Quadrupole moments of radium isotopes from the 7p^2P_3/2 hyperfine structure in Ra II

The hyperfine structure and isotope shift of ^{221- 226}Ra and ^{212, 214}Ra have been measured in the ionic (Ra 11) transition 7s^2 S_{1/2} - 7p ^2 P_{3/2} (\lamda = 381.4 nm). The method of on-line collinear fast-beam laser spectroscopy has been applied using frequency-doubling of cw dye laser radiation in an external ring cavity. The magnetic hyperfine fields are compared with semi-empirical and ab initio calculations. The analysis of the quadrupole splitting by the same method yields the following, improved values of spectroscopic quadrupole moments: Q_s(^221 Ra)= 1.978(7)b, Q_s (^223 Ra)= 1.254(3)b and the reanalyzed values Q_s(^209 Ra) = 0.40(2)b, Q_s(^211 Ra) = 0.48(2)b, Q_s(^227 Ra)= 1.58(3)b, Q_s (^229 Ra) = 3.09(4)b with an additional scaling uncertainty of ±5%. Furthermore, the J-dependence of the isotope shift is analyzed in both Ra II transitions connecting the 7s^2 S_{1/2} ground state with the first excited doublet 7p^ P_{1/2} and 7p^ P_{3/2}.

Development of hybrid UV VCSEL with organic active material and dielectric DBR mirrors for medical, sensoric and data storage applications

Lasers play an important role for medical, sensoric and data storage devices. This thesis is focused on design, technology development, fabrication and characterization of hybrid ultraviolet Vertical-Cavity Surface-Emitting Lasers (UV VCSEL) with organic laser-active material and inorganic distributed Bragg reflectors (DBR). Multilayer structures with different layer thicknesses, refractive indices and absorption coefficients of the inorganic materials were studied using theoretical model calculations. During the simulations the structure parameters such as materials and thicknesses have been varied. This procedure was repeated several times during the design optimization process including also the feedback from technology and characterization. Two types of VCSEL devices were investigated. The first is an index coupled structure consisting of bottom and top DBR dielectric mirrors. In the space in between them is the cavity, which includes active region and defines the spectral gain profile. In this configuration the maximum electrical field is concentrated in the cavity and can destroy the chemical structure of the active material. The second type of laser is a so called complex coupled VCSEL. In this structure the active material is placed not only in the cavity but also in parts of the DBR structure. The simulations show that such a distribution of the active material reduces the required pumping power for reaching lasing threshold. High efficiency is achieved by substituting the dielectric material with high refractive index for the periods closer to the cavity. The inorganic materials for the DBR mirrors have been deposited by Plasma- Enhanced Chemical Vapor Deposition (PECVD) and Dual Ion Beam Sputtering (DIBS) machines. Extended optimizations of the technological processes have been performed. All the processes are carried out in a clean room Class 1 and Class 10000. The optical properties and the thicknesses of the layers are measured in-situ by spectroscopic ellipsometry and spectroscopic reflectometry. The surface roughness is analyzed by atomic force microscopy (AFM) and images of the devices are taken with scanning electron microscope (SEM). The silicon dioxide (SiO2) and silicon nitride (Si3N4) layers deposited by the PECVD machine show defects of the material structure and have higher absorption in the ultra violet range compared to ion beam deposition (IBD). This results in low reflectivity of the DBR mirrors and also reduces the optical properties of the VCSEL devices. However PECVD has the advantage that the stress in the layers can be tuned and compensated, in contrast to IBD at the moment. A sputtering machine Ionsys 1000 produced by Roth&Rau company, is used for the deposition of silicon dioxide (SiO2), silicon nitride (Si3N4), aluminum oxide (Al2O3) and zirconium dioxide (ZrO2). The chamber is equipped with main (sputter) and assisted ion sources. The dielectric materials were optimized by introducing additional oxygen and nitrogen into the chamber. DBR mirrors with different material combinations were deposited. The measured optical properties of the fabricated multilayer structures show an excellent agreement with the results of theoretical model calculations. The layers deposited by puttering show high compressive stress. As an active region a novel organic material with spiro-linked molecules is used. Two different materials have been evaporated by utilizing a dye evaporation machine in the clean room of the department Makromolekulare Chemie und Molekulare Materialien (mmCmm). The Spiro-Octopus-1 organic material has a maximum emission at the wavelength λemission = 395 nm and the Spiro-Pphenal has a maximum emission at the wavelength λemission = 418 nm. Both of them have high refractive index and can be combined with low refractive index materials like silicon dioxide (SiO2). The sputtering method shows excellent optical quality of the deposited materials and high reflection of the multilayer structures. The bottom DBR mirrors for all VCSEL devices were deposited by the DIBS machine, whereas the top DBR mirror deposited either by PECVD or by combination of PECVD and DIBS. The fabricated VCSEL structures were optically pumped by nitrogen laser at wavelength λpumping = 337 nm. The emission was measured by spectrometer. A radiation of the VCSEL structure at wavelength 392 nm and 420 nm is observed.

