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An IC-ECL with different waveguide concepts and a MEMS device as tuning element for high acquisition rates is presented. Characterization results and use for detection of trace gases in the MIR region will be shown.

IC-ECLs with straight and curved waveguide concepts are analyzed and presented. The results of the characterization and the use for the detection of trace gases with acquisition rates above 1 kHz are shown.

Although external cavity diode lasers have become firmly established for their excellent properties for species detection, they have severe limitations in terms of high acquisition rates. In this paper, we present our new ECDL design based on a resonantly driven MEMS scanner. By using the MEMS technology, a defined frequency range can be tuned extremely fast and without mode-hops. This allows scanning frequencies in the high kHz range to be achieved. The results of the characterization of the spectral properties of the MEMS-based system and its use for rapid detection of trace gases are presented.

The detection and identification of molecular gases are of high relevance in many applications within healthcare, production monitoring and safety as well as environmental monitoring. One of the major difficulties of trace gas analysis is due to the bulky and expensive systems, what excludes both mobile and handheld use. For this purpose we present our new system based on the Quartz Enhanced PhotoAcoustic Spectroscopy (QEPAS), which can provide the required properties for gas analysis. We have developed a compact detection unit where DFB laser, collimation optics and QTF are integrated in a 14-pin butterfly housing. Therefore an optimization of the DFB laser chips will be presented too. The results show, that the laser diodes not only provide excellent performance, but also allow a detection limit for the greenhouse gas methane and carbon dioxide in the ppm range.

An ultrafast ECDL design based on a MEMS device with optimized curved gain chip at 2020 nm is presented. Results of the characterization and its use for the detection of trace gases are shown.

The rapid detection of trace gases is of great relevance for various spectroscopy applications. In this regard, the technology of external cavity diode lasers (ECDLs) has firmly established itself due to its excellent properties. Outside of the laboratory environment, however, these still have some restrictions, especially with regard to high acquisition rates for sensitive spectroscopy applications and mode-hop-free tuning. In this article, we present our innovative GaSb-based ECDL concept, in which a resonantly driven microelectromechanical system actuator is used. With this, a defined frequency range can be tuned extremely fast and without mode hops. Results of the characterization and its use for the rapid detection of trace gases are presented.

An optimized D-DFB design is presented, which guarantees the best possible performance in the range from 1.9 µm to 4.5 µm. Results for the performance and its suitability for detecting trace gases are shown.

An MEMS based ECDL design with optimized curved gain chip for the MIR region is presented. Results of the characterization and its use for the rapid detection of trace gases are shown.

Optimized DFB lasers are presented. Results for the performance and its suitability for detecting trace gases are shown. We present our new QEPAS compact detection unit where everything is integrated into 14-pin butterfly housing.

In this work, a monolithic Y-branch laser diode is used for continuous wave Terahertz generation and detection. The output of the laser diode is fiber coupled, amplified and fed into a photoconductor based cw Terahertz setup. While this system can be used for time domain measurements using a fiber coupled delay stage, we'll present sample thickness determination based on laser current induced frequency sweeping without delay stage.

External cavity diode lasers (ECDLs) are a well-established laboratory tool due to their excellent emission properties. However, if the ECDLs are used outside the laboratory, they have limitations in terms of tuning speed and robustness. For overcoming these limitations, we developed a new micro-electro-mechanical system (MEMS) based ECDL cavity concept. The 1D MEMS actuator defines the angle of incidence at the diffraction grating as well as the cavity length of the ECDL. Due to the high resonance frequency of the MEMS actuator in the kHz range, the switching speed of the ECDL emission wavelength is drastically reduced. Furthermore, the MEMS actuator minimizes the sensitivity to external disturbance which opens a path to handheld wide mode-hop free tunable ECDLs in the near future. Therefore we have also optimized our curved waveguide concept based on GaSb for the ECDL design, whereby a wavelength range from NIR to the MIR range can be better covered. These features qualify the new developed MEMS tunable ECDL for the high demands of the high resolution multi-species molecular spectroscopy. Application examples of the MEMS based ECDL and the curved gain chips will be provided.

GaSb based types of diode lasers may cover the spectral regime from below 1.8 μm up to 5 μm. For the wavelength regime of 1.8 μm to 2.5 μm InGaAsSb/GaSb MQW material is used. For 2.5 μm to 3.4 μm InAlGaAsSb/GaSb MQW material is used. For above 3μm, an ICL type of design is required. We realized a growth campaign of 10 GaSb based wavers for covering the wavelength regime from 1.9μm to 3μm. We report on the test, performance and applications results in molecular gas sensing of both, gain chips within an external cavity laser as well as on digital DFB lasers.

