D. F. McAlister

Optical phase retrieval by phase-space tomography and fractional-order Fourier transforms

Phase-space tomography is experimentally demonstrated for the determination of the spatially varying amplitude and phase of a quasi-monochromatic optical field by measurements of intensity only. Both fully and partially coherent sources are characterized. The method, which makes use of the fractional-order Fourier transform, also yields the Wigner distribution of the field and works in one or two dimensions.

Measuring the Quantum Polarization State of Light

Quantum-state tomography is proposed as a means to achieve a complete measurement of the quantum polarization state of a light wave. A set of measurements using dual-polarization balanced homodyne detection is shown to be tomographi-cally complete with respect to the statistics of the SU(2) Stokes operators on the Poincare sphere. Complete reconstruction of the polarization sector of the density matrix of a partially polarized optical field can be achieved while randomizing the overall phase of the dual-polarization local oscillator.

Correlation and joint density matrix of two spatial–temporal modes from balanced-homodyne sampling

A theoretical treatment is given which establishes dual-mode balanced-homodyne detection as a practical and well characterized technique for measuring optical field correlations, photon-number correlations, or the full quantum state of a pair of optical modes. The definition of modes used includes temporal wave packets, Gaussian or other beam profiles, or two-frequency fields. The proposed method allows the measurement of two-time correlations on sub-picosecond scales, the disentangling of the statistics of signal light in two spatially overlapping modes, and the measurement of field correlations, such as squeezing, over 100 THz bandwidths. We show how to estimate from the data the statistical errors on the measured correlations and the density matrix arising from finite data sets, and the errors introduced by using finite numbers of phases and relative amplitudes of the two local oscillator fields.

Ultrafast balanced-homodyne chronocyclic spectrometer

We describe an optical detection system for simultaneous time- and frequency-resolved measurements: the Balanced-Homodyne Chronocyclic Spectrometer (chrono equals time; cyclic equals frequency). This system uses balanced, optical homodyne detection, with a wavelength- tunable, pulsed local-oscillator (LO) field to time resolve the spectrum of weak light pulses. The LO field defines the time and frequency window in which the signal field is sampled. The method time resolves the photon statistics as well as the mean intensity. Measurement examples are given for: (1) Temporal oscillations of laser pulses transmitted through a semiconductor quantum well in an optical microcavity and (2) The time-frequency profile of a linearly chirped ultrashort laser pulse.

Spatial and Temporal Optical Field Reconstruction Using Phase-Space Tomography

Phase-space tomography has recently been developed for the experimental determination of the amplitude and phase structure of a multimode optical field in either the space or time domain. The methods can be applied to the precise characterization of optical fields, in the cases of fully or partially coherent sources.

Ultrafast field-polarization dynamics in an optically pumped semiconductor microcavity laser

Summary form only given. The polarization properties of vertical cavity surface emitting lasers (VCSEL) originate in the change of electron total angular momentum J/sub z/ projected along the vertical axis for transitions from the conduction to the valence band. For quantum wells, J/sub z/=/spl plusmn/1/2 for the conduction band, and J/sub z/=/spl plusmn/3/2 for the heavy hole valence band, the highest energy valence band in unstrained quantum wells. The dipole allowed transitions are between J/sub z/=-1/2 and J/sub z/=-3/2 producing right circularly polarized light and between J/sub z/=+1/2 and J/sub z/=+3/2 producing left circularly polarized light. In CW, electrically pumped VCSELs, polarization states and fluctuations are well described by a model based on these transitions (San Miguel et al, 1995). We are investigating the polarization properties of VCSELs optically pumped with ultrashort pulses (<1 ps) which allows us to control the relative population of the angular momentum states and monitor the development of the intensity, noise, and correlations of the polarized-modes as a function of time.

Ultrafast two-time photon-number correlations in an optically pumped semiconductor microcavity laser

Summary form only given. Semiconductor microcavity systems can display complex dynamics resulting from the coupling of excitons and photons to form cavity polaritons, as well as the creation of excitons that are localized by quantum-well interface fluctuations. We are performing experiments to probe the time-domain quantum dynamics of a semiconductor microcavity pumped above the band edge. Initial results show 20-ps oscillations in the emitted lights second-order coherence function, g/sup (2)/(t,t+/spl tau/), versus /spl tau/ when the microcavity wavelength is tuned to a regime where localized excitons can reach lasing threshold at densities below the (saturation, or Mott) density where excitons ionize.