Dielectrics in a time-dependent electric field: a real-time approach based on density-polarization functional theory

In the presence of a (time-dependent) macroscopic electric field the electron dynamics of dielectrics cannot be described by the time-dependent density only. We present a real-time formalism that has the density and the macroscopic polarization P as key quantities. We show that a simple local function of P already captures long-range correlation in linear and nonlinear optical response functions. Specifically, after detailing the numerical implementation, we examine the optical absorption, the second- and third-harmonic generation of bulk Si, GaAs, AlAs and CdTe at different level of approximation. We highlight links with ultranonlocal exchange-correlation functional approximations proposed within linear response time-dependent density functional theory framework.

Evidence of dispersion relations for the nonlinear response of the Lorenz 63 system

Along the lines of the nonlinear response theory developed by Ruelle, in a previous paper we have proved under rather general conditions that Kramers-Kronig dispersion relations and sum rules apply for a class of susceptibilities describing at any order of perturbation the response of Axiom A non equilibrium steady state systems to weak monochromatic forcings. We present here the first evidence of the validity of these integral relations for the linear and the second harmonic response for the perturbed Lorenz 63 system, by showing that numerical simulations agree up to high degree of accuracy with the theoretical predictions. Some new theoretical results, showing how to derive asymptotic behaviors and how to obtain recursively harmonic generation susceptibilities for general observables, are also presented. Our findings confirm the conceptual validity of the nonlinear response theory, suggest that the theory can be extended for more general non equilibrium steady state systems, and shed new light on the applicability of very general tools, based only upon the principle of causality, for diagnosing the behavior of perturbed chaotic systems and reconstructing their output signals, in situations where the fluctuation-dissipation relation is not of great help.

Medidas de espectroscopia Raman em cristais KDP e Nanotubos de Carbono: implementação da técnica

Atualmente, os físicos vêm desenvolvendo novas técnicas de caracterização de materiais, principalmente os novos materiais que os cientistas (de todas as áreas) estão produzindo a partir de outros já existentes como vidros, cerâmicas, polímeros, materiais semicondutores e supercondutores, materiais magnéticos, dentre outros. Seguindo esta linha, o Grupo de Física de Materiais da Amazônia vem adquirindo novas técnicas para caracterização de materiais e este trabalho marca o início da incorporação de mais uma técnica de caracterização junto ao laboratório de física da UFPA, a Espectroscopia Raman. Neste trabalho, utilizamos como amostras para realizar e testar a técnica implantada, cristais KH2PO4 (KDP) e nanotubos de carbono de parede simples (SWNT). O KDP foi escolhido devido ao fato de ter os espectros Raman muito conhecidos e ser um material de simples produção. O KDP puro ou dopado continua sendo alvo de pesquisa (teórica e/ou experimental) atual, principalmente por apresentar uma transição de fase ferroelétrica e ser um material que tem muitas aplicações nas indústrias que utilizam tecnologia de lasers, sensores, gerador de segundo e terceiro harmônico. Já os nanotubos de carbono também foram utilizados como amostras por ser um material de grande interesse científico, tecnológico e de grande aplicação no mundo moderno, pois podem ser empregados em nanotecnologia na produção de transistores e diodos, além disso, podem ser incorporados a certos materiais aumentando, assim, a resistência mecânica dos mesmos.Para as amostras de KDP foram realizadas medidas em temperatura ambiente, pressão uniaxial e temperatura. Nas medidas com a temperatura conseguimos observar o inicio da decomposição e de uma possível transição de fase em alta temperatura no KDP. As medidas com pressão uniaxial mostram que embora não se observe uma transição de fase bem definida é possível se identificar alteração que podem indicar o inicio de uma quebra de simetria devido aos efeitos de pressão. Nas amostras de nanotubos (nanotubos de paredes simples-SWNT) foram realizadas medidas de Raman em temperatura ambiente. Nessas medidas identificamos as bandas D e G bastante conhecidas as quais são reportadas em quase todos os artigos sobre esse tema. O mais importante foi a implantação da nova técnica que é uma técnica forte que pode ser aplicada em diferentes campos do conhecimento científico fortalecendo o Grupo de Física de Materiais da Amazônia.

