Development of the iterative correction method in laser interferometry for plasma diagnostics

Laser interferometry is widely used for plasma density diagnostics. However, the result can give inaccurate values in some cases. For example, a near-critical high-density plasma with a steep density gradient can deflect the laser beam, leading to a deformed interferogram. As a result, the plasma density profile in space, which is obtained from the deformed interferogram, can lead to an inaccurate density reconstruction. In this paper, we propose a novel method to solve the problem, which is based on iterative corrections using the Hamiltonian ray optics in the analysis of the deformed laser interferogram. We employed this method for spatio-temporal diagnostics of a laser-produced plasma and demonstrated that the method performs well for high-density (n_e ∼ 10²¹ cm^-3) plasmas with steep density gradients, where the plasma was generated by focusing a 1 TW/35 fs Ti:sapphire laser pulse on the surface of an aluminum target, and a weak probe laser pulse was used in the interferometer.