Digital holographic interferometry for diagnosing the density profile of laser-produced collisionless shock

A digital holographic interferometry based on Fresnel biprism has been developed to measure the electron density profile of laser-produced collisionless shocks in laboratory, which used the Fourier transform method to solve the wrapped phase. The discontinuous surfaces of shocks will produce the break and split of the interference fringes, which cannot be processed by the conventional path-following phase unwrapping algorithm when reconstructing the real phase of the plasma. Therefore, we used a least-squares method to extract the real phase, which is proportional to the line-integrated electron density. We obtained fine density profiles of collisionless shocks in the line-integrated density region around 10¹⁸ cm⁻² with a density resolution of 3.38 × 10¹⁶ cm⁻². The shock structure is in well agreement with that measured by the dark-field schlieren methods and that predicted by shock jump condition. Synthetic holograms are used to confirm the effectiveness of our algorithm, and it is shown that correct results can still be obtained even if part of the diagnostic light is refracted out of the optical system by the shock.