Los autores desean reconocer y agradecer el apoyo financiero para este estudio realizado por la National Science Foundation (Grant No: CMMI-0.653.578, CBET-0853890).

1. Configuración del sistema óptico (Fig. 1) <ol><li> Establecer una placa de media onda y un polarizador tras la salida del láser para ajustar la energía del impulso láser. </li><li> Establecer un divisor de haz después de que el polarizador para dividir el pulso del láser a dos impulsos: pulso de la bomba y el pulso de la sonda. </li><li> Utilice cuatro espejos que reflejan y una etapa de traslación manual para construir un dispositivo de retardo óptico para el pulso de la bomba. </li><li> Utilizar otros espejos que reflejan cuatro para guiar el pulso de la bomba para alcanzar la superficie del blanco verticalmente. </li><li> Establecer un generador de segunda armónica (SHG) para transformar la longitud de onda del láser de impulsos de 800 nm a 400 nm. </li><li> Utilizar un separador armónica para transmitir el pulso 800-nm y reflejar el pulso 400-nm. </li><li> Establecer un reductor de haz y un par de lentes focally para ajustar el tamaño y la convergencia del impulso de la sonda. </li><li> Establecer otro dispositivo de retardo óptico, como se mencionó en el paso 1,3, para el pulso de la sonda. </li><li> Usar un anillo de iris para ajustar el área de lasonda de pulso y asegurarse de que el pulso de la sonda pasará la superficie del objetivo en horizontal y se cruzan con el pulso de la bomba. </li><li> Establecer dos lentes del objetivo y varios filtros para generar la imagen de la región de plasma para ser recibido por la intensificación de dispositivo de carga acoplada (ICCD) de la cámara. </li><li> Conecte el ordenador, el láser, la cámara ICCD y su controlador usando cables BNC o cables USB. </li><li> Ajuste el tiempo de retardo del controlador de la cámara hasta que la cámara captura una imagen del pulso de la sonda. Así, el pulso de la sonda y la cámara están sincronizados. </li></ol> 2. La bomba-sonda de sincronización <ol><li> Colocar un divisor de haz en la intersección de la bomba de pulso y el pulso de la sonda, y la creación de dos fotodiodos para recibir estos dos impulsos. Estos dos fotodiodos debe tener una misma distancia desde el divisor de haz. </li><li> Utilice un osciloscopio para recibir las señales de estos dos fotodiodos, y mover la etapa de retardo en el camino de la bomba hasta que el rayo de luz pulso Proarchivos de la bomba de pulso y el pulso de la sonda se superponen unos con otros en la pantalla del osciloscopio. Una precisión de 20 ps se consigue debido a la resolución temporal del osciloscopio. </li><li> Quitar el divisor de haz y los dos fotodiodos como se ha mencionado en el Paso 2,1. </li><li> Ajuste de la etapa de retardo en el camino de la bomba hasta que el rayo de luz pulso región de ruptura del aire podía observar en la pantalla el documento ICCD. El momento en que la formación de desglose de aire podría ser detectada en lugar de un fondo uniforme se determina como cero retardo de tiempo. </li></ol> 3. Y preparación de muestras Etapa <ol><li> Establecer un laboratorio-jack y dos etapas lineales manuales con el fin de mover la muestra con tres grados de libertad. </li><li> Utilice un indicador de cuadrante y cuñas de alta precisión para lograr una llanura alta de las etapas. La diferencia de altura debe estar dentro de 1 micra por una distancia de 25,4 mm. </li><li> Cortar una pieza cuadrada (30 mm x 30 mm) de una hoja de Cu con un espesor de 0,8 mm utilizando una moliendamáquina. </li><li> Pulir un lado estrecho (30 mm x 0,8 mm) de la pieza de Cu hasta que la rugosidad de la superficie es inferior a 0,5 micras. </li><li> Fijar la pieza de cobre en el escenario manual de la parte superior de la cara estrecha pulido. </li><li> Mueva el objetivo por la etapa manual de una como se ha mencionado en el Paso 3,1) mientras que el seguimiento de su posición a través de la cámara ICCD tal que cualquier inclinación puede ser ajustado mediante la inserción de cuñas de alta precisión por debajo del objetivo. </li><li> Repita el paso 3.6 con la etapa de otro manual. </li><li> Taladre una docena de agujeros en el objetivo, mientras que variar la posición de la focal del objetivo en un tercio la etapa de alta manual de precisión. La posición del punto focal corresponde a la posición de la lente focal donde se perfora el orificio más pequeño. </li></ol> 4. La ablación y medición <ol><li> Mover la lente focal hasta una distancia de aproximadamente 50 micras de distancia del punto focal. </li><li> Mueva la etapa de retardo en la trayectoria del haz de la sonda de pulso con un intervalo de 0,3 mm para capturar la imagen cada 2 hasta 10 ps ps, ocon un intervalo de 3 mm para capturar la imagen todos los PS 20 y PS 480. </li><li> Repita el paso 4.2 para varias veces para la repetibilidad y precisión. </li><li> Mueva la focal del objetivo hasta una distancia de unos 50 m de distancia del punto focal, y repita el Paso 4.3. </li></ol> 5. Los resultados representativos Las imágenes shadowgraph medidos se muestran en la figura. 