Spins, moments and radii of cd isotopes

The complex nature of the nucleon-nucleon interaction and the wide range of systems covered by the roughly 3000 known nuclides leads to a multitude of effects observed in nuclear structure. Among the most prominent ones is the occurence of shell closures at so-called ”magic numbers”, which are explained by the nuclear shell model. Although the shell model already is on duty for several decades, it is still constantly extended and improved. For this process of extension, fine adjustment and verification, it is important to have experimental data of nuclear properties, especially at crucial points like in the vicinity of shell closures. This is the motivation for the work performed in this thesis: the measurement and analysis of nuclear ground state properties of the isotopic chain of 100−130Cd by collinear laser spectroscopy.rnrnThe experiment was conducted at ISOLDE/CERN using the collinear laser spectroscopy apparatus COLLAPS. This experiment is the continuation of a run on neutral atomic cadmium from A = 106 to A = 126 and extends the measured isotopes to even more exotic species. The required gain in sensitivity is mainly achieved by using a radiofrequency cooler and buncher for background reduction and by using the strong 5s 2S1/2 → 5p 2P3/2 transition in singly ionized Cd. The latter requires a continuous wave laser system with a wavelength of 214.6 nm, which has been developed during this thesis. Fourth harmonic generation of an infrared titanium sapphire laser is achieved by two subsequent cavity-enhanced second harmonic generations, leading to the production of deep-UV laser light up to about 100 mW.rnrnThe acquired data of the Z = 48 Cd isotopes, having one proton pair less than the Z = 50 shell closure at tin, covers the isotopes from N = 52 up to N = 82 and therefore almost the complete region between the neutron shell closures N = 50 and N = 82. The isotope shifts and the hyperfine structures of these isotopes have been recorded and the magnetic dipole moments, the electric quadrupole moments, spins and changes in mean square charge radii are extracted. The obtained data reveal among other features an extremely linear behaviour of the quadrupole moments of the I = 11/2− isomeric states and a parabolic development in differences in mean square nuclear charge radii between ground and isomeric state. The development of charge radii between the shell closures is smooth, exposes a regular odd-even staggering and can be described and interpreted in the model of Zamick and Thalmi.

Characterizing a single photon detector

I will present my work about constructing and characterizing a single photon detector. Using the 1550nm laser and second harmonic light generation, I am able to count single photons on a Multi‐Pixel Photon Counter (MPPC) silicon APD. My results show that upwards of 22% quantum efficiency is achievable with the MPPC. Future work will include coincidence detection of correlated photon‐pair.

Comparative numerical study of energy deposition in femtosecond laser microfabrication with fundamental and second harmonics of Yb-doped laser

We present the results of comparative numerical study of femtosecond laser inscription for fundamental and second harmonic of Yb-doped laser. We have found that second harmonic is more efficient in terms of amount of absorbed energy which leads to lower inscription threshold. Hence this regime is more attractive for applications in femtosecond laser microfabrication. We observed the different size of modified domain on initial pulse energy and different spectrum dynamics during the pulse propagation for fundamental and second harmonics.

Efficiency of energy deposition by fundamental and second harmonics in femtosecond laser inscription

We present the results of numerical modelling of energy deposition in single-shot femtosecond laser inscription for fundamental and second harmonics, which shows that second harmonic is more efficient considering the amount of absorbed energy

Comparative numerical study of efficiency of energy deposition in femtosecond microfabrication with fundamental and second harmonics of Yb-doped fiber laser

We present the results of comparative numerical study of energy deposition in single shot femtosecond laser inscription for fundamental and second harmonic of Yb-doped fiber laser. We have found that second harmonic is more efficient in absorbing energy which leads to lower inscription threshold. Hence this regime is more attractive for applications in femtosecond laser microfabrication.

