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Optics Letters

Enhancement of cascaded frequency upconversion by ultrafast temporal correlation of twin beams

Yujiro Eto

Published May 20, 2024• 2 citations
Publisher

Abstract

We experimentally and numerically study the effect of ultrafast temporal correlations in two-stage frequency upconversion pumping by using intense twin beams. Enhancement in the upconversion efficiency of each stage due to ultrafast temporal correlation is evaluated by varying the time delay between pumping beams. It is found that the temporal correlation of the twin beams is transferred to the first upconverted beam, thereby also enhancing the efficiency of the second sum-frequency generation (SFG). This result suggests that temporal correlations play an important role in enhancing the efficiency of light sources that incorporate a parametric downconversion process.

DOI
10.1364/ol.522156

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We experimentally and numerically study the effect of ultrafast temporal correlations in two-stage frequency upconversion pumping by using intense twin beams. Enhancement in the upconversion efficiency of each stage due to ultrafast temporal correlation is evaluated by varying the time delay between pumping beams. It is found that the temporal correlation of the twin beams is transferred to the first upconverted beam, thereby also enhancing the efficiency of the second sum-frequency generation (SFG). This result suggests that temporal correlations play an important role in enhancing the efficiency of light sources that incorporate a parametric downconversion process.
Sum-frequency generation (SFG) driven by bright twin beams yields a coherent contribution from correlated signal–idler mode pairs together with an incoherent background. To explore conditions for high-contrast upconversion against the background, we systematically measure SFG from focused twin beams by scanning the SFG crystal position z and signal–idler delay τ\tauτ. For a nearly single-Gaussian spatial mode, the incoherent background forms a single symmetric peak along the z-axis, whereas the coherent component peaks at a displaced position, enabling contrast enhancement by offsetting the SFG crystal from the incoherent peak position. With multiple spatial modes, the reduction in the coherent component at the incoherent peak position becomes more pronounced. We attribute this behavior mainly to Gouy-phase evolution during propagation. These results highlight the longitudinal position z as a key parameter for achieving high-contrast coherent upconversion of focused twin beams.
We investigate the use of entangled photons generated by parametric downconversion to improve the efficiency of second harmonic generation (SHG). Using a fully three-dimensional model for the nonlinear interactions, we obtain quantitative predictions of the efficiency of quantum-enhanced SHG and identify the critical parameters to optimize the process. By a careful control of the spatial and temporal degrees of freedom, we demonstrate a robust quantum advantage, extending to illumination fluxes well above the limits traditionally considered in the literature. Our analysis offers valuable insights into the ongoing debate on quantum-enhanced two-photon processes and helps establish their usefulness in applications.
Abstract Properties of intense twin beams generated in parametric down-conversion in periodically poled LiNbO3 crystals and their chirped variants by intense pump fields are analyzed along the model of intense parametric down-conversion that allows for pump depletion and uses the dual spatio-spectral Schmidt modes. Spectral and spatial intensity auto- and cross-correlation functions are determined as they depend on the pump power. Temporal correlations in intense twin beams at the fs time scale are investigated using the Hong-Ou-Mandel interferometer and the process of sum-frequency generation.
We report on the observation of broadband (40 THz) bright twin beams through high-gain parametric downconversion in an aperiodically poled lithium niobate crystal. The output photon number is shown to scale exponentially with the pump power and not with the pump amplitude, as in homogeneous crystals. Photon number correlations and the number of frequency/temporal modes are assessed by spectral covariance measurements. By using sum-frequency generation on the surface of a non-phase-matched crystal, we measure a cross-correlation peak with the temporal width of 90 fs. (C) 2018 Optical Society of America
We report on the observation of broadband (40 THz) bright twin beams through high-gain parametric downconversion in an aperiodically poled lithium niobate crystal. The output photon number is shown to scale exponentially with the pump power and not with the pump amplitude, as in homogeneous crystals. Photon number correlations and the number of frequency/temporal modes are assessed by spectral covariance measurements. By using sum-frequency generation on the surface of a non-phase-matched crystal, we measure a cross-correlation peak with the temporal width of 90 fs.
Intense twin beams generated by high-gain parametric downconversion exhibit simultaneous correlations in time and frequency. To characterize the simultaneous correlations, it is important to determine the temporal correlation profile and the corresponding phase. Although sum frequency generation (SFG) is often used to characterize the temporal correlation of the twin beams, the SFG spectra reconstruct the pump intensity spectrum shape used to generate the twin beams, so useful information for phase reconstruction cannot be obtained from the SFG spectra. We propose and demonstrate frequency-resolved optical gating measurement for ultranarrow temporal correlation of twin beams (referred to as quantum FROG measurement). Quantum FROG measurement for twin beam correlations is realized using a cross-correlator based on four-wave mixing (FWM). We show theoretically that although the quantum FROG trace exhibits a different functional form obtained by the conventional FROG trace for ultrashort pulses, it is sensitive to phase dispersion. In experiments, we observed a shift of the FWM frequency, i.e., frequency chirping, within a correlation time of hundreds of femtoseconds, and the sign of the chirp was also identified.