In this research, the carrier-envelope phase CE phase) evolution of the pulse train from a Kerr-lens mode-locked chirped-mirror dispersion compensated Ti:Sapphire laser oscillator was stabilized. The offset frequency corresponding to the rate of change of the CE phase was obtained by spectrally broadening the oscillator pulses in a photonic crystal fiber and interfering the f and 2f components. An offset frequency linewidth of 100 mHz was obtained and could be locked over several hours. The effect of path length drift in the interferometer used for CE phase stabilization of the laser oscillator was investigated. By stabilizing the path length drift, the interferometer noise was reduced by several orders of magnitude. The CE phase drift through a grating-based chirped-pulse multi-pass amplifier was investigated. Varying the grating separation by 1microm in the stretcher was found to cause a shift of 3.7 ＋/-1.2 rad of the CE phase. The CE phase could be stabilized to within 160 mrad rms error by feedback controlling the grating separation. By locking the path length in the f-to-2f interferometer used to stabilize the CE phase of the oscillator pulses, the fast ＞3 Hz) CE phase drift of the amplified laser pulses was reduced from 79 to 48 mrad. It was also found that the CE phase could be shifted and set to any value within a 2pi range by changing the grating separation. Also, the CE phase could be continuously modulated within a 2pi range while maintaining a relative phase error of 171 mrad. The CE phase shift of a grating-based compressor was found to be stabilized to 230 mrad rms. The effect of laser power fluctuation on the CE phase measurement was also investigated. It was found that a 1% fluctuation of the laser energy caused a 160 mrad error in the CE phase measurement. A two-step model is proposed to explain the phase-energy coupling in the CE phase measurement. The model explains the experimentally observed dependence of the group delay between the f and 2f pulses on the laser energy. Few-cycle pulses were CE phase stabilized to 134 mrad rms and were used to perform above-threshold ionization and high harmonic generation.

This dissertation describes the advancements made towards the implementation of Tip-Enhanced Fluorescence Microscopy TEFM) in imaging biological specimens. This specialized type of microscopy combines the chemical specificity of optical microscopy techniques with the resolution of atomic force microscopy AFM). When an AFM probe is centered in the focal spot of an excitation laser with axial polarization, the probe concentrates the optical field such that it can be used to induce nanometer scale fluorescence. The physical mechanisms of this optical field enhancement are set forth in detail. The feasibility of this technique for imaging bimolecular networks is discussed in regard to the requirements for adequate image contrast, as well as for obtaining field enhancement in aqueous environments. A semianalytical model for image contrast for TEFM has been developed. This model shows that using demodulation techniques greatly increases the image contrast attainable with this technique, and is capable of predicting the requisite enhancement factors to achieve imaging of biomolecular networks at good contrast levels. This model predicts that signal enhancement factors on the order of 20 are needed to image densely packed samples. This dissertation also highlights a novel tomographical imaging approach. By timestamping the uorescence photon arrival times, and subsequently correlating them to the time-stamped motion of a vertically oscillating probe, a three-dimensional map of tip-sample interactions can be constructed. The culmination of these advancements has led to the ability to map the interactions between single carbon nanotubes and single fluorescent nanocrystals quantum dots). Various attempts at using TEFM in water have been thus far unsuccessful. Several explanations for this shortfall have been identified—understanding these shortcomings has helped to identify the optimal excitation conditions for field enhancement.

More and more researchers and clinicians are looking to molecular sensing to predict how cells will behave, seeking the answers to questions like will these tumor cells become malignant? or how will these cells respond to chemotherapy? Optical methods are attractive for answering these questions because optical radiation is safer and less expensive than alternative methods, such as CT which uses X-ray radiation, PET/SPECT which use gamma radiation, or MRI which is expensive and only available in a hospital setting. In this dissertation, three distinct optical methods are explored to detect at the molecular level: optical coherence tomography OCT), laser-induced fluorescence LIF), and optical polarimetry. OCT has the capability to simultaneously capture anatomical information as well as molecular information using targeted contrast agents such as gold nanoshells. LIF is less useful for capturing anatomical information, but it can achieve significantly better molecular sensitivity with the use of targeted fluorescent dyes. Optical polarimetry has potential to detect the concentration of helical molecules, such as glucose. All of these methods are noninvasive or minimally invasive. The work is organized into four specific aims. The first is the design and implementation of a fast, high resolution, endoscopic OCT system to facilitate minimally invasive mouse colon imaging. The second aim is to demonstrate the utility of this system for automatically identifying tumor lesions based on tissue microstructure. The third is to demonstrate the use of contrast agents to detect molecular expression using OCT and LIF. The last aim is to demonstrate a new method based on optical polarimetry for noninvasive glucose sensing.