2 y la fig. 3, para el punto focal ligeramente por encima y por debajo de la superficie del blanco, respectivamente. Las posiciones de expansión longitudinal y radial se representan en la figura. 4 y la figura. 5. Las ampliaciones longitudinales de estos dos casos en los primeros 100 ps son significativamente diferentes, sin embargo, sus ampliaciones longitudinales en los siguientes 400 ps y sus expansiones radiales son similares. Para el primer caso, el plasma temprana dentro de 100 ps tiene una estructura unidimensional de expansión que consiste en capas múltiples. Para el segundo caso, la primera plasma tiene una estructura de expansión de dos dimensiones que no cambia mucho a menos de 100 ps. El modelo de simulación 12 se utiliza para investigar el mecanismo de la evolución de plasma temprana. El tiempo cero se define como el tiempo cuando el láser de impulsos pico alcanza la superficie del blanco. Los primeros procesos simulados evolución de plasma de acuerdo con los resultados medidos para ambos de estos dos casos, como se muestra en la fig. 6 y la figura. 7, respectivamente. La formación del plasma temprana dentro de 1 ps también está previsto para el primer caso utilizando el modelo de simulación y se muestra en la fig. 8. El plasma temprano se encuentra que tiene una región de ruptura del aire y una región de plasma de Cu. La distribución de aire por primera vez causada por múltiples fotones de ionización y luego seguido por ionización avalancha. Para el segundo caso, sin embargo, el punto focal está por debajo de la superficie del blanco y no hay región de aire desglose separada se forma. En su lugar, se produce la ionización del aire cerca de la pla CuSMA frontal y es causada por el impacto debido a la ionización de los electrones libres expulsados ​​de la meta de Cu. <img alt="Figura 1" src="/files/ftp_upload/4033/4033fig1.jpg" /> Figura 1. Esquemática de la medición shadowgraph bomba-sonda. <img alt="Figura 2" src="/files/ftp_upload/4033/4033fig2.jpg" /> Figura 2. Cúbicos de plasma de expansión en los tiempos de retardo sucesivas con el punto focal ligeramente por encima de la superficie. Láser de longitud de onda: 800 nm, la duración del impulso: 100 fs; densidad de potencia: 4,2 × 10 14 W / cm 2; objetivo: Cu. <img alt="Figura 3" src="/files/ftp_upload/4033/4033fig3.jpg" /> Figura 3. Cu plasma expansión en los tiempos de retardo sucesivas con el punto focal ligeramente por debajo de la superficie. Láser de longitud de onda: 800 nm, la duración del impulso: 100 fs; densidad de potencia: 4,2 × 10 14 W / cm 2; objetivo: Cu. &lt;img alt = &quot;Figura 4&quot; src = &quot;/ files/ftp_upload/4033/4033fig4.jpg&quot; /&gt; Figura 4. Plasma longitudinal y posiciones radiales de expansión en los tiempos de retardo sucesivas con el punto focal ligeramente por encima de la superficie. Láser de longitud de onda: 800 nm, la duración del impulso: 100 fs; densidad de potencia: 4,2 × 10 14 W / cm 2; objetivo: Cu. <img alt="Figura 5" src="/files/ftp_upload/4033/4033fig5.jpg" /> Figura 5. Plasma longitudinal y posiciones radiales de expansión en los tiempos de retardo sucesivas con el punto focal ligeramente por debajo de la superficie. Láser de longitud de onda: 800 nm, la duración del impulso: 100 fs; densidad de potencia: 4,2 × 10 14 W / cm 2; objetivo: Cu. Figura 6. Animación de expansión del plasma, medida y calculada en un tiempo de retardo de 70 CV con el punto focal ligeramente por encima de la superficie. Láser de longitud de onda: 800 nm, la duración del impulso: 100 fs; la densidad de potencia: 4,2 × 10 14 </sup&gt; W / cm 2; objetivo: Cu. <a href="http://www.jove.com/files/ftp_upload/4033/4033movie6.avi" target="_blank">Haga clic aquí para ver la animación</a> . Figura 7. Animación de expansión del plasma medidos y calculados dentro de un tiempo de retardo de 70 ps con el punto focal ligeramente por debajo de la superficie. Láser de longitud de onda: 800 nm, la duración del impulso: 100 fs; densidad de potencia: 4,2 × 10 14 W / cm 2; objetivo: Cu. <a href="http://www.jove.com/files/ftp_upload/4033/4033movie7.avi" target="_blank">Haga clic aquí para ver la animación</a> . Figura 8. Animación de la expansión del plasma, medida y calculada en un tiempo de retardo de 1 ps con el punto focal ligeramente por encima de la superficie. Láser de longitud de onda: 800 nm, la duración del impulso: 100 fs; densidad de potencia: 4,2 × 10 14 W / cm 2; objetivo:. Cu <a href="http://www.jove.com/files/ftp_upload/4033/4033movie8.avi" target="_blank">Haga clic aquí para ver la animación &lt;</a>/ A&gt;.