Comparative numerical study of efficiency of energy deposition in femtosecond microfabrication with fundamental and second harmonics of Yb-doped fiber laser

We present the results of comparative numerical study of energy deposition in single shot femtosecond laser inscription for fundamental and second harmonic of Yb-doped fiber laser. We have found that second harmonic is more efficient in absorbing energy which leads to lower inscription threshold. Hence this regime is more attractive for applications in femtosecond laser microfabrication.

Efficiency of energy deposition by fundamental and second harmonics in femtosecond laser inscription

We present the results of numerical modelling of energy deposition in single-shot femtosecond laser inscription for fundamental and second harmonics, which shows that second harmonic is more efficient considering the amount of absorbed energy

Broadly tunable CW green-to-red laser source based on frequency doubling of a quantum-dot external cavity diode laser in a PPKTP waveguide

Here we present a compact tunable all-room-temperature frequency-doubling scheme, using a periodically poled potassium titanyl phosphate (PPKTP) waveguide and a QD-ECDL. A broad wavelength tunability of the second harmonic generated light (SHG) in the spectral region between 567.7 and 629.1 nm was achieved, with maximum conversion efficiencies in range of 0.34%-7.9%. The maximum output power for the SHG light was 4.11 mW at 591.5 nm, achieved for 52 mW of launched pump power at 1183 nm, resulting in a conversion efficiency of 7.9%.

Photochemical dynamics of laser-irradiated semiconductor nanostructures

Thesis (Ph.D.)--University of Washington, 2016-08

Absorption Measurements of Periodically Poled Potassium Titanyl Phosphate (PPKTP) at 775 nm and 1550 nm

The efficient generation of second-harmonic light and squeezed light requires non-linear crystals that have low absorption at the fundamental and harmonic wavelengths. In this work the photo-thermal self-phase modulation technique is exploited to measure the absorption coefficient of periodically poled potassium titanyl phosphate (PPKTP) at 1,550 nm and 775 nm. The measurement results are (84 +/- 40) ppm/cm and (127 +/- 24) ppm/cm, respectively. We conclude that the performance of state-of-the-art frequency doubling and squeezed light generation in PPKTP is not limited by absorption.

Electro-spinning of pure collagen nano-fibres – just an expensive way to make gelatin?

Scaffolds manufactured from biological materials promise better clinical functionality, providing that characteristic features are preserved. Collagen, a prominent biopolymer, is used extensively for tissue engineering applications, because its signature biological and physico-chemical properties are retained in vitro preparations. We show here for the first time that the very properties that have established collagen as the leading natural biomaterial are lost when it is electro-spun into nano-fibres out of fluoroalcohols such as 1,1,1,3,3,3-hexafluoro-2-propanol or 2,2,2-trifluoroethanol. We further identify the use of fluoroalcohols as the major culprit in the process. The resultant nano-scaffolds lack the unique ultra-structural axial periodicity that confirms quarter-staggered supramolecular assemblies and the capacity to generate second harmonic signals, representing the typical crystalline triple-helical structure. They were also characterised by low denaturation temperatures, similar to those obtained from gelatin preparations ( p > 0.05). Likewise, circular dichroism spectra revealed extensive denaturation of the electro-spun collagen. Using pepsin digestion in combination with quantitative SDS-PAGE, we corroborate great losses of up to 99% of triple-helical collagen. In conclusion, electro-spinning of collagen out of fluoroalcohols effectively denatures this biopolymer, and thus appears to defeat its purpose, namely to create biomimetic scaffolds emulating the collagen structure and function of the extracellular matrix.

