High-harmonic generation from an atomically thin semiconductor

Liu, Hanzhe; Li, Yilei; You, Yong Sing; Ghimire, Shambhu; Heinz, Tony F.; Reis, David A.

doi:10.1038/nphys3946

Cited by 616 publications

(506 citation statements)

References 30 publications

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“…One of the most fundamental and prominent aspects of nonlinear optics is higher-order harmonic generation (HHG) in condensed matter systems, [54][55][56] which is both a source of fundamental insight into electron motion and a promising new method to realize compact ultraviolet and ultrafast light sources. One of the most fundamental and prominent aspects of nonlinear optics is higher-order harmonic generation (HHG) in condensed matter systems, [54][55][56] which is both a source of fundamental insight into electron motion and a promising new method to realize compact ultraviolet and ultrafast light sources.…”

Section: High Harmonic Generationmentioning

confidence: 99%

Photoexcitation in Solids: First‐Principles Quantum Simulations by Real‐Time TDDFT

Lian

Guan

et al. 2018

Advcd Theory and Sims

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An efficient and state-of-the-art real-time time-dependent density functional theory (rt-TDDFT) method is presented, as implemented in the time-dependent ab initio package (TDAP), which aims at performing accurate simulations of the interaction between laser fields and solid-state materials. The combination of length-gauge and velocity-gauge electromagnetic field has extended the diversity of materials under consideration, ranging from low dimensional systems to periodic solids. Meanwhile, by employing a local basis presentation, systems of a large size are simulated for long electronic propagation time, with moderate computational cost while maintaining a relatively high accuracy. Non-perturbative phenomena in materials under a strong laser field and linear responses in a weak field can be simulated, either in the presence of ionic motions or not. Several quintessential works are introduced as examples for applications of this approach, including photoabsorption properties of armchair graphene nanoribbon, hole-transfer ultrafast dynamics between MoS 2 /WS 2 interlayer heterojunction, laser-induced nonthermal melting of silicon, and high harmonic generation in monolayer MoS 2 . The method demonstrates great potential for studying ultrafast electron-nuclear dynamics and nonequilibrium phenomena in a wide range of quantum systems.ultrafast dynamics and phenomena either in perturbative or non-perturbative regimes. [3][4][5][6][7][8] Therefore, it has been a unique ab initio quantum method applicable for the exploring of strong field physics beyond linear response theory, for instance, high harmonic generation [9,10] and ultrafast photoelectron emission. [11] Recently, the scope of rt-TDDFT applications has greatly extended from treating isolated atomic and molecular systems to condensed phase materials. In most previous works, numerical implementations of rt-TDDFT that aim at handling solid materials were built on real-space grids, [12,13] including some well-known program packages such as OCTOPUS [9,14] and SALMON. [15,16] Real-time TDDFT has also been implemented in plane wave codes, for example, the ELK FP-LAPW [17] and FPSID, [18] whose encouraging results have shown the effectiveness of the rt-TDDFT approaches. However, if one is interested in high energy excitation that is on the energy scale of tens to hundreds of electron volts (eV), extremely dense real-space grids and high kinetic energy of plane waves are indispensable. Meanwhile, to describe a system with N a atoms, 10 3 to 10 4 × N a real-space grids or plane waves have to be used, which makes the simulation of large-size systems impractical using computer resources available at the present stage. The above two factors will significantly increase the computational cost and in turn limit the practicability of the rt-TDDFT methods.Here we introduce a real-time ab initio approach based on local atomic basis for simulating electron-nuclear dynamics under laser excited conditions. This approach has been successfully implemented in the time-dependent ab initi...

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Section: High Harmonic Generationmentioning

confidence: 99%

Photoexcitation in Solids: First‐Principles Quantum Simulations by Real‐Time TDDFT

Lian

Guan

et al. 2018

Advcd Theory and Sims

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“…As the creation of polarization and charge carriers, as well as their acceleration inside the bands are strongly coupled, both emission sources contribute simultaneously to the total emission

E_{out} false(t false) \propto \frac{\partial}{\partial t} P false(t false) + J false(t false)

. The frequency spectrum is obtained by a Fourier transform of

E_{out} false(t false)

and reads

\begin{matrix} true \\ right I_{out} false(ω false) = | E_{out} {(ω) false|}^{2} \propto {false| ω P (ω) + normali J (ω) false|}^{2} . \end{matrix}

