Nearly-degenerate Four-wave Mixing Research Articles

Influence of a repump laser on a nearly degenerate four-wave-mixing spectrum in atomic vapors

The influence of a repump laser on a nearly degenerate four-wave-mixing (NDFWM) spectrum was investigated. We found the amplitude and line shape of the NDFWM depended strongly on the detuning of the repump field. A five-peak structure was observed. And at some certain repump detuning a dip appeared at the central peak. A rough analysis was proposed to explain this effect.

Variable optical delay using population oscillation and four-wave-mixing in semiconductor optical amplifiers

We investigate variable optical delay of a microwave modulated optical beam in semiconductor optical amplifier/absorber waveguides with population oscillation (PO) and nearly degenerate four-wave-mixing (NDFWM) effects. An optical delay variable between 0 and 160 ps with a 1.0 GHz bandwidth is achieved in an InGaAsP/InP semiconductor optical amplifier (SOA) and shown to be electrically and optically controllable. An analytical model of optical delay is developed and found to agree well with the experimental data. Based on this model, we obtain design criteria to optimize the delay-bandwidth product of the optical delay in semiconductor optical amplifiers and absorbers.

Polarisation-resolved chaos and instabilities in a vertical cavity surface emitting laser subject to optical injection

Instabilities in the polarisation-resolved output of a vertical cavity surface emitting laser (VCSEL) subject to optical injection have been investigated experimentally. It is found that regions of chaotic behaviour exist for both positive and negative detuning from the stable injection locking regime. Outside the chaos regimes, several nonlinear dynamical phenomena including frequency pushing, nearly degenerate four-wave mixing (NDFWM), injection locking, limit cycle and period doubling, were also observed.

Polarization dependence of four-wave mixing in a degenerate two-level system

Nearly degenerate four-wave mixing (NDFWM) within a closed degenerate two-level atomic transition is theoretically and experimentally examined. Using the model presented by A. Lezama et al [Phys. Rev. A 61, 013801 (2000)] the NDFWM spectra corresponding to different pump and probe polarization cases are calculated and discussed. The calculated spectra are compared to the observation of NDFWM within the $6S_{1/2}(F=4)\to 6P_{3/2}(F=5)$ transition of cesium in a phase conjugation experiment using magneto optically cooled atoms

Experimental stability diagram of a diode laser subject to weak phase-conjugate feedback from a rubidium vapor cell

We report on a systematic experimental investigation of the dynamical behavior of a diode laser subject to delayed feedback from a phase-conjugating mirror based on nearly-degenerate four-wave mixing in rubidium vapor. We present the first experimental stability diagram for this system. In the weak feedback regime, with feedback levels up to -30 dB, me demonstrate locking to the pump frequency with a reduced linewidth smaller than 8 MHz. In contrast to a laser with external injection, and contrary to predictions made for phase-conjugate feedback, the extent of this locking region is found to be limited. For increased feedback rates, the laser leaves the locking region and enters an unstable region through a series of multiple sidebands spectra. This is associated with self-excitation of the relaxation oscillation, and the observed scenario suggests a series of period-doublings after an initial Hopf bifurcation.

Analysis of nearly degenerate four-wave mixing in multisection laser diodes

The characteristics of nearly degenerate four-wave mixing (NDFWM) in above-threshold two-section single cavity Fabry-Perot (TSSC FP) laser diodes subject to weak or strong probe-injection power, are investigated numerically. The ND-PWM behaviors are significantly dependent on optical probe injection into either section of a TSSC FP laser diode, and the injected probe power. It is shown that both carrier diffusion and pump depletion effects play very important roles in determining the reflectivity efficiency of conjugate wave, and that a greater than /spl sim/3.5-dB enhancement of reflectivity efficiency can be obtained in an asymmetric laser diode, compared to a symmetric laser, for strong injection probe power. Calculations suggest that the TSSC FP laser diodes may be applied to control the influence of carrier diffusion on NDFWM reflectivity efficiency.

