A High Resolution XUV Grating Monochromator for the Spectral Selection of Ultrashort Harmonic Pulses

• Main Authors: Nicola Fabris, Paolo Miotti, Fabio Frassetto, Luca Poletto
• Format: Article
• Language: English
• Published: MDPI AG 2019-06-01
• Series: Applied Sciences
• Subjects: high-order harmonic generation; ultrafast pulses; extreme ultraviolet; high resolution; monochromators
• Online Access: https://www.mdpi.com/2076-3417/9/12/2502

A new monochromator with high spectral resolution in the extreme ultraviolet (XUV) has been developed for high-order laser harmonics selection. The system has three optical elements&#8212;a cylindrical (or spherical) focusing mirror, a uniform-line-spaced plane grating, and a plane mirror. The last element is required to maintain the focus on a fixed vertical slit when the grating subtended angle is changed in order to minimize the spectral defocusing aberration. The parameters of the focusing mirror are determined to introduce a coma that compensates for the coma given by the grating. The possibility of using two interchangeable gratings made the set-up optimized for a broad energy range of 12&#8722;50 eV. As a design test case, the set-up has been applied to a selection of the discrete spectral lines emitted by a gas-discharge lamp as the XUV source, obtaining a resolving power E/<inline-formula> <math display="inline"> <semantics> <mo>&#916;</mo> </semantics> </math> </inline-formula>E &gt; 3000.