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Light absorption in matter often induces ultrafast electron dynamics within the system. Here, the authors record a femtosecond movie of the electron density of an argon ion as it oscillates in a quantum beat of two fine-structure states.

Few methods can produce orbital angular momentum beams in the extreme ultraviolet or X-ray, and controlling orbital angular momentum on these beams remains challenging. Here the authors apply wave mixing to a tabletop high-harmonic source and control the topological charge of extreme ultraviolet beams.

Structured beams of light are used to engineer conduction band populations and pattern currents. Using the approach, dynamic optoelectronic interconnects and other applications are demonstrated.

High-harmonic spectroscopy provides attosecond-scale information about optical processes in molecules. Present techniques, however, cannot simultaneously measure the phase as a function of molecular angle and photon frequency. An approach that retrieves both the amplitude and the phase of high-harmonic emission is now demonstrated, and could enable a full reconstruction of the molecular wavefunction.

Intense lasers can both ionize atoms and subsequently drive the recollision of the released electrons with their ionized parents. Holography experiments now show that the orientation of the parent can change the recollision process, requiring a refinement of the commonly used strong-field approximation.

Ultrafast pulses with controlled parameters are desirable in many applications including probing materials and their interaction with light. Here the authors demonstrate a technique for polarization control of XUV beam using high-harmonic generation and polarization shaping.

Trihydrogen cations are abundant in interstellar space and play a vital role in both star and organic molecule formation. Now it has been shown that D₃⁺ cations can be directly produced through photoionization of molecular D₂–D₂ dimers.

An all-optical photonic streaking measurement is demonstrated that provides direct experimental access to individual attosecond pulses. The effects of non-adiabatic electron dynamics and plasma formation on the generated attosecond pulse train are directly observed when the pulse train is applied to harmonic generation in gases.

Isolated attosecond pulses (IAPs) in the extreme-ultraviolet range are generated by the interaction of half-cycle mid-infrared pulses with gas (Xe, Kr or Ar) and solid media (quartz). The energy of the IAPs is optically tunable over an octave.

A new laser-field measurement technique is demonstrated that exploits nonlinear optical mixing in a gas in which attosecond pulses are being generated. The instantaneous field of an unknown pulse is imprinted onto the deflection of an attosecond pulse using an all-optical set-up with a bandwidth of up to 1 PHz.

High-harmonic spectroscopy probes atomic structure by looking at the short-wavelength emission excited from atoms by ultrafast pulses of laser light. It is now shown that this technique can even detect signatures of electron–electron interactions.

Absorption lineshape of H₂ is coherently controlled by using intense near-infrared laser pulses. Depending on the time delay between the near-infrared and extreme ultraviolet pulses, the profiles display a Lorentzian or an asymmetric Fano lineshape.

An all-optical method to measure the space–time characteristics of an isolated attosecond pulse, without temporal and spatial averaging, is now demonstrated. The approach will provide further insight into the generation of ultrafast light, and may possibly be used to finely control the pulse characteristics.

New methods are emerging that aim to image chemical reactions as they occur using X-ray diffraction, electron diffraction or laser-induced recollision, but spectral selection cannot be used to monitor the reacting molecules for these methods. These authors show that this apparent limitation offers opportunities for recollision-based high-harmonic spectroscopy, in which unexcited molecules can act as local oscillators against which structural and electronic dynamics is observed on an attosecond timescale.

Transient absorption spectroscopy is used to identify the structural characteristics of the atoms and molecules. Here the authors used extreme ultraviolet transient absorption spectroscopy to identify the Rydberg state symmetry of aligned molecules.

A method for tomographic imaging of molecular orbitals—based on the alignment of molecules in the laboratory frame and linearly polarized laser fields—has now been extended to atoms, which cannot be naturally aligned.

Near-infrared femtosecond laser pulses are sent to a Si or ZnO crystal to generate high-harmonic waves via static or transient field-induced optical nonlinearities. The beam profile of the high-harmonic emission is controlled by electronic methods.

Using the attosecond streak camera method, researchers measure the temporal characteristics of coherent, spatially separated attosecond pulses generated from the attosecond lighthouse.

Researchers in Germany have shown that an ultrafast electron beam can be used to probe the dynamics of laser-generated plasmas with picosecond resolution.

High-harmonic emission from crystalline silicon can be made ten times brighter by exploiting local plasmonic fields in arrays of nano-antennas.

Strong nonlinearities in solid state materials can lead to interesting applications in photonics. Here the authors study chiral high-harmonic generation at SiO₂ and MgO surfaces using bi-circular two-color driving fields and extract information on crystal properties.

High harmonic generation is a nonlinear optical phenomena and HHG from solid offers challenges and advantages over dilute media like gases. Here the authors report HHG from metallic thin film of titanium nitride and discuss the role of intraband current to HHG.

Conical intersections, a hallmark of polyatomic molecules, can be induced with light, leading to new reaction pathways. Here, the authors show that intense fields can create complex, beyond-conical intersections even in diatomics, resulting in an unexpected angular distribution of fragment ions.

High-harmonic generation in zinc oxide illuminated by an intense, pulsed, mid-infrared laser is found to involve a recollision effect in which electrons recollide with holes causing harmonics to be emitted, a process similar to that which occurs in atomic systems.

Generating high harmonics or attosecond pulses of light is normally thought of as a classical process, but a theoretical study has now shown how the process could be driven by quantum light.

Attosecond light pulses are used for ultrahigh-resolution observations of ultrafast phenomena in atoms, molecules and condensed matter. Measuring the durations of such pulses is challenging because the spectrum lies in the vacuum ultraviolet or soft-X-ray range. This article reviews and compares two methods — photoionization and photorecombination — for measuring the duration of attosecond pulses.

An experimental study shows how a polar molecule can be oriented in three dimensions by using a combination of laser and electrostatic fields. The approach should help to obtain molecular-frame information about strong-field ionization processes in molecules for which the orientation cannot be determined after ionization.