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S., Zhu, P., Sheng, Z., Zhang, J., Cao, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrafast+electron+beam+imaging+of+femtosecond+laser-induced+plasma+dynamics.">Ultrafast electron beam imaging of femtosecond laser-induced plasma dynamics.</a> J. Appl. Phys. 107, 083305 (2010).</li><li>Veysman, M. E., Agranat, M. B., Andreev, N. E., Ashitkov, S. I., Fortov, V. E., Khishchenko, K. V., Kostenko, O. F., Levashov, P. R., Ovchinnikov, A. V., Sitnikov, D. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Femtosecond+optical+diagnostics+and+hydrodynamic+simulation+of+Ag+plasma+created+by+laser+irradiation+of+a+solid+target.">Femtosecond optical diagnostics and hydrodynamic simulation of Ag plasma created by laser irradiation of a solid target.</a> J. Phys. B. 41, 125704 (2008).</li><li>Geindre, J. 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No hay conflictos de interés declarado.

Los métodos de medición y simulación presentados en este trabajo permiten exámenes más precisos de la dinámica del plasma temprana y una mejor comprensión de los mecanismos de ionización para el aire y el Cu. Estructuras de alta calidad de plasma se capturan con una resolución temporal de 1 ps y una resolución espacial de 1 m. Esta medida tiene una alta capacidad de repetición también. El procedimiento crítico es alinear el haz muy bien y preparar una superficie de destino con una planitud alta, así como una baja rugosidad. Este enfoque puede aplicarse a otros materiales diana y los distintos parámetros de láser. La única limitación del método shadowgraph bomba-sonda es un número demasiado bajo variación de la densidad de electrones.

