135 research outputs found
Evanescent-field Q-switched Yb:YAG Channel Waveguide Lasers with Single- and Double-pass Pumping
No full textA femtosecond-laser inscribed Yb:YAG surface channel waveguide (WG) laser with single-walled carbon nanotubes deposited on the top surface of the WG was passively Q-switched by evanescent field interaction. Q-switched operation of the 14-mm-long compact Yb:YAG WG laser was achieved near 1031 nm with two different pumping schemes (single- and double-pass pumping) with an output coupling transmission of 91%. The Q-switched pulse characteristics depending on the absorbed pump power were investigated for both pumping geometries and analyzed in detail based on theoretical modeling. The best performances (energy/pulse duration) for each configuration were 204.4 nJ/75 ns at a repetition rate of 1.87 MHz, and 201.1 nJ/81 ns at 1.75 MHz for single- and double-pass pumping, respectively.
Femtosecond-laser writing and selective etching of laser crystals for laser applications
No full textIn dieser Arbeit wurde erstmals eine systematische Analyse des selektiven Ätzprozesses fs-lasergeschriebener Strukturen in kristallinem Y_3Al_5O_12 (YAG) für verschiedene Ätz- und Strukturierungsparameter durchgeführt. In Hinblick auf die Herstellung von Mikrokanälen hoher Aspektverhältnisse von Länge zu Breite für zukünftige Laseranwendungen in seltenerddotiertem YAG wurden die Parameter optimiert.
Funktionelle Zusammenhänge von Ätztiefe und Kanalbreite mit der Zeit wurden gefunden, welche zusammen mit der Selektivität das Ätzverhalten charakterisieren. Zumeist zeigen die Ätztiefe d und der Zuwachs der Kanalbreite einen Quadratwurzelzusammenhang d = (2 · D · t)^(1/2) mit der Zeit, welcher von der Brownschen Diffusion bekannt ist, denn der Austausch der Reaktionsprodukte im Mikrokanal findet über Diffusion statt. Der Fitparameter D entspricht der Diffusionskonstanten. Der höchste Wert D = 3,69 μm^2/s wurde mit 43%H_3PO_4 48%H_2SO_4 als Ätzsubstanz bei einer Ätztemperatur von 105 °C erreicht. Mit dieser Ätzsubstanz wurde bei 83 °C (D = 3,13 μm^2/s) auch die höchste Selektivität von 1200 ± 750 gemessen.
Für die Verdünnung des Gemischs zu 22%H_3PO_4 24%H_2SO_4 wird der Ätzprozess viel schneller. Die Ätztiefe zeigt statt des Quadratwurzelzusammenhangs den zeitlichen Verlauf d = 0,0028 μm/s · t + (2 · 2,24 µm^2/s · t)^(1/2). Folglich könnten mit dieser Ätzsubstanz die in dieser Arbeit mit 85%H_3PO_4 bei 83 °C innerhalb von 9 Monaten (D = 0,53 µm^2/s) bisher längsten selektiv in kristallinem YAG geätzten Mikrokanäle von 8,9 mm Länge und 15 μm Durchmesser theoretisch innerhalb von < 10 d geätzt werden. In Bezug auf die Strukturierungsparameter erwiesen sich eine Fokussierlinse der Brennweite 4,5 mm, eine Repetitionsrate von 10 MHz (von den untersuchten 1 kHz und 10 MHz), Schreibgeschwindigkeiten zwischen 30 mm/s und 100 mm/s, Pulsenergien zwischen 75 nJ und 108 nJ und eine Polarisation des Strukturierungslasers senkrecht zur Schreibrichtung als optimal.
Für zukünftige kombinierte Anwendungen fs-lasergeschriebener Wellenleiter und selektiv geätzter Strukturen wurde auch das Schreiben von Wellenleitern in Kristallen, nämlich Yb(7 %):YAG und Yb(8,1 %):CaGdAlO_4, erstmals bei 10 MHz Pulsrepetitionsrate und rekordhohen Schreibgeschwindigkeiten bis zu 100 mm/s untersucht. Gepumpt mit einem Ti:Saphir-Laser bei 913,4 nm bzw. einem optisch gepumpten Halbleiterlaser bei 967 nm war in den hergestellten Doppelspurwellenleitern Wellenleiterlaserbetrieb mit einem differentiellen Wirkungsgrad von 40% und maximaler Ausgangsleistung P_Aus = 528 mW in Yb:YAG und einem differentiellen Wirkungsgrad von 67% sowie P_Aus = 3,9 W in Yb:CaGdAlO_4 möglich.In this work selective etching of fs-laser written structures in crystalline Y_3Al_5O_12 (YAG) is analyzed systematically concerning structuring and etching parameters for the first time. The fabrication process is optimized aiming for future laser applications of large-scale hollow microstructures in rare-earth doped YAG.
