Experimental determination of the interatomic potential in LiNbO3 via ultrafast lattice control

Chun

Applied Physics Letters

et al. 2019

Femtosecond laser pulses interacting with LiNbO 3 has been widely applied in intense terahertz generation, excitation and imaging of phonon polaritons and modulating light. It is of great importance to study the nonlinearities induced by femtosecond laser pulses in LiNbO 3 . Here, we demonstrate that both Kerr nonlinearity and Kerr-like nonlinearity induced by terahertz wave occur under the interaction between laser pulses and LiNbO 3 using optical pump-probe techniques. We show that the contribution of Kerr-like nonlinearity to pump-probe spectra varies with the interaction length because of the phase mismatching between terahertz wave and laser pulse. We also observed the excitation of the low frequency phonon polaritons. Experimental results are in consistent with theoretical calculation.

“…4(c). The frequency of the phonon polaritons, obtained from the fitting of the experimental data, is ∼ 3 THz, which is consistent with previous report 17 .…”

supporting

confidence: 92%

Observation of Kerr nonlinearity and Kerr-like nonlinearity induced by terahertz generation in LiNbO3

Chun

Applied Physics Letters

et al. 2019

“…As shown in Fig. 2, the pump-probe spectrum of the small-field response is well understood by considering the phase-matching between the probe light and the phonon-polariton propagating into the crystal 18,19 At high pump fields (20 MV/cm, Fig. 1c and d solid lines), a strongly anharmonic response was observed, with asymmetric oscillations in both PR and SH signals.…”

Section: -3mentioning

confidence: 81%

“…Extended Data Figure 6 further shows the reflectivity fit considering only the two dominating oscillators only (blue line) and the reflectivity obtained from the FDTD simulation using these two modes (green line). Both yield a satisfactory description of the optical properties in the region of interest (12)(13)(14)(15)(16)(17)(18)(19)(20).…”

Section: Anharmonic Frequency Renormalizationmentioning

confidence: 99%

Probing the interatomic potential of solids with strong-field nonlinear phononics

Hoegen

Mankowsky

Fechner

et al. 2018

Nature

121

Nonlinear optical techniques at visible frequencies have long been applied to condensed matter spectroscopy. However, because many important excitations of solids are found at low energies, much can be gained from the extension of nonlinear optics to mid-infrared and terahertz frequencies. For example, the nonlinear excitation of lattice vibrations has enabled the dynamic control of material functions. So far it has only been possible to exploit second-order phonon nonlinearities at terahertz field strengths near one million volts per centimetre. Here we achieve an order-of-magnitude increase in field strength and explore higher-order phonon nonlinearities. We excite up to five harmonics of the A (transverse optical) phonon mode in the ferroelectric material lithium niobate. By using ultrashort mid-infrared laser pulses to drive the atoms far from their equilibrium positions, and measuring the large-amplitude atomic trajectories, we can sample the interatomic potential of lithium niobate, providing a benchmark for ab initio calculations for the material. Tomography of the energy surface by high-order nonlinear phononics could benefit many aspects of materials research, including the study of classical and quantum phase transitions.

Advanced Optical Materials

“…For instance, excitation of infrared-optical phonons with intense THz pulses and tracing the anharmonic response [161] allowed one to reconstruct the atomic-scale potential the ions are moving in. [162,163] Even if the phonon of interest is infrared-inactive yet Ramanactive does THz radiation provide new means of phonon excitation by a Raman-type sum-frequency process. [164] Here, two frequencies of the incident THz pulse induce a force on the lattice oscillating at the sum frequency, rather than the difference frequency that occurs in standard Raman-type excitations.…”

Section: Properties Of Driven Modesmentioning

confidence: 99%

Laser‐Driven Strong‐Field Terahertz Sources

Fülöp

Tzortzakis

Kampfrath

2019

271

147

reason for this interest relies on the fact that THz radiation can couple resonantly to numerous fundamental motions of ions, electrons, and electron spins in all phases of matter. For example, in solids, the THz range overlaps with the frequency of lattice vibrations (phonons), the collision rates of conduction electrons, the binding energy of bound electron-hole pairs (excitons), and the precession frequency of spin waves (magnons). Consequently, THz radiation, both continuous-wave and pulsed, has been used for characterization of and gaining insight into elementary processes in complex materials. The majority of these studies used relatively weak THz fields and, thus, probed the linear response of the material, without inducing notable material modifications.Only recently, however, completely new avenues in THz science were opened up by triggering nonlinear THz responses of materials. [3][4][5][6][7][8][9][10][11][12][13] Instead of using weak fields to primarily observe selected THz modes such as phonons or magnons, strong fields allow one to actively drive them to unprecedentedly large amplitudes, potentially thereby resulting in novel states of matter. [6,8,11] For example, simulations suggest that exciting matter with intense THz transients may lead to massive modifications of electrically [14] or magnetically [15] ordered domains and enable the acceleration of free ions to ≈1 MeV, [16] and postacceleration to 50-100 MeV energies. [17] Remarkable experimental results such as switching of magnetic order, [18,19] parametric amplification of optical phonons, [20] novel insights into spin-lattice coupling, [21,22] and acceleration of free electrons in a THz linear accelerator [23] were achieved only recently. This progress has been made possible by the development of laser-driven table-top THz sources routinely providing pulses with unprecedented energies and peak electric and magnetic field strengths throughout the entire THz spectral range. Different laser-based THz pulse generation techniques can be used to access different parts of the spectral range extending from 0.1 to 10 THz. Some of the recently developed technologies enable the generation of radiation with even larger bandwidth or tuning range up to 100 THz and beyond, which lead to an extension of what is called the THz spectral range. An overview of the approximate spectral coverage and the achieved highest pulse energies and peak electric-field strengths of various laserdriven technologies is given in Figure 1. ScopeIn this work, the basic principles of femtosecond-laser-driven intense pulsed THz sources and their recent development are reviewed. These sources are capable of delivering peak electric field strengths on the MV cm −1 scale. Corresponding typical THz pulse energies are on the µJ-to-mJ level, depending on A review on the recent development of intense laser-driven terahertz (THz) sources is provided here. The technologies discussed include various types of sources based on optical rectification (OR), spintronic emitters, and laserfilame...