Ambipolar diffusion coefficient and carrier lifetime in a compressively strained InGaAsP multiple quantum well device

By using the technique of noncollinear nearly-degenerate four-wave mixing, ambipolar diffusion coefficients and carrier lifetimes were directly determined for a compressively-strained InGaAsP multiple quantum well semiconductor optical amplifier operating at 1.3 μm. A diffusion coefficient of 8.0 cm2/s and a carrier lifetime of 1.33 ns, were obtained at the amplifier current density of 1.88 kA/cm2. The current-density dependent measurements show that the diffusion coefficient will drop with increasing amplifier pumping current, which is consistent with the prediction of the conventional semiconductor theory.

Nondiffusive excitonic transport in GaAs and the effects of momentum scattering.

Measurements of exciton transport using frequency-domain nearly degenerate four-wave mixing (NDFWM) show a failure of Fick's law and near-ballistic excitonic motion for scale lengths less than 10 \ensuremath{\mu}m. A solution of the Boltzmann transport equation assuming a simple momentum-changing collision model is in agreement with the observed NDFWM line shapes and apparent subquadratic dependence on inverse scale length. The measurements show the surprising result that exciton-exciton interactions lead to a large increase in exciton linewidth with little corresponding change in exciton center-of-mass momentum, unlike exciton interactions with phonons and impurities.

Gas-phase velocimetry by nearly degenerate four-wave mixing

We demonstrate a new velocimetry technique for gas flows based on Nearly Degenerate Four-Wave Mixing (NDFWM). Measurements were performed on nitric oxide in a free-jet expansion using helium and argon as carrier gases, at flow velocities on the order of 1000 m/s. We obtained velocities by analyzing experimental spectra from the jet using a perturbative treatment of NDFWM that we extended to include an arbitrary bulk velocity. The results agreed with independent velocity measurements based on Laser-Induced Fluorescence (LIF), as well as with theoretical flow-field velocities, to better than 5% in all cases studied.

Spectroscopic properties of cold rubidium atoms in a magneto-optic trap

We investigate spectroscopic properties of cold 85Rb atoms in a magneto-optic trap. Both the transmission and the reflection spectra of the trapped atoms are recorded. The dressed-atom picture and the density-matrix formalism are appropriately used to explain the absorption profile around the F=3-F′=2,3,4 and F=2-F′=1 transitions. Around the trapping laser frequency, phaseconjugation signals are observed (reflectivity is about 10 −4), which are attributed to the degenerate and nearly-degenerate four-wave mixing.

Generation of Phase Conjugate Wave from a Visible InGaAlP Laser

This paper presents the first quantitatively measured results of detuning and spatial characteristics of the phase conjugate wave which is emitted from a Fabry-Perot cavity-type InGaAlP laser. Bandwidth of a nearly-degenerate four-wave mixing was confirmed to be due to the relaxation oscillation frequency of the laser. The reflectivity of the phase conjugate mirror and the amplification gain were larger than 10 and 100, respectively. By the off-axial injection of the probe beam to a broad stripe laser, the emitted phase conjugate wave was separated spatially from the pump beam. Non-degenerate four-wave mixing characteristics of an AlGaAs laser were also measured for the first time. Its 3-dB cutoff frequency was as large as 0.1 THz, which was determined by the reciprocal of the half-cycle time of the intracavity light-wave.

THEORETICAL CALCULATION FOR MODULATION TRANSFER SPECTROSCOPY

Based on density matrix equations, we studied the interaction process among phase-modula-ted beams, unmodulated beam and a cascade three-level system. Calculations of the line shape of optical heterodyne modulation transfer spectroscopy via nearly-degenerate four-wave mixing were made. The results show that the Doppler background due to the near resonance of the in-termediate level is eliminated and the signal of two-photon transition can be distinguished from saturation absorption.

Effects of nonlinear gain on four-wave mixing and asymmetric gain saturation in a semiconductor laser amplifier

Nearly degenerate four-wave mixing (NDFWM) and asymmetric gain saturation were studied in a 1.5 μm InGaAsP semiconductor laser amplifier at highly saturated conditions (Pout ≫ Psat) and frequency separations up to 500 GHz. Apart from modulation of the carrier density the data reveal a new mechanism of NDFWM with a characteristic time of about 650 fs which takes over when the frequency separation exceeds 100 GHz.