For the etched depth d and the change of the channel width a square-root-dependency on time, which is d = (2 · D · t)^(1/2), similar to Brownian diffusion, was found for most parameters, since the exchange of the reaction products is based on diffusion. The etching parameter D corresponds to the diffusion constant. Thus, the selective etching process is characterized by the temporal change of etched depth and channel width as well as the selectivity of the process, which is defined as the ratio of etched depth and the change of the channel width over this length. The highest value of D = 3.69 μm^2/s was reached with a 43%H_3PO_4 48%H_2SO_4 mixture at 105 °C. For the same etching agent, we observed the highest selectivity of 1200 ± 750 at a temperature of 83 °C (D = 3.13 μm^2/s).
Diluting the mixture with 50% water changes the temporal dependency of the etching depth to d = 0,0028 μm/s · t + (2 · 2,24 µm^2/s · t)^(1/2) and thus, fastens the etching significantly. Using this etching agent, the longest selectively etched microchannel of 8.9 mm long and 15 μm diameter in YAG up to now, which was etched in this work with 85%H_3PO_4 at 83 °C within 9 months (D = 0.53 μm^2/s), could be fabricated in less than 10 days. Concerning the structuring parameters, a focusing lens of 4.5 mm focal length, a pulse repetition rate of 10 MHz, writing velocities between 30 mm/s and 100 mm/s, pulse energies between 75 nJ and 108 nJ as well as a structuring laser beam polarization perpendicular to the writing direction showed the best results concerning aspect ratio and etching behaviour.
For future combined applications of fs-laser inscribed waveguides and selectively etched structures in crystals fast inscription at 10MHz repetition rate and writing velocities up to 100 mm/s was investigated in Yb(7 %):YAG and Yb(8.1 %):CaGdAlO_4 for the first time. In both materials double-track waveguide laser operation with slope efficiencies of 40 %, maximum output power P_Aus = 528 mW and slope efficiencies of 67 %, P_Aus = 3.9 W could be reached pumping with a Ti:sapphire laser at 913.4 nm and an optically pumped semiconductor laser at 967 nm, respectively
Ytterbium-laser-driven THz generation in thin lithium niobate at 1.9 kW average power in a passive enhancement cavity
No full textSingle-cycle, high-power, high-repetition-rate THz pulse sources are becoming the cornerstone of several scientific and industrial applications. A promising and versatile method for high-power THz generation is optical rectification in nonlinear crystals pumped by powerful near-infrared ultrafast laser systems. In this context, ytterbium-based laser sources are particularly advantageous in terms of power scalability and technology establishment. However, as the repetition rate increases toward hundreds of MHz, the conversion efficiency typically decreases, as most laser systems do not reach sufficiently high average powers to correspondingly enhance the peak power to drive the nonlinear conversion process efficiently. An alternative approach to achieving a sufficiently high average power at a high repetition rate is based on passive enhancement cavities, which boost the pulse energy of standard watt-level ytterbium lasers by orders of magnitude. We present the first demonstration of optical rectification in a passive enhancement cavity at multi-kW levels, achieved by a 240-fold power enhancement. By irradiating a 50-μm thin lithium niobate plate with 1.9-kW average power inside the enhancement cavity, we generate milliwatt-level THz pulses with 2-THz bandwidth and 93-MHz repetition rate, mostly limited by the driving pulse duration. To the best of our knowledge, this represents the highest driving average power used for optical rectification. This methodology represents a promising new step toward high-repetition-rate and high average power single-cycle THz sources using widely available multi-watt level Yb lasers
First principle study of heterostructure of BaBi3-stanene for topological superconductor applications
No full textOn the role of innovation and market structure on trade performance: is Schumpeter right?
