No description available.

Thesis advisor: Willie J. Padilla / Progress in the field of metamaterials has started coming to a point where the field may finally begin to emerge as a viable solution to many electromagnetic challenges facing the community. No where is that more true then at terahertz frequencies where there lies an immense opportunity for growth. The development of mature technologies within this region of the electromagnetic spectrum would provide a valuable resource to become available for a multitude of applications. In order to achieve this, the necessary first steps of identifying viable materials and paths to integrate these with metamaterials will need to be completed. In this dissertation, we examine several different paths to achieve dynamic metamaterial electromagnetic response at terahertz frequencies, and demonstrate several paths to package these devices into imaging systems. In Chapter 1, we introduce the basic theory and design principles of metamaterials. We also describe the experimental techniques involved in the study of terahertz metamaterials. Chapter 2 presents a computational and experimental study investigating the integration of high electron mobility transistors with metamaterials allowing for high speed modulation of incident terahertz radiation. In Chapters 3 and 4, we investigate several different paths to create tunable terahertz metamaterial absorbers. Chapter 3 presents an investigation where we encapsulate a metametarial absorber unit cell with liquid crystals. We study both computationally and experimentally the tuning mechanism of the absorber as the liquid crystal refractive index is controlled as a function of the applied electric field strength and modulation frequency. In Chapter 4, we form a doped semiconducting metamaterial spatial light modulator with multi-color super-pixels composed of arrays of electronically controlled terahertz metamaterial absorbers. We computationally and experimentally study the independent tunability of each pixel in the spatial array and demonstrate high speed modulation. Chapter 5 introduces a multiplex imaging approach by using a terahertz spatial light modulator to enable terahertz imaging with a single pixel detector. We demonstrate the capability for high speed image acquisition, currently only limited by the commerical software used to reconfigure the spatial masks. We also configure the system to capture high fidelity images of varying complexity. In Chapter 6, we show how a metamaterial absorber can be implemented into a detector focal plane array for high sensitivity, low mutual coupling, and broad angle performance. Finally, we summarize in Chapter 7 the achievments of the research presented and highlight the direction of future work. / Thesis (PhD) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

No description available.

The purpose of this thesis is to develop a low-cost, high power laser diode/fiber illumination system and to design the driver electronics of the spatial light modulator (SLM) for holographic, three dimensional (3D) imaging. A miniaturized laser diode/fiber/polarizing illumination system capable of 15mW of output at a wavelength of 690nm is designed, fabricated, and tested. The size limitations of various commercially available SLM drivers are described and the design to overcome them is suggested. The design describes in detail the timing considerations of the hardware interface and the psuedocode of the software interface between the host computer and the SLM. Experiments carried out to study the spatial uniformity of the SLM and the distortion due to the beam splitter on the structured output from the LIM are explained. / Master of Science

A miniaturized spatial light modulator (SLM)-based structured-light illumination module with optical fiber input is designed to generate a coded 256 x 256 spots pattern for 3-D areal mapping applications. The projector uses the light from a He-Ne laser coupled to a polarization-maintaining (PM) fiber to illuminate a specially made hologram so that four virtual point sources are regenerated. The interference pattern of the four sources are filtered and modulated by an SLM. The output intensity can thus be encoded to form any arbitrary pattern through the electronic input applied to the SLM with a high speed. In this thesis, a complete optical diffraction analysis of the system is presented to provide guidelines for the optimal design of the system parameters. Through the theoretical analysis for square beam array generation, the important parameters for fabricating a hologram are given. The final system optical design and arrangement based on optical analysis are described. The detailed opto-mechanical construction of the LIM and the associated alignment, the computer simulation and the preliminary test results of the developed LIM are also provided. / Master of Science

No description available.

Laser beams with precisely controlled intensity profiles are essential for many areas. We developed a beam shaping system based on the digital micromirror device (DMD) for ultra-cold atom experiments and other potential applications. The binary DMD pattern was first designed by the error diffusion algorithm based on an accurate measurement of the quasi-Gaussian incident beam from a real-world laser. The DMD pattern was projected to the image plane by a bandwidth-limited 4f telescope that converted this pattern to the grayscale image. The system bandwidth determined the theoretical limit of image precision by the digitization error. In addition, it controlled the spatial shape of the point spread function (PSF) that reflected the tradeoff between image precision and spatial resolution. PSF was used as a non-orthogonal basis set for iterative pattern refinement to seek the best possible system performance. This feedback process, along with stable performance of DMD, the blue-noise spectrum of the error diffusion algorithm, and low-pass filtering, guaranteed high-precision beam shaping performance. This system was used to produce various beam profiles for different spatial frequency spectra. First, we demonstrated high-precision slowly-varying intensity beam profiles with an unprecedented high intensity accuracy. For flattop and linearly-tilted flattop beams, we achieved 0.20-0.34% root-mean-square (RMS) error over the entire measurement region. Second, two-dimensional sinusoidal-flattop beams were used to evaluate image precision versus system bandwidth. System evaluation confirmed that this system was capable of producing any spatial pattern with <3% RMS error for the most system bandwidth. This experiment extended the beam shaping to any system bandwidth and provided a reference to estimate the output image quality based on its spatial spectrum. Later experiment using a Lena-flattop beam profile demonstrated the arbitrary beam profile generation. We implemented this system for applications on the homogenous optical lattice and dynamic optical trap generation. The DMD pattern was optimized by the iterative refinement process at the image feedback arm, and projected through a two-stage imaging system to form the desired beam profile at the working plane. Experiments demonstrated a high-precision beam shaping as well as a fast and dynamic control of the generated beam profile. / text

Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: In this work we investigate a new method to measure the electric field of ultrafast laser pulses by extending a known measurement technique, ptychography, in the spatial domain to the time domain which we call time domain ptychography. The technique requires the measurement of intensity spectra at different time delays of an unknown temporal object and a known probe pulse. We show for the first time by measurement and calculation that this technique can be applied with excellent results to recover both the amplitude and phase of a temporal object. This technique has several advantages, such as fast convergence, the resolution is limited by the usable measured spectral bandwidth and the recovered phase has no sign ambiguity. We then extend the technique to pulse characterization where the probe is derived form the temporal object by filtering meaning the probe pulse is also unknown, but the spectrum of the probe pulse must be the same as the spectrum of the temporal object before filtering. We modify the reconstruction algorithm, now called ptychographic iterative reconstruction algorithm for time domain pulses (PIRANA), in order to also reconstruct the probe and we show for the first time that temporal objects, a.k.a laser pulses, can be reconstructed with this new modality. / AFRIKAANSE OPSOMMING: In hierdie werk het ons ’n nuwe metode ondersoek om die elektriese veld van ’n ultravinnige laser puls te meet deur ’n bekende meettegniek wat gebruik word in die ruimtelike gebied, tigografie, aan te pas vir gebruik in die tyd gebied genaamd tyd gebied tigografie. Die tegniek vereis die meting van ’n reeks intensiteit spektra by verskillende tyd intervalle van ’n onbekende ‘tyd voorwerp’ en ’n bekende monster puls. Ons wys vir die eerste keer deur meting en numeriese berekening dat hierdie tegniek toegepas kan word met uitstekende resultate, om die amplitude en fase van ’n ‘tyd voorwerp’ te meet. Hierdie tegniek het verskeie voordele, die iteratiewe proses is vinnig, die resolusie van die tegniek word bepaal deur die spektrale bandwydte gemeet en die fase van die ‘tyd voorwerp’ word met die korrekte teken gerekonstrueer. Ons het hierdie tegniek uitgebrei na puls karakterisering waar die monster pulse afgelei word, deur ’n bekende filter te gebruik, van die onbekende ‘tyd voorwerp’ nl. die inset puls. Ons het die iteratiewe algoritme wat die ‘tyd voorwerp’ rekonstrueer aangepas om ook die monster puls te vind en ons wys dat ons hierdie metode suksesvol kan gebruik om laser pulse te karakteriseer

Thesis (PhD)--Stellenbosch University, 2015.

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Ultra-short laser pulses are useful in materials processing like melting and cutting metals, and medical applications such as surgery and many other fields. In this study, we characterize and control the temporal shape of the ultra-short pulses generated from a Ti:Sapphire femtosecond laser. It operates in the near infra-red spectral region, with a centre wavelength of 800 nm. The 4f pulse shaper is the main setup used to modulate spectral shape and characterize the laser pulse. The shaper consists of two diffraction gratings, two cylindrical lenses and a computer controlled liquid crystal spatial light modulator (LC-SLM). Gratings, lenses and LC-SLM are arranged in a 4f geometry, f being the focal length of the lenses. This setup is first analysed analytically and numerically using Fourier transform and the results obtained are then compared to those obtained from the experiment. The characterization of ultra-short pulses was done using three different autocorrelation techniques such as the intensity autocorrelation, the interferometric autocorrelation, and the pulse shaping autocorrelation which can act as interferometric autocorrelation when a nonlinear crystal ß-barium borate (BBO) is placed exactly at the position of the experiment. These characterization techniques are based on the interaction between the laser pulse and a replica of it with a nonlinear crystal. The setups were implemented and measurements using the last two techniques were successfully conducted, with the pulse duration result in the range from 80-86 fs. / AFRIKAANSE OPSOMMING: Ultrakort laserpulse het baie nut in verskeie velde waaronder materiaalprosessering (soos die smelt en sny van metale) en mediese toepassings (soos chirurgie) maar net twee voorbeelde is. In hierdie studie karakteriseer en beheer ons die vorm van n ultrakort laserpuls, afkomstig vanaf n Ti:Saffier femtosekonde laser, in tyd. Die laser straal in die nabyinfrarooi spektrale gebied uit met n sentrale golflengte van 800 nm. Ons gebruik n sogenaamde 4f-pulsvormer om die spektrum van die laserpuls te moduleer en die laserpuls te karakteriseer. Die vormer bestaan uit twee diffraksieroosters, twee silindriese lense en n rekenaarbeheerde vloeibare kristal ruimtelike-lig-modulator (LC-SLM). Die diffraksieroosters, lense en LC-SLM is in n 4f-geometrie gerangskik, met f die brandpunt van die lense. Die opstelling is eers analities en numeries beskou deur van Fourier-transformasies gebruik te maak waarna die resultate wat verkry is met die van n eksperiment vergelyk is. Die karakterisering van ultrakort laserpulse was met drie verskillende outokorrelasie tegnieke gedoen, naamlik n intensiteits-outokorrelasie, n interferometriese-outokorrelasie en n pulsvormer-outokorrelasie. Die pulsvormer kan as n interferometriese-outokorrelator optree indien n nie-lineêre kristal ß-bariumboraat (BBO) by die uitset van die pulsvormer geplaas word. Hierdie karakteriseringstegnieke is gebaseer op die interaksie tussen die oorspronklike laserpuls en n kopie van die laserpuls in n nie-lineêre kristal. Die nodige opstellings virdie metings is gemaak en die metings was suksesvol uitgevoer. Die pulslengte wat gemeet is, is in die orde van 80-86 fs.