3 research outputs found
Spatial aberrations in high-order harmonic generation
We investigate the spatial characteristics of high-order harmonic radiation
generated in argon, and observe cross-like patterns in the far field. An
analytical model describing harmonics from an astigmatic driving beam reveals
that these patterns result from the order and generation position dependent
divergence of harmonics. Even small amounts of driving field astigmatism may
result in cross-like patterns, coming from the superposition of individual
harmonics with spatial profiles elongated in different directions. By
correcting the aberrations using a deformable mirror, we show that fine-tuning
the driving wavefront is essential for optimal spatial quality of the
harmonics
Ultra-stable and versatile high-energy resolution setup for attosecond photoelectron spectroscopy
Attosecond photoelectron spectroscopy is often performed with interferometric
experimental setups that require outstanding stability. We demonstrate and
characterize in detail an actively stabilized, versatile, high spectral
resolution attosecond beamline. The active-stabilization system can remain
ultra-stable for several hours with an RMS stability of 13 as and a total
pump-probe delay scanning range of \sim 400 fs. A tunable femtosecond laser
source to drive high-order harmonic generation allows for precisely addressing
atomic and molecular resonances. Furthermore, the interferometer includes a
spectral shaper in 4f-geometry in the probe arm as well as a tunable bandpass
filter in the pump arm, which offer additional high flexibility in terms of
tunability as well as narrowband or polychromatic probe pulses. We show that
spectral phase measurements of photoelectron wavepackets with the rainbow
RABBIT technique (reconstruction of attosecond beating by two photon
transitions) with narrowband probe pulses can significantly improve the
photoelectron energy resolution. In this setup, the temporal-spectral
resolution of photoelectron spectroscopy can reach a new level of accuracy and
precision
Measuring the quantum state of photoelectrons
A photoelectron, emitted due to the absorption of light quanta as described
by the photoelectric effect, is often characterized experimentally by a
classical quantity, its momentum. However, since the photoelectron is a quantum
object, its rigorous characterization requires the reconstruction of the
complete quantum state, the photoelectron's density matrix. Here, we use
quantum state tomography to fully characterize photoelectrons emitted from
helium and argon atoms upon absorption of ultrashort, extreme ultraviolet light
pulses. While in helium we measure a pure photoelectronic state, in argon,
spin-orbit interaction induces entanglement between the ion and the
photoelectron, leading to a reduced purity of the photoelectron state. Our work
shows how state tomography gives new insights into the fundamental quantum
aspects of light-induced electronic processes in matter, bridging the fields of
photoelectron spectroscopy and quantum information, and offering new
spectroscopic possibilities for quantum technology