Elements of optical solitons: an overview

Existence of solitons in nonlinear optical fibres was first predicted by Hasegawa and Tappert in 1973 and its experimental verification came in 1980. Ever since, both experimental and theoretical physicists have shown keen interest in this topic due to its versatile applications. Optical solitons are formed due to the balance between the group velocity dispersion and the self phase modulation in the anomalous dispersion regime, and the governing wave equation is the Nonlinear Schröddinger (NLS) equation. Optical solitons can exist in various systems like photonic crystal fibres, bulk materials like photorefractive materials, photopolymers, etc. What follows is an introduction to optical soiltons and their application

Hybrid organic-inorganic polariton laser

Organic materials exhibit exceptional room temperature light emitting characteristics and enormous exciton oscillator strength, however, their low charge carrier mobility prevent their use in high-performance applications such as electrically pumped lasers. In this context, ultralow threshold polariton lasers, whose operation relies on Bose-Einstein condensation of polaritons - part-light part-matter quasiparticles, are highly advantageous since the requirement for high carrier injection no longer holds. Polariton lasers have been successfully implemented using inorganic materials owing to their excellent electrical properties, however, in most cases their relatively small exciton binding energies limit their operation temperature. It has been suggested that combining organic and inorganic semiconductors in a hybrid microcavity, exploiting resonant interactions between these materials would permit to dramatically enhance optical nonlinearities and operation temperature. Here, we obtain cavity mediated hybridization of GaAs and J-aggregate excitons in the strong coupling regime under electrical injection of carriers as well as polariton lasing up to 200 K under non-resonant optical pumping. Our demonstration paves the way towards realization of hybrid organic-inorganic microcavities which utilise the organic component for sustaining high temperature polariton condensation and efficient electrical injection through inorganic structure

Chemical Structure - Nonlinear Optical Property Relationships For A Series Of Two-photon Absorbing Fluorene Molecules

This dissertation reports on the investigation of two-photon absorption (2PA) in a series of fluorenyl molecules. Several current and emerging technologies exploit this optical nonlinearity including two-photon fluorescence imaging, three-dimensional microfabrication, site-specific photodynamic cancer therapy and biological caging studies. The two key features of this nonlinearity which make it an ideal candidate for the above applications are its quadratic dependence on the incident irradiance and the improved penetration into absorbing media that it affords. As a consequence of the burgeoning field which exploits 2PA, it is a goal to find materials that exhibit strong two-photon absorbing capabilities. Organic materials are promising candidates for 2PA applications because their material properties can be tailored through molecular engineering thereby facilitating optimization of their nonlinear optical properties. Fluorene derivatives are particularly interesting since they possess high photochemical stability for organic molecules and are generally strongly fluorescent. By systematically altering the structural properties in a series of fluorenyl molecules, we have determined how these changes affect their two-photon absorbing capabilities. This was accomplished through characterization of both the strength and location of their 2PA spectra. In order to ensure the validity of these results, three separate nonlinear characterization techniques were employed: two-photon fluorescence spectroscopy, white-light continuum pump-probe spectroscopy, and the Z-scan technique. In addition, full linear spectroscopic characterization was performed on these molecules along with supplementary quantum chemical calculations to obtain certain molecular properties that might impact the nonlinearity. Different designs in chemical architecture allowed investigation of the effects of symmetry, solvism, donor-acceptor strengths, conjugation length, and multi-branched geometries on the two-photon absorbing properties of these molecules. In addition, the means to enhance 2PA via intermediate state resonances was investigated. To provide plausible explanations for the experimentally observed trends, a conceptually simple three level model was employed. The subsequent correlations found between chemical structure and the linear and nonlinear optical properties of these molecules provided definitive conclusions on how to properly optimize their two-photon absorbing capabilities. The resulting large nonlinearities found in these molecules have already shown promise in a variety of the aforementioned applications

Optical properties of vanadyl phthalocyanine thin films and nonlinear refractive index of vanadyl phthalocyanine doped PMMA by using thermal lens spectrometry technique

