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.

Ultra-strong nonlinear optical processes and trigonal warping in MoS2 layers.

Abstract: Nonlinear optical processes, such as harmonic generation, are of great interest for various applications, e.g., microscopy, therapy, and frequency conversion. However, high-order harmonic conversion is typically much less efficient than low-order, due to the weak intrinsic response of the higher-order nonlinear processes. Here we report ultra-strong optical nonlinearities in monolayer MoS2 (1L-MoS2): the third harmonic is 30 times stronger than the second, and the fourth is comparable to the second. The third harmonic generation efficiency for 1L-MoS2 is approximately three times higher than that for graphene, which was reported to have a large χ (3). We explain this by calculating the nonlinear response functions of 1L-MoS2 with a continuum-model Hamiltonian and quantum mechanical diagrammatic perturbation theory, highlighting the role of trigonal warping. A similar effect is expected in all other transition-metal dichalcogenides. Our results pave the way for efficient harmonic generation based on layered materials for applications such as microscopy and imaging. Harmonic generation is a nonlinear optical process occurring in a variety of materials; the higher orders generation is generally less efficient than lower orders. Here, the authors report that the third-harmonic is thirty times stronger than the second-harmonic in monolayer MoS2.

Attosecond extreme ultraviolet vortices from high-order harmonic generation.

Abstract: We present a theoretical study of high-order harmonic generation (HHG) and propagation driven by an infrared field carrying orbital angular momentum (OAM). Our calculations unveil the following relevant phenomena: extreme-ultraviolet harmonic vortices are generated and survive to the propagation effects, vortices transport high-OAM multiples of the corresponding OAM of the driving field and, finally, the different harmonic vortices are emitted with similar divergence. We also show the possibility of combining OAM and HHG phase locking to produce attosecond pulses with helical pulse structure.

Femtosecond thin-disk laser with 141 W of average power

Abstract: We present a semiconductor saturable absorber mirror mode-locked thin disk laser based on Yb:Lu2O3 with an average power of 141W and an optical-to-optical efficiency of more than 40%. The ideal soliton pulses have an FWHM duration of 738fs, an energy of 2.4μJ, and a corresponding peak power of 2.8MW. The repetition rate was 60MHz and the beam was close to the diffraction limit with a measured M2 below 1.2.

Development and applications of compact high‐intensity lasers

Abstract: The development of compact high‐intensity lasers, made possible by the technique of chirped pulse amplification, is reviewed. This includes the complexities of high‐power laser implementation, such as the generation of short pulses, pulse cleaning, wide‐bandwidth amplification, temporal stretching and compression, and the requirements for high‐average powers. Details of specific solid‐state laser systems are given. Some applications of these lasers to short‐pulse coherent short‐wavelength [x‐ray ultraviolet (XUV)] sources are also reviewed. This includes several nonlinear effects observed by focusing a subpicosecond laser into a gas; namely, an anomalous scaling of harmonic generation in atomic media, an upper limit on the conversion efficiency of relativistic harmonics in a plasma, and the observation of short‐pulse self‐focusing and multifoci formation. Finally, the effects of large ponderomotive pressures (100 Mbars) in short‐pulse high‐intensity laser–plasma interactions are discussed, with relevance both to recombination x‐ray lasers and a novel method of igniting thermonuclear fusion.

Broadband, electrically tuneable, third harmonic generation in graphene

Abstract: Optical harmonic generation occurs when high intensity light (>1010 W m–2) interacts with a nonlinear material. Electrical control of the nonlinear optical response enables applications such as gate-tunable switches and frequency converters. Graphene displays exceptionally strong light–matter interaction and electrically and broadband tunable third-order nonlinear susceptibility. Here, we show that the third-harmonic generation efficiency in graphene can be increased by almost two orders of magnitude by controlling the Fermi energy and the incident photon energy. This enhancement is due to logarithmic resonances in the imaginary part of the nonlinear conductivity arising from resonant multiphoton transitions. Thanks to the linear dispersion of the massless Dirac fermions, gate controllable third-harmonic enhancement can be achieved over an ultrabroad bandwidth, paving the way for electrically tunable broadband frequency converters for applications in optical communications and signal processing.