Browsing by Author "Dwapanyin, George Okyere"

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    Development of a multimodal nonlinear imaging system for biophotonic applications
    (Stellenbosch : Stellenbosch University., 2020-04) Dwapanyin, George Okyere; Rohwer, Erich G.; Neethling, Pieter H.; Bosman, Gurthwin W.; Stellenbosch University. Faculty of Science. Dept. of Physics.
    ENGLISH ABSTRACT: Multiphoton microscopy techniques have gained wide prominence in biophotonics imaging applications since their inventions. Compared to conventional optical imaging, these nonlinear optical microscopy (NLOM) techniques are intrinsically confocal, and thus enables three-dimensional imaging with submicron spatial resolution. Additional advantages include decreased photodamage to tissue, increased depth of penetration as well as the ability to perform label-free imaging. Signal response in NLOM techniques depend nonlinearly on the peak intensity, therefore requiring a high peak intensity laser as source. Control of ultrashort pulses enables the generation of high peak intensity pulses with lower excitation pulse energies. This dissertation focuses on the development of a nonlinear microscopy system for biological applications based on the control of the spectral phase of broadband supercontinuum pulses generated in a polarization maintaining all normal dispersion photonic crystal fibre. We further demonstrate, for the first time, the real world application of a time domain ptychographic phase measurement technique known as i2PIE which allows for phase correction at the object plane, in microscopy, and how this phase control contributes to image enhancement in two photon excitation fluorescence (TPEF) and second harmonic generation (SHG) imaging of biological tissue. By comparing this new technique to the commonly used multiphoton intrapulse interference phase scan (MIIPS) measurement technique, we show that i2PIE offers an improved spectral phase measurement which can be used to generate shorter temporal pulses and ultimately produce higher peak intensities, even at lower pulse energies. Our results also show that for the same input pulse energies, i2PIE provides a higher contrast image and an improved signal to noise ratio compared to MIIPS. The results obtained from this work projects i2PIE as a promising phase measurement technique for the coherent control of ultrashort pulses used in nonlinear microscopy.