Dissertations / Theses on the topic 'Two photo microfabrication'

Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2006.
Tolbert, Laren, Committee Member ; Perahia, Dorva, Committee Member ; Perry, Joseph, Committee Member ; Collard, David, Committee Member ; Bunz, Uwe, Committee Chair.

Two-photon absorption (2PA) has been used for a number of scientific and technological applications, exploiting the fact that the 2PA probability is directly proportional to the square of the incident light intensity (while one-photon absorption bears a linear relation to the incident light intensity). This intrinsic property of 2PA leads to 3D spatial localization, important in fields such as optical data storage, fluorescence microscopy, and 3D microfabrication. The spatial confinement that 2PA enables has been used to induce photochemical and photophysical events in increasingly smaller volumes and allowed nonlinear, 2PA-based, technologies to reach sub-diffraction limit resolutions. The primary focus of this dissertation is the development of novel, efficient 2PA, fluorene-based molecules to be used either as photoacid generators (PAGs) or fluorophores. A second aim is to develop more effective methods of synthesizing these compounds. As a third and final objective, the new molecules were used to develop a write-once-read many (WORM) optical data storage system, and stimulated emission depletion probes for bioimaging. In Chapter I, the microwave-assisted synthesis of triarylsulfonium salt photoacid generators (PAGs) from their diphenyliodonium counterparts is reported. The microwave-assisted synthesis of these novel sulfonium salts afforded reaction times 90 to 420 times faster than conventional thermal conditions, with photoacid quantum yields of new sulfonium PAGs ranging from 0.01 to 0.4. These PAGs were used to develop a fluorescence readout-based, nonlinear three-dimensional (3D) optical data storage system (Chapter II). In this system, writing was achieved by acid generation upon two-photon absorption (2PA) of a PAG (at 710 or 730 nm). Readout was then performed by interrogating two-photon absorbing dyes, after protonation, at 860 nm. Two-photon recording and readout of voxels was demonstrated in five and eight consecutive, crosstalk-free layers within a polymer matrix, generating a data storage capacity of up to 1.8 x 1013 bits/cm3. The possibility of using these PAGs in microfabrication is described in Chapter III, where two-photon induced cationic ring-opening polymerization (CROP) crosslinking of an SU8 resin is employed to produce free-standing microstructures. Chapter IV describes the investigation of one- and two-photon stimulated emission transitions by the fluorescence quenching of a sulfonyl-containing fluorene compound in solution at room temperate using a picosecond pump-probe technique. The nature of stimulated transitions under various fluorescence excitation and quenching conditions were analyzed theoretically, and good agreement with experimental data was demonstrated. Two-photon stimulated transitions S1 to S0 were shown at 1064 nm. The two-photon stimulated emission cross section of the sulfonyl fluorophore was estimated as aproximately 240 - 280 GM, making this compound a good candidate for use in two-photon stimulated emission depletion (STED) microscopy.
Ph.D.
Department of Chemistry
Sciences
Chemistry PhD

