In this study, the pulse laser was used as writing beam, and He-Ne laser as the probe beam. The liquid-crystal has several mesomorphic phase: Smectic C, Smectic A, Nematic and Isotropic. The laser-induced holographic gratings in the azo-dye-doped liquid crystals have been investigated by changing the temperature, and the polarization of the probe beam.

Volume phase holographic (VPH) gratings have been designed for use in many areas of science and technology such as optical communication, medical imaging, spectroscopy and astronomy. The goal of this dissertation is to design a volume phase holographic grating that provides diffraction efficiencies of at least 70% for the entire visible wavelengths and higher than 90% for red, green, and blue light when the incident light is unpolarized. First, the complete design, simulation and optimization of the volume hologram are presented. The optimization is done using a Monte Carlo analysis to solve for the index modulation needed to provide higher diffraction efficiencies. The solutions are determined by solving the diffraction efficiency equations determined by Kogelnik's two wave coupled-wave theory. The hologram is further optimized using the rigorous coupled-wave analysis to correct for effects of absorption omitted by Kogelnik's method. Second, the fabrication or recording process of the volume hologram is described in detail. The active region of the volume hologram is created by interference of two coherent beams within the thin film. Third, the experimental set up and measurement of some properties including the diffraction efficiencies of the volume hologram, and the thickness of the active region are conducted. Fourth, the polarimetric response of the volume hologram is investigated. The polarization study is developed to provide insight into the effect of the refractive index modulation onto the polarization state and diffraction efficiency of incident light.

Optical interconnects are important to the future development of microelectronics. Volume grating couplers (VGCs) provide a compact, efficient coupling mechanism that is compatible with microelectronics fabrication processes. In this dissertation, some of the performance characteristics of VGCs are investigated. Also, integration of VGCs with Sea of Polymer Pillars (SoPP), an emerging high-density input/output interconnect technology, is demonstrated and its performance quantitatively investigated. First, the polarization-dependent performance of VGCs is analyzed, and the design constraints for achieving high-efficiency polarization-dependent and polarization-independent VGCs are examined. The effects of loss on VGC performance are also presented. Then, the wavelength response of VGCs and its dependence on grating parameters is quantitatively examined. Experimental demonstrations of polarization-dependent and polarization-independent VGCs are then presented. Finally, a VGC integrated with a SoPP is demonstrated and its performance characterized.

In this thesis, a 6-beam combiner using multiplexed holograms in dye-doped polymer is investigated. It is realized by recording six superimposed holographic gratings, which show uniform diffraction efficiency. The coupled wave theory for N superimposed gratings is more generalized and is used to analyze the amplitudes of diffracted waves in three different boundary conditions. Multiple-ring diffracted beam analysis is proposed to determine the dynamic range of a holographic material. The M/# is evaluated by recording a single hologram and counting the number of ring patterns in the diffracted beam. This analysis is extended to assess the equalized grating strength of N superimposed holograms. Six holograms with the equalized grating strength which can be assigned within the dynamic range of our material and show maximum diffraction efficiency are recorded. The phase locking of five beams to one reference beam is performed using PZT controller. The designs of lock-in amplifier, ramp generator and servo using commercial chips are demonstrated. The readout set-up used to split one single beam into six coherent copies is presented. The function of each part of the PZT controller in the readout set-up is discussed in detail. The intensity profile of an N-beam combiner is investigated by varying the phase angle between adjacent input waves. The entire solution which describes the amplitude of a combined beam is derived from generalized coupled wave theory. A simplified experimental set-up without a complicated PZT controller is demonstrated using a planoconvex lens. In order to provide six coherent light sources in future work, the injection locking of a single laser diode to the master laser diode is performed. An expected read-out setup is proposed to carry out both the achievement of six coherent sources and a 6 beam combination.

