Parametric Four-wave Mixing Process Research Articles

Raman parametric four-wave mixing mechanism of the first-order Stokes generated in CO2 and H2.

Without the axial component, an annular spatial profile of the first-order Stokes (S1) was observed during the SRS process in low-energy pumped CO2 gas, which is supposed to be generated by a parametric four-wave mixing process (PFWM), i.e., 2ωP = ωAS1 + ωS1. In order to verify such a mechanism, similar experiments were conducted in H2, and the annular S1 intensity distribution was also noticed. Furthermore, simulations of S1 radial intensity distributions were carried out based on the proposed PFWM phase matching geometry. The PFWM has been verified to be a process that directly annihilates two pump photons and simultaneously produces one AS1 photon and one S1 photon.

Correlation interference demultiplexer controlled by phase transition for Pr3+/Eu3+: YPO4

We propose a model of optical demultiplexer based on second- and third-order temporal interference of intensity-noise correlation, which is based on the superposition principle in Feynman's path integral theory. The switch from two-mode bunching to anti-bunching is controlled by gate position for pure hexagonal-phase of Pr3+/Eu3+: YPO4 crystal. We report, robust side correlation peaks caused by the destructive interference between two spontaneous parametric four-wave mixing processes from mixed (hexagonal and tetragonal)-phase of Pr3+/Eu3+: YPO4. By adjusting power of laser beam, the transition from asymmetric correlation side peaks to symmetric correlation side peaks are investigated. The robust center peak comes from the interference between two-mode and three-mode bunching. The switching from single correlation peak to multi-peaks is controlled by laser power. The multi-sharp peaks are translated into multi-dips through gate position. Such results may be used for the design of the optical multiplexer and demultiplexer. Our experimental results provide a technique to achieve larger linewidth change rate about 93% and higher channel equalization ratio about 70%.

Coherent blue light enhancement via repumping laser in cesium vapor

We demonstrate the generation of coherent and collimated blue light (CBL) based on cesium (Cs) 6S<sub>1/2</sub>(<i>F</i> = 4)→6P<sub>3/2</sub>(<i>F'</i> = 5)→6D<sub>5/2</sub>(<i>F''</i> = 6)→7P<sub>3/2</sub>(<i>F'</i> = 5)→6S<sub>1/2</sub>(<i>F</i> = 4) diamond-type atomic system in a heated vapor cell. Two infrared pumping lasers with wavelengths at 852 nm (6S<sub>1/2</sub>→6P<sub>3/2</sub>) and 917 nm (6P<sub>3/2</sub>→6D<sub>5/2</sub>), provide step-wise excitation to the 6D<sub>5/2</sub> excited state, and induce strong two-photon coherence between the 6S<sub>1/2</sub> state and 6D<sub>5/2</sub> state. The atoms undergo a double cascade accompanied with the amplified spontaneous emission at 15.1 μm via the 7P<sub>3/2</sub> intermediate excited state, and produce a beam of 455 nm (7P<sub>3/2</sub>→6S<sub>1/2</sub>) CBL with highly spatiotemporal coherence through a parametric four-wave mixing process. We investigate the influence of experimental parameters such as polarization combination of the two pumping lasers, and their power, and the temperature of Cs vapor cell on the CBL. Especially, we add a beam of 894 nm laser operating at the 6S<sub>1/2</sub>(<i>F</i> = 3) →6P<sub>1/2</sub> transition as repumping laser, which can pump atoms back to the 6S<sub>1/2</sub>(<i>F</i> = 4) state from the 6S<sub>1/2</sub>(<i>F</i> = 3) state, thus significantly improving the power of CBL. This technique of the CBL enhancement via optical pumping is also useful for the other alkali metal atoms.

Trans-spectral vector beam nonlinear conversion via parametric four-wave mixing in alkali vapor.

Coherent frequency conversion of vector beams (VBs) without distorting their intensity profile or spatial polarization distribution is important for novel applications in quantum and classical regimes. Here, we experimentally and theoretically investigate VB transfer from near-infrared to blue light using a Sagnac interferometer, combining the parametric four-wave mixing process in atomic vapor. The vector probe beam is converted into a completely different wavelength, and the vector mode of the generated blue beam is highly similar to the incident probe beam. These results may provide a feasible solution for communication interfaces in classical and quantum science fields based on atomic ensembles.

Narrowband and broadband single-photon sources using custom-tapered waveguides

In this paper, we present a thorough investigation for a spontaneous parametric four-wave mixing process in third-order nonlinear waveguides with various continuous tapering patterns. It has been previously shown that these devices can quasi-phase-match the four-wave mixing process and enhance its conversion efficiency by orders of magnitude. By altering the tapering profile curve we found that these devices can enable single-photon sources with either narrow or broadband spectral widths at on-demand frequencies. Using our model, we were also able to identify the waveguide length at which the single-photon spectral purity is maximized.

