Effect of spatial incoherence of the laser in photon-correlation spectroscopy

Abstract

The effects of spatial incoherence of the laser output in photon-correlation spectroscopy are examined both theoretically and experimentally. It is shown that, when several transverse cavity modes oscillate simultaneously at different frequencies, the amplitude of fluctuations in the intensity of scattered light can be reduced significantly. For simultaneous operation of TEM₀₀ and TEM₀₁* (doughnut) modes the reduction of the zero-time-delay intercept g⁽²⁾(0) − 1 [where g⁽²⁾(τ) is the normalized intensity-correlation function] can amount to a factor of 3. The effects are shown to be particularly marked when high-gain ion lasers are used, and hitherto unexplained apparently random changes of intercept have been found. Possible implications of these observations for speckle applications, holography, and other forms of coherent optical processing are pointed out.