Willadsenmelchiorsen2752

Carrier dynamics in high-Al-content AlGaN epilayers with different dislocation densities from 5 × 10(8) cm(-2) to 5 × 10(9) cm(-2) is studied by comparing the photoluminescence decay with the decay of carrier density. The carrier density decay was investigated using the light-induced transient grating technique. This comparison shows that the luminescence at the nonequilibrium carrier densities expected in operating light-emitting diodes depends on the recombination of free carriers and the localized exciton-like electron-hole pairs and localization-delocalization processes. In addition, a fraction of the nonequilibrium carriers is captured by the deep capture centers with extremely long lifetimes. These carriers have an insignificant contribution to the band-to-band radiative recombination. This capture is an important factor in decreasing the emission efficiency.We present a novel method to discretely tune the emission wavelength of pulsed fiber-integrated lasers. As spectral filter, a step-chirped fiber Bragg grating (FBG) array is employed combining a monolithic structure with an unrivaled design freedom enabling large tuning bandwidths as well as tailored spectral characteristics towards fingerprint tuning features. Veliparib PARP inhibitor Together with an electrical control mechanism ensuring programmable operation, this tuning method promotes fiber-integrated lasers to access new fields of applications e.g. in biophotonics and distributed sensing. The potential of this tuning concept is investigated based on an Ytterbium-doped fiber laser. The system shows superb emission properties including excellent wavelength stability, high spectral signal contrast (up to 50dB) and narrow linewidth (15GHz) as well as adjustable pulse durations in the nanosecond range with peak powers up to 100W. Additionally, the unique spectral potential of this method is demonstrated by realizing filter designs enabling e.g. a record tuning range of 74nm for fiber-integrated lasers.We theoretically and experimentally perform a comparative study on performance of the linear standing-wave cavity and ring cavity for external cavity frequency doubling at the wavelength from 795 nm to 397.5 nm. The two cavities show obvious differences of the thermal effect of nonlinear crystal, cavity sensitivity, and maximum output power. The results show that ring cavity as the external enhancement cavity is a better choice than standing-wave cavity at short wavelength region. At last, a 397.5 nm violet laser with 408 mW corresponding to an input power of 992 mW is obtained by using the ring cavity, considering the original mode-matching efficiency of 98% between the 795 nm laser and frequency doubling cavity, the conversion efficiency is 41.9%.We report on a ceramic YbLuAG thin-disk laser in continuous wave operation. The YbLuAG ceramic was fabricated using solid-state reactive sintering method. In multi-mode operation in open-air, an output power of 1.74 kW with an optical-to-optical efficiency of 65.0% and slope efficiency of 71.2% was obtained. In near-fundamental mode operation we obtained an output power of 1.29 kW and an average beam quality factor of M2 = 1.44 with an optical-to-optical efficiency of 48.2%. The near-fundamental mode result was realized with a simple evacuated, stable resonator cavity with just the thin-disk gain medium and output coupler. To the best of the authors' knowledge, this is not only the first time more than 1 kW has been demonstrated from a ceramic YbLuAG medium, but this is also currently the brightest continuous wave Yb-doped ceramic laser.A new iterative technique for calculating the eikonal function of a light field providing the focusing into a set of points is introduced. This technique is a modification of the supporting quadric method widely used for design of reflecting and refracting optical surfaces for generating prescribed illuminance distributions at given discrete set of points. As an example, we design a refractive optical element which focuses an incident beam into a set of points with energy pattern forming an image of a keyboard of a calculator. It is shown that the proposed technique is well-suited for the design of diffractive optical elements producing continuous intensity distributions within the scalar theory of diffraction. It is also shown that the calculated eikonal function is a good initial guess when designing diffractive optical elements using the iterative Gerchberg-Saxton algorithm.We report ultra-broadband supercontinuum generation in high-confinement Si3N4 integrated optical waveguides. The spectrum extends through the visible (from 470 nm) to the infrared spectral range (2130 nm) comprising a spectral bandwidth wider than 495 THz, which is the widest supercontinuum spectrum generated on a chip.We introduce and experimentally validate a pulse picking technique based on a travelling-wave-type acousto-optic modulator (AOM) having the AOM carrier frequency synchronized to the repetition rate of the original pulse train. As a consequence, the phase noise characteristic of the original pulse train is largely preserved, rendering this technique suitable for applications requiring carrier-envelope phase stabilization. In a proof-of-principle experiment, the 1030-nm spectral part of an 74-MHz, carrier-envelope phase stable Tisapphire oscillator is amplified and reduced in pulse repetition frequency by a factor of two, maintaining an unprecedentedly low carrier-envelope phase noise spectral density of below 68 mrad. Furthermore, a comparative analysis reveals that the pulse-picking-induced additional amplitude noise is minimized, when the AOM is operated under synchronicity. The proposed scheme is particularly suitable when the down-picked repetition rate is still in the multi-MHz-range, where