hyper-Raman Process Research Articles

Resonant hyper-Raman scattering of light by LO phonons in wurtzite semiconductors

Theoretical treatment of resonant hyper-Raman scattering of light by LO phonons in wurtzite semiconductors is given. The hyper-Raman process was considered for the scattering geometry y(xxz)x at which it involves the two-photon transitions to the B and C excitons of the s-type. Allowance was made for different sequences of intermediate virtual states. On the example of a CdS crystal the influence of the possible dipole transitions to the deeper valence band on the frequency dependence of the scattering cross section was investigated.

Interplay between quantum Zeno and anti-Zeno effects in a nondegenerate hyper-Raman nonlinear optical coupler

Quantum Zeno and anti-Zeno effects are studied in an asymmetric nonlinear optical coupler composed of a probe waveguide and a system waveguide. The system is a nonlinear waveguide operating under non-degenerate hyper-Raman process, while both the pump modes in the system are constantly interacting with the probe waveguide. The effect of the presence of probe on the temporal evolution of the system in terms of the number of photons in Stokes and anti-Stokes modes as well as phonon number is quantified as Zeno parameter. The negative (positive) values of the Zeno parameter in the specific mode are considered as the signatures of the quantum Zeno (anti-Zeno)effect in that mode of the system. It is observed that the phase mismatch in Stokes and anti-Stokes generation processes can be controlled to induce a transition between quantum Zeno and anti-Zeno effects for both off-resonant and resonant hyper-Raman process. However, in case of off-resonant hyper-Raman process in the system waveguide, the frequency detuning parameters can also be used analogously to cause the desired crossover. Further, the general nature of the physical system and the perturbative technique used here allowed us to analytically study the possibilities of observing quantum Zeno and anti-Zeno effects in a large number of special cases, including situations where the process is spontaneous, partially spontaneous and/or the system is operated under degenerate hyper-Raman process, or a simple Raman process.

Lower- and higher-order nonclassical features in non-degenerate hyper-Raman processes

The nonclassical properties of the different modes in the stimulated, spontaneous, and partially spontaneous multi-photon pump non-degenerate hyper-Raman processes are investigated by obtaining a perturbative analytic operator solution of a completely quantum mechanical Hamiltonian of this process, which can be considered as the most general Raman process. The nonclassical nature of the multi-photon pump non-degenerate hyper-Raman processes is witnessed by means of intermodal entanglement of different orders as well as lower- and higher-order photon antibunching. Interestingly, manifesting the multi-photon nature of the pump modes, a bunch of nonclassicality involving them are observed due to self-interaction of various pump modes. Further, it is shown that the obtained solution is very general in nature as the solutions of various other Raman processes (e.g., degenerate hyper-Raman and stimulated Raman processes) can be obtained as special cases of the present solution, and thus the nonclassical properties of those processes can also be witnessed.

Effective hyper-Raman scattering via inhibiting electromagnetically induced transparency in monolayer graphene under an external magnetic field

We propose and analyze an effective scheme to generate hyper-Raman scattering via inhibiting electromagnetically induced transparency (EIT) in a monolayer graphene under a magnetic field. By solving the Schrödinger-Maxwell formalism, we derive explicitly analytical expressions for linear susceptibility, nonlinear susceptibility, and generated Raman electric field under the steady-state condition. Based on dressed-state theory, our results show a competition between EIT and hyper-Raman scattering, and the hyper-Raman process is totally dominant when multiphoton destructive interference is completely suppressed.

Highly efficient, broadband coherent surface-mixing-wave generation using amplified surface plasmonic polaritons

We show that coherent broadband surface mixing-wave (SMW) by a hyper-Raman process can be efficiently generated near a metallic surface abutting a quasi-three-level gain medium. The generation process is significantly enhanced by the amplified surface plasmonic polaritons (SPPs) in the gain layer, resulting in rapid growth of both fields. The highly efficient and directional amplified SPP and hyper-Raman SMW may facilitate engineering applications in which amplified-SPP propagation is desirable.

