The process of spontaneous parametric downconversion is an important source of single-photons and quantum states of light. Much recent theoretical and experimental work focuses on engineering the properties of the photons emitted from downconversion. For multi-photon experiments generating photon pairs that are spectrally pure, meaning the signal and idler photons are uncorrelated, has been an active area of investigation. For fundamental tests of quantum mechanics, such as loop-hole-free Bell tests, optimizing the coupling of photons to single-mode fiber is an important consideration.
While the principles behind the nonlinear process of downconversion are well understood, calculating the properties of the photons can be difficult and time-consuming when considering photons emitted at an angle with respect to the pump (non collinear) when the signal, idler, and pump can experience birefringent walk off. Here we present a program designed to simplify these calculations that builds on previous work. The application is web-based, open-sourced, and is designed to run in a user's browser. The program allows a user to easily determine the phasematching properties as well as the emission characteristics and joint spectrum of the signal and idler photons. The program also allows a user to quickly find phasematching parameters that generate spectrally pure states. The Hong-Ou-Mandel dip between the signal and idler is also calculated, and the joint spectrum in the dip can also be easily examined. Finally, the spatial mode structure and single-mode fiber coupling efficiency can be computed. The program is designed to be flexible, and can handle periodically-poled crystals that have been apodized with a Gaussian function.
SPDCalc is currently in beta testing. If you find any errors, or have suggestions, send them to Krister Shalm (krister [AT] dancingphysicist.com).