Renormalizing the high-harmonic interference via double-slit and grating

A method to utilize high-harmonic interference in Young's double-slit followed by a grating holds promise for precisely measuring the refractive-index spectrum in the extreme ultraviolet (EUV) region. The measurement is currently bottlenecked by the time it takes to fit the Fresnel interference patterns. The conventional fitting procedure, involving multiple numerical integrals for evaluating the EUV propagation through the slit and grating, takes ≳30min on a standard laptop computer, while the data acquisition time is ∼200s. Here, we apply an analytic Gaussian integral and bypass one of the numerical integrals associated with the grating. The analysis reduces to evaluating a renormalized EUV propagation in a simple double-slit interferometer, and the estimated fitting time on a laptop becomes as short as 112 s. Our study enables real-time analysis during measurements, facilitating mass optical-data collection of EUV lithography materials.