The optical properties of vanadyl phthalocyanine (VOPc) thin films have been studied in the spectral range 300-900 nm. Variations in the optical constants with wavelength are found to be thickness dependent of the films. The optical band gap Eg and optical conductivity ?opt were determined. The analysis of the optical absorption data indicates that the optical band gap Eg was indirect transitions. The optical band gap of the VOPc thin films was found to increase with thickness of the film. According to Wemple and DiDomenico method, the optical dispersion parameters Eo and Ed were determined. Thermal lens spectrometry is applied to measure the thermo-optic coefficient dn/dT and nonlinear refractive index for VOPc doped Poly methylmeth acrylate (PMMA) film. The measurements were carried out using the SDL laser at wavelength 635 nm, as both probe and excite source. Keywords: Thin film, Optical constants, Nonlinear refractive index, Thermal lens spectrometr

Study of the Excited-State Absorption Properties of Polymethine Molecules

This dissertation investigates excited-state nonlinearities in a series of polymethine dyes for the application of nanosecond optical limiting. Optical limiters are devices that for low intensity light exhibit a high linear transmittance, but for high intensity light strongly attenuate the incident radiation. These devices would serve to protect optical sensors from intense laser radiation by clamping the maximum energy allowed through an optical system below the damage threshold of the sensor. The search is ongoing for optical materials that are both broadband and have high damage thresholds to be effective materials for limiting applications. Polymethine dyes are promising compounds due to a strong and broad excited-state absorption (ESA) band in the visible region. However, the effectiveness of polymethine molecules as applied to optical limiting is hindered by a saturation of the ESA process at high fluences. Experiments and theoretical modeling are performed to determine the root causes of this saturation effect in both the picosecond and nanosecond time regime. The polymethine molecules studied have chromophore lengths from di- to pentacarbocyanine (2 to 5 -CH=CHgroups) with various bridge structures. This allows us to develop relationships between the molecular parameters of the polymethine molecules and overall nonlinear absorption performance. The experiments conducted included femtosecond white light continuum pumpprobe experiments to measure ESA spectra, picosecond two-color polarization-resolved pumpprobe to measure excited-state dynamics and the orientation of transition dipole moments, and picosecond and nanosecond optical limiting and z-scans. From these experiments we are able to develop energy level models that describe the nonlinear absorption processes in polymethines from the picosecond to nanosecond time regime. This work, along with the quantum chemical modeling performed at the Institute of Physics and National Academy of Sciences of Ukraine, has resulted in the creation of dyes that have improved photochemical stability with larger nonlinearities. These are useful not only for optical limiting but also for a wide variety of nonlinear optical applications

Nonlinear Optics

This book examines nonlinear optical effects in nonlinear nanophotonics, plasmonics, and novel materials for nonlinear optics. It discusses different types of plasmonic excitations such as volume plasmons, localized surface plasmons, and surface plasmon polaritons. It also examines the specific features of nonlinear optical phenomena in plasmonic nanostructures and metamaterials. Chapters cover such topics as applications of nanophotonics, novel materials for nonlinear optics based on nanoparticles, polymers, and photonic glasses

Photonic application of proteins

The currently faced biggest challenge in integrated optics (IO) is finding or developing materials that can be used as active components for optical circuits. In order for a material to be considered for IO applications, it has to possess optimal non-linear optical (NLO) properties, such as a large light-induced refractive index change, but also mechanical stability. In my thesis, I investigated the photoactive yellow protein (PYP) with various experimental methods to assess the protein’s IO applicability. During the measurements, a glycerol-doped (GL) PYP film was used to maintain high mechanical stability and optical homogeneity of the investigated PYP-films. First, the kinetics of certain photocycle intermediates of PYP were monitored with absorption kinetics measurements to find the optimal environment to use the protein films in. This was followed by measuring the linear and non-linear refractive index of GL-PYP films. The NLO refractive index was investigated with the Z-scan technique as a function of excitation laser pulse parameters, i.e., average and peak intensities, and repetition rate of the pulses. For investigating the potential miniaturization and the possibility of creating homogeneous protein monolayers for further IO applications, PYP films were monitored with vibrational sum-frequency spectroscopy (VSFG). Finally, IO switching was demonstrated utilizing different photocycle intermediates. Mach- Zehnder interferometer was used for slow, while transient grating spectroscopy was applied to perform sub-ps optical switching. Based on the results, GL-PYP films are viable alternatives as IO active materials

Optical Properties and Excitation Dynamics in 3d and 2d Systems

Ph.DDOCTOR OF PHILOSOPH