Quartz-Enhanced-Photo-Acoustic-Spectroscopy (QEPAS) is a modern, promising trace gas measuring technique. One main advantage of QEPAS over other trace-gas spectroscopes is its size. The miniaturization of the sensor-system is the next big challenge in the development.

10 GaSb based wafers for covering the wavelength regime from 1.9 pm to 3 pm were realized. We report on the test, performance and applications-results in gas spectroscopy with ECDL and D-DFB lasers.

En un mundo en el que las tecnologias avanzan a pasos agigantados, es necesario proponer y aplicar nuevas mejoras de forma continua aplicadas a cualquier campo. El mundo de la tecnologia laser, incluido dentro del campo anterior, tiene infinidad de aplicaciones en las que son necesarios nuevos laseres a diario para facilitar las medidas y mejorar los resultados de los ambitos en los que estos dispositivos se usen. En esta tesis se presenta un nuevo concepto de tecnologia para la fabricacion de laseres sintonizables. Existen laseres fabricados con gases, tintes o incluso con elementos de estado solido como el rubi, aunque es habitual que los laseres sintonizables, que son aquellos en los que se puede variar su longitud de onda de emision, que esten fabricados con diodos de semiconductor. Los semiconductores, combinados adecuadamente, generan unas bandas de emision que comprenden las longitudes de onda, o colores, entre el ultravioleta y el infrarrojo. Actualmente, hay distintas tecnologias con las que llevar a cabo la sintonizacion de la luz coherente emitida por un laser de semiconductor. Con objeto de crear un laser sintonizable, hacen falta distintos elementos: un material activo que proporcione ganancia en el rango de longitudes de onda necesarios; reflectores que creen una cavidad resonante en el que la emision laser estimulada se pueda producir, generando distintas longitudes de onda (o frecuencias) en todo el rango habilitado; y un filtro que seleccione el modo adecuado de emision, ya que estamos hablando de laseres con una unica frecuencia. Entre las distintas tecnologias habilitadoras para la fabricacion de laseres sintonizables, cabe destacar los mas utilizados laseres de realimentacion distribuida (DFBs segun sus siglas en ingles, Distributed FeedBack Lasers, o DBRs, tambien segun sus siglas en ingles, Distributed Bragg Reflector Lasers) y los laseres de cavidad externa. La diferencia principal entre estas dos tecnologias es que en los DFBs y DBRs, la seleccion de frecuencia se hace mediante una red de difraccion distribuida a lo largo del material semiconductor. Esta red de difraccion, conocida por red de Bragg ya que fue el quien primero la planteo, sirve como reflector y como filtro a la vez, ya que se encarga de reflejar unicamente la frecuencia de emision deseada. De esta forma, el laser se estabiliza a la longitud de onda fijada por la red de Bragg, que esta inscrita directamente en el chip de semiconductor. Esta solucion genera unos dispositivos compactos y estables, pero con inconvenientes muy ligados al propio concepto de filtrado que se plantea con ellos. Al ser las inscripciones hechas directamente en el material, se generan perdidas de potencia ligadas a las propias irregularidades encargadas de filtrar. Ademas, el rango de sintonizacion de estos dispositivos es muy limitado, ya que hacen uso de un efecto termico con el que expandir o contraer la propia red de difraccion inscrita en el chip. Los semiconductores, al no ser materiales con un alto coeficiente de expansion termica, se ven limitados a un rango muy estrecho de sintonizacion si se emplea esta tecnologia. En contraposicion a los dispositivos ya descritos, encontramos la tecnologia de los laseres sintonizables de cavidad externa. Esta se basa mayormente en dos configuraciones distintas: cavidades tipo Littrow y cavidades tipo Littman-Metcalf. La primera de ellas es relativamente mas sencilla. Un material activo es colocado entre dos reflectores. Uno de ellos es un reflector comun, como un espejo, mientras que el otro consiste en una red de difraccion externa que realimenta la longitud de onda deseada al material activo, estabilizando el laser. Para sintonizar este tipo de cavidades, es necesario girar en un angulo determinado la red de difraccion y, de esta manera, variar la frecuencia reflejada al material activo para su estabilizacion. El segundo tipo de cavidad, la cavidad tipo Littman-Metcalf, agrega un elemento mas a la configuracion: el material semiconductor activo se coloca entre un reflector comun y una red de difraccion, pero en este caso el angulo de la red de difraccion es distinto y apunta a un segundo reflector comun, que sera el encargado de girar para realizar la sintonizacion de la longitud de onda del laser. Los laseres presentados en esta tesis de