Detuning characteristics and conversion efficiency of nearly degenerate four-wave mixing in a 1.5- mu m traveling-wave semiconductor laser amplifier

The optical nonlinearity in a semiconductor laser gain medium is investigated through copropagating nearly degenerate four-wave mixing (NDFWM) in a 1.5- mu m InGaAsP traveling-wave laser amplifier (TWA). The FWM signal output powers vary symmetrically with the sign of probe detuning with respect to the pump frequency, while the pump and probe output powers vary asymmetrically. The NDFWM conversion efficiency from the probe input to the FWM signal output is a maximum of 8.3 dB around zero detuning and has positive gain in the range of +or-6 GHz. This demonstrates highly efficient nonlinear interaction due to both large optical gain and large third-order susceptibility. The NDFWM efficiency is also investigated in connection with the TWA gain saturation characteristics and is found to be a maximum for operation around the saturation intensity of the TWA. >

Frequency conversion by nearly-degenerate four-wave mixing in traveling-wave semiconductor laser amplifiers

The paper describes a scheme for frequency conversion of optical data signals with use of NDFWM in travelling wave semiconductor laser amplifiers. The frequency conversion range is limited by the gain bandwidth of the optical amplifier, which is about 4000 GHz in the considered case. The experimental arrangement of the conversion scheme is described and a theoretical analysis is presented. Finally the advantages and disadvantages of this scheme are discussed.

Saturation behavior and dynamic Stark splitting of nearly-degenerate four-wave and multiwave mixing in a forward boxcar configuration

We analyze the saturation behavior of nearly degenerate forward four-wave mixing in a Doppler broadened vapor. Theoretical predictions as well as experiments on Cs vapor resonance line (λ=852 nm) reveal that the dynamic Stark splitting is directly observable in the case of a two-level system. Extensions to multiwave mixing are also discussed.

Optical phase conjugation and nonlinear optical bandpass filter characteristics in CdSSe microcrystallite-doped glass

Experimental measurements of the backward CW four-wave mixing response in semiconductor-doped glass in a regime important to applications are described. In particular, it is shown that lowering the operating temperature to 125 K yields a chi /sup 3/ approximately=2*10/sup -4/ ESU. Aberration correction through optical phase conjugation is demonstrated with a phase conjugate reflectivity of 0.3% along with a wide-angle field-of-view response. In addition, the nearly-degenerate four-wave mixing response of importance to tunable bandpass optical filters is reported.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Four-wave mixing in a semiconductor laser amplifier

The letter reports on nearly degenerate four-wave mixing (NDFWM) of two copropagating light waves inside a travelling wave amplifier (1.3μm) at input light powers of less than 10μW. It describes the first experimental determination of the range of frequency spacing of the two light waves for efficient NDFWM and of the dependence on the state of polarisation.

Effects of population pulsations on backward, nearly degenerate four-wave mixing spectroscopy and optical phase conjugation

We discuss the effects of population pulsations on the spectral response of backward nearly degenerate four-wave mixing (NDFWM). We include the effects of state-specific decay and spontaneous emission on both two-level and inverted-v-type three-level systems. We compare the results with experiments in both the gas phase and the condensed phase that show ultranarrow resonances. In addition, we examine the response in the presence of strong pump fields. We show that in a simple two-level system, the NDFWM response results in an ac-Stark splitting of the spectral response, whereas in a simple three-level system with decay to a metastable state, a single narrow resonance is observed, which broadens in the presence of strong pumps.

Nearly degenerate four-wave mixing in a traveling-wave semiconductor laser amplifier

Nearly degenerate four-wave mixing (NDFWM) in a traveling-wave semiconductor laser amplifier is demonstrated by simultaneously injecting two lights of slightly different frequencies in the same direction. A new frequency light at an expected frequency for NDFWM is observed with the same order of output as that of the injected light. The output power ratio of the three beams is strongly dependent on the sign of the frequency detuning. Theoretical analysis, in which the carrier rate equation is coupled with nonlinear Maxwell’s equations, explains the experimental results well. The observed behaviors are attributed to a unique third-order nonlinearity stemming from saturation-induced refractive index change in the semiconductor gain medium.