Interference between atomic Rb (5d 5/2–5p 3/2) and (5p 3/2–5s 1/2) coherences: observation of an exceptional point by quantum beating at ∼2.1 THz

Coupled oscillators are prevalent in nature and fundamental to fields as disparate as astrophysics, photonics, the mechanical sciences, and geophysics. Theory has identified singularities in the response of coupled oscillators, known as exceptional points (EPs), that are associated with non-Hermitian operators and lie at the transition between weak and strong coupling of the oscillator. Although several EPs have been reported or predicted to exist in nanophotonic resonators and Feshbach resonances, for example, tuning the phase of two interfering atomic or molecular coherences near an EP has not been demonstrated previously. We report the observation of an EP associated with a pair of interfering atomic coherences in Rb, oscillating at 386.3 and 384.2 THz, and confirm the theoretical prediction of an abrupt phase shift of ∼π/4 as the EP is traversed by independently varying two experimental parameters. Pairs (and trios) of coupled coherences in thermal Rb atoms are established among the 7s 1/2, 5d 5/2, 5p 3/2, and 5s 1/2 states in pump–probe experiments with <200 fs laser pulses, and observed directly in the temporal and spectral domains through the ensuing quantum beating in the ∼2–36 THz interval. Interference between the (5d 5/2–5p 3/2) and (5p 3/2–5s 1/2) coherences is mediated by the 5p 3/2 state and detected through quantum beating in the vicinity of the (5d 5/2–5p 3/2)–(5p 3/2–5s 1/2) difference frequency of 2.11 THz which is monitored by a parametric four-wave mixing process. Phase of this composite atomic oscillator is first controlled by varying the mean Rb–Rb nearest neighbor distance (⟨R⟩) in a thermalized vapor. A discontinuous transition of (0.8 ± 0.2) ∼ π/4 radians in the phase of the coupled oscillator occurs when ⟨R⟩ is varied over the ∼80–90 nm interval, a phase shift associated with the transformation of a broadband, dissipative oscillator (characterized by a Fano interference window) into a strongly-coupled system resonant at 2.1 THz.

Coherent near-infrared light generation based on self-seeded parametric four-wave mixing in Rb vapor

We demonstrate 1.37 µm coherent near-infrared light generation via self-seeded parametric four-wave mixing (FWM) process in Rb atomic vapor. Two lasers (780 nm and 776 nm) in the co-propagating configuration, drive the Rb atoms from the 5S1/2 ground state to the 5D5/2 excited state. The parametric FWM around the 5P3/2–5D5/2–6P3/2–6S1/2–5P3/2 transition loop is effectively established under phase matching conditions. The generated coherent light wavelength is confirmed using an optical spectrum analyzer, and the output power is investigated with the input laser frequency, power and atomic density. Consequently, a 1.37 µm coherent light with the power of 27 µW and the beam quality of = 1.22 and = 1.25 is obtained. An additional 795 nm laser is introduced to enhance the output power by 1.5 times through velocity-selective optical hyperfine repumping.

Broadband phononic frequency comb generation in a parametrically excited capacitive micromachined ultrasonic transducer

Optical frequency combs consisting of evenly spaced discrete frequencies have been used for a number of applications such as frequency metrology, range finding and molecular fingerprinting. Recently, the acoustic equivalent of these frequency combs, known as phononic frequency combs (PFCs), have been demonstrated in micro and nanoscale resonators. However, such demonstrations are restricted to PFC generation in high-Q mechanical resonators under carefully controlled operating conditions with limited practical applications. In this work, we demonstrate a novel method of generating PFCs with a parametrically driven capacitive micromachined ultrasonic transducer (CMUT) operating in a fluid medium. The proposed system consists of an electrically driven CMUT array that forms part of a resonant RLC circuit of frequency w0. By applying two drive tones of frequency w0 and w0+Δ, we are able to generate broadband acoustic frequency combs via a parametric four-wave mixing process. The intensity and number of combs generated is strongly dependent on the relative strength of the two driving tones whereas the comb spacing is determined by the frequency difference Δ between the drive signals. We also briefly discuss a potential application of PFCs in extended non-ambiguous range (NAR) distance metrology with interferometric resolution.

