30 research outputs found
Generation of isolated attosecond pulses in the far field by spatial filtering with an intense few-cycle mid-infrared laser
We report theoretical calculations of high-order harmonic generation (HHG) of
Xe with the inclusion of multi-electron effects and macroscopic propagation of
the fundamental and harmonic fields in an ionizing medium. By using the
time-frequency analysis we show that the reshaping of the fundamental laser
field is responsible for the continuum structure in the HHG spectra. We further
suggest a method for obtaining an isolated attosecond pulse (IAP) by using a
filter centered on axis to select the harmonics in the far field with different
divergence. We also discuss the carrier-envelope-phase dependence of an IAP and
the possibility to optimize the yield of the IAP. With the intense few-cycle
mid-infrared lasers, this offers a possible method for generating isolated
attosecond pulses.Comment: 8 figure
N2 HOMO-1 orbital cross section revealed through high-order-harmonic generation
Citation: Troß, J., Ren, X., Makhija, V., Mondal, S., Kumarappan, V., & Trallero-Herrero, C. A. (2017). N2 HOMO-1 orbital cross section revealed through high-order-harmonic generation. Physical Review A - Atomic, Molecular, and Optical Physics, 95(3). doi:10.1103/PhysRevA.95.033419We measure multi-orbital contributions to high harmonic generation from aligned nitrogen. We show that the change in revival structure in the cutoff harmonics has a counterpart in the angular distribution when a lower-lying orbital contributes to the harmonic yield. This angular distribution is directly observed in the laboratory without any further deconvolution. Because of the high degree of alignment we are able to distinguish angular contributions of the highest occupied molecular orbital 1 (HOMO-1) orbital from angle-dependent spectroscopic features of the HOMO. In particular, we are able to make a direct comparison with the cross section of the HOMO-1 orbital in the extreme ultraviolet region. © 2017 American Physical Society
Generation and control of non-local quantum equivalent extreme ultraviolet photons
We present a high precision, self-referencing, common path XUV interferometer
setup to produce pairs of spatially separated and independently controllable
XUV pulses that are locked in phase and time. The spatial separation is created
by introducing two equal but opposite wavefront tilts or using superpositions
of orbital angular momentum. In our approach, we can independently control the
relative phase/delay of the two optical beams with a resolution of 52 zs (zs =
zeptoseconds). In order to explore the level of entanglement between the
non-local photons, we compare three different beam modes: Bessel-like, and
Gaussian with or without added orbital angular momentum. By reconstructing
interference patterns one or two photons at a time we conclude that the beams
are not entangled, yet each photon in the attosecond pulse train contains
information about the entire spectrum. Our technique generates non-local,
quantum equivalent XUV photons with a temporal jitter of 3 zs, just below the
Compton unit of time of 8 zs. We argue that this new level of temporal
precision will open the door for new dynamical QED tests. We also discuss the
potential impact on other areas, such as imaging, measurements of non-locality,
and molecular quantum tomography.Comment: 11 pages 5 figures and supplemental materials with 12 pages and 7
figure
Measuring the Angle-Dependent Photoionization Cross Section of Nitrogen using High-Harmonic Generation
We exploit the relationship between high harmonic generation (HHG) and the molecular photorecombination dipole to extract the molecular-frame differential photoionization cross section (PICS) in the extreme ultraviolet (XUV) for molecular nitrogen. A shape resonance and a Cooper-type minimum are reflected in the pump-probe time delay measurements of different harmonic orders, where high-order rotational revivals are observed in N₂. We observe the energy- and angle-dependent Cooper minimum and shape resonance directly in the laboratory-frame HHG yield by achieving a high degree of alignment, [SEE FORMULA IN ABSTRACT cos2 θ] 0.8. The interplay between PICS and rotational revivals is confirmed by simulations using the quantitative rescattering theory. Our method of extracting molecular-frame structural information points the way to similar measurements in more complex molecules
Atomic photoionization experiment by harmonic-generation spectroscopy
Citation: Frolov, M. V., Sarantseva, T. S., Manakov, N. L., Fulfer, K. D., Wilson, B. P., Tross, J., . . . Trallero-Herrero, C. A. (2016). Atomic photoionization experiment by harmonic-generation spectroscopy. Physical Review A, 93(3), 5. doi:10.1103/PhysRevA.93.031403Measurements of the high-order-harmonic generation yield of the argon (Ar) atom driven by a strong elliptically polarized laser field are shown to completely determine the field-free differential photoionization cross section of Ar, i.e., the energy dependence of both the angle-integrated photoionization cross section and the angular distribution asymmetry parameter
Self referencing attosecond interferometer with zeptosecond precision
In this work we demonstrate the generation of two intense, ultrafast laser pulses that allow a controlled interferometric measurement of higher harmonic generation pulses with 12.8 attoseconds in resolution (half the atomic unit of time) and a precision as low as 680 zeptoseconds (10−21 seconds). We create two replicas of a driving femtosecond pulse which share the same optical path except at the focus where they converge to two foci. An attosecond pulse train emerges from each focus through the process of high harmonic generation. The two attosecond pulse trains from each focus interfere in the far field producing a clear interference pattern in the extreme ultraviolet region. By controlling the relative optical phase (carrier envelope phase for pulsed fields) between the two driving laser pulses we are able to actively influence the delay between the pulses and are able to perform very stable and precise pump-probe experiments. Because of the phase shaping operation occurs homogeneously across the entire spatial profile, we effectively create two indistinguishable intense laser pulses or a common path interferometer for attosecond pulses. Commonality across the two beams means that they are extremely stable to environmental and mechanical fluctuations up to a Rayleigh range from the focus. In our opinion this represents an ideal source for homodyne and heterodyne spectroscopic measurements with sub-attosecond precision
Strong field coherent control of atomic population transfer
We demonstrate a population inversion in a three-level system via three-photon absorption from a single shaped ultrafast laser pulse. The optimal pulse shape for the inversion is discovered using closed-loop learning control and interpreted via pulse shape parameter scans and numerical integration of the Schr\uf6dinger equation. The population inversion is measured using a combination of spontaneous and stimulated emissions. Our results illustrate the importance of dynamic Stark shifts in coherent multi-photon excitation.Peer reviewed: YesNRC publication: Ye