Spectrum Analysis of a Pulsed Photon Source Generated from Periodically Poled Lithium Niobate

We present a theoretical and experimental study on the bandwidth of parametric down-converted photons generated from periodically poled lithium niobate (PPLN) crystal pumped by a pulsed laser. By comparison of crystals with different lengths and pump beams of different bandwidths, we demonstrate that the bandwidth of down-converted photons will increase for a broader bandwidth of pump pulse and decrease for a longer crystal, but the influence of crystal length will become weaker along with increase of both crystal length and pump pulse bandwidth. Especially under the conditions of our experiment, the bandwidth almost remains unchanged for longer crystals when pumped by a femtosecond laser. This may be helpful for schemes in which pulsed lasers are used to pump PPLN crystals.