摘要： Spontaneous parametric down-conversion (SPDC) is one of the most important sources for entangled or correlated photon pairs, which are the foundation of the emerging fields of quantum-optical imaging and spectroscopy. Using periodically poled materials as an SPDC-source allows broad emission spectra in widely tunable wavelength ranges in an efficient and walk-off-free process. For applications that employ nonlinear interference setups [1,2], maximum interferometric contrast is only achieved when signal and idler modes are overlapped precisely in the second crystal. Thus, accurate knowledge of the spectral-angular characteristic of SPDC is crucial for designing such devices. In our work, we extend an analytic approach introduced by Byer and Harris [3] and develop an application- oriented model for the signal power density of broadband SPDC. For spectrally broad emission, non-collinear phasematching has to be described properly. Here, the finite pump diameter is taken into account by introducing an angular dependent effective interaction length. As an exemplary case, we calculate the angular characteristics, the spectral power density and the total signal power for SPDC in periodically poled lithium niobate pumped at 532 nm. For verification, we compare the calculations to experimental results obtained with a 2 cm long, 5 % MgO-doped lithium niobate crystal at 40 °C crystal temperature. The crystal contains 11 poling channels with periods ranging from 8.2 μm to 11.2 μm. It is pumped by a narrowband laser with 2 W power at 532 nm wavelength focused to a beam waist of 120 μm. Using the different poling periods, we cover a signal wavelength range of 613 nm to 750 nm, which corresponds to correlated idler wavelengths ranging from 4 μm to 1.8 μm. In figure 1a, the calculated spectral power density for different poling channels (solid lines) is compared to measured spectra. To account for the angular-dependent coupling efficiency to the spectrometer fiber input, each measured spectrum is scaled with a constant factor to the best fit with the calculated power density and thus only allows a qualitative comparison. The quantitative comparison of the calculated (solid lines) and measured (black dots) total signal power for the different channels as a function of the collinear (peak) signal wavelength in figure 1b) further verifies our calculations. The presented analytical model is easily applicable to a wide range of experimental configurations for SPDC in periodically-poled crystals, without the need for time-consuming numerical simulations. The exact knowledge of the spatial and spectral structure of SPDC emission allows predictions on design criteria for functionalized devices that employ SPDC as a photon pair source.