Optical methods can provide useful tissue characterization tools. For this project, two-photon microscopy and polarized light examinations (polarimetry) were used to assess the organizational state of myocardium in healthy, infarcted, and stem-cell regenerated states. Two-photon microscopy visualizes collagen through second-harmonic generation and myocytes through two-photon excitation autofluorescence, providing information on the composition and structure/organization of the tissue. Polarimetry measurements yield a value of linear retardance that can serve as an indicator of tissue anisotropy, and with a dual-projection method, information about the anisotropy axis orientation can also be extracted. Two-photon microscopy results reveal that stem-cell treated tissue retains more myocytes and structure than infarcted myocardium, while polarimetry findings suggest that the injury caused by temporary ligation of a coronary artery is less severe and more diffuse that than caused by a permanent ligation. Both these methods show potential for tissue characterization.

Biomedical imaging requires high resolution to see the fine features of a sample and fast acquisition to observe live cells that move. Optical coherence tomography (OCT) is a powerful technique which uses optical interference for non-invasive high resolution 3D imaging in biological samples. The resolution of OCT is determined by the length over which the light used will in- terfere. Unfortunately, dispersion hurts the imaging resolution by broadening interference features. A technique called quantum-OCT (QOCT)[1] is immune to dispersion but re- quires entangled photon pairs. The need for entanglement drastically reduces the number of photons available for imaging, making QOCT too slow to be practical. Chirped-pulse interferometry (CPI) is also immune to dispersion. A chirped pulse is one where the fre- quency, or colour, of the light changes from red to blue from one end of the pulse to the other. CPI relies on frequency correlations created by applying different chirps to two sep- arate pulses. This method had the disadvantage of being limited to a single predetermined chirp rate, and discarded 50% of the power. However CPI has better resolution than OCT, automatic dispersion cancellation, and 10,000,000 times the signal strength of QOCT [13]. A new, much more flexible and efficient method of CPI will be demonstrated by creating the frequency correlations entirely in a single pulse. This new method is referred to as non- linear chirped pulse interferometry (NL-CPI). The non-linear chirp required in NCPI is very difficult to produce using only conven- tional optics. In this thesis we document the construction and characterization of a new method of creating the desired chirp using a programmable pulse-shaper (PS). We build a PPS and then demonstrated its functionality by compressing a 105nm FWHM bandwidth pulse to under 17f s, near its transform limited time duration. We also show that the values given to the PPS for dispersion are accurate by calculating and then compensating the dispersion caused by various optical elements in the CPI interferometer. Conventional OCT systems are immune to dispersion common to both arms of the interferometer. Non-linear interferometers experience broadening due to this dispersion, making them more difficult to use with fibre based interferometers common in conventional OCT. We show that NL-CPI can compensate for dispersion common to both arms of the interferometer, making NL-CPI more appealing as a replacement for conventional OCT. In this thesis we experimentally implement and demonstrate a prototype setup using non-linear CPI for dispersion-cancelled imaging of a mirror, with a resolution comparable to conventional OCT systems. We then use the system to produce 2-D cross sectional images of a biological sample, an onion. Q-OCT has previously been used to image an onion[16], but required treating the onion with gold nano particles to achieve a useful signal. The onion we used had no special treatment. In addition our axial scanning rate is also 10000 times faster than Q-OCT.

