An adaptive mid-infrared ultrashort pulse source for applications in coherent control

An adaptive mid-infrared (MIR) ultrashort pulse source is investigated for application to the coherent control of molecules. The MIR regime will allow access to vibrational modes of common organic bonds, and ultrashort pulse durations should enable the required interaction to occur before the energy is redistributed throughout the molecule. By using the molecular system as part of an adaptive learning loop, one can deliver the desired MIR pulse without the need for prior lengthy calculations to solve the Hamiltonian. The adaptive MIR pulse shaper is presented as a feasibility study in this thesis. It involves shaping a near-infrared (NIR) pulse using a spatial light modulator in a phase-only pulse shaper. The shaped NIR pulse is then transferred to the MIR via a synchronously pumped optical parametric oscillator (SPOPO), which is consequently measured using a nonlinear detector whose signal is used as the feedback parameter to be optimised. Using a global optimisation algorithm, initial experiments demonstrated adaptive MIR pulse shaping, achieving pulse compression and double pulse generation. The transfer of the pulse shape from the NIR to the MIR in the SPOPO however, is non-trivial and is discussed in detail, both numerically and experimentally, in this thesis. The results show that parameters such as the signal pulse bandwidth, temporal walk-off of the interacting pulses, signal gain, pump depletion, and group velocity dispersion should be considered when high fidelity transfer is required. It is also shown that, for an SPOPO based on periodically poled LiNbO3 high-fidelity transfer is possible for wavelengths centred around 3.5µm with a tunability of ±0.5µm. The investigation then progresses to the femtosecond regime where the demonstration of coherent control experiments becomes more accessible. Using a fibre-based chirped pulse amplification system, which is an attractive pump source for the SPOPO, adaptive pulse shaping is demonstrated, showing significant improvement in the quality of the 500 fs source at high pulse energies of 65µJ, as a result of the learning loop. Thus the individual components to make the adaptive MIR ultrashort pulse shaping system have all been demonstrated; namely the adaptive shaping of MIR pulses via an SPOPO, the high-fidelity transfer of NIR pump pulses to the MIR in an SPOPO, and the femtosecond NIR pump source

Control of Optically Induced Currents in Semiconductor Crystals

The generation and control of optically induced currents has the potential to become an important building block for optical computers. Here, shift and rectification currents are investigated that emerge from a divergence of the optical susceptibility. It is known that these currents react to the shape of the impinging laser pulse, and especially to the shape of the pulse envelope. The main goal is the systematic manipulation of the pulse envelope with an optical pulse shaper that is integrated into a standard THz emission setup. The initial approach, the chirping of the laser pulse only has a weak influence on the envelope and the currents. Instead, a second approach is suggested that uses the combined envelope of a phase-stable pulse-pair as a parameter. In a laser pulse, the position of the maxima of the electrical field and the pulse envelope are shifted relative to each other. This shift is known as the Carrier-Envelope Phase (CEP). It is a new degree of freedom that is usually only accessible in specially stabilized systems. It is shown, that in a phase-stable pulse-pair, at least the relative CEP is usable as a new degree of freedom. It has a great influence on the shape of the pulse envelope and thus on the current density. It is shown that this approach enables the coherent control of the current density. The experiments are corroborated by a theoretical model of the system. The potential of this approach is demonstrated in an application. A framework is presented that uses an iterative genetic algorithm to create arbitrarily shaped THz traces. The algorithm controls the optical pulse shaper, and varies the phase of the impinging laser pulses until the desired target trace is found