Diode Pumped Alkali Lasers (DPALs) offer a promising approach for high power lasers in military applications that will not suffer from the long logistical trails of chemical lasers or the thermal management issues of diode pumped solid state lasers. This research focuses on characterizing a DPAL-type system to gain a better understanding of using this type of laser as a directed energy weapon. A rubidium laser operating at 795 nm is optically pumped by a pulsed titanium sapphire laser to investigate the dynamics of DPALs at pump intensities between 1.3 and 45 kW/cm2. Linear scaling as high as 32 times threshold is observed, with no evidence of second order kinetics. Comparison of laser characteristics with a quasi-two level analytic model suggests performance near the ideal steady-state limit, disregarding the mode mis-match. Additionally, the peak power scales linearly as high as 1 kW, suggesting aperture scaling to a few cm2 is sufficient to achieve tactical level laser powers. The temporal dynamics of the 100 ns pump and rubidium laser pulses are presented, and the continually evolving laser efficiency provides insight into the bottlenecking of the rubidium atoms in the 2P3/2 state. Lastly, multiple excited states of rubidium and cesium were accessed through two photon absorption in the red, yielding a blue and an IR photon through amplified stimulated emission. Threshold is modest at 0.3 mJ/pulse, and slope efficiencies increase dramatically with alkali concentrations and peak at 0.4%, with considerable opportunity for improvement. This versatile system might find applications for IR countermeasures or underwater communications.

An image mapping spectrometer (IMS) for microscopy applications is presented. Its principle is based on the redirecting of image zones by specially organized thin mirrors within a custom fabricated component termed an image mapper. The demonstrated prototype can simultaneously acquire a 140nm spectral range within its 2D field of view from a single image. The spectral resolution of the system is 5.6nm. The FOV and spatial resolution of the IMS depend on the selected microscope objective and for the results presented is 45x45mu2 and 0.45mum respectively. The system requires no scanning and minimal post. data processing. In addition, the reflective nature of the image mapper and use of prisms for spectral dispersion make the system light efficient. Both of the above features are highly valuable for real time fluorescent-spectral imaging in biological and diagnostic applications.

Abstract not available.

Pathological conditions give rise to mechanical changes in tissue that can be exploited for the purpose of diagnosis and treatment of disease. Elasticity imaging is a field developed to creating images of tissue stiffness by mechanically exciting tissue and tracking the tissue response. Acoustic Radiation Force Impulse ARFI) imaging is one such modality that measures the micron-scale displacements induced in tissue by local acoustic radiation forces using a high intensity ultrasound pulses generated by a standard diagnostic ultrasound scanner. Ultrasound pulses track displacements that are quantified using conventional correlation-based speckle-tracking methods. Generated displacement images can exhibit improved contrast of diseased tissue than conventional ultrasound techniques. In this thesis, the spatial resolution limits of ARFI imaging have been measured using novel simulation and experimental techniques. The full-width, half-maximum FWHM) of the point-spread function PSF), a measure of the resolution limit of an imaging system, was extracted by imaging a tissue-mimicking phantom composed of two bonded materials. The ARFI image of the material interface was an estimate of the step response of the system. The ARFI imaging resolution limit was further explored using FEM/acoustic field simulations and linear shift invariant LSI) models. The ARFI imaging resolution limit was submillimeter, but was highly dependent on imaging parameters. ARFI axial resolution was limited by the correlation window length and tracking pulse parameters. When the correlation window length was less than 1 mm, FEM and LSI models suggest the mechanical response of the tissue influences the resolution, resulting in a larger FWHM than would be predicted by imaging and signal processing parameters alone. ARFI lateral resolution limit corresponded to the lateral two-way beamwidth of the tracking beam. Measuring ARFI imaging resolution capabilities on small phantom inclusions and tissue ablation lesions proved the validity of the step-response based estimated resolution limits on objects of relevant, circular geometry. ARFI imaging resolution was again primarily a function of imaging and signal processing parameters, in good agreement with modulus step phantom derived results. To improve the ability of ARFI imaging to resolve targets near bright boundaries, a method called envelope weighted normalization EWN) was developed to reduce amplitude modulation of ultrasound signals, thereby reducing displacement estimation bias.