Protein Folding Simulations: Confinement, External Fields and Sequence Design

The present Thesis looks at the problem of protein folding using Monte Carlo and Langevin simulations, three topics in protein folding have been studied: 1) the effect of confining potential barriers, 2) the effect of a static external field and 3) the design of amino acid sequences which fold in a short time and which have a stable native state (global minimum). Regarding the first topic, we studied the confinement of a small protein of 16 amino acids known as 1NJ0 (PDB code) which has a beta-sheet structure as a native state. The confinement of proteins occurs frequently in the cell environment. Some molecules called Chaperones, present in the cytoplasm, capture the unfolded proteins in their interior and avoid the formation of aggregates and misfolded proteins. This mechanism of confinement mediated by Chaperones is not yet well understood. In the present work we considered two kinds of potential barriers which try to mimic the confinement induced by a Chaperon molecule. The first kind of potential was a purely repulsive barrier whose only effect is to create a cavity where the protein folds up correctly. The second kind of potential was a barrier which includes both attractive and repulsive effects. We performed Wang-Landau simulations to calculate the thermodynamical properties of 1NJ0. From the free energy landscape plot we found that 1NJ0 has two intermediate states in the bulk (without confinement) which are clearly separated from the native and the unfolded states. For the case of the purely repulsive barrier we found that the intermediate states get closer to each other in the free energy landscape plot and eventually they collapse into a single intermediate state. The unfolded state is more compact, compared to that in the bulk, as the size of the barrier decreases. For an attractive barrier modifications of the states (native, unfolded and intermediates) are observed depending on the degree of attraction between the protein and the walls of the barrier. The strength of the attraction is measured by the parameter $\epsilon$. A purely repulsive barrier is obtained for $\epsilon=0$ and a purely attractive barrier for $\epsilon=1$. The states are changed slightly for magnitudes of the attraction up to $\epsilon=0.4$. The disappearance of the intermediate states of 1NJ0 is already observed for $\epsilon =0.6$. A very high attractive barrier ($\epsilon \sim 1.0$) produces a completely denatured state. In the second topic of this Thesis we dealt with the interaction of a protein with an external electric field. We demonstrated by means of computer simulations, specifically by using the Wang-Landau algorithm, that the folded, unfolded, and intermediate states can be modified by means of a field. We have found that an external field can induce several modifications in the thermodynamics of these states: for relatively low magnitudes of the field ($<2.06 \times 10^8$ V/m) no major changes in the states are observed. However, for higher magnitudes than ($6.19 \times 10^8$ V/m) one observes the appearance of a new native state which exhibits a helix-like structure. In contrast, the original native state is a $\beta$-sheet structure. In the new native state all the dipoles in the backbone structure are aligned parallel to the field. The design of amino acid sequences constitutes the third topic of the present work. We have tested the Rate of Convergence criterion proposed by D. Gridnev and M. Garcia ({\it work unpublished}). We applied it to the study of off-lattice models. The Rate of Convergence criterion is used to decide if a certain sequence will fold up correctly within a relatively short time. Before the present work, the common way to decide if a certain sequence was a good/bad folder was by performing the whole dynamics until the sequence got its native state (if it existed), or by studying the curvature of the potential energy surface. There are some difficulties in the last two approaches. In the first approach, performing the complete dynamics for hundreds of sequences is a rather challenging task because of the CPU time needed. In the second approach, calculating the curvature of the potential energy surface is possible only for very smooth surfaces. The Rate of Convergence criterion seems to avoid the previous difficulties. With this criterion one does not need to perform the complete dynamics to find the good and bad sequences. Also, the criterion does not depend on the kind of force field used and therefore it can be used even for very rugged energy surfaces.