<table border="1"><tbody><tr><td> Nombre del equipo </td><td> Empresa </td><td> Número de catálogo </td></tr><tr><td> Láser </td><td> Spectra-Physics </td><td> FFPS-100F-1K-1P </td></tr><tr><td> ICCD cámara </td><td> Princeton Instruments </td><td> 7467-0028 </td></tr><tr><td> Osciloscopio </td><td> Rigol </td><td> DS1302CA </td></tr><tr><td> Fotodiodo </td><td> Newport </td><td> 818-BB30 </td></tr><tr><td> Fase lineal </td><td> Newport </td><td> 433 </td></tr><tr><td> Marque el indicador de </td><td> Mitutoyo </td><td> ID-C112E </td></tr></tbody></table>

investigation of early plasma evolution induced by ultrashort laser pulses

A principios de plasma se genera debido a la irradiación láser de alta intensidad de destino y la ionización material diana posterior. Su dinámica juega un papel importante en la interacción láser-materia, especialmente en el entorno de aire 1-11. La evolución temprana de plasma se ha recogido en shadowgraphy bomba-sonda de 1-3 y 1,4-7 interferometría. Sin embargo, los rangos láser estudiados marcos de tiempo y se aplican los parámetros son limitados. Por ejemplo, los exámenes directos de localizaciones del frente de plasma y las densidades de electrones número dentro de un tiempo de retardo de 100 picosegundos (ps) con respecto al pico del láser de impulsos son todavía muy pocos, especialmente para el pulso ultracorto de una duración de alrededor de 100 femtosegundos (FS) y una baja densidad de potencia alrededor de 10 14 W / cm 2. A principios de plasma generada en estas condiciones sólo se ha capturado recientemente con altas resoluciones espaciales y temporales 12. La estrategia de instalación detallada yprocedimientos de esta medición de alta precisión se ilustra en este documento. El fundamento de la medición es óptico bomba-sonda shadowgraphy: un láser de impulsos ultracortos se divide a un pulso de bomba y un pulso de la sonda, mientras que el tiempo de retardo entre ellos puede ser ajustado cambiando sus longitudes trayectoria del haz. El pulso de bombeo ablaciona el objetivo y genera el plasma temprana, y el impulso de la sonda se propaga a través de la región de plasma y detecta la falta de uniformidad de la densidad de número de electrones. Además, las animaciones se generan utilizando los resultados calculados a partir del modelo de simulación de ref. 12 para ilustrar la formación de plasma y la evolución con una resolución muy alta (0,04 ~ 1 ps). Tanto el método experimental y el método de simulación se puede aplicar a una amplia gama de marcos de tiempo y los parámetros del láser. Estos métodos se pueden utilizar para examinar el plasma generado temprana no sólo a partir de metales, pero también de semiconductores y aislantes.

Watch this Scientific Journal Video about Investigation of Early Plasma Evolution Induced by Ultrashort Laser Pulses at JoVE.com

Investigation of Early Plasma Evolution Induced by Ultrashort Laser Pulses

Un método experimental para examinar la evolución de plasma precoz inducida por pulsos láser ultracortos se describe. Usando este método, las imágenes de alta calidad de plasma a principios se obtienen con altas resoluciones espaciales y temporales. Una novela modelo de integración atomista se utiliza para simular y explicar los mecanismos de plasma temprano.

Investigación de la Evolución de plasma precoz inducida por pulsos láser ultracortos

Early plasma is generated owing to high intensity laser irradiation of target and the subsequent target material ionization. Its dynamics plays a ...

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Research

JoVE Journal

Engineering

14.8K vistas.  Purdue University. Un método experimental para examinar la evolución de plasma precoz inducida por pulsos láser ultracortos se describe. Usando este método, las imágenes de alta calidad de plasma a principios se obtienen con altas resoluciones espaciales y temporales. Una novela modelo de integración atomista se utiliza para simular y explicar los mecanismos de plasma temprano.

