Coherent broadband light effects in grating spectrometer studies of emission from alkali atoms at surfaces.
With ordinary grating spectrometers, strong bands that are due to broadband coherent light emission from samples containing various amounts of alkali atoms can be observed. The coherent light is proposed to be emitted by the alkali Rydberg states that are easily formed in these systems. The edges of the bands are observed at angles corresponding to low numbers of standing waves along the grating surface and perpendicular to it. This type of band is observed both with thermal sources and with broadband light sources created by pulsed laser light, and it is observed only with s-polarized (TE-mode) light. The band intensities are independent of the entrance slit width in the spectrometer, which shows that strong interference effects exist. The number of interference fringes observed on top of the most intense band is directly proportional to the width of the entrance slit. The time-resolved signal shows that large photon peaks from thermal sources are emitted in bursts within 2 mus, probably corresponding to the lifetime of the emitting Rydberg states and Rydberg clusters.
Holmlid
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Reaction Dynamics Group, Department of Chemistry, Göteborg University, Sweden. holmlid@phc.chambers.se