Patent DE10 2004 037 519 B4 “Sensor Process and Device for Determining a Physical Value“. A Proof of Concept

At present, a fraction of 0.1 - 0.2% of the patients undergoing surgery become aware during the process. The situation is referred to as anesthesia awareness and is obviously very traumatic for the person experiencing it. The reason for its occurrence is mostly an insufficient dosage of the narcotic Propofol combined with the incapability of the technology monitoring the depth of the patient’s anesthetic state to notice the patient becoming aware. A solution can be a highly sensitive and selective real time monitoring device for Propofol based on optical absorption spectroscopy. Its working principle has been postulated by Prof. Dr. habil. H. Hillmer and formulated in DE10 2004 037 519 B4, filed on Aug 30th, 2004. It consists of the exploitation of Intra Cavity Absorption effects in a two mode laser system. In this Dissertation, a two mode external cavity semiconductor laser, which has been developed previously to this work is enhanced and optimized to a functional sensor. Enhancements include the implementation of variable couplers into the system and the implementation of a collimator arrangement into which samples can be introduced. A sample holder and cells are developed and characterized with a focus on compatibility with the measurement approach. Further optimization concerns the overall performance of the system: scattering sources are reduced by re-splicing all fiber-to-fiber connections, parasitic cavities are eliminated by suppressing the Fresnel reflexes of all one fiber ends by means of optical isolators and wavelength stability of the system is improved by the implementation of thermal insulation to the Fiber Bragg Gratings (FBG). The final laser sensor is characterized in detail thermally and optically. Two separate modes are obtained at 1542.0 and 1542.5 nm, tunable in a range of 1nm each. Mode Full Width at Half Maximum (FWHM) is 0.06nm and Signal to Noise Ratio (SNR) is as high as 55 dB. Independent of tuning the two modes of the system can always be equalized in intensity, which is important as the delicacy of the intensity equilibrium is one of the main sensitivity enhancing effects formulated in DE10 2004 037 519 B4. For the proof of concept (POC) measurements the target substance Propofol is diluted in the solvents Acetone and DiChloroMethane (DCM), which have been investigated for compatibility with Propofol beforehand. Eight measurement series (two solvents, two cell lengths and two different mode spacings) are taken, which draw a uniform picture: mode intensity ratio responds linearly to an increase of Propofol in all cases. The slope of the linear response indicates the sensitivity of the system. The eight series are split up into two groups: measurements taken in long cells and measurements taken in short cells.

Model Calculations and Implementation of Filters and Hybrid Green VCSELs based on Optical Thin Film Stacks

This work introduced the novel conception of complex coupled hybrid VCSELs for the first time. Alternating organic and inorganic layers in the lasers provide periodic variation of refractive index and optical gain, which enable single mode operation and low threshold of the VCSELs. Model calculations revealed great reduction of the lasing threshold with factors over 30, in comparison with the existing micro-cavity lasers. Tunable green VCSEL has been also designed, implemented and analyzed taking advantage of the broad photoluminescence spectra of the organics. Free standing optical thin films without compressive stress are technologically implemented. Multiple membrane stacks with air gap in between have been fabricated for the implementation of complex coupled VCSEL structures. Complex coupled hybrid VCSEL is a very promising approach to fill the gaps in the green spectral range of the semiconductor lasers.

Highly Sensitive Sensor Based On Intracavity Laser Absorption Spectroscopy By Means of Relative Intensity Noise

This thesis concerns with the main aspects of medical trace molecules detection by means of intracavity laser absorption spectroscopy (ICLAS), namely with the equirements for highly sensitive, highly selective, low price, and compact size sensor. A novel two modes semiconductor laser sensor is demonstrated. Its operation principle is based on the competition between these two modes. The sensor sensitivity is improved when the sample is placed inside the two modes laser cavity, and the competition between the two modes exists. The effects of the mode competition in ICLAS are discussed theoretically and experimentally. The sensor selectivity is enhanced using external cavity diode laser (ECDL) configuration, where the tuning range only depends on the external cavity configuration. In order to considerably reduce the sensor cost, relative intensity noise (RIN) is chosen for monitoring the intensity ratio of the two modes. RIN is found to be an excellent indicator for the two modes intensity ratio variations which strongly supports the sensor methodology. On the other hand, it has been found that, wavelength tuning has no effect on the RIN spectrum which is very beneficial for the proposed detection principle. In order to use the sensor for medical applications, the absorption line of an anesthetic sample, propofol, is measured. Propofol has been dissolved in various solvents. RIN has been chosen to monitor the sensor response. From the measured spectra, the sensor sensitivity enhancement factor is found to be of the order of 10^(3) times of the conventional laser spectroscopy.