When Ebbesen et al. first reported in a now famous paper that a thin metal film perforated with an array of subwavelength-sized holes can transmit much more light than expected, they immediately suggested the involvement of surface plasmons. Surface plasmons are electromagnetic surface waves that propagate at the interface between a metal and a dielectric by the collective motion of electrons. Unlike most guided modes, the electric fields associated with surface plasmon modes are evanescent, and decay exponentially with distance from the interface. But once excited by an optical field at a hole in a metal film, they can travel several micrometers along the films surface before eventually being absorbed. However, they can turn back into a freely propagating optical wave when they are scattered at another hole or groove. This interplay between light waves and surface plasmons apparently enables enhancement of transmission. More importantly, the realization that surface plasmons can give rise to potentially useful phenomena has given birth to an entire new field, known as plasmonics. Recently however, the explanation of enhanced optical transmission through nano-holes in terms of plasmons has been challenged. In this dissertation, light transmission enhancement through metallic subwavelength holes and emission of a dipole antenna inside the cavity has been studied to understand the coupling mechanism of the transmission behaviors, as well as the limiting role of the cavity on emitting antennas inside the cavity. In our experimental research with various aperture sizes, the transmission and emission resonances have been measured and characterized for the relationships between the holes geometry and transmission as well as the quantum efficiency of the emission inside the cavity. Throughout this work, we have achieved several outstanding breakthroughs in the study of light transmission enhancement which consist of the following: 1) Photoluminescence effects with optically thin metal film. 2) The relationship between the transmission behaviors and aperture size. 3) The quantum efficiency of cavities with regards to dipole position and cavity size. 4) The significant role of cavity geometry in fluorescence excitation spectrum inside the cavity.

In this thesis, we present the results of three experiments that combine techniques from the fields of ultrafast nonlinear optics and plasmonics, with the aim of developing tools for improved surface-enhanced Raman spectroscopy and biological cell transfection. We first describe the use of femtosecond laser pulses to generate large areas of a nanostructured silicon surface which is used as a new type of substrate for surface-enhanced Raman scattering (SERS). We perform spectroscopic characterization of this substrate and find its Raman cross-section enhancement factor to be on the order of 107. This large, spatially-uniform, and reproducible enhancement factor is nearly constant across the near-infrared spectral region. In a second experiment, we develop a technique to spatially isolate the “hot spots” on SERS substrates. This technique leverages the plasmonic near field enhancement of metallic nanostructures to preferentially expose a commercial photoresist using femtosecond laser pulses. By isolating the hot spots, analyte molecules adsorb only to the regions of largest electromagnetic enhancement. Compared to an unprocessed substrate covered with a sub-monolayer of benzenethiol molecules, a processed substrate shows a 27-fold improvement in its average Raman cross-section enhancement factor. Finally, we present a proof-of-principle experiment which demonstrates high-throughput ultrafast laser transfection of biological cells using large-area plasmonic substrates. Utilizing the field localization properties of a substrate fabricated using photolithography, wet etching, and template stripping, we demonstrate the introduction of silence RNA (siRNA) molecules into cells with an efficiency of approximately 50% after exposure to femtosecond laser pulses.

The few-cycle femtosecond laser pulse has proved itself to be a powerful tool for controlling the electron dynamics inside atoms and molecules. By applying such few-cycle pulses as a driving field, single isolated attosecond pulses can be produced through the high-order harmonic generation process, which provide a novel tool for capturing the real time electron motion. The first part of the thesis is devoted to the state of the art few-cycle near infrared (NIR) laser pulse development, which includes absolute phase control (carrier-envelope phase stabilization), amplitude control (power stabilization), and relative phase control (pulse compression and shaping). Then the double optical gating (DOG) method for generating single attosecond pulses and the attosecond streaking experiment for characterizing such pulses are presented. Various experimental limitations in the attosecond streaking measurement are illustrated through simulation. Finally by using the single attosecond pulses generated by DOG, an attosecond transient absorption experiment is performed to study the autoionization process of argon. When the delay between a few-cycle NIR pulse and a single attosecond XUV pulse is scanned, the Fano resonance shapes of the argon autoionizing states are modified by the NIR pulse, which shows the direct observation and control of electron-electron correlation in the temporal domain.