by Anhui Liang. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (p. D1-D4). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web.

Lee Ka-lun. / "September 2003." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Tang Wing-Wa. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgement --- p.iv / Table of contents --- p.v / List of figure --- p.viii / Chapter 1. --- Introduction --- p.1 / Chapter 1.1. --- Introduction to ultrashort optical pulse generation --- p.2 / Chapter 1.2. --- Introduction to wavelength-tunable pulse generation --- p.5 / Chapter 1.3. --- Introduction to chapters --- p.7 / Chapter 2. --- Principles and Theories --- p.11 / Chapter 2.1. --- Principle of dispersion tuning --- p.12 / Chapter 2.2. --- SOA nonlinear optical loop mirror --- p.16 / Chapter 2.3. --- Principle of dispersion tuning in harmonically mode-locked fiber laser using nonlinear optical loop mirror --- p.19 / Chapter 2.4. --- Principle of re-configurable multi-wavelength pulses generationin a self-seeded laser diode incorporating SOA loop mirror --- p.22 / Chapter 3. --- Rational harmonic mode-locking of an optically triggered fiber laser incorporating a non-linear optical loop modulator --- p.25 / Chapter 3.1. --- Introduction --- p.26 / Chapter 3.2. --- Experiment --- p.27 / Chapter 3.3. --- Result and discussion --- p.30 / Chapter 3.4. --- Summary --- p.37 / Chapter 4. --- Generation of amplitude-equalized optical pulses from a rational harmonic mode-locked fiber laser incorporating a SOA loop modulator --- p.40 / Chapter 4.1. --- Introduction --- p.41 / Chapter 4.2. --- Experiment --- p.42 / Chapter 4.3. --- Result and discussion --- p.44 / Chapter 4.4. --- Summary --- p.47 / Chapter 5. --- Optically controlled dispersion-tuning in harmonically mode-locked erbium doped fiber laser using SOA nonlinear loop modulator --- p.49 / Chapter 5.1. --- Introduction --- p.50 / Chapter 5.2. --- Experiment --- p.51 / Chapter 5.3. --- Result and discussion --- p.54 / Chapter 5.4. --- Summary --- p.58 / Chapter 6. --- Alternate method of constructing harmonically mode-locked fiber laser incorporating SOA nonlinear loop modulator --- p.60 / Chapter 6.1. --- Introduction --- p.61 / Chapter 6.2. --- Experiment --- p.62 / Chapter 6.3. --- Result and discussion --- p.65 / Chapter 6.4. --- Summary --- p.69 / Chapter 7. --- Optically re-configurable multi-wavelength pulse source constructed from a self-seeded laser diode --- p.71 / Chapter 7.1. --- Introduction --- p.72 / Chapter 7.2. --- Experiment --- p.74 / Chapter 7.3. --- Result and discussion --- p.77 / Chapter 7.4. --- Summary --- p.82 / Chapter 8. --- Tunable alternating multi-wavelength pulse source constructed using non-linear optical control of wavelength switching in a self-seeded laser diode --- p.85 / Chapter 8.1. --- Introduction --- p.86 / Chapter 8.2. --- Experiment --- p.87 / Chapter 8.3. --- Result and discussion --- p.89 / Chapter 8.4. --- Summary --- p.92 / Chapter 9. --- Conclusion and future works --- p.94 / Chapter 9.1. --- Conclusion --- p.94 / Chapter 9.2. --- Possible future works --- p.98 / Appendix / List of publications --- p.A-1

In this thesis, simulations of laser-driven many-electron dynamics in molecules are presented, i.e., the interaction between molecules and an electromagnetic field is demonstrated. When a laser field is applied to a molecular system, a population of higher electronic states takes place as well as other processes, e.g. photoionization, which is described by an appropriate model. Also, a finite lifetime of an excited state can be described by such a model. In the second part, a method is postulated that is capable of describing electron correlation in a time-dependent scheme. This is done by introducing a single-electron entropy that is at least temporarily minimized in a further step. / Im Rahmen dieser Doktorarbeit werden Simulationen lasergetriebener Vielelektronendynamik in Molekülen präsentiert, d.h., die Wechselwirkung zwischen Molekülen und einem elektromagnetischen Feld wird demonstriert. Bei Laseranregungen finden nicht nur elektronische Übergänge statt, sondern auch weitere Prozesse wie die Photoionisation, die mit einem geeigneten Modell beschrieben wird. Auch die endliche Lebensdauer angeregter Zustände kann mit einem solchen Modell beschrieben werden. Im zweiten Teil wird eine Methode postuliert, die fähig ist, die Elektronenkorrelation zeitabhängig zu beschreiben. Dies wird durch die Einführung einer Einelektronenentropie erreicht, die in einem weiteren Schritt zumindest kurzzeitig minimiert wird.

Femtosecond time-resolved photoelectron spectroscopy (fsTRPES) experiments have been used to study the photoelectron energy spectra of simple molecules since the 1980’s. Analysis of these spectra provides information about the ultrafast internal conversion dynamics of the parent ions. However, ultraviolet pulses must be used for these pump-probe experiments in order to ionize the molecules. Since current solid state lasers, such as the Ti:sapphire laser, typically produce pulses centered at 800nm, it is necessary to generate UV pulses with nonlinear frequency mixing techniques. I therefore constructed an optical setup to generate the 3rd and 4th harmonics, at 266.7nm and 200nm, respectively, of a Ti:sapphire (Ti:sa) chirped-pulse amplified (CPA) laser system that produces 35fs pulses centered at 800nm. Thin Beta-Barium Borate (β-BaB2O4 or BBO) crystals were chosen to achieve a compromise between short pulse durations and reasonable conversion efficiencies, since ultrashort pulses are quite susceptible to broadening from group velocity dispersion (GVD). Output energies of around 11μJ and 230nJ were measured for the 266.7nm and 200nm pulses, respectively. The transform limits of the 3rd and 4th harmonic pulse lengths were calculated from their measured spectral widths. We found that the 266.7nm bandwidth was large enough to support sub-30fs pulses, and due to cutting at the lower-wavelength end of the 200nm spectrum, we calculated an upper limit of 38fs. The pulses were compressed with pairs of CaF2 prisms to compensate for dispersion introduced by transmissive optics. Two-photon absorption (TPA) intensity autocorrelations revealed fully compressed pulse lengths of 36 ± 2 fs and 42 ± 4 fs for the 3rd and 4th harmonics, respectively.

