Electromagnetic radiation from the radio waves used in nuclear magnetic resonance spectroscopy through to X-rays used in crystallography have provided a wealth of knowledge about the structure, function, and dynamics of protein molecules. Terahertz waves, the topic of this thesis, are lower in frequency than radiation from the infrared, not to the frequencies of individual bond vibrations, but to the frequency range where slower longer range protein librations (low frequency vibrations) are expected to occur. The role of low frequency protein dynamics remains controversial, with some arguing that these motions are crucial for enzyme and protein function. Terahertz spectroscopy may provide key evidence to contribute to this interdisciplinary debate. In this thesis, terahertz (THz) spectroscopy has been applied in studying a number of proteins experimentally. In the first results chapter, the effect of protein concentration and ionic strength in the 0.1-2.5 THz region was investigated using Terahertz time domain spectroscopy. The results confirm the presence of terahertz excess for a number of proteins, which results from the increased absorption of THz waves when protein is introduced into the system. THz spectroscopy was then used to detect the difference between a folded protein, myoglobin, and folding intermediates, including the molten globule form, apomyoglobin. The results collected using THz spectroscopy were unable to differentiate between the folded and molten globule states. A further study was susceptible to the formation of higher order protein complexes and explored structures formed using PduA*. These experiments were primarily biochemical in nature with showing that PduA* assembles into nanotubes of 20nm diameter in vitro. The final results chapter explores the sub-THz circular dichroism signal from a vector network analyser driven by quasi-optical circuits. Wherever possible, the THz experiments were benchmarked using established analytical techniques.

Orientador: Newton Cesário Frateschi / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-14T11:19:53Z (GMT). No. of bitstreams: 1 Jarschel_PauloFelipe_M.pdf: 3096320 bytes, checksum: f09830dd682d577e43058480d256c5a1 (MD5) Previous issue date: 2009 / Resumo: A radiação eletromagnética em Terahertz (THz) situa-se na faixa de 1012 Hz, com comprimentos de onda associados variando de 30 µm até 3 mm. É possível então usar esta radiação para investigar propriedades físicas de materiais que requerem uma definição desta ordem. Além de aplicações na espectroscopia, estes comprimentos de onda são capazes de penetrar em papel, tecidos, pele e até neblina atmosférica, gerando um grande interesse em sistemas de segurança, medicina e aviação 1. Neste trabalho será apresentado o desenvolvimento de emissores de Terahertz baseados em SI-GaAs (GaAs Semi-Isolante), incluindo uma discussão detalhada da teoria desta emissão, descrição dos processos de fabricação e resultados obtidos de várias amostras. Esta antena consiste em eletrodos interdigitados depositados no topo de um substrato, de forma similar a fotodetectores MSM 2. A principal diferença entre estes dois dispositivos é que no emissor é feita uma segunda metalização,"opaca " e acima da anterior, separada por uma camada isolante de Si3N4. O princípio físico básico envolvido neste dispositivo é a emissão de radiação por cargas aceleradas. A idéia é que pares elétron-buraco sejam gerados por um laser de femtossegundo incidente na amostra, que se movem rapidamente entre os eletrodos, devido à tensão aplicada. Para obter a máxima eficiência de absorção, a camada isolante também serve como anti-refletora para o laser. A segunda metalização possui um papel essencial, pois ela garante que todos os portadores são acelerados no mesmo sentido, possibilitando então a interferência construtiva no campo distante (Far-Field) 3. Considerando a grande dificuldade de obtenção de lasers com pulsos de femtossegundos no período deste trabalho, utilizamos nosso dispositivo para a geração de ondas na faixa de MHz a partir de um laser pulsado eletronicamente, para verificação do princípio. Muito boa concordância entre nossa simulação e as medidas foi obtida. No entanto, deve-se observar que as propriedades da onda gerada neste caso são mais dependentes do pulso óptico em si do que da velocidade do dispositivo. De toda forma, o resultado mostra que o princípio de geração de ondas de rádio a partir de pulsos ópticos foi demonstrado com sucesso com nosso dispositivo. / Abstract: Terahertz electromagnetic radiation (THz) is situated around 1012 Hz in the electromagnetic wave spectrum, with associated wavelengths varying from 30 µm to 3 mm. It is possible then to use this radiation to investigate physical properties of materials that requires a definition of this order. Besides spectroscopy applications, these wavelengths are capable of penetrating deep into paper, skin, clothes, and even atmospheric fog, generating a great interest in using it for security systems, medicine and aviation¹. In this work, the development of Terahertz emitters based on photoconductive SI-GaAs (Semi-Insulator GaAs) will be presented, including a detailed discussion on the theory of this emission, description of the fabrication processes and results obtained from various samples. This antenna consists on interdigitated finger electrodes deposited on the top of a substrate, similar to MSM Photodetectors². The main difference between these two devices is that on our emitter,a second "opaque " metallization is done on top of the previous,separated by a Si3N4 dielectric layer. The basic physical concept involved in this device is radiation emission from accelerated charges. The idea is to generate electron-hole pairs by an incident femtosecond laser, which rapidly move between the electrodes, due to the bias voltage applied. To have maximum absorption efficiency, the insulating layer also serves as an anti-reflective coating for the pump laser. The second metallization plays an essential role, for it ensures that all carriers are accelerated in the same direction, thus allowing constructive interference on the far-field³. Giving the unavailability of a femtosecond laser for this work, we have used our device to generate radio waves in the MHz range using an electronically driven laser source. Very good agreement between our simulation and the results was obtained. One should note that in this case the emitted radiation is more dependent upon the optical pulse shape than the device speed itself. Nevertheless, our results show we have successfully demonstrated the generation of radio waves from optical pulses using our device. / Mestrado / Física da Matéria Condensada / Mestre em Física

