Abstract
We report the generation of circularly polarized high order harmonics in the extreme ultraviolet range (18-27 nm) from a linearly polarized infrared laser (40 fs, 0.25 TW) focused into a neon filled gas cell. To circularly polarize the initially linearly polarized harmonics we have implemented a four-reflector phase-shifter. Fully circularly polarized radiation has been obtained with an efficiency of a few percents, thus being significantly more efficient than currently demonstrated direct generation of elliptically polarized harmonics. This demonstration opens up new experimental capabilities based on high order harmonics, for example, in biology and materials science. The inherent femtosecond time resolution of high order harmonic generating table top laser sources renders these an ideal tool for the investigation of ultrafast magnetization dynamics now that the magnetic circular dichroism at the absorption M-edges of transition metals can be exploited.
Highlights
High order harmonic generation (HHG) has attracted significant attention as a compact, femtosecond pulsed, coherent light source covering the extreme ultraviolet (EUV) photon energy range [1]
We report the generation of circularly polarized high order harmonics in the extreme ultraviolet range (18–27 nm) from a linearly polarized infrared laser (40 fs, 0.25 TW) focused into a neon filled gas cell
It is not surprising that HHG sources have been used for numerous applications ranging from atomic and molecular physics [3], microscopy [4], phonon dynamics [5] and EUV metrology to ”seeding” of EUV free electron lasers (FEL) [6] or EUV laser plasma amplifiers [7]
Summary
High order harmonic generation (HHG) has attracted significant attention as a compact, femtosecond pulsed, coherent light source covering the extreme ultraviolet (EUV) photon energy range [1]. A second key advantage of EUV radiation with respect to IR or visible laser light is the significantly shorter wavelength, pushing the diffraction limit in photon based microscopy towards a few ten nanometers. We note that all previous studies have focused on rather low order harmonics and only sparse data are available for wavelengths lower than 25 nm In contrast to these previous reports, we chose a two-step procedure to obtain circularly polarized harmonics. A conversion efficiency of 10−7 has previously been measured for one harmonic at 18 nm with the same laser [2] but conversion efficiencies of up to 10−4 can be obtained [1] The reflectivity of the p component is very low and this significantly lowers the efficiency of the polarizer To overcome this difficulty, multiple mirror designs have been proposed. We will describe the experimental setup, derive a theoretical model of the optical system and present our results
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