Femtosecond time-resolved photoelectron spectroscopy (fsTRPES) experiments have been used to study the photoelectron energy spectra of simple molecules since the 1980’s. Analysis of these spectra provides information about the ultrafast internal conversion dynamics of the parent ions. However, ultraviolet pulses must be used for these pump-probe experiments in order to ionize the molecules. Since current solid state lasers, such as the Ti:sapphire laser, typically produce pulses centered at 800nm, it is necessary to generate UV pulses with nonlinear frequency mixing techniques. I therefore constructed an optical setup to generate the 3rd and 4th harmonics, at 266.7nm and 200nm, respectively, of a Ti:sapphire (Ti:sa) chirped-pulse amplified (CPA) laser system that produces 35fs pulses centered at 800nm. Thin Beta-Barium Borate (β-BaB2O4 or BBO) crystals were chosen to achieve a compromise between short pulse durations and reasonable conversion efficiencies, since ultrashort pulses are quite susceptible to broadening from group velocity dispersion (GVD). Output energies of around 11μJ and 230nJ were measured for the 266.7nm and 200nm pulses, respectively. The transform limits of the 3rd and 4th harmonic pulse lengths were calculated from their measured spectral widths. We found that the 266.7nm bandwidth was large enough to support sub-30fs pulses, and due to cutting at the lower-wavelength end of the 200nm spectrum, we calculated an upper limit of 38fs. The pulses were compressed with pairs of CaF2 prisms to compensate for dispersion introduced by transmissive optics. Two-photon absorption (TPA) intensity autocorrelations revealed fully compressed pulse lengths of 36 ± 2 fs and 42 ± 4 fs for the 3rd and 4th harmonics, respectively.

The thesis analyses the process of pair annihilation into one photon in a laser pulse. The theory of how to include pulse shapes in Strong Field QED and the resulting cross section is presented. The cross section is calculated and estimated for lasers of ELI and XFEL facilites. It is found that the effect may be experimentally verifiable at high frequency XFEL facilities for very finely tuned particle kinematics, but negligible at high intensity optical laser facilities such as ELI.

In the last decade, there has been tremendous progress in the field of ultrashort-pulse measurement. However, this effort has focused mostly on the temporal behavior of 100-fs, 800-nm ultrashort pulse, ignoring other pulse lengths, wavelengths, and the very common space-time couplings or so called spatio-temporal distortions. In this thesis work, I do an extensive study of spatio-temporal distortions and their measurement using Frequency Resolved Optical Gating (FROG) and its relatives. I clarify some ambiguities in the descriptions of these effects in the existing theory and establish a more general description of such distortions in ultrashort pulses. I also extend these measurement techniques to different wavelengths and pulse lengths. Specifically, I develop measurement devices for few-cycle NIR pulses, weak and narrowband fiber laser pulses, long (several-ps) NIR pulses, and visible pulses from NOPAs.

A new pulse-retrieval software for Frequency-Resolved Optical Gating (FROG) technique has been developed. The new software extends the capacity of the original FROG algorithm in two major categories. First is a new method to determine the uncertainty of the retrieved pulse field in FROG technique. I proposed a simple, robust, and general technique?tstrap method?ch places error bars on the intensity and phase of the retrieved pulse field. The bootstrap method was also extended to automatically detect ambiguities in the FROG pulse retrieval. The second improvement deals with the spatiotemporal effect of the input laser beam on the measured GRENOUILLE trace. I developed a new algorithm to retrieve the pulse information, which includes both pulse temporal field and the spatiotemporal parameters, from the spatiotemporal distorted GRENOUILLE trace. It is now possible to have a more complete view of an ultrashort pulse. I also proposed a simple method to remove the spatial profile influence of the input laser beam on the GRENOUILLE trace. The new method extends the capacity of GRENOUILLE technique to measure the beams with irregular spatial profiles.

We have used ultrafast optics, primarily focused on the nonlinear processes of Polarization Gating and of Optical Parametric Amplification, one for measurement and the other for imaging purposes. For measurement, we have demonstrated a robust method of measurement to simultaneously measure both optical pulses used in a pump-probe type configuration. We refer to this method of pulse measurement as Double Blind Polarization Gating FROG. We have demonstrated this single-shot method for measuring two unknown pulses using one device. In addition to pulse measurement, we have demonstrated the processes of Optical Parametric Amplification (OPA) applicability to imaging of complex objects. We have done this where the Fourier transform plane is used during the interaction. We have amplified and wavelength converted a complex image. We observe a gain of ~100, and, although our images were averaged over many shots, we used a single-shot geometry, capable of true single-shot OPA imaging. To our knowledge, this is the first Fourier-plane OPA imaging of more than a single spatial-frequency component of an image. We observe more than 30 distinct spatial frequency components in both our amplified image and our wavelength shifted image. We have demonstrated all-optical spatial filtering for these complex images. We have demonstrated that direct Fourier filtering of spatial features is possible by using a shaped pump beam. We can isolate certain portions of the image simply by rotating the crystal.