Questions concerning the relative importance of the emission sources in a strongly excited semiconductor as well as the interplay between them are a topic of ongoing discussions . Nevertheless, both emission sources are intrinsically coupled and equally important as demonstrated in Refs.…”

Section: Microscopic Theory Of Strong‐field Excitations In Semiconducmentioning

confidence: 99%

Ultrahigh Off‐Resonant Field Effects in Semiconductors

Huttner

Kira

Koch

2017

Laser & Photonics Reviews

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The excitation of semiconductors with short, off-resonant, high-power terahertz pulses yields extremely nonlinear, ultrafast, dynamical processes including very-high harmonic generation, the occurence of high-order sidebands, dynamical Bloch oscillations, as well as quasi-particle collisions. This review overviews the experimental findings and the microscopic theory used for the consistent quantitative analysis of the observations.

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“…They may come from the interference of HHG trajectories in the different valence bands [12]. It may also come from the Berry phase [13]. In this work, we will present a new mechanism for even-order harmonic generation in symmetric periodic potentials.…”

mentioning

confidence: 99%

Nonadiabatic redshifts in high-order harmonic generation from solids

2017

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We studied the multi-plateau high-order harmonic generation (HHG) from solids numerically. It is found that the HHG spectrum in the second or higher plateau is redshifted in short laser pulses due to the nonadiabatic effect. The corresponding FWHMs also increase, suggesting the step-by-step excitation process of higher conduction bands in the HHG process. Even order harmonics in the higher plateaus of HHG are present due to the break of symmetry in the k space. It may stimulate related experimental work. High-order harmonic generation (HHG) from gases has been well studied. It has been used to generate attosecond laser pulses [1,2]. It is described by the three-step model [3]. The cutoff energy of HHG is around Ip+3.17Up (Ip is the ionization potential, and Up=A0 2 /4 is the ponderomotive energy). The HHG from bulk crystals has been reported recently [4,5] as the development of long-wavelength lasers. It is quite different from the HHG from gases. The cutoff energy of solid HHG depends on the amplitude of the laser field linearly [4]. It also exhibits multi-plateau structure [6]. However, the mechanisms of HHG from solids are much debated. Inter-and intra-band transitions [4,7,8] are proposed. Three-step model in the coordinate space [9] and vector k space [10] are investigated. Recently, multi-plateau HHG from solids are studied theoretically [7,8,11] and experimentally. Our theoretical model [10] propose that the multi-plateau structure reflects the population of higher conduction bands which are pumped step by step.In the solid systems, even-order harmonics are measured experimentally. They may come from the interference of HHG trajectories in the different valence bands [12]. It may also come from the Berry phase [13]. In this work, we will present a new mechanism for even-order harmonic generation in symmetric periodic potentials.Redshifts of HHG spectra were predicted in the HHG from gases and plasmas [14][15][16][17][18][19][20]. They originate from delayed emission times of HHG from the excited state, resonate state, or dissociation of molecules. It is a nonadiabatic effect. The feature is that most of the HHG signals are generated from the trailing edge of the laser pulse, where dI/dt<0. The driving force from the laser fields is weaker than the previous cycle. The electrons obtain less energy compared to the previous cycle and redshifts of HHG occur. They have been experimentally confirmed [18,[21][22][23]. It was reported that redshift was observed in the optical absorption of crystals in the presence of an intense mid-infrared laser field [24]. In this letter, we find that redshift also exists in emission of HHG from solids. It is universal. The higher conduction bands are excited step by step. As a result, the HHG process in the higher plateau is delayed compared to ultrafast process in the lower conduction bands. As will be shown next, even the system is symmetric in the coordinate space, the electron motion is not symmetric in the k space. Consequently, redshifts of HHG and even-order harmonics ar...

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High-harmonic generation from an atomically thin semiconductor

Cited by 616 publications

References 30 publications

Photoexcitation in Solids: First‐Principles Quantum Simulations by Real‐Time TDDFT

Photoexcitation in Solids: First‐Principles Quantum Simulations by Real‐Time TDDFT

Ultrahigh Off‐Resonant Field Effects in Semiconductors

Nonadiabatic redshifts in high-order harmonic generation from solids

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