic barium. An intermediate,
6s5d1D2 metastable state of barium atoms in an atomic beam was populated by electron bombardment, and a pulsed cw laser was employed to excite atoms from the metastable state to the
5d6p1F3 state. A time-to-amplitude convertor was used to measure the time distribution of the fluorescent light. The value obtained for the lifetime was (44.5\ifmmode\pm\else\textpm\fi{}1.8) nsec.
Expressions are derived for the intensity correlations or degrees of second-order coherence within and between two light beams of different frequency generated by cascade emission from a three-level atom. The atoms are assumed to be excited by two monochromatic coherent light beams in resonance with the upper and lower pairs of levels that constitute the triplet. The two emitted beams individually show photon antibunching and the correlation between the beams shows another complementary kind of non-classical effect. It is suggested that measurements on the system described here would provide more detailed information on quantum effects in cascade emission than previous observations with direct excitation to the uppermost atomic level by electron bombardment.
An apparatus is described which has produced and detected narrow Hβ and Hγ spectral lines in an electron-bombarded atomic hydrogen beam. Hydrogen atoms produced in an electrodeless 50-Mc/sec discharge in wet hydrogen, diffused through a slit in the discharge tube wall to form a beam in a vacuum chamber. An electron gun bombarded the atomic beam along an axis perpendicular to the beam and optical axes; light produced in the decay of atoms excited by the bombardment was analyzed by a pressure-scanned Fabry–Perot interferometer and detected by a cooled photomultiplier. The output pulses from the photomultiplier were amplified and then stored as counts in a 400-channel analyzer. Linewidths characteristic of a source at about 33°K were obtained; however, the signals were so small and the line shapes sufficiently uncertain that no precise wavelength measurements could be made.