Pockels cells cannot be applied due to piezoelectric ringing.We analyze and demonstrate a method for increasing the efficiency of thermo-optic phase shifters on a silicon-on-insulator platform. The lack of cross-coupling between dissimilar waveguides allows highly dense waveguide routing under heating elements and a corresponding increase in efficiency. We demonstrate a device with highly dense routing of 9 waveguides under a 10 µm wide heater and achieve a low switching power of 95 µW, extinction ratio greater than 20 dB, and less than 0.1 dB ripple in the through spectrum with a footprint of less than 800 µm × 180 µm. The increase in waveguide density is found not to negatively impact the switch response time.The resonance associated with plasmonic nanostructures strongly enhances local optical fields, and can thus dramatically enhance the nonlinear response of the composite structure. However, the origin of the nonlinear signal generated from hybrid nanostructures consisting of both metallic and dielectric components can be ambiguous when all constituents possess nonlinearities. In this paper, we introduce a method for specifically identifying the third harmonic generation (THG) originating from different nonlinear sources in a film-coupled nanostripe. The nanostripe consists of a metallic patch separated from a metallic film by a dielectric spacer. By considering the THG from each nonlinear source separately, we show that the near- and far-field behaviors of the THG generated within the various constituents of the nanostripe are distinguishable due to fundamental differences in the THG radiation properties. The THG signal from the metal is shown to be suppressed by the structure itself, while the THG signal from the spacer is enhanced by the gap plasmon modes supported by the structure. The total THG signal is found to be the sum of all nonlinear sources, with the far-field radiation pattern determined by the ratio between the third-order susceptibilities of the dielectric and the metal.We perform Monte Carlo light scattering simulations to study the angular distribution of the fluorescence emission from turbid media and compare the results to measured angular distributions from fluorescing white paper samples. The angular distribution of fluorescence emission is significantly depending on the concentration of fluorophores. The simulations show also a dependence on the angle of incidence that is however not as evident in the measurements. A detailed analysis of the factors affecting this angular distribution indicates that it is strongly correlated to the mean depth of the fluorescence process. The findings can find applications in fluorescence spectroscopy and are of particular interest when optimizing the impact of fluorescence on e.g. the appearance of paper as the measured values are angle dependent.The Diode Pumped Optical Laser for Experiments (DiPOLE) project at the Central Laser Facility aims to develop a scalable, efficient high pulse energy diode pumped laser amplifier system based on cryogenic gas cooled, multi-slab ceramic YbYAG technology. We present recent results obtained from a scaled down prototype laser system designed for operation at 10 Hz pulse repetition rate. At 140 K, the system generated 10.8 J of energy in a 10 ns pulse at 1029.5 nm when pumped by 48 J of diode energy at 940 nm, corresponding to an optical to optical conversion efficiency of 22.5%. To our knowledge, this represents the highest pulse energy obtained from a cryo cooled Yb laser to date and the highest efficiency achieved by a multi-Joule diode pumped solid state laser system. Additionally, we demonstrated shot-to-shot energy stability of 0.85% rms for the system operated at 7 J, 10 Hz during several runs lasting up to 6 hours, with more than 50 hours in total. We also demonstrated pulse shaping capability and report on beam, wavefront and focal spot quality.Asymmetric transmission (AT) effect has attracted great interest in recent years, due to its potential application in integrated photonics from GHz to optical frequency. To realize AT effect, numerous metamaterials have been proposed, mainly based on the chirality of the structure. In this paper, we demonstrate that achiral metamaterials can also have AT effect. Furthermore, it is shown that modal conversion is more essential than chirality to achieve AT effect. In particular, we have proposed a mirror symmetric metamaterial with broadband high efficiency AT effect for circular polarization wave operating at THz region. With further optimization of the unit cell, >80% of the central frequency bandwidth and average 74.05 (maximum150) transmission ratio can be obtained. The idea demonstrated here can also be applied to other frequency regions.Laser induced periodic surface structures (LIPSS or ripples) were generated on single crystal germanium after irradiation with multiple 3 µm femtosecond laser pulses at a 45° angle of incidence. High and low spatial frequency LIPSS (HSFL and LSFL, respectively) were observed for both s- and p-polarized light. The measured LSFL period for p-polarized light was consistent with the currently established LIPSS origination model of coupling between surface plasmon polaritons (SPP) and the incident laser pulses. A vector model of SPP coupling is introduced to explain the formation of s-polarized LSFL away from the center of the damage spot. Additionally, a new method is proposed to determine the SPP propagation length from the decay in ripple depth. This is used along with the measured LSFL period to estimate the average electron density and Drude collision time of the laser-excited surface. Finally, full-wave electromagnetic simulations are used to corroborate these results while simultaneously offering insight into the nature of LSFL formation.