Within this thesis, photo-induced mechanisms of the light-matter interaction are investigated in tailored and photofunctional materials that differ significantly in their optical and structural properties. The individual coupling mechanisms in congruently melted, nominally undoped or iron doped lithium niobate crystals as well as in structurally disordered photoswitchable molecules embedded into a solid state polymer are examined in particular by the principle of holographic grating recording and transient absorption spectroscopy which provide new insight into a variety of material response properties. In case of photoswitchable ruthenium sulfoxide compounds, the underlying mechanism can be unambiguously assigned to a photochromic material response evoked by a photochemical reaction, i.e., a non-instantaneous, local ligand isomerisation. Comparable results are obtained for iron-doped, oxidized lithium niobate where holographic grating recording is related to the photophysical generation of transient excitonic states whose photochromic properties are characterized by targeted ns-pump, supercontinuum probe spectroscopy. In the event of nominally undoped lithium niobate, the holographic amplification of two sub-picosecond pulses is attached to the phenomenon of two-beam coupling on a self-induced dynamic grating. By correlating the individually obtained mechanisms of the light-matter interaction and the light-induced material response, generally accepted conclusions on a microscopic level can be achieved. A major influence of the internal structure and orientation of the excited states, i.e., an appropriate threedimensional structural arrangement, is deduced as a prerequisite for the formation of light-induced, macroscopic refractive index changes while absorption and microscopic refractive index alterations linked via the Kramers-Kronig relation are unaffected. In systems featuring a random distribution of excited states, an orientational order might be achieved as a consequence of linear polarized light, i.e., by polarization structuring. Moreover, if the photorefractive effect can be ruled out, the material response in lithium niobate can be solely assigned to a local alteration of the transient electronic states, i.e., to the photochromic properties of polarons and/or excitonic states, which is in particular comparable to the linkage isomerism of molecular photoswitchable molecules. In addition, the influence of structural parameters on the light-matter/surface interaction is studied on the μm-scale by analyzing the diffraction phenomenon arising from a relief grating. A considerable impact on the surface grating assisted coupling is determined by the transition from cw-lasers to ultrashort laser pulses which enables interference quenching. However, this phenomenon is of no consequence in case of selfinduced holographic gratings.

SALT HRS (Southern African Large Telescope High Resolution Échelle Spectrograph) is a high-resolution, high-efficiency spectrograph for the 11m SALT telescope in Sutherland, South Africa. The initial optical design work was performed at the University of Canterbury, New Zealand. Revisions to the concept, the mechanical design, manufacture, assembly and testing have been handled by the Centre for Advanced Instrumentation, at Durham University in the United Kingdom. SALT HRS is a fibre-fed echelle grating spectrograph with four operational modes: low-, medium- and high-resolution and high-stability modes, having spectral resolutions of R ≈16000, 37000, 67000 and 67000 respectively over a wavelength range of 370-890nm. The instrument is of a dual channel, ‘white pupil’ design, in which the primary mirror acts to collimate light onto a single R4 echelle grating, and also to focus dispersed light to an intermediate focus. A dichroic beam-splitter separates the dispersed light into two separate spectral channels. Spherical pupil mirrors transfer the separated beams via a fold mirror to two wavelength-specific volume-phase holographic gratings (VPHGs) used as cross-dispersers. Cross-dispersed spectra are then imaged by two fully dioptric camera systems onto optimized CCD detectors. This thesis presents the results of the laboratory testing and specification of several critical sub-systems of SALT HRS, as well as the development of key software tools for the design verification and operation at the telescope. In Chapter 1 we first review the technical development of high-resolution spectroscopy and its specific implementation in SALT HRS. In Chapter 2 we develop a comprehensive throughput model of the entire system based on a combination of as-built performance and specific throughput measurements in the laboratory. This is used to make some specific predictions for the on-sky performance of SALT HRS and the magnitude limits for science targets. We also present a graphical exposure time calculator based on these measurements which can be used by an astronomer to plan their observations with SALT HRS. Chapter 3 contains a detailed treatise on the optical fibre system of SALT HRS. Considerations for the use of optical fibres in astronomy are provided, as are details of an optional double scrambler, and the various instrument fibre modes. Extensive measurements of focal ratio degradation (FRD) are also presented, with testing of input beam speed; wavelength; fibre bending; variable pupil mirror illumination; and vacuum tank pressure dependency. The systems for fibre management are reviewed, as is the fibre bundle assembly process. Testing of two further sub-systems is described in Chapter 4. Firstly the long-term stability of the mirror mounting mechanisms is determined. The advantages of cross-dispersion of echelle spectra using volume-phase holographic gratings are then discussed, and the results of diffraction efficiency measurements are given for both red and blue channel gratings. Modern CCD technologies are examined in Chapter 5, and the blue detector is experimentally characterized using photon transfer and quantum efficiency curves. It is also used for an investigation into cosmic ray events in CCDs. Results from shielding the detector using lead are described, as is an attempt to distinguish the source of the events based on their morphology. Finally, Chapter 6 deals with the handling of data produced by SALT HRS. Methods of wavelength calibration of the spectra are discussed, including the use of Thorium-Argon lamps and an iodine absorption cell. The implementation of a Python based quick-look data reduction pipeline is reviewed, with a description of the processes performed. A summary of the thesis is given in Chapter 7.

