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Updated: May 9, 2026

An Experimental Protocol for Femtosecond NIR/UV - XUV Pump-Probe Experiments with Free-Electron Lasers
Published on: October 23, 2018
High-precision spectroscopy with counterpropagating femtosecond pulses
Itan Barmes1, Stefan Witte, Kjeld S E Eikema
1Department of Physics and Astronomy, LaserLaB, VU University, de Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
Abstract:
An experimental realization of high-precision direct frequency comb spectroscopy using counterpropagating femtosecond pulses on two-photon atomic transitions is presented. The Doppler broadened background signal, hampering precision spectroscopy with ultrashort pulses, is effectively eliminated with a simple pulse shaping method. As a result, all four 5S-7S two-photon transitions in a rubidium vapor are determined with both statistical and systematic uncertainties below 10(-11), which is an order of magnitude better than previous experiments on these transitions.
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