Neste trabalho usamos pulsos de femtossegundos na fabricação de estruturas poliméricas em escala microscópica, através da técnica de fotopolimerização via absorção de dois fótons. Graças ao confinamento espacial da polimerização, resultante do processo de absorção de dois fótons, este método permite a fabricação de microestruturas tridimensionais complexas, com alta resolução, visando diversas aplicações tecnológicas, de fotônica até biologia. Inicialmente, desenvolvemos a técnica de fotopolimerização via absorção de dois fótons, desde a implantação da montagem óptica até a confecção dos sistemas de movimentação e controle do posicionamento do feixe laser. Através da fabricação e caracterização de microestruturas, produzidas em resinas acrílicas, o sistema foi aperfeiçoado permitindo a produção de microestruturas da pordem de 30um com razoável resolução espacial. Uma vez que a maior parte as microestruturas reportadas na literatura são elementos passivos, ou seja, suas propriedades ópticas não podem ser controladas por meios externos, numa segunda etapa deste projeto produzimos microestruturas opticamente ativas. Neste caso, a microfabricação foi feita em resinas acrílicas dopadas Rodamina B, exibindo, portanto, fluorescência quando excitadas com luz de comprimento de onda em torno de 540nm. Finalmente, visando a produção eficiente de estruturas em escala milimétrica para aplicações biológicas, implementamos também um sistema de fotopolomerização via absorção de um fóton.
In this work we used femtosecond pulses to fabricate polymeric structures at microscopic scale, by using the two-photon photopolymerization technique. Due to the spatial confinement of the polymerization, provided by the two-photon absorption, this method allows for the fabrication of complex three-dimensional microstructures, with high resolution, aiming to several technological applications, from photonics to biology. Initially, we developed the two-photon polimerization technique, from the optical setup to the mechanical systems to control the movement and the positioning of the laser beam. Through the fabrication and characterization os microestrutures, produced in acrylic resin, the apparatus was improved, allowing the fabriation of 30-um microstructures with reasonable spatial resolution. Since most the report in the literature are passive elements that is, their optical properties cannot be altered by any external means, in a second stage of this project we fabricated optical active microstructures. In this case, the microfabrication was carried out in acrylic resins doped with Rodamine B, exhibiting, consenquently, fluorescence when excited with light at 540nm. Finally, in order to eficiently produce milimetric structures for biological applications, we also implemented a one-photon polimerization setup.

L’avènement des lasers impulsionnels nanosecondes à femtosecondes a permis un développement rapide de techniques permettant de sonder et/ou de transformer les matériaux à l’échelle locale par des processus d’absorption non linéaire. Ce saut technologique a vu l’émergence de nombreuses applications associées au phénomène de confinement spatial. La stéréolithographie 3D par photopolymérisation biphotonique constitue un exemple typique d’application à forte valeur ajoutée qui offre de prometteuses perspectives en terme d’écriture à l’échelle nanométrique. Un enjeu fondamental constitue alors l’élaboration de nouveaux photoamorceurs très réactifs et activables à deux photons. Dans ce contexte, ce manuscrit présente une étude photophysique et photochimique de deux séries de photoamorceurs biphotoniques ‘Donneur/Accepteur’ intégrants des stilbènes comme relais électroniques avec pré-organisation dans des structures bichromophores. Les processus primaires photoinduits, les mécanismes de photoamorçage, la photoréactivité à l’echelle locale sont décrits et étudiés méthodiquement. Enfin, le potentiel appliqué de cette nouvelle génération de photoamorceurs est mis en évidence en microfabrication multiphotonique à travers l’élaboration de structure 3D à l’échelle µm
The advent of pulsed laser technologies has promoted the rapid growth of new emerging research domains which aim at probing and/or transforming materials at local scale using non linear absorption processes. A large range of applications takes benefit of the inherent spatial containment observed in non linear absorption processes so as to control photoreactions at nm-scale. The field of multiphoton fabrication (or stereolithography) addresses this fundamental issue and has developed rapidly so that it is no longer a rapid prototyping technology but a real manufacturing technique that is commercially available. The development of multiphoton stereolitography also requires highly reactive two-photon activable (2PA) initiators whose design and elaboration are the subject of considerable molecular engineering research. In this context, the present manuscript describes the photophysical and photochemical properties of two series of 2PA initiators. Such novel D--A structures have be designed by associating distinctive Donor and Acceptor groups into stilbene arms used as ‘electron relay’ and organized into a (multi)branched architecture. The photoinduced primary processes, the global photoinitiating mechanisms as well as the photoreactivity are described methodically. We finally demonstrate the applied potential of this new type of two-photon initiators in multiphoton stereolitography