doctorado se basan en esta segunda configuracion para su sintonizacion de frecuencia. Presentamos aqui la aplicacion de micro sistemas electro mecanicos en la fabricacion de laseres de semiconductor de cavidad externa, con una serie de ventajas muy evidentes en comparacion con los sistemas habituales. Tradicionalmente, los laseres sintonizables de cavidad externa se basan en componentes mecanicos. Esto se traduce en unos dispositivos voluminosos en el que su ambito de aplicacion se ve muy limitado dada su poca capacidad de movilidad. Con la introduccion de los MEMS en la configuracion de los laseres, podemos sustituir los componentes mecanicos voluminosos y asi reducir el tamano de los dispositivos y aumentar su portabilidad. Este punto habilita el incremento de aplicaciones en las que estos laseres pueden ser aplicados, ya que pudiendo ser portatiles se hace posible su uso directamente en campo o crear dispositivos ligeros para su inclusion en aparatos de mano, mucho mas convenientes para el dia a dia. Otro de los puntos a favor de estos laseres es la potencia de salida proporcionada. La red de difraccion externa, ya sea de transmision o de reflexion, se puede ajustar en su punto optimo de reflexion para maximizar el nivel de potencia optica a la salida del laser. Ademas, estas redes no estan inscritas sobre el material semiconductor y no producen perdidas adicionales como si ocurre en el caso de los laseres de realimentacion distribuida descritos anteriormente. Lo mismo sucede con el rango de sintonizacion de los dispositivos presentados. Este no esta limitado por ningun efecto como si que pasa en los DFBs y DBRs, y de esta manera la sintonizacion de la longitud de onda se extiende hasta el total del ancho de banda de ganancia proporcionado por el material semiconductor que empleemos en la cavidad. El ancho de linea de la emision laser de las configuraciones que presentamos son muy estrechos. Esto implica que los valores ofrecidos por cavidades Littrow y Littman-Mettcalf se hallan en las decenas de kilohercios, disminuyendo asi en uno o dos factores de magnitud la anchura de las lineas laser de otras configuraciones. Mediante esta alta selectividad en longitud de onda, sumado al alto nivel de potencia ofrecido por los dispositivos desarrollados en esta tesis, se incrementa la sensitividad y la resolucion de cualquiera de las aplicaciones en las que se usen estos laseres. Adicionalmente a las caracteristicas ya mencionadas, hay un factor que hace de este desarrollo un avance clave para la tecnologia: la velocidad de sintonizacion. Las cavidades externas tradicionales hacen uso, como ya se ha mencionado anteriormente, de piezas mecanicas para la sintonizacion del dispositivo. Para poder sintonizar el rango completo de longitudes de onda ofrecidos por la cavidad, hace falta un tiempo del orden de segundos en el mejor de los casos, que es cuando se emplea un motor para mover el brazo mecanico correspondiente. Con el dispositivo que presentamos, estos tiempos se reducen en varios ordenes de magnitud, situandose en las decenas de milisegundos. Este efecto se consigue mediante la aplicacion de un voltaje que, de manera instantanea, traslada este valor a un angulo de giro que se aplica a los MEMS para sintonizar la longitud de onda del laser. Este avance, aparte de aportar una capacidad de medida practicamente en tiempo real a distintas frecuencias, va ligado a la precision de los sistemas electromecanicos que se han introducido, mejorando asi en comparacion los resultados ofrecidos por las piezas puramente mecanicas. Se ha medido la estabilidad de estos laseres, con resultados por debajo de los picometros y muchas veces estas medidas han estado incluso limitadas por la resolucion disponible para su adquisicion aun a pesar de utilizar instrumentos con la ultima tecnologia, lo que indica el alto grado de precision y estabilidad de los dispositivos desarrollados. El desarrollo de la cavidad externa para los dispositivos presentados no ha sido un proceso trivial, sino que ha necesitado de varias iteraciones hasta llegar a un resultado estable. Estos ciclos se muestran en la tesis, de manera que se ve la evolucion de los dispositivos. Como ultimo punto a destacar, la tecnologia aqui presentada es aplicable a distintos materiales de ganancia, pudiendo cubrir el espectro optico que se necesite con solo ajustar los componentes necesarios. La posibilidad de extrapolar esta tecnologia a todo el espectro optico, cubriendo desde el ultravioleta al infrarrojo lejano. Las conclusiones de esta tesis se reflejan en todos los puntos a favor de los dispositivos presentados: alta potencia de salida, gran rango de sintonizacion, estabilidad y velocidad de conmutacion entre distintas longitudes de onda para mediciones en tiempo real.

