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Active deformable diffraction grating can be used for the realization of a time compensated pulses in the XUV. We present the preliminary tests of time compensation operated in the visible at 800nm.
The compensated monochromator consists in a couple of deformable diffraction gratings. The devices consist of a laminar diffractive layer realized by UV lithography that is deposited on the top of a bimorph deformable mirror. The deformable diffraction gratings have been designed to have high optical quality, robustness and compatible with any coating deposition and have only vacuum-compatible materials. We present the characterization of the prototypes in the vacuum ultraviolet and in the visible, showing that the active grating can optimize the beam focusing through its rotation and deformation.
Two active gratings have been mounted in a compensated configuration to realize a grazing-incidence time-delay compensated monochromator for high-order laser harmonics. The wavelength selection is performed through the grating rotation, the intermediate slit carries out the spectral selection of a single harmonic and the spectral focusing is maintained by adjusting the grating radii. The instrument has been initially tested in air with a Ti:Sa laser operated at 800 nm. We have been able to demonstrate that the double-grating configuration with active gratings compensates for the pulse front-tilt. The front-tilt given by the first grating is 1 ps and is reduced to 100 fs after the second stage. The final value is limited by the group delay dispersion of the monochromator within the 10-nm bandwidth of the laser centered around 800 nm.
Active gratings may be considered as a cheaper and more flexible alternative to standard gratings for the realization of extreme-ultraviolet ultrafast monochromators.