Coherent 420 nm laser beam generated by four-wave mixing in Rb vapor with a single continuous-wave laser**Project supported by the National R&D Program of China (Grant No. 2017YFA0304203), the National Natural Science Foundation of China (Grant Nos. 61875112, 61705122, 91736209, and 61728502), the Program for Sanjin Scholars of Shanxi Province, China, the Applied Basic Research Project of Shanxi Province, China

We demonstrate the generation of the coherent 420 nm laser via parametric four-wave mixing process in Rb vapor. A single 778 nm laser with circular polarization is directly injected into a high-density atomic vapor, which drives the atoms from the 5S1/2 state to the 5D5/2 state with monochromatic two-photon transition. The frequency up-conversion laser is generated by the parametric four-wave mixing process under the phase matching condition. This coherent laser is firstly certified by the knife-edge method and a narrow range grating spectrometer. Then the generated laser power is investigated in terms of the power and frequency of the incoming beam as well as the density of the atoms. Finally, a 420 nm coherent laser with power of 19 μW and beam quality of , is obtained with optimal experimental parameters. This novel laser shows potential prospects in the measurement of material properties, information storage, and underwater optical communication.

Focus on lasers, imaging, and microscopy

Focus on lasers, imaging, and microscopy

Nonlinear phase matching in parametric four-wave mixing process of Cs vapor

Phase matching plays an important role on the nonlinear process. The linear phase matching in parametric four-wave mixing (FWM) process of Cs vapor is firstly studied and we find out that linear phase matching can be implemented within narrow range of frequency offsets for involved pumping light. Considering the high pumping power intensity, we innovatively take the influence of nonlinear refractive index to phase matching into account. The relationship between threshold pump intensity and frequency offsets is discovered, and it makes up a complicated curved surface. The threshold has the minimum value when the frequency offset satisfies the condition of v1 + v2 = 0. In addition, these simulation results could provide support for further study and pumping parameters selection in FWM process of Cs vapor.

Two- and three-mode intensity-difference squeezing in cascaded four-wave mixing inside an optical cavity

We report a theoretical study about the two- and three-mode intensity-difference squeezing inside an atom-like optical cavity. A cascaded parametric amplification four-wave mixing process is considered, and the cavity dressing and ‘dressing-like’ effects with different nonlinear coefficients affecting the degree of squeezing of the fluctuation spectra are researched. The altering of the nonlinear coupling coefficient changes the relationship between the cavity dressing and ‘dressing-like’ effects, which determines the squeezing degree and results in a new type of multi-dip squeezing and double-peak anti-squeezing.

Generation of coherent mid-IR light by parametric four-wave mixing in alkali vapor.

The parametric four-wave mixing (4WM) process responsible for the generation of coherent blue light in alkali vapors is a self-seeded process which starts by population inversion and amplified spontaneous emission (ASE). Lately, attention has been turned toward frequency up- and down-conversion in alkali vapors, using relatively low pump powers with CW diode lasers. In this Letter, we investigate the interplay between ASE and 4WM in rubidium (Rb) vapors by studying the mid-infrared (mid-IR) radiation emitted in the forward direction at 5.23μm. We show that the ASE can be suppressed by 4WM in the CW regime. Thus, we demonstrate the generation of coherent mid-IR light at 5.23μm in hot Rb vapors via parametric 4WM.

Nonparametric High-Resolution Coherent 3D Spectroscopy as a Simple and Rapid Method for Obtaining Excited-State Rotational Constants.

A new method for generating high-resolution coherent 3D (HRC3D) spectra has been developed that is based on the nonparametric four-wave mixing process MENS (multiply enhanced nonparametric spectroscopy). The resulting spectra have rotational patterns that are different from those produced previously using the parametric four-wave mixing process CARS. A change in the rotational pattern facilitates a new approach to scanning where orthogonal 2D slices in 3D space are combined to make a 3D rotational pattern. This 3D rotational pattern may then be used to calculate rotational constants for levels in the excited electronic state and upper regions of the ground electronic state. Unlike previous forms of HRC3D spectroscopy, this new approach provides a stand-alone rapid and simple tool for the rotational analysis of electronic spectra without the need for obtaining peak positions or molecular constants from other (1D or 2D) forms of spectroscopy.

Hybrid correlation and squeezing with Rabi oscillation in the diamond nitrogen-vacancy center at room temperature

For the first time, the energy level structure of the nitrogen-vacancy center in diamond is introduced in conjunction with a spontaneous parametric four-wave mixing (SP-FWM) process and fluorescence (FL) generation in heteronuclear-like (V-type level) systems. The obtained output signals are characterized by their decaying components and differentiated by Rabi oscillation, while their lifetimes are modulated by changing the power of the laser field. Two- and three-mode correlation and squeezing among the SP-FWM and FL composite signals are investigated theoretically and experimentally. By selecting different time delayed positions and changing the power of the laser field, competition between the SP-FWM and FL composite signals is demonstrated; this can also control the two-stage line shape of hybrid correlation and the magnitude of squeezing. Such results may find potential applications in optical transistors and optical hybrid communications.

