Improvements in combined laser interferometry technique for laser ablation research

Imaging and quadrature phase shift interferometry of laser irradiated surface and laser-induced gas-plasma flows has been used to investigate laser ablation processes in a number of works. Processing of experimental data obtained using of these techniques reveals some data insufficiency or results ambiguity, e.g. caused by surface shielding or unknown ablated mass flow rate. Previously, we used Michelson scheme for surface and Mach-Zehnder – for plume interferometry. Although some valuable results were obtained, there were several restrictions and complications in techniques implementation due to temporal coherence of probing ultra-short laser pulses, reflective properties of irradiated surface and probing wavelength to ablation crater ratio. Also beam-splitting interferometers are not always suitable for multi-wavelength probing and are sensitive to optical paths fluctuations. To solve these problems we investigated performance of the modified Nomarski scheme for multi-wavelength plume and speckle surface interferometry. (author)