Video: Investigation of Early Plasma Evolution Induced by Ultrashort Laser Pulses

Fabrication of Nano-engineered Transparent Conducting Oxides by Pulsed Laser Deposition

Nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas allows the deposition of metal oxides with tunable morphology, structure, density and stoichiometry by a proper control of the plasma plume expansion dynamics. Such versatility can be exploited to produce nanostructured films from compact and dense to nanoporous characterized by a hierarchical assembly of nano-sized clusters. In particular we describe the detailed methodology to fabricate two types of Al-doped ZnO (AZO) films as transparent electrodes in photovoltaic devices: 1) at low O2 pressure, compact films with electrical conductivity and optical transparency close to the state of the art transparent conducting oxides (TCO) can be deposited at room temperature, to be compatible with thermally sensitive materials such as polymers used in organic photovoltaics (OPVs); 2) highly light scattering hierarchical structures resembling a forest of nano-trees are produced at higher pressures. Such structures show high Haze factor (&gt;80%) and may be exploited to enhance the light trapping capability. The method here described for AZO films can be applied to other metal oxides relevant for technological applications such as TiO2, Al2O3, WO3 and Ag4O4.

We describe the experimental method to deposit nanostructured oxide thin films by nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas. By using this method Al-doped ZnO (AZO) films, from compact to hierarchically structured as nano-tree forests, can be deposited.

La fabricación de nano-ingeniería óxidos conductores transparentes por deposición por láser pulsado

Nanosecond Pulsed  Laser Deposition (PLD) in the presence of a background gas allows the deposition  of metal oxides with tunable morphology, structure, ...

Investigación

Ingeniería

Laser-induced Breakdown Spectroscopy: A New Approach for Nanoparticle's Mapping and Quantification in Organ Tissue

Emission spectroscopy of laser-induced plasma was applied to elemental analysis of biological samples. Laser-induced breakdown spectroscopy (LIBS) performed on thin sections of rodent tissues: kidneys and tumor, allows the detection of inorganic elements such as (i) Na, Ca, Cu, Mg, P, and Fe, naturally present in the body and (ii) Si and Gd, detected after the injection of gadolinium-based nanoparticles. The animals were euthanized 1&#160;to 24 hr&#160;after intravenous injection of particles. A two-dimensional scan of the sample, performed using a motorized micrometric 3D-stage, allowed the infrared laser beam exploring the surface with a lateral resolution less than 100 &#956;m. Quantitative chemical images of Gd element inside the organ were obtained with sub-mM sensitivity. LIBS offers a simple and robust method to study the distribution of inorganic materials without any specific labeling. Moreover, the compatibility of the setup with standard optical microscopy emphasizes its potential to provide multiple images of the same biological tissue with different types of response:&#160;elemental, molecular, or cellular.

Laser-induced Breakdown Spectroscopy: A New Approach for Nanoparticle&#039;s Mapping and Quantification in Organ Tissue

Laser-induced breakdown spectroscopy performed on thin organ and tumor tissue successfully detected natural elements and artificially injected gadolinium (Gd), issued from Gd-based nanoparticles. Images of chemical elements reached a resolution of 100 &#956;m and quantitative sub-mM sensitivity. The compatibility of the setup with standard optical microscopy emphasizes its potential to provide multiple images of a same biological tissue.

Inducida por láser Breakdown Spectroscopy: un nuevo enfoque para el mapeo y cuantificación de nanopartículas en tejidos de órganos

Emission spectroscopy of laser-induced plasma was applied to elemental analysis of biological samples. Laser-induced breakdown spectroscopy (LIBS) ...

Laser-induced Forward Transfer for Flip-chip Packaging of Single Dies

Flip-chip (FC) packaging is a key technology for realizing high performance, ultra-miniaturized and high-density circuits in the micro-electronics industry. In this technique the chip and/or the substrate is bumped and the two are bonded via these conductive bumps. Many bumping techniques have been developed and intensively investigated since the introduction of the FC technology in 19601 such as stencil printing, stud bumping, evaporation and electroless/electroplating2. Despite the progress that these methods have made they all suffer from one or more than one drawbacks that need to be addressed such as cost, complex processing steps, high processing temperatures, manufacturing time and most importantly the lack of flexibility. In this paper, we demonstrate a simple and cost-effective laser-based bump forming technique known as Laser-induced Forward Transfer (LIFT)3. Using the LIFT technique a wide range of bump materials can be printed in a single-step with great flexibility, high speed and accuracy at RT. In addition, LIFT enables the bumping and bonding down to chip-scale, which is critical for fabricating ultra-miniature circuitry.

