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Method and applications of time-resolved space-heterodyne imaging


Technological progress in the ultrashort pulse laser physics and digital image acquisition and analysis systems opens broad opportunities for the new generation of optical characterization methods and tools for investigation of ultrafast phenomena in various research fields. Ultrashort optical pulses bring unprecedented temporal resolution, allowing characterization of ultrafast phenomena on the femtosecond time scale, while digital holography methods allow real time characterization of optical fields in amplitude and phase. In this dissertation we develop and demonstrate application of time-resolved spatial heterodyne interferometry -- a novel method for simultaneous spatial and temporal characterization of femtosecond-scale optical fields. We analyze spatial and temporal resolution of the method in single and two-photon absorption configurations and identify main limitations due to detector dynamic range, temporal shape of the reference optical pulse waveform and detection noise. Application of time-resolved spatial heterodyne interferometry is first demonstrated for characterization of ultrashort pulse propagation through multimode optical fibers. Complex optical field at the fiber output is reconstructed in time and space from single and two-photon absorption digital holograms yielding 3-dimensional optical impulse response of the multimode fiber. Optical impulse response of the fiber is found to critically depend on the coupling and environmental conditions, limiting applicability of the measured impulse response for signal equalization. Finally we demonstrate excitation and characterization of ultrafast surface plasmon polariton pulses, propagating on the surface of a nanostructured metallic film. Optical pulses are coupled from free space into various surface modes using a 2-dimensional array of circular nanoholes. Spatial amplitude and phase characteristics of the scattered surface field are measured with femtosecond- scale time resolution. Demonstrated in-plane focusing of SPP pulse provides additional electromagnetic field localization with possible applications in surface plasmon polariton nanophotonics, nonlinear surface dynamics, biochemical sensing and ultrafast surface studies

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