Depuis les années 60, la génération d’acide fort de Brönsted par un processus photoinduit à un photon est utilisée dans des nombreux domaines de recherche de plus en plus nombreux. Cependant, de tels acides peuvent-être facilement obtenus par voie biphotonique ce qui présente de nombreux avantages comme par exemple : une meilleure réactivité via une excitation direct du photoacide, l’utilisation possible d’une atmosphère non contrôlée, l’utilisation de microlasers à impulsions sub-nanosecondes peu couteux, mais aussi l’augmentation de la résolution spatiale des micro-objets 3D fabriqués. La génération d’acide se fait généralement par transfert d’électron entre un sensibilisateur et un générateur de photoacide (PAG). Une approche prometteuse consiste à associer, sur une même molécule, un PAG et un chromophore actif à deux photons. Il a donc semblé intéressant de développer de nouveaux PAG capables, par excitation biphotonique, d’amorcer directement la photopolymérisation. Nous avons choisi de préparer des systèmes capto-datifs stilbéniques, de nature neutre ou ionique. Aussi, une série de PAG neutres substitués par des groupements diphénylamino- donneur et iminosulfonates -cyanés accepteurs a été synthétisée. Nous avons également commencé, mais non achevé, la synthèse de PAG neutres portant des groupements iminosulfonates -trifluorométhylés. Puis, nous avons cherché à synthétiser des PAG ioniques substitués soit par un groupement éthoxy soit par un groupement diphénylamino soit par un groupement julolidine. Néanmoins, la dernière étape de la synthèse est pour l’instant un verrou synthétique
Since the 60’s, the generation of strong Brönsted acids by a one-proton photoinduced process has been used in more and more research areas. Recently, it has been shown, that such acids are easily obtained by a two-photon process. This offers many advantages such as: i) a better reactivity owing to a direct excitation of the photoacid, ii) the possible use of a non-controlled atmosphere, iii) the use of inexpensive microlasers with sub-nanosecond impulsions, iv) the increase of spatial resolution in 3D microfabrication. The acid generation generally proceeds through a photo-induced electro transfer from an excited sensitizer to the photoacid generator (PAG). A promising approach should be the introduction on a single molecule of both a PAG and a two-photon active chromophore moiety. In this context, we have developed new PAGs able to initiate photopolymerisation through a two-photon activation process. The syntheses were focused on stilbenic push-pull systems having either a neutral or an ionic nature. A series of neutral PAGs bearing a diphenylamino donor group and an α-cyano iminosulfonate acceptor moiety has been synthesized. The preparation of neutral PAGs bearing iminosulfonate α-trifluoromethylated groups were not yet completed. The syntheses of ionic PAGs substituted by an ethoxy group, a diphenylamino group or a julolidine one, could not be completed either