HITRAN promises better gas detection possibilities in the MIR wavelength regime than the NIR or the visible region because of the higher absorbencies. These promises are tested with different lasers on TDLAS and QEPAS applications.

The commercially available semiconductor lasers for the mid-infrared (MIR) region often do not reach the desired performance and represent a limitation for gas sensor technology. Here we present our digital distributed feedback filter (D-DFB) laser diodes based on GaSb gain material, which have been optimized in terms of facet reflectivity, chip length, and output power. These diodes now cover the wavelength range from 1900 nm up to 4500 nm and show excellent quality regarding their spectral characteristics. Results for the performance of the D-DFB laser design and its suitability for the detection of trace gases are shown in this publication.

Molecular gases are highly relevant in healthcare, production control, safety, and environmental monitoring. They often appear in small concentrations. The measurement of trace gases has increasingly become a key technique in those domains. Quartz-enhanced photoacoustic spectroscopy (QEPAS) is a suitable method that can provide the required low detection limits in such applications at comparatively low cost and small size. For mobile implementation, the size of an entire sensor unit matters. In this paper, we present a QEPAS sensor that fits into a standard butterfly package, its characterization, and its application on C H 4 and C O 2 .

The NIR/MIR region between 1.8μm and 3.5μm contains important absorption lines for gas detection. State of the art are InP laser based setups, which show poor gain above 1.8μm and cannot be applied beyond 2.1μm. GaSb laser show a significantly higher output power (100mW for Fabry-Perot, 30mW for DFB). The laser design is presented with simulation and actual performance data. The superior performance of the GaSb lasers is verified in gas sensing applications. TDLAS and QEPAS measurements at trace gases like CH4, CO2 and N2O are shown to prove the spectroscopy performance.

The wavelength, λ, range of 1.8 μm≤λ≤3.5 μm contains strong spectral absorption lines of many gases used in health, industry, safety, and medicine and whose sensitive and quantitative detection is desirable. However, the performance of InP diode lasers markedly deteriorates beyond λ∼2 μm. In this paper we present new results on developing tunable high power single mode laser diodes based on the GaSb material system with emission in the wavelength range of 1.8 μm≤λ≤2.2 μm.

The thermal management of high power LED bears the potential of achieving higher efficiencies as well as an increased lifetime. Yet so far none of the conventional cooling techniques are suitable for use with general illumination: The devices emit audible noise, have a short life time, or are sensitive against dust and debris. The goal behind this work was to develop a solution that has none of these drawbacks. The effect of acoustic streaming was chosen for a closer look and delivered very good results during first experiments. Within this paper a device will be presented that is able to cool a 5000 lm LED light engine without emitting any audible sound. To achieve this all aspects of the device were examined and optimized.

A new approach for forced convection cooling based on “Reynolds streaming” is presented, which allows for additional heat dissipation in situations where conventional active cooling devices (e.g. fans) are not suitable. The system operates inaudible, has no moving parts and is therefore durable and immune to dust. Its operation is dependent on numerous influences that have been identified and analyzed through experiment and simulation. It employs a new kind of acoustic driver delivering high intensity fields within air, while maintaining a small build volume. This transducer was designed and optimized using FEM-Simulation and verified with real-world prototypes at each major simulation milestone. All of the taken measures improved the performance by a factor of nearly 2 while reducing the system size by a factor of over 6 at the same time when compared to the first working system. This last generation device delivers comparable cooling performance.

The paper contains the results of temperature measurements for reliability investigations on IGBT modules actually working in inverters for industrial and traction applications. For this, the chip temperature and its transient behaviour have been monitored under different driving conditions of the inverters. Specially prepared IGBT-modules have been used to investigate the industrial and the traction inverters in their electrical and thermal behaviour. The measurement techniques were suitably adapted to the different configurations of the two inverters.

An array of 2/spl times/2 switches with integrated tapers has been pigtailed using a silicon submount to self-align both chip and single-mode fibers. Electrical contacts were wirebonded through an opening etched in the submount. We report fiber-to-fiber insertion loss below 10 dB and measurements of wavelength and temperature dependence of the module. >