Stimulated electronic Raman and hyper-Raman scattering in potassium vapor

Stimulated electronic Raman scattering and hyper-Raman processes in potassium vapor near the D1 and D2 lines have been observed using a stable resonator and pulsed laser excitation. First and second order Stokes and anti-Stokes lines were observed simultaneously and independently for a pump laser tuning range exceeding 70cm−1. The output energy increases by more than a factor of 103 as the potassium concentration increases from 0.25 to 2.2×016cm−3. When the pump is tuned between the K D1 and D2 lines, an efficient hyper-Raman process dominates with a slope efficiency that exceeds 10%. The threshold for the hyper-Raman process is about 6mJ per pulse, or 3.8MW/cm2 peak intensity. This Raman shifted laser may be useful as a target illuminator or atmospheric compensation beacon for a high power diode pumped alkali laser.

Cooperative quantum correlations between Stokes and anti-Stokes modes in four-wave mixing

We study the cooperative effects between Raman and hyper-Raman processes in which two quanta from a pumping field are absorbed and another two entangled photons are generated. The symmetries of the involved operators can be reduced to SU(2)-algebra in which the Casimir vector of quasi-momentum of the two fields is conserved. Quantum correlations between the pump and the generated field states are investigated. Cooperative stabilization of two-mode coherent states between Stokes and anti-Stokes photons is shown using both semiclassical and quantum approaches. We show that the relaxation of the system is described by coherent states of the two-mode field. The possibilities of observing cross-correlations between the pump field and the generated field are analyzed.

Amplitude-squared squeezing in spontaneous degenerate hyper Raman process

The approximate analytical solutions of various field modes for spontaneous hyper Raman process are used to obtain the amplitude squared squeezing for pump field mode. We observe that the percentage of squeezing increases with the increase of the order.

Squeezing, photon bunching, photon antibunching and nonclassical photon statistics in degenerate hyper Raman processes

An initially prepared coherent state coupled to a second-order nonlinear medium is responsible for stimulated and spontaneous hyper Raman processes. By using an intuitive approach based on perturbation theory, the Hamiltonian corresponding to the hyper Raman processes is analytically solved to obtain the temporal development of the field operators. It is true that these analytical solutions are valid for small coupling constants. However, the interesting part is that these solutions are valid for reasonably large time. Hence, the present analytical solutions are quite general and are fresh compared to those solutions under short-time approximations. By exploiting the analytical solutions of field operators for various modes, we investigate the squeezing, photon antibunching and nonclassical photon statistics for pure modes of the input coherent light responsible for hyper Raman processes. At least in one instance (stimulated hyper Raman processes for vibration phonon mode), we report the simultaneous appearance of classical (photon bunching) and nonclassical (squeezing) effects of the radiation field responsible for hyper Raman processes.

Collision-induced spectroscopy with long-range intermolecular interactions: A diagrammatic representation and the invariant form of the induced properties

Collision-induced properties of two interacting molecules $a$ and $b$ are derived by means of a general diagrammatic method involving $M$ molecule-molecule and $N$ photon-molecule couplings. The method is an extension of previous graphical treatments of nonlinear optics because it exhaustively determines interaction-induced polarization mechanisms in a trustworthy and handy fashion. Here we focus on long-range intermolecular interactions. Retardation effects are neglected. A fully quantum-mechanical treatment of the molecules is made whereas second quantization for the electromagnetic field, in the nonrelativistic approximation, is implicitly applied. The collision-induced absorption, Raman, and hyper-Raman processes are viewed and studied, through guiding examples, as specific cases $N=1$, 2, and 3, respectively. In Raman $(N=2)$, the standard first-order $(M=1)$ dipole-induced dipole term of the incremental polarizability, $\mathrm{\ensuremath{\Delta}}\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\ensuremath{\alpha}}$, is the result of a coupling of the two photons with distinct molecules, $a$ and $b$, which perturb each other via a dipole-dipole mechanism. Rather, when the two photons interact with the same molecule, $a$ or $b$, the ($N=2$, $M=1$) graphs predict the occurrence of a nonlinear polarization mechanism. The latter is expected to contribute substantially to the collision-induced Raman bands by certain molecular gases.