This thesis is concerned with the fabrication methodology of polymeric photonic crystals operating in the visible to near infrared regions and the correlation between the chemical deposition morphologies and the resultant photonic stopband enhancements of photonic crystals. Multiphoton lithography (MPL) is a powerful approach to the fabrication of polymeric 3D micro- and nano-structures with a typical minimum feature size ~ 200 nm. The completely free-form 3D fabrication capability of MPL is very well suited to the formation of tailored photonic crystals (PCs), including structures containing well defined defects. Such structures are of considerable current interest as micro-optical devices for their filtering, stop-band, dispersion, resonator, or waveguiding properties. More specifically, the stop-band characteristics of polymer PCs can be finely controlled via nanoscale changes in rod spacings and the chemical functionalities at the polymer surface can be readily utilized to impart new optical properties. Nanoscale features as small as 65 ± 5 nm have been formed reproducibly by using 520 nm femtosecond pulsed excitation of a 4,4'-bis(di-n-butylamino)biphenyl chromophore to initiate crosslinking in a triacrylate blend. Dosimetry studies of the photoinduced polymerization were performed on chromophores with sizable two-photon absorption cross-sections at 520 and 730 nm. These studies show that sub-diffraction limited line widths are obtained in both cases with the lines written at 520 nm being smaller. Three-dimensional multiphoton lithography at 520 nm has been used to fabricate polymeric woodpile photonic crystal structures that show stop bands in the visible to near-infrared spectral region. 85 ± 4 nm features were formed using swollen gel photoresist by 730 nm excitation MPL. An index matching oil was used to induce chemical swelling of gel resists prior to MPL fabrication. When swollen matrices were subjected to multiphoton excitation, a similar excitation volume is achieved as in normal unswollen resins. However, upon deswelling of the photoresist following development a substantial reduction in feature size was obtained. PCs with high structural fidelity across 100 µm × 100 µm × 32 layers exhibited strong reflectivity (>60% compared to a gold mirror) in the near infrared region. The positions of the stop-bands were tuned by varying the swelling time, the exposure power (which modifies the feature sizes), and the layer spacing between rods. Silver coatings have been applied to PCs with a range of coverage densities and thicknesses using electroless deposition. Sparse coatings resulted in enhanced reflectivity for the stop band located at ~5 µm, suggesting improved interface reflectivity inside the photonic crystal due to the Ag coating. Thick coatings resulted in plasmonic bandgap behavior with broadband reflectivity enhancement and PC lattice related bandedge at 1.75 µm. Conformal titania coatings were grown onto the PCs via a surface sol-gel method. Uniform and smooth titania coatings were achieved, resulting in systematically red-shifted stopbands from their initial positions with increasing thicknesses, corresponding to the increased effective refractive index of the PC. High quality titania shell structures with modest stopbands were obtained after polymer removal. Gold replica structures were obtained by electroless deposition on the silica cell walls of naturally occurring diatoms and the subsequent silica removal. The micron-scaled periodic hole lattice originated from the diatom resulted in surface plasmon interferences when excited by infrared frequencies. The hole patterns were characterized and compared with hexagonal hole arrays fabricated by focused ion beam etching of similarly gold plated substrate. Modeling of the hole arrays concluded that while diatom replicas lack long-ranged periodicity, the local hole to hole spacings were sufficient to generate enhanced transmission of 13% at 4.2 µm. The work presented herein is a step towards the development of PCs with new optical and chemical functionalities. The ability to rapidly prototype polymeric PCs of various lattice parameters using MPL combined with facile coating chemistries to create structures with the desired optical properties offers a powerful means to produce tailored high performance photonic crystal devices.

Este trabalho demonstra o uso da fotopolimerização via absorção de dois fótons na produção de microestruturas dopadas com compostos orgânicos e nanopartículas de Au. A capacidade de produção de microestruturas com propriedades variadas é extremamente relevante, pois viabiliza o desenvolvimento de uma nova geração de dispositivos ópticos. Além disso, realizamos a conexão entre as microestruturas fabricadas e fontes de excitação, por meio de nanofibras de vidro. A integração entre essas estruturas, e destas com meios externos de excitação e detecção, é um passo essencial para o desenvolvimento de microcircuitos fotônicos, que podem representar uma nova revolução tecnológica, a exemplo do que foram os microcircuitos eletrônicos. Exploramos as possibilidades de dopagem da resina usando: (i) um composto fluorescente, (ii) um composto com birrefringência fotoinduzida e (iii) nanopartículas de ouro. Microestruturas contendo Rodamina B apresentaram boa integridade estrutural e fluorescência, tendo sido usadas para demonstrar a conexão dos microelementos com meios externos de excitação. Através de nanofibras e de micromanipuladores, comprovamos a capacidade de excitação seletiva de microestruturas através do guiamento da luz de um laser de Ar+. Estruturas birrefringentes foram obtidas pela dopagem com o azopolímero HEMA-DR13. Montamos um aparato que permite a observação da dinâmica de indução de birrefringência nas microestruturas, o qual representa um grande passo na caracterização deste tipo de microelementos. Com base nesse estudo, foi possível alcançar uma fração de birrefringência residual nas microestruturas de 35%. Por fim, propomos um método para a dopagem de microestruturas poliméricas com nanopartículas de ouro. Por se tratar de um método de dopagem indireta, ele evita interferências das nanopartículas no processo de microfabricação. Dessa forma, este trabalho abre possibilidades para a fabricação de microdispositivos funcionais com diversas propriedades especiais, bem como a integração desses microdispositivos em circuitos fotônicos.
This work demonstrates the use of two-photon photopolymerization in the fabrication of microstructures doped with organic compounds and gold nanoparticles. The ability to produce microstructures with different properties is extremely relevant, because it opens the possibility for the development of a new generation of optical devices. Besides, we have accomplished the connection between fabricated microstructures and excitation sources by means of silica nanowires. The connection among structures and with external means of detection and excitation is an essential step towards the development of new technological breakthrough in photonic microcircuits. We have explored the resin doping possibilities by using: (i) a fluorescent compound, (ii) a photoinduced birefringent compound and (iii) gold nanoparticles. Rhodamine B doped microstructures present good structural integrity and fluorescence, and were able to demonstrate the connection of microelements with external means of excitation. Through the use of nanofiber tapers and micromanipulators, we have shown the selective excitation capability of this method by guiding Ar+ laser light onto one single microstructure. Birefringent samples were obtained by doping the resin with the azopolymer HEMA-DR13. We have assembled an apparatus that allows observing the photoinduced birefringence dynamics, which represents a great step towards a better characterization of these kinds of microelements. Based on this study we were able to achieve a residual birefringence fraction of 35% in microscopic samples. Finally, we have proposed a new method for the doping of polymeric microstructures with gold nanoparticles. Because it is an indirect doping technique, it prevents gold nanoparticles from interfering with the microfabrication process. Thus, the work presented here paves the way for the fabrication of functional microdevices with a wide range of special properties, as well as for the connection of these microstructures for photonic microcircuit.

