Generation and complete polarimetry of ultrashort circularly polarized extreme-ultraviolet pulses

Abstract

The generation of ultrashort circularly polarized pulses in the extreme-ultraviolet spectral range has recently attracted considerable interest for applications in time-resolved circular-dichroism experiments. Here, we demonstrate a simple approach to generate near-circularly polarized femtosecond pulses in the vacuum-ultraviolet. The ellipticity of the generated light can be continuously tuned from linear to near-circular, as demonstrated by detailed polarimetry measurements. Combining optical polarimetry with photoelectron circular-dichroism (PECD) measurements, we demonstrate a novel approach to characterizing the polarization state of light in terms of all four Stokes parameters. For photon energies of 9.3 eV, we obtained S3 = 0.96 ± 0.02 and a degree of polarization of 97±2%, i.e. the highest values reported from any harmonic-generation source so far. This source is directly applicable to circular-dichroism experiments, also enabling time-resolved PECD in the extreme-ultraviolet, a general approach to probing time-dependent chirality during chemical processes on (sub)-femtosecond time scales.

Femtosecond photoelectron circular dichroism of chemical reactions

“…The second harmonic beam was separated from the fundamental beam by reflections on four dichroic mirrors. The polarization of the beam was controlled by a motorized rotational stage with a quarter-wave plate for 400 nm ( 45 ). The beam was focused by a f = 500-mm spherical mirror into a semi-infinite gas cell filled with Xe.…”

“…In both cases, the C─I bond is selectively dissociated following one-photon absorption at 266 nm. The subsequent dynamics is tracked by a circularly polarized laser pulse centered at 133 nm generated with a new tabletop source described in section S1 and in ( 45 ). Our measurements reveal intriguing changes in the PECD signal on the time scale of the bond-breaking dynamics and additionally reveal the chirality of the molecular-radical products.…”

Ground‐State Photoelectron Circular Dichroism of Methyl p‐Tolyl Sulfoxide by Single‐Photon Ionisation from a Table‐Top Source

“…This is frequency doubled in a β-barium borate crystal to obtain 400 nm, which is circularly polarised with a quarter-wave plate and subsequently used to generate quasi-circularly polarised low-order harmonics in a gas cell filled with 10 mbar of xenon as the generation gas. [26] This favours the output of the third harmonic (H3, 133 nm), which is further selected using dielectric mirrors (Layertec). The polarisation state of this source has been completely characterised using reflective in-vacuum polarimetry and benchmark PECD measurements, showing that the magnitude of the third Stokes parameter of this source amounted to S 3 = 0.96 � 0.02.…”

Attosecond metrology in circular polarization

“…In the time domain this corresponds to a pulse train of three linearly polarized attosecond bursts per laser cycle, where the polarization rotates 120 • between each burst (28)(29)(30). Resonant HHG of an elliptical laser field can produce bright low-order harmonics with an ellipticity of up to 0.7 (31) or 0.86 (32). The coherent superposition of two orthogonal linearly-polarized HHG beams was demonstrated to yield circular polarizations (33,34).…”

“…Therefore, the complete characterization of a circularly polarized sub-femtosecond pulses, i.e. including their temporal structure (28,37) and polarization state (32,(38)(39)(40), has remained out of reach so far, due to the lack of suitable metrologies.…”