Giant Nonlinear Susceptibility Research Articles

Nonlinear Optical Properties of 2D Materials and their Applications.

2D materials are a subject of intense research in recent years owing to their exclusive photoelectric properties. With giant nonlinear susceptibility and perfect phase matching, 2D materials have marvelous nonlinear light-matter interactions. The nonlinear optical properties of 2D materials are of great significance to the design and analysis of applied materials and functional devices. Here, the fundamental of nonlinear optics (NLO) for 2D materials is introduced, and the methods for characterizing and measuring second-order and third-order nonlinear susceptibility of 2D materials are reviewed. Furthermore, the theoretical and experimental values of second-order susceptibility χ(2) and third-order susceptibility χ(3) are tabulated. Several applications and possible future research directions of second-harmonic generation (SHG) and third-harmonic generation (THG) for 2D materials are presented.

Optical Harmonic Generation in 2D Materials

Abstract2D materials are emerging as ideal candidates for fundamental investigations and new technologies due to their unique optoelectronic properties. Giant nonlinear susceptibility and perfect phase matching in 2D materials lead to extraordinary nonlinear light matter interactions, thus enabling several potential applications and fundamental scientific discoveries in nonlinear optics. For instance, second harmonic generation in 2D materials play an important role in optical devices such as, lasers, tunable waveguides, electro‐optic modulators, and switches. This review will discuss optical harmonic generation (OHG) processes, various characterization modes, and tuning techniques in 2D materials. The future prospectives for OHG in 2D materials is discussed. The extremely promising attributes of combining nonlinear optics and 2D materials is becoming a highly important multidisciplinary field.

Giant non-linear susceptibility of hydrogenic donors in silicon and germanium

Implicit summation is a technique for the conversion of sums over intermediate states in multiphoton absorption and the high-order susceptibility in hydrogen into simple integrals. Here, we derive the equivalent technique for hydrogenic impurities in multi-valley semiconductors. While the absorption has useful applications, it is primarily a loss process; conversely, the non-linear susceptibility is a crucial parameter for active photonic devices. For Si:P, we predict the hyperpolarizability ranges from χ(3)/n3D = 2.9 to 580 × 10−38 m5/V2 depending on the frequency, even while avoiding resonance. Using samples of a reasonable density, n3D, and thickness, L, to produce third-harmonic generation at 9 THz, a frequency that is difficult to produce with existing solid-state sources, we predict that χ(3) should exceed that of bulk InSb and χ(3)L should exceed that of graphene and resonantly enhanced quantum wells.

Bistable scattering in graphene-coated dielectric nanowires.

In nonlinear plasmonics, the switching threshold of optical bistability is limited by the weak nonlinear responses from the conventional Kerr dielectric media. Considering the giant nonlinear susceptibility of graphene, here we develop a nonlinear scattering model under the mean field approximation and study the bistable scattering in graphene-coated dielectric nanowires based on the semi-analytical solutions. We find that the switching intensities of bistable scattering can be smaller than 1 MW cm-2 at the working frequency. To further decrease the switching intensities, we show that the most important factor that restricts the bistable scattering is the relaxation time of graphene. Our work not only reveals some general characteristics of graphene-based bistable scattering, but also provides a guidance to further applications of optical bistability in the high speed all-optical signal processing.

Monte Carlo analysis of the terahertz difference frequency generation susceptibility in quantum cascade laser structures.

Based on self-consistent ensemble Monte Carlo simulations coupled to the optical field dynamics, we investigate the giant nonlinear susceptibility giving rise to terahertz difference frequency generation in quantum cascade laser structures. Specifically, the dependence on temperature, bias voltage and frequency is considered. It is shown that the optical nonlinearity is temperature insensitive and covers a broad spectral range, as required for widely tunable room temperature terahertz sources. The obtained results are consistent with available experimental data.

High performance terahertz quantum cascade laser sources based on intracavity difference frequency generation

We demonstrate high power, room temperature, single-mode THz emissions based on intracavity difference frequency generation from mid-infrared quantum cascade lasers. Dual active regions both featuring giant nonlinear susceptibilities are used to enhance the THz power and conversion efficiency. The THz frequency is lithographically tuned by integrated dual-period distributed feedback gratings with different grating periods. Single mode emissions from 3.3 to 4.6 THz with side-mode suppression ratio and output power up to 40 dB and 65 µW are obtained, with a narrow linewidth of 5 GHz.

Enhancement of nonlinear susceptibility in a four-level tripod scheme

We propose a scheme for the enhancement of nonlinear susceptibility in a four-level tripod-type atomic system in the presence of a microwave field. With a microwave field, nonlinear susceptibility can be enhanced. Nonlinearity can also be ulteriorly enhanced by controlling the coupling field under the optimal intensity of the microwave field. The physical mechanism of the obtained giant nonlinear susceptibility is mainly based on interactions between microwave field and coupling fields. We present a physical understanding of our numerical results using a dressed-state approach and an analytical explanation.

Coupled quantum well semiconductors with giant electric field tunable nonlinear optical properties in the infrared

Coupled quantum wells present unique opportunities for engineering new semiconductors with large optical nonlinearities associated with intersubband transitions in the infrared. In this paper we report an in depth study of these properties in the AlInAs/GaInAs heterostructure material system grown by molecular beam epitaxy. We show that by judicious control of the tunnel coupling between wells and of the thickness of the latter one can design the wavefunctions and the energy levels in such a may that these new structures behave as quasi-molecules with extremely large dipole matrix elements and strongly field tunable nonlinear optical properties. Structures with giant nonlinear susceptibilities /spl chi//sup (2)/(2/spl omega/) and /spl chi//sup (3)/(3/spl omega/) (compared to the bulk constituents of the quantum wells) have been designed and demonstrated. They exhibit large linear Stark shifts of the intersubband transitions which have been used to efficiently tune the nonlinear susceptibilities. The second order nonlinear susceptibility |/spl chi//sup (2)/(2/spl omega/)| exhibits a peak as a function of the electric field corresponding to the energy levels being made equally spaced via the Stark effect. In a three-coupled-well structure triply resonant third harmonic generation has been observed. This process is associated with four equally spaced bound states. The corresponding |/spl chi//sub (3/spl omega/)//sup (3)/| (10/sup -14/ (m/V)/sup 2/ at 300 K and 4/spl times/10/sup -14/ (m/V)/sup 2/ at 30 K) is the highest measured third order noniinear susceptibility in any material. The equivalent of multiphoton ionization of a molecule has also been investigated in this structure. Electrons are photoexcited to a continuum resonance above the barrier via a three-photon transition enhanced by intermediate energy levels. The effect of this resonance on /spl chi//sup (3)/(3/spl omega/) as the electric field is varied is also investigated. Finally, appropriate figures of merit are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Atomically abrupt semiconductor heterointerfaces: their role in advanced electronic and photonic devices and quantum phenomena

Atomically abrupt heterojunction interfaces have played a unique role in the emergence of a new generation of electronic and photonic devices. These include quantum-well lasers, low-noise superlattice avalanche photodiodes and solid-state photomultipliers, quantum-well infrared photodetectors, ultrahigh-speed heterojunction bipolar transistors and resonant-tunneling devices. The monolayer abruptness of heterojunction interfaces has also made possible the observation of exciting quantum phenomena including resonant tunneling, giant nonlinear susceptibilities associated with the quantum size effect and electron Bragg reflection phenomena. The latter have been observed in transport and in the creation of new bound states at energies in the classical continuum above potential wells. A brief discussion of recent work on tunable band discontinuities concludes this paper.