Thesis (MScEng (Electrical and Electronic Engineering))--Univerity of Stellenbosch, 2011. / ENGLISH ABSTRACT: The design and simulation of hot electron bolometer sensors for the detection of millimeter and terahertz wave radiation is presented. These devices can be used for the formation of images or for spectroscopy in these frequency ranges. Many molecules resonate and have absorption spectra over these ranges, allowing for the identi cation, non-destructively and at a distance, of the constitution of many di erent materials. The penetrating ability of the radiation makes mm-wave and THz wave detectors ideal for security imaging. The design and simulation of these devices predicts performance as mixers and as interferometers. Manufacturing processes used while fabricating these thin lm devices are outlined and experimental results are reported. / AFRIKAANSE OPSOMMING: Hierdie tesis bespreek die ontwerp en simulasie van warm-elektron bolometers vir die waarneming van millimetergolf- en terahertz-straling. Sodanige toestelle kan in bogenoemde frekwensiebereike gebruik word vir beeldvorming of spektroskopie. Aangesien heelwat molekules binne hierdie bande resoneer, kan die samestelling van 'n verskeidenheid materiale oor 'n afstand en op 'n nie-vernietigende wyse gedenti seer word. Die deurdringingsvermo van millimetergolf- en terahertz-straling maak sulke detektors ideaal vir beeldvorming in veiligheidstoepassings. Met die ontwerp en simulasie van hierdie toestelle word gewys wat hul werkverrigting as mengers en interferometers kan wees. Die prosesse wat gebruik is om hierdie dun lmtoestelle mee te vervaardig word ook bespreek en eksperimentele resultate word aangebied.

L’objectif de ma thèse est d’étendre les modèles électromagnétiques existants à l’Institut Fresnel pour les fréquences optiques vers le domaine des fréquences térahertz (THz), pour mieux comprendre les phénomènes physiques mis en jeu lors d’interaction onde-matière. Cette compréhension permettrait d’améliorer l’analyse des images THz acquises et de mieux définir les configurations des systèmes optiques utilisés. Ce travail est réalisé en comparant les résultats issus de la modélisation avec ceux provenant d’expériences menées par imagerie THz au sein de l’entreprise Terahertz Waves Technologies. Dans le futur, la modélisation pourrait devenir un outil prédictif pour la caractérisation de matériaux dans le domaine THz.Les ondes THz se situent entre l’infrarouge lointain et les micro-ondes dans le spectre électromagnétique allant de 0.01 mm à 3 mm (ou 100 GHz à 30 THz). Ces ondes bénéficient des avantages des ondes optiques et des micro-ondes dépendant des longueurs d’ondes utilisées. L’imagerie THz présente un fort potentiel pour la caractérisation de la matière, car ces ondes peuvent pénétrer beaucoup de matériaux qui sont opaques dans le visible et dans l’infrarouge. La détection de défauts, les délaminations, la présence d’humidité, etc…, sont un exemple des problématiques qui peuvent être investiguées grâce au rayonnement THz.Dans un premier temps, j’ai pu simuler la réponse optique d’échantillons polymères plans homogènes et isotropes avec de bons accords entre le calcul et la mesure. Ces résultats ont permis de réaliser de premières modélisations d’images en adéquation avec l’imagerie THz. L’étude est ensuite élargie aux matériaux anisotropes qui existent dans l’environnement industriel actuel ainsi qu’aux objets de forme cylindrique. Les modèles développés considèrent l’indice de réfraction complexe d’un échantillon et son épaisseur, c’est pourquoi un chapitre est dévolu à la méthode d’estimation de ces paramètres à partir de mesures issues de spectroscopie THz dans le domaine temporel mise en œuvre. / The aim of my thesis is to extend the electromagnetic models already existing at the Institut Fresnel for the optical frequencies towards the terahertz (THz) range, to have a better knowledge of the physical phenomena involved in THz light-matter interactions. This understanding would allow to improve the analysis of the THz images acquired and to have a better definition of the optical systems configurations that we use. To achieve this work, we compare the results coming from the model with those from the experiments led by THz imaging by Terahertz Waves Technologies. In the future, the modelling could become a predictive tool for the characterization of materials in the THz domain.THz waves are located between far infrared and microwaves in the electromagnetic spectrum going from 0.01 mm to 3 mm (or 100 GHz to 30 THz). These waves benefit from advantages of the optical waves and from microwaves depending on used frequencies. THz imaging presents a high potential one for the characterization on the material, because these waves can penetrate a lot of materials which are opaque in the visible and the infrared lights. Detection of defects, delaminations, the presence of humidity, etc…, are examples of the problems which can be investigated with THz light.At first, I was able to model the optical response of planar, homogenous, isotropic and polymeric samples with good agreements between the calculation and the measurement. These results allowed to realize first modellings of images which are consistent with THz imaging. Therefore, the study is enlarged to anisotropic materials which exist in the current industrial environment as well as the objects of full cylindrical shape. The developed models consider the complex refractive index of a sample and its thickness, that is why a chapter is devoted to the method of estimation of these parameters from measurements coming from THz Time-Domain Spectrocopy signals which was implemented.