Efficient hyper-Raman scattering in resonant coherent media.

We propose and analyze a hyper-Raman scheme for generation of coherent light in a five-level atomic system based on electromagnetically induced transparency (EIT). We show that EIT suppresses linear and nonlinear photon absorption and enables the hyper-Raman process to proceed through real, near-resonant intermediate states. The scheme greatly enhances hyper-Raman efficiency and may be used for generating short-wavelength radiation at low pump intensities.

Two-Photon Rabi Splitting and Optical Stark Effect in Microcavities

We have investigated resonant two-photon absorption and second harmonic generation in a microcavity geometry. In a single beam arrangement, the transmission depends on the intensity according to a simple two-level picture with an intensity-dependent coupling; at resonance, in particular, the system exhibits a two-photon Rabi splitting. In a pump and probe arrangement, the presence of the strong incident pump beam substantially modifies the absorption spectrum of the weak probe beam: for moderate pump intensities the behaviour can be interpreted as a two-photon version of the well-known optical Stark effect. At higher intensities, more complicated hyper-Raman processes take place, which give also rise to gain in well-determined spectral regions. Finally, we have shown how the non-linear coupling coefficient appearing in the model Hamiltonian is related to the material constants and geometrical parameters of a specific microcavity configuration.

Two-photon Rabi splitting and optical Stark effect in semiconductor microcavities

We have studied two-photon nonlinear optical effects arising in a microcavity geometry from resonant two-photon absorption or second-harmonic generation. The transmission spectrum of the cavity is shown to depend on light intensity according to a simple two-level picture with an intensity-dependent coupling: at resonance the system exhibits a two-photon Rabi splitting. The absorption spectrum of a weak probe beam in a pumped cavity is found to strongly depend on pump intensity and detuning; the resulting effect is a sort of two-photon analogue of the usual optical Stark effect. For moderate pump intensities a two-level picture with a pump-dependent coupling can account for the main results, while at higher intensities new unexpected features show up; in particular, we predict the appearance of gain in well-determined spectral regions due to hyper-Raman processes. Finally, we have shown how the coupling coefficients appearing in our formalism can be obtained from a detailed knowledge of the material and geometrical properties of a specific system. For illustrative purposes, we have estimated the required light intensities using realistic data for a GaAs-based semiconductor microcavity.

Quantum interference and gain processes in optically-driven n-doped quantum wells with Ξ configurations

We study the electron distributions, intersubband dephasing rates and linear gain and absorption spectra in n-doped asymmetric quantum wells driven by one or two IR fields. The fields couple the partially occupied ground conduction subband of the quantum well to the second subband, and couple the latter to the third subband forming a Ξ configuration. By consistent treatment of the electron–electron scattering process and inclusion of dynamic screening we show how these processes generate non-Fermi electron distributions in the coupled subbands and contribute dynamically to the dephasing rates associated with transitions between the ground subband and higher ones. We also show how these processes affect the gain and absorption spectra in the first to second and the second to third subband transitions when the system is monitored by a weak probe field. These transitions and that between the first and third subbands include dispersive features and strong gain-absorption suppression. We explain these results in terms of extension of the hyper-Raman process, one- and two-photon dressed effects, stimulated Rayleigh scattering and quantum interference effects.

Hyper Raman Scattering in Microcavity Quantum Wells: A Quantum Optical Process in the Strong Coupling Regime

We analyze the hyper Raman scattering process in a quantum well grown inside a semiconductor microcavity and present a microscopic calculation of emission spectra as a function of excitation energy, detuning, and angles. The exciton-photon coupling is treated non-perturbatively to include polariton effects and the Coulomb interaction between electrons is treated beyond the mean field approximation. The observation of hyper Raman scattering in semiconductor microcavities would represent an important step for the realization of non-classical optical states based on excitons. We find that the polaritons emitted in this scattering process are strongly correlated. This correlation,can be efficiently transferred to output photons, resulting in emission of two correlated non-classical light beams. As a probe of the quantum correlation we calculate the output spectrum of fluctuations in the intensity difference of the two beams generated in the hyper Raman process.