No full textPurpose – The goal of the paper is to examine the dynamics between innovation, market structure and trade performance. Firstly, the author first investigates the effects of innovation on trade performance. Secondly, the author then examines how market structure affect trade by classifying industries based on their innovation intensity. Design/methodology/approach – The author uses a detailed level data set of eight OECD countries in a panel of 17 industries from the STAN and ANBERD Database. The author employs both a pooled regression and a two-stage quantile regression analysis. The author first investigates the effects of innovation at the aggregate level, and then the author assesses the effects at the disaggregated or firm level. Findings – The author finds that at the aggregate level, innovation and market size have a positive and significant effect on competitivity in most of the specifications. However, innovation is negatively associated with trade performance in the case of bilateral trade between Spain and the Netherlands. Also, the sectoral analysis provides evidence that the innovation-trade nexus depends on technological classification. The author shows that: (1) the effect of innovation activity on trade performance economic performance is lower for the high technology and high concentration (HTHC) market compared to the low technology (LT) market; (2) the impact of innovation on economic performance is ambiguous for firms in the high technology and low concentration (HTLC) market. Research limitations/implications – Although the database provides a rich data set on industrial data, it fails to provide innovation output such as patent data which may underestimate the innovation activities of firms that do not have a separate R&D records. In the current context of subdue economic growth these research results have important policy implications. Firstly, the positive impact of innovation on trade performance strengthens its role for sustainable development. The negative coefficient on innovation is an indication that research intensity in some cases has not been able to create a new demand capable to boost economic performance. Practical implications – The market classification analysis provides new evidence that innovation in the LT market has the potential to enhance competition. Secondly, market size supports industries that are competing in the international market. Policy makers must therefore put in place incentives to encourage firms to grow in size if they want to remain globally competitive. Social implications – Sustainable development can be supported through investment in research and development in the low technology sector. Originality/value – The study is the first as far as the author knows, to examine the impact of innovation on bilateral trade performance using industry level data from OECD countries. Secondly, the author complements the existing literature by examining how innovation activities (classified as high technological intensive or low technological intensive) affect trade performance. – 本研究擬探討創新觀念、市場結構和貿易表現之間的相互變革動力關係。我們首先研究創新觀念對貿易表現的影響,繼而探討市場結構對貿易表現的影響。根據各個行業的創新觀念強度,我們把行業分為不同類別。我們採用八個經濟合作暨發展組織國家的詳細級數據庫,而這八個國家、乃是STAN and ANBERD 數據庫內一個包括17個行業組別內的國家。我們採用混合估計和兩階段分位數回歸分析; 我們首先探討創新觀念所帶來的整體影響,繼而評估細分層面 (即公司層面) 上的影響。我們發現、在整體的層面上,創新觀念和市場規模、在我們大部份的規格上,均對競爭力帶來積極和重要的影響。唯在西班牙與荷蘭兩國之間的雙邊貿易上,創新觀念與貿易表現卻出現負相關的情況。而且,行業分析證實創新與貿易的關係是取決於技術分類的。我們的研究顯示:(1) 與低技術市場相比,於高技術、高集中程度的市場,創新觀念的活動對貿易表現和經濟表現的影響會較低; (2) 對處於高技術、低集中程度市場的公司而言、創新觀念對經濟表現的影響是不明確的。雖然該數據庫在工業數據方面提供一個豐富的數據集,卻未能提供如專利數據等的創新產出,這可能會導致沒有單獨研發記錄公司的創新觀念活動會被低估的情況。在現時經濟成長受到壓制的環境下,這些研究結果提供重要的政策啟示; 首先,創新觀念對貿易表現的積極影響增強了它在可持續發展方面所扮演的角色。創新觀念上的負系數顯示、在某些情況下,研究強度未能創造一個可提高經濟表現的新需求。市場分類分析提供新的證據、證明在低技術市場,創新觀念有提高競爭力的潛力; 其次,市場規模為於國際市場競爭的行業提供支援; 因此,政策制定者必須提供誘因、以鼓勵希望繼續具有全球競爭力的公司擴大其規模
Identitats "queer", cossos i sexualitat en les narratives fílmiques de la infància de Kore-eda Hirokazu
No full textEn aquest article s'interpreta la relació entre la construcció de les identitats a la infància i l'educació en el cinema de Kore-eda Hirokazu. L'estudi de les identitats es fonamenta a partir de la teoria queer, els estudis de masculinitats i la teoria postcolonial, aplicats a la infància. Concretament, s'analitzarà la construcció visual i pedagògica de les identitats, el gènere, els cossos, els efectes i la sexualitat a través de les narratives de la infància d'aquest director. L'article es centra, principalment, en l'anàlisi de les narratives de la infància en tres de les seves pel·lícules: Kiseki (2011), Still walking (2008) i Nobody knows (2004), però manté un diàleg amb els temes que emergeixen del conjunt de l'obra i la trajectòria de Kore-eda. Les reflexions sobre les relacions, la vida quotidiana, l'educació, la cura i la família, presents també a Like father, like son (2013), s'entrellacen amb