Intracavity Spontaneous Parametric Down-Conversion in Bragg Reflection Waveguide Edge Emitting Diode**Supported by the National Key Basic Research Program of China under Grant Nos 2013CB933304 and 2014CB643904, the National Natural Science Foundation of China under Grant Nos 61435012 and 61274125, and the Strategic Priority Research Program (B) of Chinese Academy of Sciences under Grant No XDB01010200.

A four-wavelength Bragg reflection waveguide edge emitting diode based on intracavity spontaneous parametric down-conversion and four-wave mixing (FWM) processes is made. The structure and its tuning characteristic are designed by the aid of FDTD mode solution. The laser structure is grown by molecular beam epitaxy and processed to laser diode through the semiconductor manufacturing technology. Fourier transform infrared spectroscopy is applied to record wavelength information. Pump around 1.071 μm, signal around 1.77 μm, idler around 2.71 μm and FWM signal around 1.35 μm are observed at an injection current of 560 mA. The influences of temperature, carrier density and pump wavelength on tuning characteristic are shown numerically and experimentally.

Parametric Raman crystalline anti-Stokes laser at 503 nm with collinear beam interaction at tangential phase matching

Stimulated-Raman-scattering in crystals can be used for the single-pass frequency-conversion to the Stokes-shifted wavelengths. The anti-Stokes shift can also be achieved but the phase-matching condition has to be fulfilled because of the parametric four-wave mixing process. To widen the angular-tolerance of four-wave mixing and to obtain high-conversion-efficiency into the anti-Stokes, we developed a new scheme of the parametric Raman anti-Stokes laser at 503 nm with phase-matched collinear beam interaction of orthogonally-polarized Raman components in calcite oriented at the phase-matched angle under 532 nm 20 ps laser excitation. The excitation laser beam was split into two orthogonally-polarized components entering the calcite at the certain incidence angles to fulfill the nearly collinear phase-matching and also to compensate walk-off of extraordinary waves for collinear beam interaction. The phase matching of parametric Raman interaction is tangential and insensitive to the angular mismatch if the Poynting vectors of the biharmonic pump and parametrically generated (anti-Stokes) waves are collinear. For the first time it allows to achieve experimentally the highest conversion efficiency into the anti-Stokes wave (503 nm) up to 30% from the probe wave and up to 3.5% from both pump and probe waves in the single-pass picosecond parametric calcite Raman laser. The highest anti-Stokes pulse energy was 1.4 $$\upmu$$ J.

Two- and three-mode dressed entanglement multichannel in cavity four-wave mixing of Pr3+: YSO

We report a theoretical study into the two- and three-mode entanglement inside an atom-like optical cavity. A five-level system is considered and the influence of the multi-dressed parametric amplification four-wave mixing (PA-FWM) process on the quantum correlation of fluctuation spectra is researched. Three-mode entanglement is determined by the coupling of two nonlinear gains; one of enhanced gains via the dressing state plays a dominant role in controlling and optimizing the profile of three-mode entanglement via vacuum Rabi splitting, enhancement/suppression of entanglement as well as two-mode. Specifically, increasing the quantity of dressing fields may result in the single-channel entanglement turning into nonlocal multichannel (multiple anti-crossing behaviors). Moreover, these entanglement channels can be squashed via the lateral squeezing effect of the cavity. Such multichannel entanglement has potential applications in nonlocal quantum imaging and quantum key distribution.

Switching Correlation and Noise Level in Pr(3+):YSO Crystal via Dressing Nonlinear Phase.

We propose and experimentally demonstrate that the intensity noise correlation and the noise level of intensity-difference and intensity-sum in Stokes and anti-Stokes channel can be well controlled by the relative nonlinear phase in spontaneous parametric four-wave mixing process. By modulating the relative nonlinear phase, including self-phase modulation and cross-phase modulation, switching the correlation into anti-correlation and the relative intensity noise level between the intensity-difference and intensity-sum are realized. We also show that the variation tendencies of the relative intensity noise level and the corresponding intensity fluctuations correlation are in accordance with each other.

Noise correlations controlled by dressed suppression and enhancement

The intensity noise correlations between anti-Stokes and Stokes fields, generated from spontaneous parametric four-wave mixing (SP-FWM) process have been investigated in a ladder-type three-level system of sodium atomic vapor. By introduction of an external dressing field, the strengthened (weakened) correlations are obtained under enhancement (suppression) condition of SP-FWM. Besides, sharp correlations have been obtained as attributed to a pair of non-classical beams generated from amplified spontaneous emission.