Development of a VMI spectrometer: first photoelectron spectra obtained with a plasma-based 32.6nm soft x-ray laser.

The “DIRAM” group of the Institut des Sciences Moléculaires d’Orsay (ISMO) led by Annie Klisnick is developing cutting edge technics to fully characterise the pulse temporal structure of modern XUV sources (plasma based soft x-ray laser, X-ray free electron lasers, high order harmonics…). With the support of the OPT2X project, they have build a Velocity Mapping Imager

or VMI. In this type of photoelectron spectrometer, a soft x-ray pulse photo ionises atoms from a gas jet. The photoelectrons are collected and focussed on a micro-channel plate. In this device, the impact points of electrons with the same kinetic energy are forming a circle, as shown in the present figure. During this experiment, the ISMO group took benefit from the high monochromaticity of a  32.6 nm soft x-ray laser to test the VMI and optimise the energy resolution: the thinner the circle, the higher the resolution. This figure of merit is import for future applications. Coupled to an auxilliary IR or THz beam, this device will be a fantastic tool to measure the XUV pulse duration in multiple pulses mode (“cross-correlation”) or even in single shot (“streaking”).

 

Courtesie of Tatyana Sinyakova, Amira Gharbi, Cédric Bommes, Denis Cubaynes and Annie Klisnick

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