Raman-resonant Four-wave Mixing Research Articles

Diamond Raman laser with continuously tunable output from 3.38 to 3.80 μm.

We report a pulsed mid-infrared diamond Raman laser with output tuned from 3.38 to 3.80 μm through varying the optical parametric oscillator (OPO) pump wavelength. To our knowledge this is the longest reported wavelength from a solid-state Raman laser. We generated up to 80 μJ with good beam quality and 22% quantum conversion efficiency. Whilst the conversion process itself is efficient, approximately 40% of the generated Stokes light is lost to multiphonon absorption. By introducing a secondary pump beam at the anti-Stokes wavelength to initiate a seed at the Stokes wavelength through Raman resonant four-wave mixing, the laser threshold was reduced by approximately half, and the maximum output increased by 44% to 115 μJ.

Opportunities for wavelength conversion with on‐chip diamond ring resonators

AbstractRecent progress in the fabrication of high‐quality synthetic diamond and of diamond waveguide structures has enabled photonics researchers to start exploiting the unique optical properties of diamond for various applications. In this article the promise of on‐chip diamond ring resonators for wavelength conversion based on Kerr and Raman‐resonant four‐wave mixing is numerically demonstrated. After examining to what extent both dispersion‐engineered phase‐matching and “automatic” quasi‐phase‐matching can be established in diamond ring converters, it is shown that such a “double‐matching” approach can yield high conversion efficiencies for a wide range of wavelengths in the near‐infrared/mid‐infrared domain, as well as in the ultraviolet/visible domain.

Wavelength Conversion Based on Raman- and Non-Resonant Four-Wave Mixing in Silicon Nanowire Rings Without Dispersion Engineering

We propose an efficient wavelength conversion scheme that is based on either Raman-resonant four-wave mixing or non-resonant Kerr-induced four-wave mixing in a silicon nanowire ring, and that does not require dispersion engineering of the nanowire. We rely on the spatial variation of the Raman and Kerr susceptibilities around the ring to quasi-phase match the wavelength conversion processes for TE polarized fields. The flexibility of this quasi-phase-matching scheme can lead to wavelength conversion efficiencies from -26.7 dB to values larger than 0 dB, and in certain circumstances makes it possible to outperform conventional phase-matched conversion in a dispersion-engineered silicon ring by factors exceeding 6 dB.

Phase-Matched Raman-Resonant Four-Wave Mixing in a Dispersion-Compensated High-Finesse Optical Cavity

A highly efficient intracavity four-wave mixing in a Raman-active medium pumped by a continuous-wave laser is first demonstrated. Managing the intracavity dispersion to satisfy the phase matching in a high-finesse cavity substantially enhances the anti-Stokes emission. This process is observed in a region far beyond small signal approximation, indicating the generation of phase-locked sidebands arising from molecular modulation. This points to a novel approach of an optical modulator and mode-locked laser operating at a frequency of more than 10 THz.

Approaching quantum-limited cw anti-Stokes conversion through cavity-enhanced Raman-resonant four-wave mixing

Building on previous efficient Raman downconversion achievements, we present analytical theoretical results predicting that the upconversion efficiency from a continuous-wave pump beam into a single Raman anti-Stokes order can approach the quantum limit of 50%. We consider high-finesse cavity enhancement of the Raman-resonant four-wave mixing process to enable pumping with relatively low-power lasers. In addition to its practical value as a means of efficiently upconverting visible and near-infrared continuous-wave laser light, this technique can offer a probe into the fundamental limits and gain-suppression subtleties associated with Raman-resonant four-wave mixing.

Phase-front transformation of a first-order Bessel beam in Raman-resonant four-wave mixing

We have studied the evolution of the phase front of an apertured first-order Bessel beam (J1) generated by a diffractive axicon during free-space propagation and its transformation in a Raman-resonant four-wave mixing process in hydrogen gas. It is demonstrated that the order of the phase singularity (vortex) of a Bessel beam can easily be detected by interferometry at the boundaries of the beam propagation range. With a J1 beam and a Gaussian beam at the Stokes and the pump frequencies and vice versa, anti-Stokes light is generated as a singular, conical beam. In both cases the observed phase front agrees with theoretical predictions. In particular, the transformation of the topological charge is consistent with the conservation of angular momentum.

