Professor Ian Walmsley CBE FRS FCGI

Abstract:

We present an experimental method to measure the transverse spatial quantum state of an optical field in coordinate space at the single-photon level. The continuous-variable measurements are made with a photoncounting, parity-inverting Sagnac interferometer based on all-reflecting optics. The technique provides a large numerical aperture without distorting the shape of the wavefront, does not introduce astigmatism, and allows for characterization of fully or partially coherent optical fields at the single-photon level. Measurements of the transverse spatial Wigner functions for highly attenuated coherent beams are presented and compared with theoretical predictions. © 2005 Optical Society of America.

Abstract:

We show that tailored group velocity matching in non- linear chi((2)) crystal sequences interspersed with birefringent chi((1)) compensators can be used to generate time-bin entangled states. By choosing the crystal and compensator materials appropriately it is possible to generate all four time-bin Bell states without resorting to time non- stationary devices. This scheme, in addition, lends itself well to the generation of higher-dimensionality states such as time-bin qutrits.

Abstract:

A noncollinear optical parametric amplifier in which blue pump pulse generation as well as parametric amplification takes place in the same nonlinear crystal is presented. Broadband spectra tunable throughout over 100 nm in the visible were generated in a simple setup. The green output pulses were compressed to 65 fs, and efficiency (IR-to-visible) of 1.8% was achieved.