We demonstrate the use of the Laser-induced Forward Transfer (LIFT) technique for flip-chip assembly of optoelectronic components. This approach provides a simple, cost-effective, low-temperature, fast and flexible solution for fine-pitch bumping and bonding on chip-scale for achieving high-density circuits for optoelectronic applications.

Transferencia Forward inducida por láser para Flip-chip de embalaje de muñones individuales

Flip-chip (FC) packaging is a key technology for realizing high performance, ultra-miniaturized and high-density circuits in the micro-electronics ...

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75&#176;. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm2, respectively, has decreased the CA to near 15&#176;, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafer&#8217;s surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of&#160;the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm2 and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103&#176;. The XPS results indicate ArF laser induced formation of Si&#8211;(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals.

We report on a process of in situ alteration of HF treated Si (001) surface into a hydrophilic or hydrophobic state by irradiating samples in microfluidic chambers filled with&#160;H2O2/H2O solution (0.01%-0.5%) or methanol solutions using pulsed UV laser of a relative low pulse fluence.

Área selectivo Modificación de humectabilidad de la superficie del silicio por pulsos láser UV irradiación en Ambiente Líquido

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of ...

How to Ignite an Atmospheric Pressure Microwave Plasma Torch without Any Additional Igniters

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a stable and continuous operation of the plasma is possible and the plasma torch can be used for many different applications. On one hand, the hot (3,600 K gas temperature) plasma can be used for chemical processes and on the other hand the cold afterglow (temperatures down to almost RT) can be applied for surface processes. For example chemical syntheses are interesting volume processes. Here the microwave plasma torch can be used for the decomposition of waste gases which are harmful and contribute to the global warming but are needed as etching gases in growing industry sectors like the semiconductor branch. Another application is the dissociation of CO2. Surplus electrical energy from renewable energy sources can be used to dissociate CO2 to CO and O2. The CO can be further processed to gaseous or liquid higher hydrocarbons thereby providing chemical storage of the energy, synthetic fuels or platform chemicals for the chemical industry. Applications of the afterglow of the plasma torch are the treatment of surfaces to increase the adhesion of lacquer, glue or paint, and the sterilization or decontamination of different kind of surfaces. The movie will explain how to ignite the plasma solely by microwave power without any additional igniters, e.g., electric sparks. The microwave plasma torch is based on a combination of two resonators &#8212; a coaxial one which provides the ignition of the plasma and a cylindrical one which guarantees a continuous and stable operation of the plasma after ignition. The plasma can be operated in a long microwave transparent tube for volume processes or shaped by orifices for surface treatment purposes.

This movie shows how an atmospheric plasma torch can be ignited by microwaves with no additional igniters and provides a stable and continuous plasma operation suitable for plenty of applications.

Cómo Encender una presión atmosférica de microondas de la antorcha de plasma sin ningún Encendedores adicionales

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a ...

Automation of Mode Locking in a Nonlinear Polarization Rotation Fiber Laser through Output Polarization Measurements

When a laser is mode-locked, it emits a train of ultra-short pulses at a repetition rate determined by the laser cavity length. This article outlines a new and inexpensive procedure to force mode locking in a pre-adjusted nonlinear polarization rotation fiber laser. This procedure is based on the detection of a sudden change in the output polarization state when mode locking occurs. This change is used to command the alignment of the intra-cavity polarization controller in order to find mode-locking conditions. More specifically, the value of the first Stokes parameter varies when the angle of the polarization controller is swept and, moreover, it undergoes an abrupt variation when the laser enters the mode-locked state. Monitoring this abrupt variation provides a practical easy-to-detect signal that can be used to command the alignment of the polarization controller and drive the laser towards mode locking. This monitoring is achieved by feeding a small portion of the signal to a polarization analyzer measuring the first Stokes parameter. A sudden change in the read out of this parameter from the analyzer will occur when the laser enters the mode-locked state. At this moment, the required angle of the polarization controller is kept fixed. The alignment is completed. This procedure provides an alternate way to existing automating procedures that use equipment such as an optical spectrum analyzer, an RF spectrum analyzer, a photodiode connected to an electronic pulse-counter or a nonlinear detecting scheme based on two-photon absorption or second harmonic generation. It is suitable for lasers mode locked by nonlinear polarization rotation. It is relatively easy to implement, it requires inexpensive means, especially at a wavelength of 1550 nm, and it lowers the production and operation costs incurred in comparison to the above-mentioned techniques.