Absorptionsspektrometrie in der Kavität eines Halbleiterlasers unter Ausnutzung der Modenkonkurrenz zwischen zwei Moden

Motivation dieser Arbeit ist die Idee, ein höchst sensitives und selektives Spektroskop, welches gleichzeitig robust ist, auf Basis von Halbleiterlasern zum Einsatz in der Atemgasdiagnostik zu entwickeln. Technische Grundlage ist die Idee, die Probe innerhalb des Laserresonators zu vermessen (sogenannte intra cavity absorption spectroscopy, ICAS). Im speziellen soll durch die Verwendung des relativen Intensitätsrauschens zur Messwertbestimmung und die Verwendung von nur zwei Moden statt der sonst für ICAS verwendeten multimodigen Laser, die Empfindlichkeit erhöht, sowie die Messwerterfassung vereinfacht werden. Die Probe im Laserresonator zu Messen, hat den Vorteil, dass durch die multiple Hin­ und Rückreflektion die wirksame Pfadlänge durch die Probe vervielfacht wird. Dabei werden Verluste an den Resonatorspiegeln durch die Verstärkung der aktiven Zone des Lasers kompensiert. Außerdem wird durch die Konkurrenz der Moden um die idealerweise homogen verbreiterte Verstärkung im Laser die Empfindlichkeit noch einmal bedeutend erhöht. Schon eine geringe Absorption bei einer bestimmten Wellenlänge wird die Intensität des betroffenen Modes zugunsten der anderen Moden verringern. Die Arbeit beschäftigt sich zum einen mit der spektroskopischen Untersuchung zwei- er für die Atemgasdiagnostik relevanter Stoffe, Aceton und das in der Anästhesie häufig eingesetzte Propofol, um das Umfeld, in dem der Laser Verwendung finden soll, zu beleuchten. Diese Untersuchungen flossen in die Entwicklung des später zum Sensor auszubauenden Lasers ein. Für den Laser wurden in der Telekommunikation übliche, glasfaserbasierte, robuste Standardbauteile wie ein optischer Halbleiterverstärker (semiconductor optical amplifier, SOA), Faserkoppler und Faser­Bragg­Gitter verwendet. Die Bauteile wurden charakterisiert. Teilaspekte des Aufbaus wurden mit der Software CAMFR simuliert. Schließlich wurde der Laser als solcher aufgebaut und charakterisiert. Das Ziel der Zweimodigkeit, in einem Intervall von 2 nm durchstimmbar, konnte erreicht werden. An einem vom Heinrich­Hertz­Institut in Berlin entwickelten zweimodigen Halbleiterlasers wurden Untersuchungen der Idee zur Vereinfachung der Messwerterfassung mittels relativen Intensitätsrauschens (relative intensity noise, RIN) durchgeführt. Als Messgröße stellt das RIN die Amplituden der Intensitätsschwankungen des Lasers gegen die Frequenzen der Intensitätsschwankungen als Rauschspektrum dar. Es konnte nachgewiesen werden, dass das Rauschspektrum charakteristisch für das Oszillationsverhalten des Lasers ist.

High-Speed Semiconductor Lasers based on Low-Dimensional Active Materials for Optical Telecommunication

