Chiral molecules are composed of the same constituent atoms, but are inherently different due to being mirror images of each other. The physical properties of such molecules are nearly identical, but the biochemical interactions can differ wildly, which has extreme implications in the pharmaceutical industry. It is for this reason that it is important to be able to characterize and study individual enantiomers, and develop physical methods to do so. Optical techniques have evolved over the past two decades of scientific work which have been shown to be able to distinguish one enantiomer from another. These techniques tend to involve the use of circularly polarized light to induce a forward/backward asymmetry along the axis of light's propagation. The resulting sensitivity difference between enantiomers is typically on the order of a few percent. Recently, a novel optical pulse scheme has been developed whose electric field is fully three-dimensional and inherently chiral. This field was computationally used to demonstrate that the signal difference between enantiomers can reach upwards of 100\% sensitivity through the generation of high harmonics. Presented in this thesis are the results of an experimental measurement performed using just such a novel pulse scheme. A cold target recoil ion momentum spectroscopy machine is used to detect the photoelectron spectra from the ionization of each enantiomer of propylene oxide. A comprehensive discussion on the practical realization of the novel pulse scheme is presented, and the circular dichroism due to the novel field is shown. Also discussed are fragmentation of propylene oxide, three dimensional chiral signals found in the data, and a new measure to define the magnitude of chirality in a photoelectron distribution. Finally, measurements pertaining to the ionic yield of each enantiomer under varying handedness of light are shown. These results are the first experimental realization of optical measurements using synthetically designed chirality.

The ability to perceive the dynamics of nature is ultimately limited by the temporal resolution of the instruments available. With the help of the ultrashort optical pulse, people now are able to observe and steer the electronic dynamics on the atomic scale. Meanwhile, high power attainable in such short time scale helps to boost the study of nonlinear physics. Most commercial femtosecond lasers are based on Ti:sapphire, but such systems can only be tuned in a spectral range around 800 nm. Few applications need only a single wavelength in this spectral region and pulses tunable from the UV to the IR are highly desirable. Based on the soliton characteristics of ultrashort laser pulses, we are the first ones who propose to make use of resonant dispersive waves, which are phase-matched non-solitonic linear waves, to extend the spectral tuning range of ultrashort laser without involving complicated amplifiers. Experimentally, we achieve the tuning of dispersive wave wavelengths by changing the dispersion parameters of the laser cavity, and confirm dispersive waves are ultrashort pulses under appropriate conditions. We successfully apply such a system into a multi-wavelength operation Ti:sapphire laser. The proposed idea is general, and can be applied to systems where solitons dominate, for example fiber lasers. Thanks to the newly developed novel fiber -photonic crystal fiber- we obtain widely tunable and gap-free femtosecond pulse by extending this mechanism to waveguides. This is the largest reported tuning range for efficient nonlinear optical frequency conversion obtained with such a simple and low energy laser. We apply such a Ti:sapphire laser to Raman micro-spectroscopy. Because of the different temporal behaviors of the Raman process and other parametric processes, we can efficiently separate the coherent Raman signal from the unwanted background, and obtain a high chemical contrast and high resolution image. This high repetition rate and low energy laser oscillator makes it very suitable for biological Raman micro-spectroscopy, especially living samples for which damage is a big concern.

Pulse Compression and Dispersion Control in Ultrafast Optics Vikrant K. Chauhan 116 Pages Directed by Dr. Rick P. Trebino In this thesis, we introduced novel pulse compressors that are easy to align and which also compensate for higher order dispersion terms. They use a single dispersive element or a combination of dispersive elements in single-element-geometry. They solve the problem of extra-cavity pulse compression by providing control of the pulse width in almost all of the experiments performed using ultrashort pulses, and they even compensate for higher order dispersion. We performed full spatiotemporal characterization of these compressors and demonstrated their performance. We also developed a theoretical simulation of pulse compressors which is based on a matrix based formalism. It models the full spatiotemporal characteristics of any dispersion control system. We also introduced a simple equation, in its most general form, to relate the total dispersion and magnification introduced by an arbitrary sequence of dispersive devices. Pulse compressor characterization was done using interferometric measurements in the experiments presented in this work, but we also developed a method to measure pulses that uses polarization gating FROG for measuring two unknown pulses. In the last part, we briefly discuss the designing of a high energy chirped pulse amplification system.

Coherent anti-Stokes Raman scattering microscopy is a versatile technique for label-free imaging and spectroscopy of systems of biophysical interest. Due to the coherent nature of the generated signals, CARS images and spectra can often be difficult to interpret. In this thesis, we document how distortions and enhancements can be produced in CARS hyperspectroscopy as a result of the instrument, geometrical optical effects, or unique molecular states, and discuss how these effects may be suppressed or exploited in various CARS applications.