A protocol to detect and automate mode locking in a pre-adjusted nonlinear polarization rotation fiber laser is presented. The detection of a sudden change in the output polarization state when mode locking occurs is used to command the alignment of an intra-cavity polarization controller in order to find mode-locking conditions.

Automatización de modo de bloqueo de rotación en un láser de fibra no lineal de polarización a través de mediciones de polarización de salida

When a laser is mode-locked, it emits a train of ultra-short pulses at a repetition rate determined by the laser cavity length. This article outlines a ...

Laser-induced Forward Transfer of Ag Nanopaste

Over the past decade, there has been much development of non-lithographic methods1-3 for printing metallic inks or other functional materials. Many of these processes such as inkjet3 and laser-induced forward transfer (LIFT)4 have become increasingly popular as interest in printable electronics and maskless patterning has grown. These additive manufacturing processes are inexpensive, environmentally friendly, and well suited for rapid prototyping, when compared to more traditional semiconductor processing techniques. While most direct-write processes are confined to two-dimensional structures and cannot handle materials with high viscosity (particularly inkjet), LIFT can transcend both constraints if performed properly. Congruent transfer of three dimensional pixels (called voxels), also referred to as laser decal transfer (LDT)5-9, has recently been demonstrated with the LIFT technique using highly viscous Ag nanopastes to fabricate freestanding interconnects, complex voxel shapes, and high-aspect-ratio structures. In this paper, we demonstrate a simple yet versatile process for fabricating a variety of micro- and macroscale Ag structures. Structures include simple shapes for patterning electrical contacts, bridging and cantilever structures, high-aspect-ratio structures, and single-shot, large area transfers using a commercial digital micromirror device (DMD) chip.

We demonstrate the use of the Laser-induced forward transfer technique (LIFT) for the printing of high-viscosity Ag paste. This technique offers a simple, low temperature, robust process for non-lithographically printing microscale 2D and 3D structures.

Transferencia Forward inducida por láser de Ag nanopasta

Over the past decade, there has been much development of non-lithographic methods1-3 for printing metallic inks or other functional materials. Many of ...

An Atmospheric Pressure Plasma Setup to Investigate the Reactive Species Formation

Non-thermal atmospheric pressure (&#39;cold&#39;) plasmas have received increased attention in recent years due to their significant biomedical potential. The reactions of cold plasma with the surrounding atmosphere yield a variety of reactive species, which can define its effectiveness. While efficient development of cold plasma therapy requires kinetic models, model benchmarking needs empirical data. Experimental studies of the source of reactive species detected in aqueous solutions exposed to plasma are still scarce. Biomedical plasma is often operated with He or Ar feed gas, and a specific interest lies in investigation of the reactive species generated by plasma with various gas admixtures (O2, N2, air, H2O vapor, etc.) Such investigations are very complex due to difficulties in controlling the ambient atmosphere in contact with the plasma effluent. In this work, we addressed common issues of &#39;high&#39; voltage kHz frequency driven plasma jet experimental studies. A reactor was developed allowing the exclusion of ambient atmosphere from the plasma-liquid system. The system thus comprised the feed gas with admixtures and the components of the liquid sample. This controlled atmosphere allowed the investigation of the source of the reactive oxygen species induced in aqueous solutions by He-water vapor plasma. The use of isotopically labelled water allowed distinguishing between the species originating in the gas phase and those formed in the liquid. The plasma equipment was contained inside a Faraday cage to eliminate possible influence of any external field. The setup is versatile and can aid in further understanding the cold plasma-liquid interactions chemistry.

