High harmonic generation

About: High harmonic generation is a research topic. Over the lifetime, 11694 publications have been published within this topic receiving 222650 citations. The topic is also known as: HHG.

Investigation of harmonic generation in the alternating magnetic response of superconducting Y‐Ba‐Cu‐O

Abstract: The magnetic behavior of a sintered Y‐Ba‐Cu‐O superconductor has been investigated by monitoring the harmonic components of its magnetic response to an alternating field. As the steady bias field is incrementally raised, a transition from a linear, reversible behavior of the magnetization to a nonlinear, irreversible behavior is indicated by the appearance of magnetic losses and odd harmonic components in the response. These harmonics disappear as the bias field or the temperature is increased above a certain point, indicating a linear behavior. The disappearance of the odd harmonics, while the magnetic losses persist, is interpreted as signifying a transition to a state of dissipative flux motion without pinning. These measurements demonstrate a new technique for determination of the lower critical field and the ‘‘irreversibility’’ field below which irreversibility in the magnetization sets in as a result of flux pinning.

Efficient generation at 421 nm by resonantly enhanced doubling of GaAlAs laser diode array emission

Abstract: The 842‐nm diffraction‐limited emission from an injection‐locked laser diode array was frequency doubled using a monolithic spherical‐mirror KNbO3 crystal cavity. Maximum unidirectional external 421 nm power of 24 mW was generated with 167 mW of pump power. Maximum total internal second‐harmonic power and conversion efficiency of 64 mW and 45% were obtained. Effects of heating in the crystal are described.

A laser-based instrument for the study of ultrafast chemical dynamics by soft x-ray-probe photoelectron spectroscopy

Abstract: A laser-based instrument is described for the study of femtosecond dissociation dynamics of gas phase molecules via time-resolved vacuum ultraviolet and soft x-ray photoelectron spectroscopy. Visible or UV pump pulses are generated with nonlinear crystal techniques on a Ti:sapphire laser output, while soft x-ray probe pulses are created via high-order harmonic generation of the same laser in rare gases. Here we describe the optical layout of the pump-probe system, the means for separation of the high-order harmonics in the soft x-ray probe beam, including a description of the two grating setup used to compress the high-harmonic pulses and the magnetic bottle photoelectron spectrometer used for data collection. The feasibility of using the generated high-harmonic pulses for an array of gaseous phase photoelectron spectroscopy experiments is established. These include measurements of valence shell and core-level photoelectron transitions in atoms and molecules, the tunability of the soft x-ray harmonic thro...

Optimisation of Quantum Trajectories Driven by Strong-field Waveforms

Abstract: Quasi-free field-driven electron trajectories are a key element of strong-field dynamics. Upon recollision with the parent ion, the energy transferred from the field to the electron may be released as attosecond duration XUV emission in the process of high harmonic generation (HHG). The conventional sinusoidal driver fields set limitations on the maximum value of this energy transfer, and it has been predicted that this limit can be significantly exceeded by an appropriately ramped-up cycleshape. Here, we present an experimental realization of such cycle-shaped waveforms and demonstrate control of the HHG process on the single-atom quantum level via attosecond steering of the electron trajectories. With our optimized optical cycles, we boost the field-ionization launching the electron trajectories, increase the subsequent field-to-electron energy transfer, and reduce the trajectory duration. We demonstrate, in realistic experimental conditions, two orders of magnitude enhancement of the generated XUV flux together with an increased spectral cutoff. This application, which is only one example of what can be achieved with cycle-shaped high-field light-waves, has farreaching implications for attosecond spectroscopy and molecular self-probing.

Theoretical analysis of dynamic chemical imaging with lasers using high-order harmonic generation

Abstract: We report theoretical investigations of the tomographic procedure suggested by Itatani et al. [Nature (London) 432, 867 (2004)] for reconstructing highest occupied molecular orbitals (HOMOs) using high-order harmonic generation (HHG). Due to the limited range of harmonics from the plateau region, we found that even under the most favorable assumptions, it is still very difficult to obtain accurate HOMO wave functions using the tomographic procedure, but the symmetry of the HOMOs and the internuclear separation between the atoms can be accurately extracted, especially when lasers of longer wavelengths are used to generate the HHG. Since the tomographic procedure relies on approximating the continuum wave functions in the recombination process by plane waves, the method can no longer be applied upon the improvement of the theory. For future chemical imaging with lasers, we suggest that one may want to focus on how to extract the positions of atoms in molecules instead, by developing an iterative method such that the theoretically calculated macroscopic HHG spectra can best fit the experimental HHG data.