La structuration sub-micrométrique de grandes surfaces avec une très bonne résolution spatiale pourrait ouvrir de nouvelles frontières dans de nombreux domaines, tels que le stockage de données optiques 3D, la biomédecine ou les micro-dispositifs mécaniques et optiques. Parmi les différentes techniques de fabrication additive, la polymérisation biphotonique a suscité un grand intérêt en raison de sa résolution spatiale, sous la limite de diffraction de la longueur d'onde considérée. Néanmoins, cette technique souffre d'une vitesse d'écriture limitée et d'un coût d'exploitation élevé qui ralentissent son entrée sur le marché. Le but de ce projet de thèse est d'accroitre la vitesse de fabrication par polymérisation biphotonique en fabriquant plusieurs structures en parallèle grâce à la combinaison d’une source laser appropriée et d’éléments optiques diffractifs (EOD) avec une résine à faible seuil de polymérisation. Dans ce cadre, deux nouveaux photoamorceurs biphotoniques ont été synthétisés et caractérisés finement au moyen de multiples techniques (spectroscopies linéaire et non-linéaire, spectroscopie de résonance paramagnétique électronique, voltampérométrie cyclique, microfabrication, spectroscopie Raman). Leur utilisation au sein d’un mélange de monomères acrylates choisis a permis de mettre en évidence le fort potentiel de ces nouveaux amorceurs, comparé à ceux de la littérature. Les seuils de polymérisation ainsi que les dimensions des structures fabriquées ont été déterminés et corrélés à un modèle mathématique. Une méthode de quantification des rendements quantiques de photoamorçage combinant l'actinométrie chimique et la spectroscopie RMN du fluor a été proposée. L’impression simultanée en parallèle de 121 structures a été réalisée, nous conduisant à soulever les problèmes liés aux effets de proximité dans de telles conditions de fabrication ainsi qu’à proposer des voies d’amélioration
The fast patterning of sub-micrometric structures with high three-dimensional (3D) spatial resolution over a large area could open new frontiers in many fields such as 3D optical data storage, biomedicine or mechanical and optical micro-devices. Among the various additive manufacturing techniques, two-photon polymerization (TPP) has attracted a high level of interest due to the spatial resolution it offers, below the diffraction limit of the wavelength used. Nevertheless, this technique suffers from a limited writing speed and a high operating cost which slow down its entry on the market.The goal of this thesis project is to increase the building speed of TPP by fabricating several structures in parallel thanks to the combination of an appropriate laser source and diffractive optical elements (DOE) with a low polymerization threshold resin. In this framework, two new two-photon photoinitiators were synthesized and finely characterized using multiple techniques (linear and nonlinear spectroscopies, electron paramagnetic resonance spectroscopy, cyclic voltammetry, TPP microfabrication, Raman spectroscopy), highlighting their strong potential compared to benchmarks. The polymerization thresholds and the dimensions of the manufactured structures were determined and correlated to a mathematical model. A method for quantifying photoinduced radical generation quantum efficiencies by combining chemical actinometry and 19F NMR spectroscopy has been proposed. Simultaneous parallel printing of 121 structures was performed, revealing issues related to the proximity effects under such fabrication conditions, which we partially solved