An experimental setup was created for the helium-operated kHz frequency plasma jet. The setup includes a cage for the plasma power supply and jet and an in-house built reactor to monitor plasma-induced reactive species without the interference of the ambient atmosphere.

Una instalación de plasma a presión atmosférica para investigar la formación de especies reactivas

Non-thermal atmospheric pressure (&#39;cold&#39;) plasmas have received increased attention in recent years due to their significant biomedical potential. ...

Fabrication of 1-D Photonic Crystal Cavity on a Nanofiber Using Femtosecond Laser-induced Ablation

We present a protocol for fabricating 1-D Photonic Crystal (PhC) cavities on subwavelength-diameter tapered optical fibers, optical nanofibers, using femtosecond laser-induced ablation. We show that thousands of periodic nano-craters are fabricated on an optical nanofiber by irradiating with just a single femtosecond laser pulse. For a typical sample, periodic nano-craters with a period of 350 nm and with diameter gradually varying from 50 - 250 nm over a length of 1 mm are fabricated on a nanofiber with diameter around 450 - 550 nm. A key aspect of such a nanofabrication is that the nanofiber itself acts as a cylindrical lens and focuses the femtosecond laser beam on its shadow surface. Moreover, the single-shot fabrication makes it immune to mechanical instabilities and other fabrication imperfections. Such periodic nano-craters on nanofiber, act as a 1-D PhC and enable strong and broadband reflection while maintaining the high transmission out of the stopband. We also present a method to control the profile of the nano-crater array to fabricate apodized and defect-induced PhC cavities on the nanofiber. The strong confinement of the field, both transverse and longitudinal, in the nanofiber-based PhC cavities and the efficient integration to the fiber networks, may open new possibilities for nanophotonic applications and quantum information science.

We present a protocol for fabricating 1-D photonic crystal cavities on subwavelength diameter silica fibers (optical nanofibers) using femtosecond laser-induced ablation.

La fabricación de 1-D de cristal fotónico cavidad en un nanofibras Uso de ablación inducida por láser de femtosegundo

We present a protocol for fabricating 1-D Photonic Crystal (PhC) cavities on subwavelength-diameter tapered optical fibers, optical nanofibers, using ...

Subsurface Defect Localization by Structured Heating Using Laser Projected Photothermal Thermography

The presented method is used to locate subsurface defects oriented perpendicularly to the surface. To achieve this, we create destructively interfering thermal wave fields that are disturbed by the defect. This effect is measured and used to locate the defect. We form the destructively interfering wave fields by using a modified projector. The original light engine of the projector is replaced with a fiber-coupled high-power diode laser. Its beam is shaped and aligned to the projector&#39;s spatial light modulator and optimized for optimal optical throughput and homogeneous projection by first characterizing the beam profile, and, second, correcting it mechanically and numerically. A high-performance infrared (IR) camera is set up according to the tight geometrical situation (including corrections of the geometrical image distortions) and the requirement to detect weak temperature oscillations at the sample surface. Data acquisition can be performed once a synchronization between the individual thermal wave field sources, the scanning stage, and the IR camera is established by using a dedicated experimental setup which needs to be tuned to the specific material being investigated. During data post-processing, the relevant information on the presence of a defect below the surface of the sample is extracted. It is retrieved from the oscillating part of the acquired thermal radiation coming from the so-called depletion line of the sample surface. The exact location of the defect is deduced from the analysis of the spatial-temporal shape of these oscillations in a final step. The method is reference-free and very sensitive to changes within the thermal wave field. So far, the method has been tested with steel samples but is applicable to different materials as well, in particular to temperature sensitive materials.

This method aims at locating vertical subsurface defects. Here, we couple a laser with a spatial light modulator and trigger its video input to heat a sample surface deterministically with two anti-phased modulated lines while acquiring highly resolved thermal images. The defect position is retrieved from evaluating thermal wave interference minima.

Localización del defecto subsuperficial mediante calentamiento estructurado mediante termografía fototérmica proyectada con láser

The presented method is used to locate subsurface defects oriented perpendicularly to the surface. To achieve this, we create destructively interfering ...