els processos de construcció de les identitats. D'aquesta forma, la fluïdesa, la transicionalitat, la diversitat i el conflicte de les identitats queer, els cossos i les sexualitats, esdevenen constitutius de l'educació de les arts visuals.En este artículo se interpreta la relación entre la construcción de las identidades en la infancia y la educación en el cine de Kore-eda Hirokazu. El estudio de las identidades se fundamenta a partir de la teoría queer, los estudios de masculinidades y la teoría poscolonial, aplicados a la infancia. Concretamente, se analizará la construcción visual y pedagógica de las identidades, el género, los cuerpos, los efectos y la sexualidad a través de las narrativas de la infancia de este director. El artículo se centra, principalmente, en el análisis de las narrativas de la infancia en tres de sus películas: Kiseki (2011), Still walking (2008) y Nobody knows (2004), pero mantiene un diálogo con los temas que emergen del conjunto de la obra y la trayectoria de Kore-eda. Las reflexiones sobre las relaciones, la vida cotidiana, la educación, el cuidado y la familia, presentes también en Like father, like son (2013), se entrelazan con los procesos de construcción de las identidades. De esta forma, la fluidez, la transicionalidad, la diversidad y el conflicto de las identidades queer, los cuerpos y las sexualidades, devienen constitutivos de la educación de las artes visuales.Dans cet article, nous interprétons la relation entre la construction des identités dans l'enfance et l'éducation dans le cinéma de Kore-eda Hirokazu. L'étude des identités est développée à partir de la théorie queer, les études de masculinités et la théorie postcoloniale, appliquées à l'enfance. Concrètement, nous analysons la construction visuelle et pédagogique des identités, du genre, des corps, des effets et de la sexualité au travers des narrations de l'enfance de ce metteur en scène. L'article se centre, principalement, sur l'analyse des narrations de l'enfance dans trois de ses films, Kiseki (2011), Still walking (2008) et Nobody knows (2004), mais il maintient un dialogue avec les thèmes qui émergent de l'ensemble de l'oeuvre et de la trajectoire de Kore-eda Hirokazu. Les réflexions sur les relations, la vie quotidienne, l'éducation, les soins et la famille, présentes aussi dans Like father, like son (2013), s'entrelacent avec les processus de construction des identités. Ainsi, la fluidité, la transition, la diversité et le conflit des identités queer, des corps et des sexualités deviennent constitutifs de l'éducation aux arts visuels.This paper examines the relationship between education and the construction of identities in childhood in Kore-eda Hirokazu's films. The study of identities is based on queer theory, masculinity studies and postcolonial theory applied to childhood. Specifically, the author analyses the visual and educational construction of identities, gender, bodies, effects and sexuality in Hirokazu's narratives of childhood. The paper mainly focuses on the narratives of childhood in three of the director's films: Kiseki (2011), Still walking (2008) and Nobody knows (2004), but also addresses other themes that emerge in the work and career of Kore-eda. Reflections on relationships, daily life, education, care and family, which are also present in Like father, like son (2013), are interlinked with processes of constructing identities. Therefore, the fluidity, transitionality, diversity and conflicts of queer identities, bodies and sexualities become constituents of education in visual arts
Identidades ‘queer’, cuerpos y sexualidad en las narrativas fílmicas de la infancia de Kore-eda Hirokazu
No full textEn aquest article s'interpreta la relació entre la construcció de les identitats a la infància i l'educació en el cinema de Kore-eda Hirokazu. L'estudi de les identitats es fonamenta a partir de la teoria queer, els estudis de masculinitats i la teoria postcolonial, aplicats a la infància. Concretament, s'analitzarà la construcció visual i pedagògica de les identitats, el gènere, els cossos, els efectes i la sexualitat a través de les narratives de la infància d'aquest director. L'article es centra, principalment, en l'anàlisi de les narratives de la infància en tres de les seves pel·lícules: Kiseki (2011), Still walking (2008) i Nobody knows (2004), però manté un diàleg amb els temes que emergeixen del conjunt de l'obra i la trajectòria de Kore-eda. Les reflexions sobre les relacions, la vida quotidiana, l'educació, la cura i la família, presents també a Like father, like son (2013), s'entrellacen amb els processos de construcció de les identitats. D'aquesta forma, la fluïdesa, la transicionalitat, la diversitat i el conflicte de les identitats queer, els cossos i les sexualitats, esdevenen constitutius de l'educació de les arts visuals.