This work is dedicated to a comprehensive experimental study on the interaction of femtosecond laser pulses with the nonlinear optical medium lithium niobate. The nonlinear optical response in the nanosecond regime was already studied extensively with a variety of techniques, whereas femtosecond pulses were mainly used in transient absorption or transient grating experiments. Naturally, the temporal resolution of these measurements depends on the pulse duration, however, dynamics during the pulse excitation were barely investigated. The motivation of this work is to widen the limits of femtosecond spectroscopy, not only to temporally resolve faster nonlinear optical processes, but further to show a sensitivity to other coupling mechanisms between the pulses and the material. Especially, the role of transient, dynamic holographic gratings is investigated with a careful determination of the pulse duration, bandwidth and frequency chirp. A basis of this work is established in the first part by studying the material response via light-induced absorption before focusing on the main topic, the pulse interaction with elementary (holographic) gratings, both self-induced and static, in the second part. By this detailed study, several features of femtosecond laser pulses, holographic gratings and the ultrafast material response can be revealed: (i) grating recording is feasible even with pulses of different frequencies, provided that their pulse duration is sufficiently short, (ii) grating based pulse coupling causes a pronounced energy transfer even in a common pump-probe setup for transient absorption measurements with (non-)degenerated frequencies, (iii) beyond expectation, oscillations in the phonon frequency range become apparent in different measurements. The presented results point towards appropriate future experiments to obtain a more consistent, microscopic model for the ultrafast response of the crystal, involving the interplay between photo-generated polarons, self-induced gratings, and phonons.

The research that is presented in this thesis can be divided into two major parts. The first part concerns longitudinally pumped, bulk Er-Yb lasers. In these lasers, the main limitation is the thermal shortcomings of the phosphate glass host material. From the laser experiments and the spectroscopic measurements on crystalline host materials, as well as an investigation to bring further light to the physical background of the involved dynamics, the thesis presents some novel results that contribute to the search for a crystalline replacement. The second part concerns novel laser concepts applied to Yb-doped double tungstate lasers. Different crystal orientations are investigated, such as an athermal orientation for reduced thermal lensing and a conical refraction orientation for complete polarization tuning. Furthermore, the introduction of volume Bragg gratings in the cavity enables wide spectral tuning ranges and extremely low quantum defects. Regarding the first part, the main results are the achievement of 15 % slope efficiency in a monolithic, continuous-wave Yb:GdCOB laser and the achievement of Q-switching of the same laser. The Q-switched pulse durations were around 5-6 ns and the Q-switched slope efficiency was 11.6 %. For both lasers, a maximum output power of 90 mW was obtained, which is close to ordinary glass lasers under similar conditions. A spectroscopic investigation into the Er,Yb-codoped double tungstates was also performed and the results have enabled mathematical modeling of the fluorescence dynamics in these materials. Finally, the temperature dependence of the dynamics in Er,Yb:YAG was studied and the results have given some insight into the physical background of the mechanisms involved. Regarding the second part, different end-pumped Yb:KReW laser cavities were constructed to demonstrate the different concepts. With a laser crystal cut for propagation along the athermal direction at 17º angle clockwise from the dielectric direction Nm, the thermal lens could be reduced by 50 %. In these experiments the maximum output power was 4 W at 60 % slope efficiency. In another cavity incorporating a volume Bragg grating in a retroreflector set-up, the wavelength could be continuously tuned between 997 - 1050 nm. The spectral bandwidth was 10 GHz and the peak output power was 3 W. The same output power could also be obtained at 1063 nm with the grating positioned as an output coupler instead. If, on the other hand, the grating was positioned as an input coupler, 3.6 W output power at 998 nm was obtained at a quantum defect of only 1.6 %. Furthermore, using a crystal oriented for propagation along an optic axis, internal conical refraction could be used to establish arbitrary control of the polarization direction as well as the extinction ratio. Even unpolarized light could be enforced despite the highly anisotropic medium. With this configuration, the maximum output power was 8.6 W at 60 % slope efficiency which equals the performance of a reference crystal with standard orientation. The completely novel concepts of laser tuning with Bragg grating retroreflectors, of low quantum defect through Bragg grating input couplers and of polarization tuning by internal conical refraction can all easily be applied to several other laser materials as well. / QC 20100713