The scope of this work is the fundamental growth, tailoring and characterization of self-organized indium arsenide quantum dots (QDs) and their exploitation as active region for diode lasers emitting in the 1.55 µm range. This wavelength regime is especially interesting for long-haul telecommunications as optical fibers made from silica glass have the lowest optical absorption. Molecular Beam Epitaxy is utilized as fabrication technique for the quantum dots and laser structures. The results presented in this thesis depict the first experimental work for which this reactor was used at the University of Kassel. Most research in the field of self-organized quantum dots has been conducted in the InAs/GaAs material system. It can be seen as the model system of self-organized quantum dots, but is not suitable for the targeted emission wavelength. Light emission from this system at 1.55 µm is hard to accomplish. To stay as close as possible to existing processing technology, the In(AlGa)As/InP (100) material system is deployed. Depending on the epitaxial growth technique and growth parameters this system has the drawback of producing a wide range of nano species besides quantum dots. Best known are the elongated quantum dashes (QDash). Such structures are preferentially formed, if InAs is deposited on InP. This is related to the low lattice-mismatch of 3.2 %, which is less than half of the value in the InAs/GaAs system. The task of creating round-shaped and uniform QDs is rendered more complex considering exchange effects of arsenic and phosphorus as well as anisotropic effects on the surface that do not need to be dealt with in the InAs/GaAs case. While QDash structures haven been studied fundamentally as well as in laser structures, they do not represent the theoretical ideal case of a zero-dimensional material. Creating round-shaped quantum dots on the InP(100) substrate remains a challenging task. Details of the self-organization process are still unknown and the formation of the QDs is not fully understood yet. In the course of the experimental work a novel growth concept was discovered and analyzed that eases the fabrication of QDs. It is based on different crystal growth and ad-atom diffusion processes under supply of different modifications of the arsenic atmosphere in the MBE reactor. The reactor is equipped with special valved cracking effusion cells for arsenic and phosphorus. It represents an all-solid source configuration that does not rely on toxic gas supply. The cracking effusion cell are able to create different species of arsenic and phosphorus. This constitutes the basis of the growth concept. With this method round-shaped QD ensembles with superior optical properties and record-low photoluminescence linewidth were achieved. By systematically varying the growth parameters and working out a detailed analysis of the experimental data a range of parameter values, for which the formation of QDs is favored, was found. A qualitative explanation of the formation characteristics based on the surface migration of In ad-atoms is developed. Such tailored QDs are finally implemented as active region in a self-designed diode laser structure. A basic characterization of the static and temperature-dependent properties was carried out. The QD lasers exceed a reference quantum well laser in terms of inversion conditions and temperature-dependent characteristics. Pulsed output powers of several hundred milli watt were measured at room temperature. In particular, the lasers feature a high modal gain that even allowed cw-emission at room temperature of a processed ridge wave guide device as short as 340 µm with output powers of 17 mW. Modulation experiments performed at the Israel Institute of Technology (Technion) showed a complex behavior of the QDs in the laser cavity. Despite the fact that the laser structure is not fully optimized for a high-speed device, data transmission capabilities of 15 Gb/s combined with low noise were achieved. To the best of the author`s knowledge, this renders the lasers the fastest QD devices operating at 1.55 µm. The thesis starts with an introductory chapter that pronounces the advantages of optical fiber communication in general. Chapter 2 will introduce the fundamental knowledge that is necessary to understand the importance of the active region`s dimensions for the performance of a diode laser. The novel growth concept and its experimental analysis are presented in chapter 3. Chapter 4 finally contains the work on diode lasers.

Development of directly modulated high speed telecommunication lasers based on surface defined feedback gratings

High-speed semiconductor lasers are an integral part in the implemen- tation of high-bit-rate optical communications systems. They are com- pact, rugged, reliable, long-lived, and relatively inexpensive sources of coherent light. Due to the very low attenuation window that exists in the silica based optical fiber at 1.55 μm and the zero dispersion point at 1.3 μm, they have become the mainstay of optical fiber com- munication systems. For the fabrication of lasers with gratings such as, distributed bragg reflector or distributed feedback lasers, etching is the most critical step. Etching defines the lateral dimmensions of the structure which determines the performance of optoelectronic devices. In this thesis studies and experiments were carried out about the exist- ing etching processes for InP and a novel dry etching process was de- veloped. The newly developed process was based on Cl2/CH4/H2/Ar chemistry and resulted in very smooth surfaces and vertical side walls. With this process the grating definition was significantly improved as compared to other technological developments in the respective field. A surface defined grating definition approach is used in this thesis work which does not require any re-growth steps and makes the whole fabrication process simpler and cost effective. Moreover, this grating fabrication process is fully compatible with nano-imprint lithography and can be used for high throughput low-cost manufacturing. With usual etching techniques reported before it is not possible to etch very deep because of aspect ratio dependent etching phenomenon where with increasing etch depth the etch rate slows down resulting in non-vertical side walls and footing effects. Although with our de- veloped process quite vertical side walls were achieved but footing was still a problem. To overcome the challenges related to grating defini- tion and deep etching, a completely new three step gas chopping dry etching process was developed. This was the very first time that a time multiplexed etching process for an InP based material system was demonstrated. The developed gas chopping process showed extra ordinary results including high mask selectivity of 15, moderate etch- ing rate, very vertical side walls and a record high aspect ratio of 41. Both the developed etching processes are completely compatible with nano imprint lithography and can be used for low-cost high-throughput fabrication. A large number of broad area laser, ridge waveguide laser, distributed feedback laser, distributed bragg reflector laser and coupled cavity in- jection grating lasers were fabricated using the developed one step etch- ing process. Very extensive characterization was done to optimize all the important design and fabrication parameters. The devices devel- oped have shown excellent performance with a very high side mode suppression ratio of more than 52 dB, an output power of 17 mW per facet, high efficiency of 0.15 W/A, stable operation over temperature and injected currents and a threshold current as low as 30 mA for almost 1 mm long device. A record high modulation bandwidth of 15 GHz with electron-photon resonance and open eye diagrams for 10 Gbps data transmission were also shown.