Nesta tese, estudamos o processo de absorção multifotônica em polímeros e resinas poliméricas, abordando tanto aspectos fundamentais quanto aplicados. Com relação aos aspectos fundamentais, estudamos processos de absorção multifotônica (absorção de dois, três e quatro fótons) no polímero conjugado MEH-PPV (poly(2-methoxy-5-(2´-ethylhexyloxy)-1,4- phenylenevinylene)), utilizando a técnica de Varredura-Z com pulsos ultracurtos. Através desta técnica, determinamos o espectro da absorção de dois, três e quatro fótons do MEHPPV. As seções de choque de absorção de multi-fótons correspondentes a cada processo foram determinadas através do ajuste das curvas experimentais com um conjunto de equações desenvolvidas neste trabalho. Os resultados obtidos permitiram traçar relações entre os espectros não lineares e os níveis de energia do polímero. Na vertente mais aplicada do projeto, estudamos a fotopolimerização de resinas acrílicas através do processo de absorção de dois fótons. Devido ao confinamento espacial da polimerização, graças à absorção de dois fótons, este método permite a confecção de micro-estruturas complexas para diversas aplicações tecnológicas. Além da fabricação de microestruturas convencionais não dopadas, neste trabalho desenvolvemos uma metodologia que possibilita a fabricação de microestruturas dopadas com MEH-PPV, visando a produção de micro-elementos fluorescentes para dispositivos fotônicos, e microestruturas dopadas com quitosana, um polímero biocompatível que pode ser utilizado em aplicações médicas e biológicas.
In this thesis we have studied the multi-photon absorption process in polymers and polymeric resins, exploiting its fundamental as well as technological aspects. Regarding the fundamental aspects, we have studied the multi-photon absorption (two-, three- and four-photon absorption) in the conjugated polymer MEH-PPV (poly(2-methoxy-5-(2´-ethylhexyloxy)-1,4-phenylenevinylene)), by using the Z-scan technique with ultrashort laser pulses. Through this technique, we determined the two-, three- and four-photon absorption spectra of MEH-PPV. The multi-photon absorption cross-sections, corresponding to each specific process, have been determined by fitting the experimental data with a set of equations developed in this work. The results allowed us to correlate the nonlinear absorption spectra to the energy level of the polymer. On the technological side of this thesis, we have investigated the photopolymerization of acrylic resins by two-photon absorption. Because of the spatial confinement of the polymerization, resulting from the two-photon excitation, this method allows the fabrication of complex microstructures which can be used for several technological applications. In addition to the fabrication of undoped microstructures, in this work we have developed a methodology that allows the fabrication of microstructures doped with MEHPPV, aiming the production of fluorescent micro-elements for photonics applications, and microstructures doped with chitosan, a biocompatible polymer, that can be used for medical and biological applications.

