Browsing by Subject "Mode-locked lasers."

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Open Access
33 Femtosecond Yb-doped optical frequency comb for frequency metrology applications
(2013) Şenel, Çağrı
Optical frequency combs have enabled many applications (high precision spectroscopy, table-top optical frequency metrology, optical atomic clocks, etc.), received considerable attention and a Nobel Prize. In this thesis, the development of a stabilized Yb-doped femtosecond optical frequency comb is presented. As a starting point in the development of the frequency comb, a new type of fiber laser has been designed using numerical simulations and realized experimentally. The developed laser is able to produce pulses that can be compressed to 33 fs without higher-order dispersion compensation. After realization of the laser, a new type of fiber amplifier has been developed to be used for supercontinuum generation. The amplifier produces 6.8 nJ pulses that can be compressed to 36 fs without higher-order dispersion compensation. The dynamics of supercontinuum generation have been studied by developing a separate simulation program which solves the generalized nonlinear Schr¨odinger equation. Using the simulation results, appropriate photonic crystal fiber was chosen and octave-spanning supercontinuum was generated. Carrier-envelope-offset frequency of the laser has been obtained by building an f-2f interferometer. Repetition rate and carrier-envelope offset frequency of the laser have been locked to Cs atomic clock using electronic feedback circuits, resulting in a fully stabilized optical frequency comb. The noise performance and stability of the system have been characterized. Absolute frequency measurement of an Nd:YAG laser, which was stabilized using iodine gas, has been performed using the developed optical frequency comb.
Open Access
Engineering the nonlinear dynamics of photonic systems : demonstration of the soliton-similariton fiber laser and nonlinear laser lithography
(2013) Öktem, Bülent
Nonlinear effects easily and unavoidably arise in ultrafast optics, often acting as sources of limitation to performance. However, many fascinating phenomena, from generation to utilization of ultrashort laser pulses rely on the very same nonlinear effects. Deep understanding of the governing dynamics, coupled with mechanisms through which they can be controlled or manipulated holds potential for observing new phenomena, as well as achieving new functionalities, which can be difficult or even impossible to achieve otherwise. This thesis presents a series of work, starting from a novel mode-locked oscillator for generating ultrashort pulses, followed by amplification of ultrashort pulses to microjoule-level energies, finally a novel nanostructuring mechanism relying on the nonlinear interaction of such pulses with the surface of a metal. The novel mode-locked laser developed in this thesis is one in which pulses propagate self-similarly in the presence of amplification, as similaritons, in one part of the cavity and as soliton-like pulses in the rest of the cavity. The coexistence of the seemingly incompatible similariton and soliton-like waves subject to the boundary conditions of a laser oscillator requires in the presence of a narrow bandpass filter and result in spectral breathing of the waves by unprecedented one order of magnitude, constituting the observation of the strongest nonlinear effects in any mode-locked laser to date. The laser reduces to the dispersion-managed laser in limit of large filter bandwidth and to the all-normal-dispersion laser in the limit of vanishing anomalous-dispersion fiber. Thus, all the four basic modelocking regimes are covered. As such, we believe the unraveling of this regime can be instrumental in deeper understanding of all the mode-locking regimes. Importantly, by showing that two attractor solutions can co-exist in a single laser cavity opens the door to new future designs. From an applications point of view, the laser is easy to mode-lock and exhibits excellent short-term and longterm stability, indicating high potential for high precision materials processing applications. We also illustrate, to our knowledge, the first high-energy, all-fiber implementation of the nonlinear chirp pulse amplification technique, which allows us to achieve in-fiber peak powers of 57 kW. We demonstrate a fiber amplifier with no free space beam pump or signal beam propagation, producing 70-ps chirped pulses with 3 μJ and 4 μJ pulse energies, which are compressible to 140 fs and 170 fs, respectively, via a grating compressor. The amplified output can be used directly, as a picosecond source, or compressed externally in a grating compressor. This approach results in a completely robust, misalignment-free system, with peak powers approaching 10 MW. This was, at the time of publication, the highest peak power obtained from an integrated fiber amplifier. Finally, we apply the laser systems we developed, together with the lessons learned from our implicit control of the nonlinear dynamics to demonstrate a method that utilizes positive nonlocal feedback to initiate, and negative local feedback to stabilize growth of self-organized metal oxide nanostructures, initiated and controlled by ultrafast pulses. We achieve unprecedented uniformity at high speed, low cost, and on non-flat or flexible surfaces. By exploiting the nonlocal nature of the feedback to stitch the nanostructures seamlessly, we are able to cover indefinitely large areas with sub-nm uniformity in periodicity. We demonstrate our approach through fabrication of TiO2 and tungsten oxide nanostructures, which can be extended in principle to a large variety of materials.