This dissertation reports the results of optical studies of epitaxial (e), polycrystalline (p) and amorphous (a) Ge2Sb2Te5 (GST) thin films. The dynamic properties of GST films in all three (e/p/a) phases were investigated by a time-resolved optical pump-probe technique in which a femtosecond pump pulse of 55 fs duration was used to excite the sample. The intensity and polarization of the reflected probe beam respectively provide information about the transient reflectance (R) and anisotropic reflectance (AR) induced in the sample, that in turn provide the information about the crystal structure, phonon spectrum, and ultimately phase transitions within the sample. The study of an epitaxial sample provides an opportunity to explore the character of the modes within the phonon spectrum. The epitaxial GST film was grown upon a homoepitaxial layer of GaSb grown upon a GaSb wafer. We observed a 6.7 THz coherent optical phonon (COP) in GaSb(001). The dependence of the signal strength upon the pump and probe polarization was explained in terms of a model that considered both Transient stimulated Raman Scattering (TSRS) and the action of a Surface Space-Charge (SSC) field. The presence of the 6.7 THz transverse COP in the AR channel and its four fold dependence on pump and probe polarization suggests a three-dimensional T2 character. The COP amplitude was maximum when the probe was polarized parallel to the cube edge (GaSb[100]) and the pump polarization was set parallel to a face diagonal (GaSb[110]). The results were fully understood using a microscopic model of selective bond breaking. The AR response of e-GST/GaSb(001) reveals the presence of a 3D 3.4 THz transverse optical phonon. The mode amplitude was independent of pump polarization indicating that the mode is excited by a SSC field. This SSC field could exist within the GST, if the distorted rock-salt structure of GST lacks inversion symmetry, or GaSb, which has the non-centrosymmetric zincblende structure, leading to impulsive excitation of phonons at the GST/GaSb interface. The mode in GST was inferred to be T2-like. The observation of a T2-like phonon mode confirms that GST is cubic in structure and challenges previous studies where 1D or 2D character was assigned to the 3.4 THz mode. While pump-probe measurements displayed the presence of a 3D 3.4 THz mode in the AR response of e-GST/GaSb(001), a 4.5 THz mode was observed in both R and AR channels for p-GST(37 nm)/Si(001) and a-GST(57 nm)/Si(001). The mode character was identified to be either of A or E type by comparing the frequency with frequencies reported in the literature. Additional Raman microscope measurements confirmed the presence of the modes observed in the pump-probe measurements and also revealed additional frequencies. The differences in the frequencies observed from the different samples are quite small suggesting the presence of similar bonds that are modified to some extent by the different structural environment found within each sample. After exposure to high pump fluence the original modes disappeared and were replaced by new modes with frequencies at 4.2 THz and 3.1 THz in e-GaSb, 4.2 THz in e-GST, 3.5 THz in p-GST and 3.6 THz in a-GST. The difference in the final frequencies observed for p and a-GST sample may result from the difference in stack structure affecting the time-dependent temperature profile in each sample. The dependence of the temperature profile on the sample stack was understood from an experimental study of the phase transition between the amorphous and crystalline states induced by exposure to a series of amplified laser pulses. The dependence of the crystalline area and its reflectivity upon the number of pulses and fluence was described using a simple algebraic model. The results justify the assumption of one-dimensional heat flow. The growth velocity of the crystalline region was calculated to be 7-9 m/s. Apparatus and methods were developed to extend the time-resolved optical studies described previously. Firstly, an apparatus was constructed for the measurement of the wavelength dependent sample reflectance with a white-light pulse. A reference arm was employed to allow normalization and hence removal of the intensity noise arising in the laser regenerative amplifier system. Secondly an electrical measurement apparatus was constructed to allow combined electro-optical measurements in future. Switching of GST vertical memory cells was successfully demonstrated. The cells were fabricated on a borosilicate substrate with TiW top and bottom electrodes. A DC voltage of 4.5 to 6 V was required to induce switching, while in pulsed measurements, the device demonstrated switching in response to a pulse with minimum duration of 100 ns.