Orientador: Daniel Pereira / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-08T18:30:13Z (GMT). No. of bitstreams: 1 Costa_LeversonFariasLamonier_D.pdf: 15914858 bytes, checksum: 1c9b9d5747ffb493f5451d81d2898051 (MD5) Previous issue date: 2007 / Resumo: Neste trabalho realizamos três importantes etapas: 1) montar e caracterizar um laser selado de 13C02, 2) empregar o laser selado de 13C02 como fonte de bombeamento óptico para a molécula de metanol CH30H, e utilizá-lo pela primeira vez, para excitar o isótopo de metanol 13CH30H para geração de ondas na região do TeraHertz (THz) e 3) Propor "assignments" para as transições THz do CH30H e do 13CH30H. Para excitar as respectivas moléculas de metanol, um tubo comercial selado de 13C02 foi montado e caracterizado num ressonador laser Fabry-Perot. Dois cabeçotes de aluminio foram conectados por 4 barras de invar, separado em 135cm. Em um dos cabeçotes, temos uma grade de difração (150 linhas/mm) na configuração Littrow para selecionar as linhas de emissao do respectivo laser. 0 2° cabeçote suporta um espelho de saída de ZnSe (90% de refletividade com 10m de raio de curvatura) acoplado num PZT para sintonia fina da frequência do laser. No sistema de alimentação, usamos uma fonte de alta tensão comercial (25kV, 8mA) operando em regime DC. Com isso, utilizamos o respectivo laser para excitar as moléculas CH30H e 13CH30H, onde fomos pioneiro no uso do mesmo para bombeio óptico da molécula 13CH30H. Decorrente disso, obtemos os espectros de absorção em torno de cada linha de emissão do 13C02 dos respectivos metanol. Estes dados serviram de referenda para investigação sistemática de novas emissões THz, onde observamos e caracterizamos 12 novas linhas THz do CH30H e 19 do 13CH30H. Todas foram caracterizadas em relação ao seu comprimento de onda, offset, pressao de trabalho, polaridade e intensidade relativa.Utilizando os dados de linhas THz observados por nós, e os espectros de absorção a Transformada de Fourier do CH30H e do 13CH30H, um programa computacional intitulado "Ritz", identificou "assignments" para 4 transições THz do CH30H e 9 emissoes THz para 13CH30H, respectivamente / Abstract: In this work we accomplish three important tasks: to mount and to characterize a laser sealed-off 13C02 to optically pump first time methanol molecules CH30H and 13CH30H for generation of TeraHertz waves; Proposed assignments for transistions THz of the CH30H and 13CH30H. For optical pumping we use a commercial sealed-off 13C02, tube in a homemade Fabry-Perot laser resonator, mounted on two aluminum blocks connected by invar rods and separeted by 1.35m. One block holds a grating (150grooves/mm) used in Littrow configuration to select the emission line, while the second block supports a ZnSe output mirror (90% reflectivity and 10m radius of curvature) mounted on a PZT for fine frequency tuning. We use high voltage power supply (25kV, 8mA) to operate the 13C02 laser in CW regime. A cooling system maintains operation of the laser tube at -10o C. Output powers of l0 W and 1l0 MHz tuning range are typical for lines with higher optical gains. After, molecules CH30H and 13CH30H, optoacoustics spectroscopy (OA) signal, obtained around each sealed-off 13C02 laser line were the starting point to search for THz laser lines. For the more intense OA signal, a systematic investigation was performed to observe and characterize 12 new THz lines of the CH30H and 19 THz emissions of 13CH30H that they had been characterized in wavelength, offset, working pressure, relativepolarity and relative intensity. The available data has been compared a Ritz analysis of the high-resolution Fourier-Transform absorption spectrum of CH30H and 13CH30H, resulting in the assignments for 4 THz transistions of the CH30H and 9 THz emissions for 13CH30H, respectively / Doutorado / Física Atômica e Molecular / Doutor em Ciências