Nondegenerate Four-wave Mixing Signal Research Articles

Characterization and application of femtosecond infrared stimulated parametric emission microscopy

A four-wave mixing (FWM) microscopy that is designed to probe third-order nonlinear susceptibilities, χ(3) of target materials with femtosecond light pulses has been constructed and investigated. Nondegenerate FWM signals (at 1500 and 639 nm) were produced in samples by a femtosecond Ti:sapphire laser (790 nm) and a femtosecond optical parametric oscillator (1035 nm). While the effect of electronic and vibrational molecular resonances on the visible FWM signal has been extensively studied, little attention has been paid to the infrared (IR) signal. This IR signal should exhibit a different dependence on the spectrum of molecular electronic resonances, and thus potentially offers a new mechanism for image contrast in microscopy. We have therefore constructed a FWM microscope to characterize these signals in a focused geometry. In polymeric films and beads containing a solute with a resonant (or near-resonant) optical response, the nonresonant polymer background signal was effectively suppressed using polarization-sensitive detection. Longitudinal scans of the beam foci through films were used to determine relative nonlinear third-order susceptibilities and second hyperpolarizabilities of selected solvents and the Rhodamine 6G dye molecule, for both the visible and IR FWM wavelengths.

Six-wave mixing phase-dispersion by optical heterodyne detection in dressed reverse N-type four-level system

We have investigated the dressed effects of non-degenerate four-wave mixing (NDFWM) and demonstrated a phase-sensitive method of studying the fifth-order nonlinear susceptibility due to atomic coherence in RN-type four-level system. In the presence of a strong coupling field, NDFWM spectrum exhibits Autler–Townes splitting, accompanied by either suppression or enhancement of the NDFWM signal, which is directly related to the competition between the absorption and dispersion contributions. The heterodyne-detected nonlinear absorption and dispersion of six-wave mixing signal in the RN-type system show that the hybrid radiation-matter detuning damping oscillation is in the THz range and can be controlled and modified through the colour-locked correlation of twin noisy fields.

Atomic coherence in nondegenerate four-wave mixing

Two-photon resonant nondegenerate four-wave mixing (NFWM) with the addition of a coupling field in Ba atomic vapour has been studied. We find that coherence of the atomic level transitions leads to suppression of the NFWM signal, giving rise to a dip with a linewidth that is linearly proportional to the intensity of the coupling field.

Modified two-photon absorption and dispersion of ultrafast third-order polarization beats via twin noisy driving fields

We investigate the color-locked twin-noisy-field correlation effects in third-order nonlinear absorption and dispersion of ultrafast polarization beats. We demonstrate a phase-sensitive method for studying the two-photon nondegenerate four-wave mixing (NDFWM) due to atomic coherence in a multilevel system. The reference signal is another one-photon degenerate four-wave-mixing signal, which propagates along the same optical path as the NDFWM signal. This method is used for studying the phase dispersion of the third-order susceptibility and for the optical heterodyne detection of the NDFWM signal. The third-order nonlinear response can be controlled and modified through the color-locked correlation of twin noisy fields.

Two-photon resonant nondegenerate four-wave mixing via quantum interference

We study the quantum interference in two-photon resonant nondegenerate four-wave mixing (NFWM) in a dressed cascade four-level system in which the two upper levels are coupled by a strong laser field. We find that in the presence of a strong coupling field, two-photon resonant NFWM spectrum exhibits Autler-Townes splitting, which reflects the levels of the dressed states. It also leads to either suppression or enhancement of the NFWM signal. This scheme involves the resonant three-photon excitation, therefore, provides a new spectroscopic tool for studying highly excited atomic states with high sensitivity.

Two-photon resonant four-wave mixing in a dressed atomic system

We study two-photon resonant nondegenerate four-wave mixing (NFWM) in a dressed cascade four-level system. In the presence of a strong coupling field, the two-photon resonant NFWM spectrum exhibits Autler-Townes splitting, accompanied by either suppression or enhancement of the NFWM signal. Such phenomena are demonstrated in Ba through inducing of atomic coherence between the ground state $6{s}^{2}$ and the doubly excited autoionizing Rydberg state $6pnd$. This technique provides a spectroscopic tool for measuring not only the resonant frequency and dephasing rate but also the transition dipole moment between two highly excited atomic states.

Suppression and Enhancement in Parametric Two-Photon ResonantNondegenerate Four-Wave Mixing via Quantum Interference

Quantum interference may lead to suppression and enhancement ofthe two-photon resonant nondegenerate four-wave mixing signal in acascade four-level system. Such phenomena are demonstrated in Bathrough inducing atomic coherence between the ground state 6s2and the doubly excited autoionizing Rydberg state 6pnd. Thismethod can be used as a new spectroscopic tool for measuring thetransition dipole moment between two highly excited atomic states.

Nondegenerate four-wave mixing in a double-? system under the influence of coherent population trapping

Nondegenerate four-wave mixing (NDFWM) in a double-L system of Rb atomic vapor was achieved for collinear pump fields. By comparison of different pump-probe configurations, direct experimental evidence of influence of coherent population trapping on the output power of the NDFWM signal was established. A maximal efficiency for generating the NDFWM signal exists for a moderate pump power in this double-L system.

Enhancement of nondegenerate four-wave mixing based on electromagnetically induced transparency in rubidium atoms

We report an experimental observation of the enhancement of nondegenerate four-wave mixing (NDFWM) based on electromagnetically induced transparency (EIT) in a lambda-type three-level system of rubidium atoms. We measured both the linear susceptibility Im chi(D)((1)) (absorption) and the third-order nonlinear coefficient chi(D)((3)) separately for the NDFWM process at a low atomic density. We found that, owing to the EIT effect, the linear absorption term Im chi(D)((1)) is greatly reduced, while the nonlinear generation term chi(D)((3)) is resonantly enhanced, permitting us to observe a significant enhancement of the NDFWM signal in an optically dense medium.

Study and characterization of new resonances in the frequency space in a two-level system with non-zero permanent dipole moments

Properties of the resonance peaks associated with the non-degenerate four-wave mixing signal in a two-level molecular system with non-zero permanent dipole moments are studied in the space defined by the pump ( omega 1) and probe ( omega 2) frequencies. An analytical expression for the Fourier components of the nonlinear homogeneous macroscopic polarization are obtained, where the terms responsible for the oscillation (at frequency omega 3=2 omega 1- omega 2) of the populations and coherences are also identified. Topological properties of the resulting nonlinear spectra are studied in frequency space using three-dimensional curves and contour plots. We have additionally identified the dominant contributions of the coherence and/or population that determine the intensity and the spectral linewidth. The critical quantities for the present analysis are the transition and permanent dipole moments when the rotating-wave approximation (RWA) is not considered.

Study of additional resonances in frequency space and permanent dipole moment effects on nondegenerate four-wave mixing signals

The characteristics of the resonances emerging as a consequence of incorporating a permanent dipole moment in the non-degenerate four-wave mixing technique, are investigated in the framework of a local homogeneous-linewidth third-order perturbation model. Results show that the effects of the permanent dipole moments on the nonlinear signal topology are a consequence of neglecting the rotating-wave approximation.