High Flux Isolated Attosecond Pulse Generation

This thesis outlines the high intensity tabletop attosecond extreme ultraviolet laser source at the Institute for the Frontier of Attosecond Science and Technology Laboratory. First, a unique Ti:Sapphire chirped pulse amplifier laser system that delivers 14 fs pulses with 300 mJ energy at a 10 Hz repetition rate was designed and built. The broadband spectrum extending from 700 nm to 900 nm was obtained by seeding a two stage Ti:Sapphire chirped pulse power amplifier with mJ-level white light pulses from a gas filled hollow core fiber. It is the highest energy level ever achieved by a broadband pulse in a chirped pulse amplifier up to the current date. Second, using this laser as a driving laser source, the generalized double optical gating method is employed to generate isolated attosecond pulses. Detailed gate width analysis of the ellipticity dependent pulse were performed. Calculation of electron light interaction dynamics on the atomic level was carried out to demonstrate the mechanism of isolated pulse generation. Third, a complete diagnostic apparatus was built to extract and analyze the generated attosecond pulse in spectral domain. The result confirms that an extreme ultraviolet super continuum supporting 230 as isolated attosecond pulses at 35 eV was generated using the generalized double optical gating technique. The extreme ultraviolet pulse energy was ∼100 nJ at the exit of the argon gas target

Articles indexats publicats per investigadors del Campus de Terrassa: 2013

Aquest informe recull els 228 treballs publicats per 177 investigadors/es del Campus de Terrassa en revistes indexades al Journal Citation Report durant el 2013Preprin

Advances in Optical Amplifiers

Optical amplifiers play a central role in all categories of fibre communications systems and networks. By compensating for the losses exerted by the transmission medium and the components through which the signals pass, they reduce the need for expensive and slow optical-electrical-optical conversion. The photonic gain media, which are normally based on glass- or semiconductor-based waveguides, can amplify many high speed wavelength division multiplexed channels simultaneously. Recent research has also concentrated on wavelength conversion, switching, demultiplexing in the time domain and other enhanced functions. Advances in Optical Amplifiers presents up to date results on amplifier performance, along with explanations of their relevance, from leading researchers in the field. Its chapters cover amplifiers based on rare earth doped fibres and waveguides, stimulated Raman scattering, nonlinear parametric processes and semiconductor media. Wavelength conversion and other enhanced signal processing functions are also considered in depth. This book is targeted at research, development and design engineers from teams in manufacturing industry, academia and telecommunications service operators

Interferometric-spatial-phase imaging for sub-nanometer three-dimensional positioning

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (p. 203-206).Current alignment technology is incapable of satisfying the needs of imminent generations of lithography. This dissertation delineates a novel method of alignment and three-dimensional position metrology that is compatible with many forms of proximity lithography. The method is called Interferometric-Spatial-Phase Imaging (ISPI), and is based on encoding three-dimensional position information in the spatial phase and frequency of interference fringes, viewed with specialized oblique-incidence, dark-field optical microscopes. Alignment detectivity is 500 gm. Unlike amplitude-based interferometers, this spatial-phase-encoding interferometer achieves high alignment detectivity without sensitivity to variations in wavelength, gap and other factors, such as resist layers and changes in the index of refraction in the beampath. Several novel gap detection methods are introduced, with gap detectivity 500 jgm.(cont.) Gap is confirmed with exposure of patterns in resist, taking advantage of near-field interference in a novel Chirped Talbot Effect. Alignment and pattern overlay are confirmed in experiments combining x-ray exposures with continuous ISPI position feedback. Dynamic overlay of patterns in resist is demonstrated to be 2.7 nm, with a clear path for further improvement. Gate structures in a double-gate MOSFET are dynamically aligned to 2.5 nm.by Euclid Eberle Moon.Ph.D

Journal of Telecommunications and Information Technology, 2017, nr 3

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Adaptive shaping of laser beams for high-harmonic generation applications

This thesis explores the use of adaptive optics to create tailored laser profiles to drive the process of high-order harmonic generation (HHG).A deformable mirror controlled by a genetic, simulated-annealing algorithm (SA), and a genetic-annealing hybrid algorithm (HA) have been used to create super-Gaussian intensity profiles of orders ranging from P = 1 to P = 2 using a low-powered He-Ne laser. Between these three algorithms it was found that there is a compromise between the algorithm performance and reliability, and the algorithm complexity.Simulated super-Gaussian beam-shaping with a phase-only SLM has been performed with a SA and HA algorithm and compared to a known π-shift method. The HA has shown an improvement in super-Gaussian quality for high orders, P ≈ 2.6.Simulations of HHG driven by super-Gaussian driver fields have been made using both the simple dipole model and the strong field approximation. It has been shown that HHG beam divergence decreases with increased order P . The fringe visibility has also been calculated as a measure of coherence