Nonlinear optics is the study of interactions of materials with intense light beams made possible by the invention of laser. Arguably the most trivial but technologically most important nonlinear optical effect is the intensity-dependent nonlinear refraction: an intense light beam can temporarily and reversibly change the refractive index of a material. However, the changes to the refractive index of a material due to the presence of a strong laser beam are very weak---maximum on the order of $10^{-3}$---and tend to be a small fraction of the linear refractive index. It must be noted that at optical frequencies vacuum has a refractive index of 1 and glass has a refractive index of 1.5. Thus, one of the foundational assumptions of nonlinear optics is that the nonlinear optical changes to material properties are always a small perturbation to the linear response. In the 58-year history of nonlinear optics, one of the overarching themes of research has been to find ways to increase the efficiency of nonlinear interactions. This thesis is a collection of six manuscripts motivated by our experimental finding that at least in a certain class of materials the above long-standing view of nonlinear optics does not necessarily hold true. We have found that in a material with low refractive index, known as an epsilon-near-zero material or ENZ material, the nonlinear changes to the refractive index can be a few times larger than the linear refractive index, i.e. the nonlinear response becomes the dominant response of the material in the presence of an intense optical beam. We believe that the results presented in this thesis collectively make a convincing case that ENZ materials are a promising platform for nonlinear nano-optics.

Laser filamentation is a highly complex and dynamic nonlinear process that is sensitive to many physical parameters. The basic properties that define a filament consist of (i) a narrow, high intensity core that persists for distances much greater than the Rayleigh distance, (ii) a low density plasma channel existing within the filament core, and (iii) a supercontinuum generated over the course of filamentation. However, there remain many questions pertaining to how these basic properties are affected by changes in the conditions in which the filaments are formed; that is the premise of the work presented in this dissertation. To examine the effects of anomalous dispersion and of different multi-photon ionization regimes, filaments were formed in solids with different laser wavelengths. The results provided a better understanding of supercontinuum generation in the anomalous dispersion regime, and of how multi-photon ionization can affect the formation of filaments. Three different experiments were carried out on filamentation in air. The first was an investigation into the effects of geometrical focusing. A simplified theoretical model was derived to determine the transition of filamentation in the linear-focusing and nonlinear- focusing regimes. The second examined the effects of polarization on supercontinuum generation, where a polarization-dependent anomalous spectral broadening phenomenon due to molecular effects was identified. The third involved the characterization of filaments in the ultraviolet. The combination of physical mechanisms responsible for filamentation in the ultraviolet was found to be different from that in the near infrared.

Ultra-short and high-peak-power laser pulses have important industrial and scientific applications. While direct laser amplification can lead to peak powers of several million watts, higher values than these cannot be achieved without causing damage to the amplifier material. Chirped pulse amplification technique is thus invented to break this barrier. By temporally stretching pulses before entering amplifier, the pulse peak power is significantly reduced and thus becomes safe to be passed through the amplifier. After amplification, a compressor is used to recover the pulse width, and high-power ultra-short laser pulses are produced. Chirped pulse amplification technology increases the pulse energy by transferring the damaging effects of high-peak power laser pulses from the vulnerable amplifier to a relatively robust compressor system. The compressor is therefore a crucial device for producing high peak powers. However, there are some major drawbacks associated with it. First, compressors in high-energy laser system are usually over 1 cubic meter in size. For many applications, this large and cumbersome size is a limiting factor. Second, compressors are sensitive to outside disturbances; a little misalignment can lead to failure of pulse compression process. Third, gratings with large uniformly ruled area are difficult to fabricate, which impose a limit on achievable peak powers and pulse durations of laser pulses through the use of conventional compressors. In this project, we present a grating-based monolithic optical compressor that offers a way around some of the major problems of existing compressors. By integrating the key optical components, one can make a robust and monolithic compressor that requires no alignment. In the new scheme, folding the optical path with reflective coatings allows one to design a compressor of significantly reduced size by minimizing both the longitudinal and transverse dimensions of the device. The configuration and operation mechanism of this novel compressor are described. A method for calculating the volume of the compressor is investigated. This is validated by computing the size of a specific monolithic compressor. Simulation results obtained through finite-difference time-domain method are presented, proving that the new compressor provides a compact, portable, and robust means for temporally compressing long duration pulses.