Characterization of Novel Fabry Pérot Filter Arrays for Nanospectrometers in Medical Applications

Optische Spektroskopie ist eine sehr wichtige Messtechnik mit einem hohen Potential für zahlreiche Anwendungen in der Industrie und Wissenschaft. Kostengünstige und miniaturisierte Spektrometer z.B. werden besonders für moderne Sensorsysteme “smart personal environments” benötigt, die vor allem in der Energietechnik, Messtechnik, Sicherheitstechnik (safety and security), IT und Medizintechnik verwendet werden. Unter allen miniaturisierten Spektrometern ist eines der attraktivsten Miniaturisierungsverfahren das Fabry Pérot Filter. Bei diesem Verfahren kann die Kombination von einem Fabry Pérot (FP) Filterarray und einem Detektorarray als Mikrospektrometer funktionieren. Jeder Detektor entspricht einem einzelnen Filter, um ein sehr schmales Band von Wellenlängen, die durch das Filter durchgelassen werden, zu detektieren. Ein Array von FP-Filter wird eingesetzt, bei dem jeder Filter eine unterschiedliche spektrale Filterlinie auswählt. Die spektrale Position jedes Bandes der Wellenlänge wird durch die einzelnen Kavitätshöhe des Filters definiert. Die Arrays wurden mit Filtergrößen, die nur durch die Array-Dimension der einzelnen Detektoren begrenzt werden, entwickelt. Allerdings erfordern die bestehenden Fabry Pérot Filter-Mikrospektrometer komplizierte Fertigungsschritte für die Strukturierung der 3D-Filter-Kavitäten mit unterschiedlichen Höhen, die nicht kosteneffizient für eine industrielle Fertigung sind. Um die Kosten bei Aufrechterhaltung der herausragenden Vorteile der FP-Filter-Struktur zu reduzieren, wird eine neue Methode zur Herstellung der miniaturisierten FP-Filtern mittels NanoImprint Technologie entwickelt und präsentiert. In diesem Fall werden die mehreren Kavitäten-Herstellungsschritte durch einen einzigen Schritt ersetzt, die hohe vertikale Auflösung der 3D NanoImprint Technologie verwendet. Seit dem die NanoImprint Technologie verwendet wird, wird das auf FP Filters basierende miniaturisierte Spectrometer nanospectrometer genannt. Ein statischer Nano-Spektrometer besteht aus einem statischen FP-Filterarray auf einem Detektorarray (siehe Abb. 1). Jeder FP-Filter im Array besteht aus dem unteren Distributed Bragg Reflector (DBR), einer Resonanz-Kavität und einen oberen DBR. Der obere und untere DBR sind identisch und bestehen aus periodisch abwechselnden dünnen dielektrischen Schichten von Materialien mit hohem und niedrigem Brechungsindex. Die optischen Schichten jeder dielektrischen Dünnfilmschicht, die in dem DBR enthalten sind, entsprechen einen Viertel der Design-Wellenlänge. Jeder FP-Filter wird einer definierten Fläche des Detektorarrays zugeordnet. Dieser Bereich kann aus einzelnen Detektorelementen oder deren Gruppen enthalten. Daher werden die Seitenkanal-Geometrien der Kavität aufgebaut, die dem Detektor entsprechen. Die seitlichen und vertikalen Dimensionen der Kavität werden genau durch 3D NanoImprint Technologie aufgebaut. Die Kavitäten haben Unterschiede von wenigem Nanometer in der vertikalen Richtung. Die Präzision der Kavität in der vertikalen Richtung ist ein wichtiger Faktor, der die Genauigkeit der spektralen Position und Durchlässigkeit des Filters Transmissionslinie beeinflusst.

