REFRACTIVE-INDEX PROFILING ACROSS A CANDLE FLAME USING SPECKLE TECHNIQUES

Refractive index profiles have been obtained at different heights in t he region above a candle flame both theoretically and experimentally b y means of double and multiple exposure speckle photography. Improved fringe visibility has been achieved in the case of the multiple exposu re technique giving rise to accurate measurement of the refractive ind ex. Theoretical analysis shows that the resulting speckle pattern is e quivalent to the ordinary pattern convolved with a function representi ng the effect of light deflection, while the interference pattern obta ined is modulated by a background representing the autocorrelation fun ction of the diffuser.