Frequency-resolved optical gating (FROG) is the standard for measuring femtosecond laser pulses. It measures relatively simple pulses on a single-shot and complex pulses using multi-shot scanning and averaging. However, experience from intensity autocorrelation suggests that multi-shot measurements may suffer from a coherent artifact caused by instability in the laser source. In this thesis, the coherent artifacts present in modern pulse measurement techniques are examined and single-shot techniques for measuring complex pulse(s) are proposed and demonstrated. The study of the coherent artifact in this work shows that modern pulse measurement techniques also suffer from coherent artifacts and therefore single-shot measurements should be performed when possible. Here, two single-shot experimental setups are developed for different scenarios. First, an extension of FROG is developed to measure two unknown pulses simultaneously on a single-shot. This setup can measure pulses that have very different center wavelengths, spectral bandwidths, and complexities. Second, pulse-front tilt is incorporated to extend the temporal range of single-shot FROG to tens of picoseconds which traditionally can only be attained by multi-shot scanning. Finally, the pulse-front tilt setup is modified to perform a single-shot measurement of supercontinuum, one of the most difficult pulses to measure due to its long temporal range, broad spectral bandwidth, and low pulse energy.

Mode-locked fiber lasers have attracted significant scientific and commercial interest since they offer a compact and highly stable platform with straightforward operation for exploiting ultrafast and nonlinear phenomena. They have enabled a vast range of applications that span from distinct disciplines such as medical diagnostics, molecular spectroscopy, and high-power precise mechanical cutting, to optical metrology. Various gain media have been utilized to achieve laser emission at different wavelengths. We have developed unique thulium/holmium (Tm/Ho) doped mode-locked fiber laser systems to address the needs of low-noise ultrafast optical sources in the wavelength vicinity of 2 μm at higher repetition rates. Since the 2 μm wavelength regime has recently attracted more attention with the emergence of thulium gain fibers, the rich underlying cavity dynamics, novel pulse operation regimes and nonlinear phenomena in compact fiber configurations have not been fully explored yet. In this thesis, research is conducted on novel Tm fiber laser cavity configurations and on the formation of unique, polarization-based pulsing regimes. Particularly, this research is focused on the exploration of novel ultrafast and nonlinear phenomena, and the development of optical sources emitting unprecedented ultrafast pulse trains beyond conventional equal-intensity distribution using Tm/Ho doped gain media. The research presented features four main results: 1) development of a high repetition rate and low-noise Tm/Ho doped mode-locked fiber laser platform as an attractive optical source for a wide variety of applications 2) investigation of a novel mode-locked state in which the ultrafast pulse train is composed of co-generated, consecutive, equal intensity and orthogonally polarized pulses in order to achieve dual RF comb generation for dual-comb spectroscopy applications, 3) exploration of controllable ultrafast waveform generation utilizing vector soliton and harmonic mode-locking mechanisms for optical telecommunication applications, and 4) demonstration of unique transitional mode-locked states showing exceptional features such as powerful irregular bursts of ultrafast pulses and rogue wave behavior without damaging the laser elements. The aim of these projects has been to explore the novel optical properties of Tm/Ho co-doped fiber lasers in order to achieve advanced functionalities in commonly practiced applications such as telecommunication, metrology and spectroscopic applications. / 2019-10-22T00:00:00Z

We have built an imaging mass spectrometer adapted for ultrashort laser pulses as its ionization technique, as an alternative to other imaging techniques. Before my arrival, the mass spectrometer has only been subject to preliminary tests on noble gases. Since then, we’ve made some modifications to the system in order to properly analyze solids. This thesis shows how we obtain our ultrashort laser pulses, the inner workings of our homemade imaging mass spectrometer, and the results that we’ve obtained with it so far. We tested two modes of operation concerning the extraction of the ions from the system into the mass analyzer: continuous and pulsed. We discuss the advantages and disadvantages of each configuration. We also display preliminary imaging results with our imaging technique of a simple WO3 and ITO structure. We conclude by comparing the resolution of this image to the different techniques in imaging mass spectrometry, how we can further improve our mass spectrometer, and the future use of this machine. Nous avons construit un spectromètre de masse adapté pour les pulses de laser très courts comme technique d’ionisation, pour acquisition des images d’un échantillon. Avant je suis arrivé, le spectromètre de masse avait seulement été utilisé pour des tests préliminaires de gaz nobles. Depuis ce moment, nous avons modifié le système pour analyser les solides. Cette thèse démontre comment on obtient nos pulses de laser très courts, comment notre spectromètre fait maison fonctionne et les résultats nous avons obtenus jusqu’à présent. Nous avons testé deux configurations différentes au sujet de l’extraction des ions du système : constant et pulsé. Nous discutons aussi les avantages et désavantages de chaque mode d’opération. Nous démontrons aussi des images préliminaires d’un substrat mixte de WO3 et ITO. Nous concluons par comparer la résolution des images aux autres techniques de collection d’images, comment nous pouvons améliorer notre spectromètre de masse et les plans pour la machine dans le futur.