Mikromechanisch durchstimmbare, dielektrische Fabry-Pérot-Filter im nahen Infrarot-Bereich: Konzept, Herstellung und Charakterisierung

Das Ziel der vorliegenden Arbeit war die Herstellung und Charakterisierung mikromechanisch durchstimmbarer, dielektrischer Fabry-Pérot-Filter im nahen Infrarot-Bereich bei einer Zentralwellenlänge von λc = 950 nm. Diese Bauelemente wurden auf Basis kostengünstiger Technologien realisiert, dank deren Entwicklung extreme Miniaturisierung und gleichzeitig hohe spektrale Anforderungen möglich sind. Der Vorteil solcher Filter liegt darin, dass sie direkt in einen Photodetektor integriert werden können und mit ganz wenigen Komponenten zu einem kompakten Spektrometermodul zusammengesetzt werden können. Die Baugröße ist nur durch die Größe des Photodetektors limitiert und die gesamte Intensität des einfallenden Lichts kann vorteilhaft auf eine einzelne Filtermembran des Fabry-Pérot-Filters fokussiert werden. Für den Filteraufbau werden zwei hochreflektierende, dielektrische DBR-Spiegel, ein organisches Opferschichtmaterial, welches zur Erzeugung einer Luftkavität im Filter dient, und zwei unterschiedliche Elektroden aus ITO und Aluminium verwendet. Die mikromechanische Auslenkung der freigelegten Filtermembran geschieht mittels elektrostatischer Aktuation, wobei auf diese Weise die Kavitätshöhe des Fabry-Pérot-Filters geändert wird und somit dieser im erforderlichen Spektralbereich optisch durchgestimmt wird. Das in dieser Arbeit gewählte Filterkonzept stellt eine Weiterentwicklung eines bereits bestehenden Filterkonzepts für den sichtbaren Spektralbereich dar. Zum Einen wurden in dieser Arbeit das vertikale und das laterale Design der Filterstrukturen geändert. Eine entscheidende Änderung lag im mikromechanisch beweglichen Teil des Fabry-Pérot-Filters. Dieser schließt den oberen DBR-Spiegel und ein aus dielektrischen Schichten und der oberen Aluminium-Elektrode bestehendes Membranhaltesystem ein, welches später durch Entfernung der Opferschicht freigelegt wird. Die Fläche des DBR-Spiegels wurde auf die Fläche der Filtermembran reduziert und auf dem Membranhaltesystem positioniert. Zum Anderen wurde im Rahmen dieser Arbeit der vertikale Schichtaufbau des Membranhaltesystems variiert und der Einfluss der gewählten Materialien auf die Krümmung der freistehenden Filterstrukturen, auf das Aktuationsverhalten und auf die spektralen Eigenschaften des gesamten Filters untersucht. Der Einfluss der mechanischen Eigenschaften dieser Materialien spielt nämlich eine bedeutende Rolle bei der Erhaltung der erforderlichen optischen Eigenschaften des gesamten Filters. Bevor Fabry-Pérot-Filter ausgeführt wurden, wurde die mechanische Spannung in den einzelnen Materialien des Membranhaltesystems bestimmt. Für die Messung wurde Substratkrümmungsmethode angewendet. Es wurde gezeigt, dass die Plasmaanregungsfrequenzen der plasmaunterstützten chemischen Gasphasenabscheidung bei einer Prozesstemperatur von 120 °C die mechanische Spannung von Si3N4 enorm beeinflussen. Diese Ergebnisse wurden im Membranhaltesystem umgesetzt, wobei verschiedene Filter mit unterschiedlichen mechanischen Eigenschaften des Membranhaltesystems gezeigt wurden. Darüber hinaus wurden optische Eigenschaften der Filter unter dem Einfluss des lateralen Designs der Filterstrukturen untersucht. Bei den realisierten Filtern wurden ein optischer Durchstimmbereich von ca. 70 nm und eine spektrale Auflösung von 5 nm erreicht. Die erreichte Intensität der Transmissionslinie liegt bei 45-60%. Diese Parameter haben für den späteren spektroskopischen Einsatz der realisierten Fabry-Pérot-Filter eine hohe Bedeutung. Die Anwendung soll erstmalig in einem „Proof of Concept“ stattfinden, wobei damit die Oberflächentemperatur eines GaAs-Wafers über die Messung der spektralen Lage seiner Bandlücke bestimmt werden kann.