We develop a theory of vectorial wave coupling in cubic photorefractive crystals placed in an alternating ac-field to enhance the nonlinear response. First we analytically and numerically investigate the dependences of the first Fourier harmonics of the space-charge field, induced in an AC-biased sillenite crystal by a light-interference pattern, on the light contrast m. The data obtained was used to extend the vectorial beam-coupling theory on the whole contrast region. In particular, we proved in the general case that despite of essential differences between thediffusion and AC nonlocal responses the later keeps the light interference fringes straight during the interaction. This fundamental feature allows, under certain restrictions, to reduce the nonlinear problem of vectorial coupling to the known linear problem of vectorial Bragg diffraction from a spatially uniform grating, which admits an exact solution. As a result, the nonlinear vectorial problem can be effectively solved for a number of practically important cases.The developed theory was applied to describe the transformation of a momentary phase changes of one of the input beams into the output intensity modulation (so-called grating translation technique). In contrast to the previous studies, we take into account the change of the space-charge field amplitude across the crystal (the coupling effects). The theory developed is employed to optimize the conditions for the linear signal detection under polarization filtering for the transverse and longitudinal optical configurations. We also analyze the possibility of the linear detection without polarization filtering.Illumination of AC-biased photorefractive BTO crystals with a coherent light beam results in development of strong nonlinear scattering. We investigate the angular and polarization characteristics of the scattered light for the diagonal optical configuration and different polarization states of the pump.

In der vorliegenden Arbeit werden die nichtlinearen optischen Eigenschaften der Materialien Lithiumniobat und Di-Zinn-Hexathiohypodiphosphat aufgrund der Suszeptibilität 3. Ordnung und kleiner Polaronen untersucht. Zudem wird gezeigt, dass die Interferenz verschiedenfarbiger Laserpulse die Aufzeichnung von statischen und dynamischen holographischen Gittern ermöglicht. Ein Teil dieser Arbeit ist in den im Anhang angegebenen 6 Publikationen bereits veröffentlicht. Lithiumniobat wird mit einer Erweiterung des Z-Scan Experiments untersucht, welches die Pulslängenabhängige Messung der nichtlinearen Absorption und der nichtlinearen Brechungsindexänderung ermöglicht. Dabei konnte festgestellt werden, dass bei sehr kurzen Pulslängen von 70 fs ein Effekt der Polaronen auf die nichtlineare Absorption vernachlässigbar ist und die Zwei-Photonen-Absorption die nichtlineare Absorption dominiert. Mit größerer Pulslänge gibt es allerdings Abweichungen zwischen der Theorie der Zwei-Photonen-Absorption und den Messergebnissen. Mit der Entwicklung eines Polaronen-Anregungs-Modells, welches eine polaronische Absorption aufgrund wiederholtem optisch induziertem Hopping annimmt, konnte dieser Effekt konsistent erklärt werden. Die Messungen der nichtlinearen Brechungsindexänderung lassen darauf schließen, dass sowohl freie Ladungsträger als auch kleine Polaronen neben der Suszeptibilität 3. Ordnung einen Einfluss auf die Brechungsindexänderung haben, da eine nichtlineare Abhängigkeit von der Intensität auch bei Pulslängen von 70 fs festgestellt werden konnte. Analog dazu konnte in Di-Zinn-Hexathiohypodiphosphat ein großer Zwei-Photonen-Absorptionskoeffizient festgestellt werden, welcher für Photonenenergien nahe der Bandkante Werte zeigt, die größer sind als theoretischen Überlegungen zeigen. Eine transiente Absorption nach optischer Anregung, gemessen durch ein Anreg-Abtast-Experiment, sowie Literatur legen nahe, dass in Di-Zinn-Hexathiohypodiphosphat gebundene Lochpolaronen durch optische Anregung entstehen können. Durch den hohen Zwei-Photonen-Absorptionskoeffizienten konnte das Aufzeichnen eines kontrastreichen, dynamischen Amplitudengitters mittels Femtosekundenpulsen gezeigt und nachgewiesen werden. Die Kürze der Femtosekundenpulse ermöglicht aber nicht nur das Aufzeichnen eines Zwei-Photonen-Absorptionsgitters aufgrund der hohen Intensitäten, sondern erlaubt zudem die Beobachtung von Interferenz zwischen verschiedenfarbigen Pulsen. In der Zeitspanne der Pulslänge beträgt die Bewegung der Interferenzstreifen, welche in der Größenordnung der Lichtgeschwindigkeit liegt, nur ein Bruchteil der Streifendistanz, sodass das Interferenzmuster eingefroren und beobachtbar erscheint. Somit lassen sich statische Hologramme in holographischen Filmen, wie auch dynamische Hologramme aufzeichnen. Über ein dynamisches holographisches Gitter mittels Zwei-Photonen-Absorption konnte so eine Frequenzkonversion durch Dopplerverschiebung in Lithiumniobat gezeigt werden.