La stéréolithographie biphotonique (TPS) est une technique de microfabrication 3D basée sur la polymérisation par absorption biphotonique qui permet d’obtenir en une seule étape des structures 3D complexes avec des détails sub-100nm. Aujourd’hui, en raison des conditions spécifiques de fabrication liées à la TPS (fort flux, confinement spatial de la photoréaction,…), un des enjeux concerne le développement de matériaux fonctionnels compatibles avec ce procédé. Dans ce contexte, l’objectif de cette thèse a été de développer de nouveaux matériaux fonctionnels à base de polymères à empreintes moléculaires (MIP) pour élaborer des capteurs chimiques. Une première partie de ce travail a consisté à mettre en place différentes méthodes dédiées à la caractérisation des propriétés géométriques, chimiques et mécaniques des matériaux élaborés par TPS. Par exemple, la vibrométrie laser a été utilisée pour la première fois afin de sonder de façon non-invasive les propriétés mécaniques de microstructures réalisées par TPS. Dans un second temps, ce travail a été mis à profit pour étudier l’impact du processus de fabrication (i.e. conditions photoniques) ainsi que des paramètres physico-chimiques affectant la photoréaction (i.e. inhibition par oxygène et nature du monomère) sur les propriétés finales des matériaux. Enfin, en s’appuyant sur les résultats obtenus, des microcapteurs chimiques à base de MIP, à lecture optique ou mécanique, ont été fabriqués. Leurs propriétés de reconnaissance moléculaire, ainsi que leurs sélectivités ont été démontrées pour une molécule cible modèle (D-L-Phe)
The two-photon stereolithography (TPS) technique is a micro-nanofabrication method based on photopolymerization by two-photon absorption that allows in a single manufacturing step to obtain complex 3D structures with high-resolution details (sub-100nm). Due to the specific conditions of TPS process (intense photon flux, spatial confinement of the photoreaction…) one of the main concerns today is the development of functional materials compatible with the TPS. According to the aforementioned, the general objective of this thesis was to develop new functional materials based on molecularly imprinted polymers (MIP) to elaborate chemical microsensors. In the first step of this work, different methods were implemented to characterize the geometrical, chemical and mechanical properties of the materials synthesized by TPS. For example, laser-Doppler vibrometry was used for first time to evaluate the mechanical properties of microstructures fabricated by TPS in a non-invasive way. In the second step, the characterization methodology was used to study the impact of the manufacturing process (i.e. photonic conditions) and the physicochemical parameters that affect the photoreaction (i.e. oxygen inhibition and the nature of the monomer) and the final properties of the materials. Finally, the obtained results enabled the prototyping of chemical microsensors based on MIP. Their molecular recognition properties and their selectivity were demonstrated for the molecule (D-L-Phe) by an optical and a mechanical sensing method

碩士
國防大學中正理工學院
應用物理研究所
94
We have chosen a self-assembled Kerr-lens modelocked Ti-Sapphire laser as a servo light source to induce the non-linear two-photon absorption (TPA) effects. The output power, wavelength, repetition rate, and pulse width of the laser are 350mW, 800nm, 86MHz, and 60fs, respectively. With the ultrahigh instantaneous light field, several micro-structures such as micro-gratings and micro-wells have been made out of the commercially available SU-8 photoresist, using the direct laser writing method through TPA photopolymerization. The sizes of the solidified voxel made in SU-8 with a 1.25 NA objective lens were measured, and the dependences on laser power and scanning speed were quantitatively studied. Finally, we have successfully made a three dimensional photonic crystal by the line scanning method.

碩士
國立臺灣大學
機械工程學研究所
103
Two-Photon Polymerization (TPP) was an accurate manufacturing method with high resolution focal spot for micron and sub-micron level complex structure. It was generally applied for MEMS, micro mechanical components, biomedical micro elements and other engineering fields. Previously, researches were concentrated on the development of photosensitive resins, control of the fabrication stage and the capability of manufacturing complicated structures, and less relative researches for the mechanical properties. However, in practice, we would need to realize the mechanical properties like young’s modulus to design the component. Because the structure of TPP was micron scale, conventional measure method like tensile and fracture test was difficult to implement. Therefore, in this thesis, we would apply optical tweezer to drag the cantilever beam, and obtain the deflection to derive the Young’s modulus. Moreover, by adjusting the parameter of laser power, distance of voxel and UV light exposal time, we could understand the relationship between young’s modulus and these parameters. Furthermore, during manufacturing the cantilever beam assembly, we had some experience for decreasing the fail rate of TPP. We would discussed those items and provide some possible solutions in this thesis. By knowing the parameter of mechanical properties, we believe the application of TPP would be extended widely in the future.