Theoretical and experimental study of intracavity laser absorption spectroscopy

In this thesis, a dual mode tunable gas sensor based on intracavity laser absorption spectroscopy (ICLAS) principle is investigated, both, numerically and experimentally. In order to minimize the cost and size of the gas sensor, relative intensity noise (RIN) is implemented as a detection parameter. Investigation is performed to determine the effect of injection current, operating temperature, mode spacing, and cavity length on RIN. It has been found that it is best to operate the gas sensor at smaller mode spacing and near the threshold current or at larger mode spacing and far above the threshold current for the use of RIN as the readout parameter.

Micro-layered-photolithography for Micro-Fabrication and Micro-Molding

A novel process based on the principle of layered photolithography has been proposed and tested for making real three-dimensional micro-structures. An experimental setup was designed and built for doing experiments on this micro-fabrication process. An ultraviolet (UV) excimer laser at the wavelength of 248 nm was used as the light source and a single piece of photo-mask carrying a series of two dimensional (2D) patterns sliced from a three dimensional (3D) micro-part was employed for the photolithography process. The experiments were conducted on the solidification of liquid photopolymer from single layer to multiple layers. The single-layer photolithography experiments showed that certain photopolymers could be applied for the 3D micro-fabrication, and solid layers with sharp shapes could be formed from the liquid polymer identified. By using a unique alignment technique, multiple layers of photolithography was successfully realized for a micro-gear with features at 60 microns. Electroforming was also conducted for converting the photopolymer master to a metal cavity of the micro-gear, which proved that the process is feasible for micro-molding.

La Presión Intra-abdominal Influye Sobre los Limites de la Presión de la Vía Aérea Durante la Ventilación Protectora Pulmonar

Background: The Intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) have a impact on the respiratory system and the recommendations for mechanical ventilation of patients with IAH/ACS remain unclear. Our study characterize the influence of elevated intra-abdominal pressure (IAP) and positive end-expiratory pressure (PEEP) on airway plateau pressure (PPLAT) and bladder pressure (PBLAD). Methods: Nine (n=9) deeply anesthetized swine were mechanically ventilated via tracheostomy: volume-controlled mode at tidal volume = 10 ml/kg, frequency=15, Inspiratory:Expiratory ratio=1:2 and PEEP of 1 and 10 cmH2O (PEEP1 and PEEP10, respectively). A tracheostomy tube was place in the peritoneal cavity and different levels of IAP were applied utilizing a CPAP system. Measurements were performed during both PEEP1 and PEEP10. Results: PBLAD increased as experimental IAP rose. Minimal underestimation of IAP by PBLAD was observed. Applying PEEP10 did not significantly affect the correlation between experimental IAP and PBLAD. PBLAD (in cmH2O) was reflected by changes in PPLAT regardless of the PEEP.

Medidas fractales de radiografías de tórax de pacientes con diferentes patologías

Introducción: La geometría fractal permite la descripción objetiva de objetos irregulares tales como las estructuras del cuerpo humano: Por ello, en este caso, se aplicó al desarrollo de una nueva metodología de caracterización de la cavidad cardiotorácica.Material y métodos: Estudio exploratorio descriptivo en el que se desarrolló una metodología de medición basada en la geometría fractal aplicada a 14 radiografías de tórax de sujetos con diferentes patologías. Se calcularon las dimensiones fractales de la cavidad torácica, la silueta cardíaca y la superposición de estas partes con el método de Box-Counting.Resultados: Se obtuvieron nuevas medidas morfométricas objetivas y reproducibles de placas de tórax a partir de dimensiones fractales.Conclusiones: La geometría fractal permite la caracterización matemática de placas de tórax de pacientes con diferentes patologías. Es posible que el desarrollo de esta metodología en posteriores investigaciones permita generar parámetros útiles de aplicación clínica, independientes de la experiencia del médico y de su observación subjetiva, de modo que garantice la reproducibilidad y objetividad de las medidas.