Peak Doubling in SPDC Coincidence Spectra with a Short-Pulse Pump
  We describe a double-peak structure of the coincidence spectrum of biphoton states in the process of spontaneous parametric down-conversion with a pump having the form of short pulses. The effect is shown to arise owing to the obligatory symmetry of bihoton wave functions, as wave functions describing states of two bozons obeying the Bose-Einstein statistics. Parameters of the peaks are found and conditions necessary for experimental observation of the effect are determined. 
Mikhail V. Fedorov, Julia M. Mikhailova and Peter A. Volkov
quant-ph