Genetic improvement of giant freshwater prawn in Vietnam

The giant freshwater prawn (Macrobrachium rosenbergii) or GFP is one of the most important freshwater crustacean species in the inland aquaculture sector of many tropical and subtropical countries. Since the 1990’s, there has been rapid global expansion of freshwater prawn farming, especially in Asian countries, with an average annual rate of increase of 48% between 1999 and 2001 (New, 2005). In Vietnam, GFP is cultured in a variety of culture systems, typically in integrated or rotational rice-prawn culture (Phuong et al., 2006) and has become one of the most common farmed aquatic species in the country, due to its ability to grow rapidly and to attract high market price and high demand. Despite potential for expanded production, sustainability of freshwater prawn farming in the region is currently threatened by low production efficiency and vulnerability of farmed stocks to disease. Commercial large scale and small scale GFP farms in Vietnam have experienced relatively low stock productivity, large size and weight variation, a low proportion of edible meat (large head to body ratio), scarcity of good quality seed stock. The current situation highlights the need for a systematic stock improvement program for GFP in Vietnam aimed at improving economically important traits in this species. This study reports on the breeding program for fast growth employing combined (between and within) family selection in giant freshwater prawn in Vietnam. The base population was synthesized using a complete diallel cross including 9 crosses from two local stocks (DN and MK strains) and a third exotic stock (Malaysian strain - MY). In the next three selection generations, matings were conducted between genetically unrelated brood stock to produce full-sib and (paternal) half-sib families. All families were produced and reared separately until juveniles in each family were tagged as a batch using visible implant elastomer (VIE) at a body size of approximately 2 g. After tags were verified, 60 to 120 juveniles chosen randomly from each family were released into two common earthen ponds of 3,500 m2 pond for a grow-out period of 16 to 18 weeks. Selection applied at harvest on body weight was a combined (between and within) family selection approach. 81, 89, 96 and 114 families were produced for the Selection line in the F0, F1, F2 and F3 generations, respectively. In addition to the Selection line, 17 to 42 families were produced for the Control group in each generation. Results reported here are based on a data set consisting of 18,387 body and 1,730 carcass records, as well as full pedigree information collected over four generations. Variance and covariance components were estimated by restricted maximum likelihood fitting a multi-trait animal model. Experiments assessed performance of VIE tags in juvenile GFP of different size classes and individuals tagged with different numbers of tags showed that juvenile GFP at 2 g were of suitable size for VIE tags with no negative effects evident on growth or survival. Tag retention rates were above 97.8% and tag readability rates were 100% with a correct assignment rate of 95% through to mature animal size of up to 170 g. Across generations, estimates of heritability for body traits (body weight, body length, cephalothorax length, abdominal length, cephalothorax width and abdominal width) and carcass weight traits (abdominal weight, skeleton-off weight and telson-off weight) were moderate and ranged from 0.14 to 0.19 and 0.17 to 0.21, respectively. Body trait heritabilities estimated for females were significantly higher than for males whereas carcass weight trait heritabilities estimated for females and males were not significantly different (P > 0.05). Maternal and common environmental effects for body traits accounted for 4 to 5% of the total variance and were greater in females (7 to 10%) than in males (4 to 5%). Genetic correlations among body traits were generally high in both sexes. Genetic correlations between body and carcass weight traits were also high in the mixed sexes. Average selection response (% per generation) for body weight (transformed to square root) estimated as the difference between the Selection and the Control group was 7.4% calculated from least squares means (LSMs), 7.0% from estimated breeding values (EBVs) and 4.4% calculated from EBVs between two consecutive generations. Favourable correlated selection responses (estimated from LSMs) were detected for other body traits (12.1%, 14.5%, 10.4%, 15.5% and 13.3% for body length, cephalothorax length, abdominal length, cephalothorax width and abdominal width, respectively) over three selection generations. Data in the second selection generation showed positive correlated responses for carcass weight traits (8.8%, 8.6% and 8.8% for abdominal weight, skeleton-off weight and telson-off weight, respectively). Data in the third selection generation showed that heritability for body traits were moderate and ranged from 0.06 to 0.11 and 0.11 to 0.22 at weeks 10 and 18, respectively. Body trait heritabilities estimated at week 10 were not significantly lower than at week 18. Genetic correlations between body traits within age and genetic correlations for body traits between ages were generally high. Overall our results suggest that growth rate responds well to the application of family selection and carcass weight traits can also be improved in parallel, using this approach. Moreover, selection for high growth rate in GFP can be undertaken successfully before full market size has been reached. The outcome of this study was production of an improved culture strain of GFP for the Vietnamese culture industry that will be trialed in real farm production environments to confirm the genetic gains identified in the experimental stock improvement program.