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.

Two-dimensional imaging of energy bands from crystal orientation dependent higher-order harmonic spectra in h − BN

Abstract: High-order harmonic generation (HHG) from hexagonal boron nitride is simulated by solving extended multiband semiconductor Bloch equations under strong laser fields. By changing the angle of the laser polarization with respect to the crystal orientation, we find that harmonic spectra present a double-plateau structure and HHG is dominantly emitted along \ensuremath{\Gamma}-M direction in the first plateau, but special anisotropic distribution is observed in the secondary plateau. In-depth analyses reveal that two plateaus originate from different pair of conduction band and valence band, and the shapes of band dispersion and transition dipole moment determine anisotropic harmonic emission in $h$-BN crystal. Furthermore, we show that band energies of high-lying unoccupied bands and low-lying occupied ones can be directly extracted from laser polarization dependent high harmonic spectra. This paves a way to image the two-dimensional band information of solid materials by using laser-induced HHG.

Single attosecond pulse from terahertz-assisted high-order harmonic generation

Abstract: High-order harmonic generation by few-cycle 800 nm laser pulses in neon gas in the presence of a strong terahertz (THz) field is investigated numerically with propagation effects taken into account. Our calculations show that the combination of THz fields with up to 12 fs laser pulses can be an effective gating technique to generate single attosecond pulses. We show that in the presence of the strong THz field only a single attosecond burst can be phase matched, whereas radiation emitted during other half cycles disappears during propagation. The cutoff is extended and a wide supercontinuum appears in the near-field spectra, extending the available spectral width for isolated attosecond pulse generation from 23 to 93 eV. We demonstrate that phase-matching effects are responsible for the generation of isolated attosecond pulses, even in conditions when single-atom response yields an attosecond pulse train.

Observation of Carrier-Envelope Phase Phenomena in the Multi-Optical-Cycle Regime

Abstract: So far the role of the carrier-envelope phase of a light pulse has been clearly experimentally evidenced only in the sub-6-fs temporal regime Here we show, both experimentally and theoretically, the influence of the carrier-envelope phase of a multi-optical-cycle light pulse on high-order harmonic generation For the first time, we demonstrate that the short and long electron quantum paths contributing to harmonic generation are influenced in a different way by the pulse carrier-envelope phase

Enhanced surface emitting waveguides for visible, monolithic semiconductor laser sources

Abstract: By using AlGaAs resonant multilayers embedded in a wave-guide geometry a ten million fold enhancement for surface emitting harmonic generation over a normal GaAs film was obtained. The multilayer system allows compensation for material losses at the harmonic and the use of thick films for efficient coupling of communication fibres to the device. The experimental results agree closely with theory and a monolithic implementation of visible, surface emitting solid state diode lasers is presented for InGaAs, InP and GaAs geometries.

Coherent hard X-ray production by cascading stages of High Gain Harmonic Generation

Abstract: We study a new approach to produce coherent hard X-rays by cascading several stages of High Gain Harmonic Generation (HGHG). Our calculation shows that such a scheme is feasible within the present technology. Compared with the Self-Amplified Spontaneous Emission (SASE) scheme for the Linac Coherent Light Source (LCLS), the HGHG scheme can provide radiation with full longitudinal coherence, narrower bandwidth, more stable central wavelength, more controllable pulse length, and much higher performance stability. The electron bunch parameters used in our calculation are those of the DESY TTF and SLAC LCLS projects. To achieve similar output power, i.e. about 15 GW , the total length of the HGHG scheme will be 88 m , while that of SASE scheme will be around 100 m .