Spectral and spatial evolution of a conical emission in Na vapor

A detailed study on yellow conical emission observed in dense sodium vapor following near-resonant one-photon excitation of the Na 42P levels was performed. The origins of conical emission are suggested to be due to Raman resonant four-wave parametric mixing processes. In order to describe spectral and spatial features of off-axis emission, we introduce self-phase modulation and induced-phase modulation as important additional nonlinear processes, explaining the nonmonotonic detuning of the wavelength of the conical radiation with the exiting laser wavelength in the vicinity of resonance transitions. The spatial evolution of emission generated via four-wave mixing is modeled by solving the two-dimensional nonlinear Schrodinger equation describing the spatial evolution of light beams in a nonlinear media. Experimental and theoretical results are presented and discussed.

Order-selective Raman conversion by dual-wavelength-pumped four-wave mixing

By choice of a suitable angular configuration of the incident beams in dual-wavelength-pumped Raman-resonant four-wave mixing, it is theoretically shown that the primary pump laser energy can be converted into collimated beams of either its first anti-Stokes, second anti-Stokes, or first Stokes wave. A typical theoretical conversion efficiency of 80–90% is obtained. For this energy conversion to occur it is required that the initial secondary pump intensity be much greater than the initial primary pump intensity. Temporal and spatial intensity evolutions of the converted and depleted waves and spatial evolutions of the pulse energy are numerically calculated. The calculations are performed under both phase-matched and phase-mismatched conditions.

Dual-wavelength-pumped Raman-resonant four-wave mixing

A new method of anti-Stokes Raman conversion is proposed, termed dual-wavelength-pumped Raman-resonant four-wave mixing, in which a relatively intense secondary pump is applied in the phase-matched direction to enhance anti-Stokes conversion of the primary pump. Conditions for optimizing the conversion efficiency and the effect of phase mismatch are investigated theoretically. A remarkable feature of this method is that the optimum coversion efficiency relative to the primary pump intensity is independent of the initial intensity of the primary pump. It has been shown that nearly 60% of anti-Stokes conversion efficiency is theoretically possible in the vacuum-UV region. The new method of Raman conversion is shown to have advantages in avoiding the effects of beam walk-off and finite coherence lengths because the interaction length required for optimum conversion with this method can be made much shorter than that required in the ordinary single-pump Raman method for a reasonable conversion efficiency.

Raman-resonant four-wave mixing and energy transfer

A common assumption that Raman-resonant four-wave mixing does not transfer energy between the light and the Raman medium is shown to be incorrect. The derivation of the correct energy-transfer picture is compared with those for stimulated Raman scattering and for nonresonant mixing. The physical mechanism for Raman-gain suppression due to Stokes/anti-Stokes coupling under phase-matched conditions is clarified by this understanding of the energy transfer. An experimental demonstration of the nature of the energy transfer is proposed.

Nonlinear mixing spectroscopy ofFexZn1−xF2andFe1−xMnxF2

We report the first observation of electronic Raman-resonant four-wave mixing (4WM) in magnetic materials. The coherent anti-Stokes Raman spectroscopy is used to measure the frequency dispersion of the ${\ensuremath{\chi}}^{(3)}$ components in ${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Zn}}_{x}{\mathrm{F}}_{2}$ and ${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}{\mathrm{F}}_{2}$. Energy, width, and polarization characteristics of the excitations of the ${\mathrm{Fe}}^{2+}$ ion within the $^{5}T_{2g}$ orbital levels manifold are studied as a function of the temperature. Below the N\'eel temperature an enhancement of the 4WM signal is observed which is due to the spin-dependent part of ${\ensuremath{\chi}}_{\mathrm{ijkl}}^{(3)}(2{\ensuremath{\omega}}_{1}\ensuremath{-}{\ensuremath{\omega}}_{2},{\ensuremath{\omega}}_{1},{\ensuremath{\omega}}_{1}\ensuremath{-}{\ensuremath{\omega}}_{2})$.