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Dans cet article, nous interprétons la relation entre la construction des identités dans l’enfance et l’éducation dans le cinéma de Kore-eda Hirokazu. L’étude des identités est développée à partir de la théorie queer, les études de masculinités et la théorie postcoloniale, appliquées à l’enfance. Concrètement, nous analysons la construction visuelle et pédagogique des identités, du genre, des corps, des effets et de la sexualité au travers des narrations de l’enfance de ce metteur en scène. L’article se centre, principalement, sur l’analyse des narrations de l’enfance dans trois de ses films, Kiseki (2011), Still walking (2008) et Nobody knows (2004), mais il maintient un dialogue avec les thèmes qui émergent de l’ensemble de l’œuvre et de la trajectoire de Kore-eda Hirokazu. Les réflexions sur les relations, la vie quotidienne, l’éducation, les soins et la famille, présentes aussi dans Like father, like son (2013), s’entrelacent avec les processus de construction des identités. Ainsi, la fluidité, la transition, la diversité et le conflit des identités queer, des corps et des sexualités deviennent constitutifs de l’éducation aux arts visuels.This paper examines the relationship between education and the construction of identities in childhood in Kore-eda Hirokazu's films. The study of identities is based on queer theory, masculinity studies and postcolonial theory applied to childhood. Specifically, the author analyses the visual and educational construction of identities, gender, bodies, effects and sexuality in Hirokazu's narratives of childhood. the paper mainly focuses on the narratives of childhood in three of the director's films: Kiseki (2011), Still walking (2008) and Nobody knows (2004), but also addresses other themes that emerge in the work and career of Kore-eda. Reflections on relationships, daily life, education, care and family, which are also present in Like father, like son (2013), are interlinked with processes of constructing identities. Therefore, the fluidity, transitionality, diversity and conflicts of queer identities, bodies and sexualities become constituents of education in visual arts.En este artículo se interpreta la relación entre la construcción de las identidades en la infancia y la educación en el cine de Kore-eda Hirokazu. El estudio de las identidades se fundamenta a partir de la teoría queer, los estudios de masculinidades y la teoría poscolonial, aplicados a la infancia. Concretamente, se analizará la construcción visual y pedagógica de las identidades, el género, los cuerpos, los efectos y la sexualidad a través de las narrativas de la infancia de este director. El artículo se centra, principalmente, en el análisis de las narrativas de la infancia en tres de sus películas: Kiseki (2011), Still walking (2008) y Nobody knows (2004), pero mantiene un diálogo con los temas que emergen del conjunto de la obra y la trayectoria de Kore-eda. Las reflexiones sobre las relaciones, la vida cotidiana, la educación, el cuidado y la familia, presentes también en Like father, like son (2013), se entrelazan con los procesos de construcción de las identidades. De esta forma, la fluidez, la transicionalidad, la diversidad y el conflicto de las identidades queer, los cuerpos y las sexualidades, devienen constitutivos de la educación de las artes visuales
Selective etching of 10 MHz repetition rate fs-laser inscribed tracks in YAG
No full textWe investigated fs-laser structuring of YAG crystals at high writing velocities up to 100 mm/s using a commercial 10 MHz fs-laser system supplied by Coherent Inc. and selective etching of these structures for fabrication of ultrahigh aspect ratio microchannels. Usage of a diluted acid mixture of 22% H3PO4 and 24% H2SO4 accelerated the etching process significantly to an etching parameter D of 11.2 μm2/s, which is three times higher than previously reported. Additionally, the selectivity of the etching process was increased by an order of magnitude
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