Coherence Measurement at Different Spatial Points Across High Harmonic Generation Source using Different Spatial Filter

Abstract

AbstractA high spatial coherence of phase‐matched high harmonic generation beam is produced from 30 fs pulses of a Ti:Sapphire laser in 55 Torr argon gas. A harmonic series up to 33rd order is obtained, and a spectrometer is used to measure the source spectrum that peaks at a wavelength of 30 nm. The spatial coherence of this source across spatial position of the beam profile for different choice of spatial filters are investigated by means of Young's double slit experiment. A circular aperture is used as spatial filter with a choice of 2 mm aperture, 100 and 200 µm pinholes, which is placed before the double slit. The interference data of 20 and 50 µm slit separations are recorded, and the results show that these measurements demonstrate good fringe visibility and high spatial coherence. High coherence sources in small scale extreme‐ultraviolet/soft X‐ray radiation are useful for applications in imaging and microscopy. Hence, the evaluation of the fringe visibility is required to characterize the spatial coherence of the source before use in imaging and microscopy application.