The role of hyper-Raman transitions in the radiation spectrum of a strongly driven two-level atom

Numerical results are presented on the spectrum of the light scattered into the vacuum modes by a two-level atom driven by a strong ramped field of frequency smaller than the natural atomic frequency. The attention is focused on the role of the hyper-Raman part of the spectrum, which is shown to decrease dramatically with increasing ramp time. It is suggested that this may explain lack of experimental observation of the hyper-Raman lines. For zero ramp time, the numerical intensity of both high-order harmonics and hyper-Raman peaks is shown to agree satisfactorily with previous analytical predictions except in the region of overlap of the two series of peaks. This lends support for the suggestion that the plateau in the spectrum is related to quantum-mechanical interference between high-order harmonics and hyper-Raman processes. There is also good agreement between the numerical amplitude of the plateau and previous analytical predictions. A physical mechanism for the cut-off frequency which terminates the plateau, based on approximate energy conservation in hyper-Raman transitions, is presented and is shown to be in agreement with present numerical and previous analytical results.

Higher-order amplitude squeezing in hyper-Raman scattering under short-time approximation

The nonclassical effect of squeezing of light in hyper-Raman processes is investigated under the short-time approximation based on a fully quantum mechanical approach. Effects of squeezing in spontaneous and stimulated processes are studied. A hyper-Raman process is looked upon as a three-photon and one-phonon interaction process. Squeezing in amplitude, squared amplitude and cubed amplitude have been investigated. Squeezing occurs invariably in the fundamental mode in both spontaneous and stimulated processes, whereas the squeezing in the Stokes mode is found to be dependent on amplitude-squared squeezing of the initial pump field.

Photon statistics in the three-photon hyper-Raman process.

An exact solution of the master equation for the three-photon hyper-Raman process is obtained by a matrix method. Several cases of the photon statistics are considered and the appearance of photon-antibunching effect and the violation of the classical Cauchy inequality are discussed. I. INTRODUCTION The photon statistics of various nonlinear optical processes has been a subject of increasing interest in recent years. In particular, photon statistics for the usual Raman process has been analyzed theoretically by Simaan in detail. ' The similar hyper-Raman (HR) process has also been studied already by Simaan, who formulated the master equation of the process giving the solution by the Laplace transform method. In this paper we consider again the HR process and give the solution of the master equation by a new matrix method similar to that used by Zubairy for multiphoton absorption processes. Our results complete the previous work by giving rather complete explicit numerical results in a number of cases of interest. In the interaction picture, the equation of motion for the density operator p of the coupled atoms-field system is given by the Liouville equation

Far-infrared laser emission by microwave-infrared-far-infrared three-photon interaction in NH<inf>3</inf>

We report low threshold Raman and hyper-Raman far-infrared laser emission associated with the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> NH <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> , <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\nu_{2}, sQ(5, 4)</tex> infrared transition. Using a circular metallic waveguide FIR resonator, which also acts as a microwave resonator, threshold pump powers were 50 W CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> -laser radiation and 150 W CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , 15 W microwave for Raman and hyper-Raman emission, respectively. The hyper-Raman process is suitable to generate frequency-tunable FIR radiation.

Photon Correlations in Multi-photon Raman Processes

Non-linear interactions between incident and scattered photons (Stokes and anti-Stokes radiation) in Raman and hyper-Raman processes considered as elementary acts, are analysed. Fluctuations of phonons are shown to cause anticorrelation effects between incident and scattered photons. Antibunching of incident laser photons in spontaneous hyper-Raman processes occurs in a similar way to their antibunching in second-harmonic generation.