REFRACTIVE-INDEX PROFILING ACROSS A CANDLE FLAME USING SPECKLE TECHNIQUES

Speckle techniques for refractive index measurements are analyzed theo retically. It is demonstrated that the resulting speckle pattern is eq uivalent to the ordinary pattern convolved with a function representin g the effect of light deflection, while the obtained interference patt ern is modulated by a background representing the autocorrelation func tion of the diffuser. The technique is applied to the region above a c andle flame. An improved quality of the interference fringes is achiev ed with a multiple-exposure technique.