碩士
國立臺灣大學
機械工程學研究所
107
This thesis studies the characteristics of hydrogel material polyethylene glycol diacrylate (PEGDA) in microfabrication using two-photon polymerization (TPP) technology. Fast microfabrication of large area TPP products are also studied by using galvanometer scanner with diffractive optical element (DOE). For fabrication of PEGDA products, a 532nm wavelength Nd:YAG picosecond laser and a 100x objective lens with numerical aperture (NA) 1.3 are used. For finding the PEGDA line width in TPP fabrication, two experimental methods, ascending scan method and suspending bridge method, are used. Different aspect ratios of line dimension with different laser power and exposure time can be obtained. It is used in precision fabrication of 3D micro structures. For the fast fabrication using ORMOCOMP® material, a 515nm wavelength femtosecond laser, a xy galvanometer scanner, a z-axis piezo stage, a 50x objective lens with NA 0.8, a 5 x 5 DOE, and a xy planar translation stage are used. A Fresnel zone plate (FZP) lens array with 100 x 100 lens number is rapidly fabricated in 70 minutes. The FZP lens array has area size of 3.32mm x 3.32mm with a resolution of 0.67 µm. From the optical test, it shows good focusing condition and imaging quality.

碩士
國防大學中正理工學院
應用物理研究所
93
This thesis investigates the application of two-photon-absorbed (TPA) photopolymerization in ultraviolet (UV)-sensitive resin and photoresist to fabrication of microstructures. We have used a self-made Ti:sapphire ultrafast laser, along with a reflective confocal alignment system and a high-precision three-dimensional piezoelectric stage for our experiment. The laser pulse width is 47fs. The operating wavelength is 790nm and the output power is 280mW. The materials we employed were UV-cure optical adhesive and SU-8 photoresist. By the laser, the microstructures which are Micro-rods, Micro grating, Micro cell and Photonic crystal, respectively, were directly written inside the materials. We have verified the applicability of TPA photopolymerization fabrication technique to SU-8, which has been one of the most widely used photoresist for semiconductor industry. High-aspect-ratio microstructures such as micro-rods and micro-wells have been successfully made with single-layer raster scanning. The wall thickness is 1.51μm and the aspect ratio reaches 3.54. In addition, we have fabricated a photonic-crystal-like 3-dimensional structure by multilayer stacking.

3D printing, also known as ”additive manufacturing”, indicates a set of fabrication techniques that build objects by adding material, typically layer by layer. The main advantages of 3D printing are unlimited shapes and geometry, fast prototyping, and cost-effective small scale production. Two-photon lithography (TPL) is a laserbased 3D printing technique with submicron resolution, that can be used to create miniaturized structures. One of the most compelling applications of TPL is the 3D printing of miniaturized optical elements with unprecedented complexity, small-scale and precision. This could be potentially beneficial in biophotonics, a multidisciplinary research field in which light-based techniques are used to study biological processes. My research has been aimed at demonstrating novel applications of 3D printing based on TPL to different biophotonic applications. In particular, here we show 3D printed micro-optical structures that enhance and/or enable novel functions in advanced biophotonics methods as two-photon microendoscopy, optical trapping and Stimulated Raman Scattering microscopy. Remarkably, the micro-optical structures presented in this thesis enable the implementation of advanced techniques in existing or simpler microscopy setups with little to no modification to the original setup. This possibility is essentially allowed by the unique miniaturization and in-situ 3D printing capabilities offered by TPL.