Biomedical imaging requires high resolution to see the fine features of a sample and fast acquisition to observe live cells that move. Optical coherence tomography (OCT) is a powerful technique which uses optical interference for non-invasive high resolution 3D imaging in biological samples. The resolution of OCT is determined by the length over which the light used will in- terfere. Unfortunately, dispersion hurts the imaging resolution by broadening interference features. A technique called quantum-OCT (QOCT)[1] is immune to dispersion but re- quires entangled photon pairs. The need for entanglement drastically reduces the number of photons available for imaging, making QOCT too slow to be practical. Chirped-pulse interferometry (CPI) is also immune to dispersion. A chirped pulse is one where the fre- quency, or colour, of the light changes from red to blue from one end of the pulse to the other. CPI relies on frequency correlations created by applying different chirps to two sep- arate pulses. This method had the disadvantage of being limited to a single predetermined chirp rate, and discarded 50% of the power. However CPI has better resolution than OCT, automatic dispersion cancellation, and 10,000,000 times the signal strength of QOCT [13]. A new, much more flexible and efficient method of CPI will be demonstrated by creating the frequency correlations entirely in a single pulse. This new method is referred to as non- linear chirped pulse interferometry (NL-CPI). The non-linear chirp required in NCPI is very difficult to produce using only conven- tional optics. In this thesis we document the construction and characterization of a new method of creating the desired chirp using a programmable pulse-shaper (PS). We build a PPS and then demonstrated its functionality by compressing a 105nm FWHM bandwidth pulse to under 17f s, near its transform limited time duration. We also show that the values given to the PPS for dispersion are accurate by calculating and then compensating the dispersion caused by various optical elements in the CPI interferometer. Conventional OCT systems are immune to dispersion common to both arms of the interferometer. Non-linear interferometers experience broadening due to this dispersion, making them more difficult to use with fibre based interferometers common in conventional OCT. We show that NL-CPI can compensate for dispersion common to both arms of the interferometer, making NL-CPI more appealing as a replacement for conventional OCT. In this thesis we experimentally implement and demonstrate a prototype setup using non-linear CPI for dispersion-cancelled imaging of a mirror, with a resolution comparable to conventional OCT systems. We then use the system to produce 2-D cross sectional images of a biological sample, an onion. Q-OCT has previously been used to image an onion[16], but required treating the onion with gold nano particles to achieve a useful signal. The onion we used had no special treatment. In addition our axial scanning rate is also 10000 times faster than Q-OCT.

Στην παρούσα εργασία μελετάται η τρίτης τάξης μη γραμμική απόκριση νανοσωματιδίων παλλαδίου σε συμπολυμερή όπως επίσης και κβαντικών ψηφίδων ιωδιούχου μολύβδου. Ο προσδιορισμός της μη γραμμικής επιδεκτικότητας τρίτης τάξης και η υπερπολωσιμότητα δεύτερης τάξης επιτυγχάνεται με την βοήθεια των τεχνικών Z-scan και οπτικού φαινομένου Kerr (OKE) χρησιμοποιώντας παλμούς λέιζερ 35 psec και 4 nsec με μήκος κύματος διέγερσης 532 nm και 1064 nm. / In this work the third order nonlinear optical response of palladium nanoparticles encapsulated in block copolymers has been investigated as well as lead iodide quantum dots. The third-order nonlinear susceptibility χ(3) and the second hyperpolarizability γ are determined by employing Z-scan and Optical Kerr Effect (OKE) techniques using 35 ps and 4 ns laser pulses at excitation wavelengths of 532 and 1064 nm.

I developed a high power blue laser for use in scientific and technical applications (eg. precision spectroscopy, semiconductor inspection, flow cytometry, etc). It is linearly polarized, single longitudinal and single transverse mode, and a convenient fiber coupled continuous wave (cw) laser source. My technique employs external cavity frequency doubling and provides better power and beam quality than commercially available blue diode lasers. I use a fiber Bragg grating (FBG) stabilized infrared (IR) semiconductor laser source with a polarization maintaining (PM) fiber coupled output. Using a custom made optical and mechanical design this output is coupled with a mode matching efficiency of 96% into the doubling cavity. With this carefully designed and optimized cavity, measurements were carried out at various fundamental input powers. A net efficie ncy of 81 % with an output power of 680 mW at 486 nm was obtained using 840 mW of IR input. Also I report an 87.5 % net efficiency in coupling of blue light from servo locked cavity into a single mode PM fiber. Thus I have demonstrated a total fiber to fiber efficiency of 71% can be achieved in our approach using periodically poled potassium titanyl phosphate (PPKTP). To obtain these results, all losses in the system were carefully studied and minimized.

No description available.

