Abstract
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—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 12–50 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/ Δ E > 3000.
Highlights
The recent upgrade of high-harmonic (HH) generation in gases towards repetition rates of50–100 kHz (10–200 μJ pulse energy), obtained with conventional Ti:Sapphire fs laser amplifiers, allowed a reduction of the single-pulse photon flux with the benefit of reduced experimental data acquisition time, and mitigates undesired phenomena such as photoelectron space-charge effects revealed during time-resolved pump–probe experiments on solid samples [1,2,3]
We demonstrate the use of an optical configuration which originates from the variable-line-spaced (VLS) grating monochromator, that uses a plane variable line-space (VLS) grating illuminated by the light converging from a concave focusing mirror and diffracts the radiation toward the exit slit
The monochromator covers a broad spectral range through the selection of one among two or more interchangeable plane gratings (PGs), illuminated along the direction perpendicular to the grooves by the converging rays coming from a focusing cylindrical mirror (CM)
Summary
The recent upgrade of high-harmonic (HH) generation in gases towards repetition rates of. The obtained intrinsic narrow-bandwidth allows time-resolved angle-resolved photo-emission spectroscopy (TR-ARPES) studies of transition metals and other materials with small lattice constants (such as graphene), a bandwidth as low as few tens of meV is required to discern the electronic structure This property can be achieved by means of synchrotron beamline setups [7] or plasma lamps [8] and can be extended to HHs generation with high-repetition laser drivers. The tunability requirement among different harmonics in a broad spectral range, i.e., from 10 to 100 eV can be satisfied with a grating monochromator as the output coupler at generation side For these purposes, a grating monochromator with high energy resolution, i.e., below 20 meV bandwidth, has been realized using an innovative cost-effective design. Minimization of aberrations, resolution, and throughput performances of the realized three-elements configuration are presented, demonstrating the good performance of the monochromator despite of the use of simple optical components, which are available on the market with high optical quality, at modest prices
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