Coherence length measurement for femtosecond lasers using digital holography and statistical fringe analysis

Abstract

A technique to measure the temporal coherence length of a femtosecond laser using digital holography and statistical fringe analysis is demonstrated experimentally. A Michelson-type holographic setup at a condition of near zero-path length difference is constructed with a small tilt between the mirrors forming a parallel fringe digital hologram. Due to the short coherence of the femtosecond laser, the hologram fringes and reconstructed phase map appear only within a local area in the transverse plane. The coherence length is then obtained based on the average width of the phase map area determined using a statistical fringe analysis algorithm, fringe spacing and the central wavelength.