High-order harmonic generation (HHG), a non-perturbative nonlinear light-matter interaction resulting in coherent emission of high-frequency light, has demonstrated promise as an optical probe of carrier dynamics, structural symmetries, and other properties of solids. HHG from bulk solids in transmission geometry, however, is influenced by nonlinear propagation of the driving laser, which leads to spectral skewing and temporal phase variations in the harmonic emission. These effects obscure the microscopic underlying physics, making HHG-based spectroscopy of bulk solids difficult to interpret. HHG in few-to mono-layer materials, however, avoids strong nonlinear propagation effects, and can provide novel material properties for HHG studies. In this work, I compare HHG driven by femtosecond mid-infrared laser pulses in bulk and thin film solids. First, HHG generated from epitaxial ZnO thin films grown using different preparations is compared with HHG from bulk ZnO. I identify spectral signatures that result from nonlinear propagation in bulk samples, while thin films generally yield clean harmonic spectra with features that depend on the crystal growth and preparation. Specifically, I find that as-grown plasma ALD (atomic layer deposition) samples yield monocrystalline polar films, which is modified by annealing. The dependence of the harmonic yield on thickness of the nano-meter scale films was also experimentally measured and found to agree with simulations which incorporated nonlinear conductivity and linear propagation effects. Next, I examine the carrier envelope phase (CEP) dependence of HHG from bulk and thin-film ZnO. I observed a stronger-than-expected sensitivity of the HHG from bulk ZnO to CEP, which results from nonlinear self-compression of the pulse to single-cycle durations. Finally, experimental studies of HHG from novel van der Waals crystals are presented. Together, these results suggest novel frontiers for HHG from few-layer materials.

This thesis presents the experimental work performed on the spectrin protein. The aim of the work was to study the direct interactions of spectrin, the cytoskeleton of RBCs, with membrane lipid to determine its effects on the mechanical properties of the lipid bilayer. Motivation for this work came from a lack of unanimity in the field of spectrin, and the hypothesized potential of the protein to perforate giant unilamellar vesicles. The work aimed to investigate and determine how spectrin-lipid interactions influence membrane mesoscopic morphology and biophysics in ways that could ultimately be important to cellular function. For this purpose, a protocol was implemented to take into account the different aspects of the binding. Direct visualisation of the spectrin-lipid interaction and distribution was achieved using confocal fluorescence microscopy. Changes in the mechanical properties of the membrane were investigated using the micropipette aspiration technique. Finally the thermodynamics of the interaction were considered with isothermal titration calorimetry experiments. This allowed evaluation of the protein-lipid interaction in a complete and coherent manner. Experiments were also performed on another elastic protein, alpha-elastin, for comparison. In addition to its similarities with spectrin (both possess hydrophobic domains and entropy elasticity), elastin is auto-fluorescent which makes it an attractive model protein. Elastin was also used as a sample model to implement new techniques using nonlinear optics microscopy.

The aim of the project described in this thesis is to synthesise new functional molecules which interact with light for neurophysiological applications. In particular, I describe a family of amphiphilic porphyrins with large first hyperpolarisabilities which are used as SHG contrast agents and voltage-sensitive probes. In addition I detail a methodological microscopy tool and a novel caged form of a neuronal ion-channel antagonist. Chapter 1 introduces the key concepts underlying the use of dyes as SHG contrast agents. In particular it focuses on aspects of molecular design, covering both the amphiphilicity and nolinearity required by the target molecule. It covers quantification of the nonlinear properties of SHG stains, then surveys a number of examples which showcase the flexibility of SHG imaging as a biomedical technique. Chapter 2 describes a family of amphiphilic porphyrins with large first hyperpolarisabilities. Working from the structure-property relationships identified in Chapter 1, we fully characterise these dyes and demonstrate that they can be used in SHG imaging. We demonstrate that these molecules may also be tuned by complexation of a metal ion which can modulate their photophysical and solubility behaviour. Chapter 3 provides a description of how to determine the orientational distribution of dipolar dyes in a membrane by multiphoton microscopy. We measure the signal intensity of the dye in a model membrane system then find distributional moments which lead to the distribution itself. Chapter 4 explores whether off-axis contributions to the first hyperpolarisability tensor can significantly augment the dominant on-axis contribution from the main dipolar charge-transfer band. We synthesise and characterise a series of cis-donor cis-acceptor porphyrin compounds and explore their biophysical characteristics. Chapter 5 is the culmination of this project and after discussing method development, goes on to show how we measure the voltage sensitivity of an amphiphilic porphyrin SHG dye. We compare the archetypal porphyrin dye chromophore with three commercially available styryl dyes and demonstrate that our dye has greater sensitivity and a more rapid response. Chapter 6 describes a side project, the use of a photolabile cage to protect MK801, a neuronal ion-channel antagonist. By developing a water soluble photolabile cage using molecular design techniques, we are able to release MK801 in neurons with precise spatiotemporal control, allowing us to pinpoint the locus of two key neurophysiological processes.