Abstracts

In the process of spontaneous parametricdownconversion, a pump photon incident on a nonlinear crystaldecays into two photons of lesser energies. It is well known thatwhen the pump is monochromatic, the two photons are highlycorrelated in energy, in time, and in direction of propagation.This thesis details a theoretical and experimental investigation ofthe phenomenon for the specific case in which the pump field is inthe form of a short optical pulse. It is found that thecharacteristics of the emitted photons are influenced both by theproperties of the pump pulse and by the physical properties of thenonlinear crystal. The theoretical model treats both type-I andtype-II downconversion. Effects are predicted in the type-IIprocess which are not seen in the more familiar cw-pumpeddownconversion. For this reason, the type-II process is studied inmore detail.
One of the interesting featuresof ultrafast type II downconversion is that the two photons do nothave identical spectra, even when the center frequencies areidentical. The spectral information carried by the photon pairleads to diminished visibility in a fourth-order interferenceexperiment. One interpretation of this effect is that the spectralinformation carried by the photon pair renders the two detectionprocesses somewhat distinguishable. The distinguishing informationmay also be regarded as temporal in nature. It is shown that bothof these interpretations are valid and that the relationshipbetween them can be understood in the context of the jointchronocyclic Wigner function, which relates the joint spectral andtemporal properties of the two photons.
Thetwo detection processes may be rendered indistinguishable bypassing the photons through a spectral filter, essentiallypreventing the distinguishing information from reaching thedetectors. Indistinguishability may also be restored by carefullyadding information to the system. An experiment is presented inwhich this is accomplished by overlapping the paths of the photonsso that they reach the detectors via one of two indistinguishablepathways.