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23 results on '"ultra-short"'

1. A Data Driven Based Ultra Short PV Forecasting Method With Sky Images

Author

Liang Liang and Xiaoyang Bai

Subjects
data-driven, long short-term memory, PV forecast, sky images, ultra-short, General Works
Abstract

With increasing levels of renewable energy in power systems, the coordination of different types of dispatchable resources, such as coal-fired power plants, hydropower plants, energy storage systems, and electric vehicles, has become more important than before. To optimally dispatch these operating units, the quality of the forecasting results becomes increasingly important for the operation of power systems. In this study, an ultra-short forecasting method was proposed for photovoltaic (PV) systems. It provided a forecast of the power output for the following 5 min using sky images obtained photographically in real time. The brightness of the key area was an important factor in determining the output power of the PV system. The output power was calculated using several different features extracted from the sky images. The brightness and other key features were then processed by a bidirectional long short-term memory network. The accuracy of the proposed PV forecasting method improved the accuracy of the forecast for the total power system. A testbed system was established to capture sky images in real time and verify the effectiveness of the proposed method.

Published
2022
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2. Efficient ablation by ultra-short pulse lasers.

Author

Žemaitis, Andrius, Gečys, Paulius, Račiukaitis, Gediminas, and Gedvilas, Mindaugas

Abstract

Ultra-short pulse lasers have already proven to be an excellent tool for material processing due to confined laser-matter interaction leading to high quality, precision and thermal-damage-free surface structuring. For the technology to be a cost-efficient and suitable for the industry, continuous research on the ways how to improve the throughput, in terms of energy and time efficiencies must be done. In this work, the ultra-short pulse lasers were used to investigate the ablation efficiency of a copper target. Laser ablation efficiency was investigated by pulse energy and beam size optimisation method for various processing parameters. Also, the efficiency of material removal by bursts of ultra-short pulses was investigated. Furthermore, it was shown that high ablation efficiency led to superior ablation quality in terms of surface roughness, which both are the most critical characteristics for industry-orientated applications. [ABSTRACT FROM AUTHOR]

Published
2020
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3. Spinopelvic alignment predicts disc calcification, displacement, and Modic changes: Evidence of an evolutionary etiology for clinically‐relevant spinal phenotypes.

Author

Zehra, Uruj, Cheung, Jason P. Y., Bow, Cora, Crawford, Rebecca J., Luk, Keith D. K., Lu, William, and Samartzis, Dino

Subjects
ETIOLOGY of diseases, CALCIFICATION, PHENOTYPES, SKELETAL maturity, SPONDYLOLISTHESIS
Abstract

Lumbar disc‐displacement, Modic changes (MCs), and UTE Disc Sign (UDS) on MRI are clinically relevant spinal phenotypes that can lead to sciatica/LBP. Not all degenerated discs result in disc‐displacement, MCs and UDS, suggesting varied etiologies. Spinopelvic parameters have been implicated in various spinal disorders. Pelvic incidence (PI) is "fixed parameter" since skeletal maturity. No study has addressed disc‐displacement, MCs and UDS in context of spinopelvic parameters. Therefore, the aim of study was to determine if spinopelvic parameters are associated and predict clinically‐relevant MRI‐phenotypes. One hundred and eight population‐based subjects (mean age: 52.3 years) were recruited. Spondylolisthesis and scoliosis individuals were excluded. Lumbar lordosis (LL), PI, sacral slope (SS), and pelvic tilt (PT) were assessed on lateral plain radiographs. Disc degeneration was assessed and summated, and presence or not of disc‐displacement and MCs were noted on T2W MRI. UDS was detected on UTE. Following exclusion criteria, 95 subjects were assessed. Disc‐displacement (82.1%), MCs (52.6%), and UDS (37.9%) were associated with lower PI, SS, LL, and LL/PI index. On multivariate analyses, lower PI was significantly related to development of these MRI phenotypes (adjusted OR range:0.95‐0.92; P <.05), with critical PI value of 42° or lower exhibiting fourfold increase risk of combined phenotypes (P =.020). Of UDS discs, 39.3% had adjacent MCs and 83.6% had disc‐displacement. 87.5% of MC had directly adjacent UDS. The first study to note that PI may "predict" the development of disc‐displacement, MCs and UDS, suggesting potential sub‐variants and mechanistic susceptibility that may be grounded in spinopelvic evolution. An "evolutionary etiological pathway" of spinal phenotype development is proposed. [ABSTRACT FROM AUTHOR]

Published
2020
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4. Short and ultra‐short (<6‐mm) locking‐taper implants supporting single crowns in posterior areas (part <scp>II</scp> ): A 5‐year retrospective study on periodontally healthy patients and patients with a history of periodontitis

Author

Giorgio Lombardo, Annarita Signoriello, Alessia Pardo, Xiomara Zilena Serpa Romero, Luis Armando Vila Sierra, Luisa Arévalo Tovar, Mauro Marincola, and Pier Francesco Nocini

Subjects
short, Dental Implants, Crowns, Alveolar Bone Loss, Implant-Supported, Dental Prosthesis, mucositis, Dental Prosthesis Design, single crown, Humans, Dental Prosthesis, Implant-Supported, Dental Restoration Failure, Oral Surgery, Periodontitis, General Dentistry, ultra-short, peri-implantitis, Follow-Up Studies, Retrospective Studies
Abstract

Short and ultra-short implants implants supporting single crowns seem to demonstrate high percentages of survival and stable marginal bone levels at a mid-term follow-up. Nevertheless, insurgence of peri-implant complications still represents a critical issue, especially for patients with history of periodontitis.The aim of this retrospective study was to evaluate implant survival, marginal bone loss and peri-implant complications in 333 short and ultra-short implants, placed in periodontally healthy patients and patients with a history of periodontitis.Implants were placed in the maxillary and mandibular posterior regions of 142 patients with (PP) and without (NPP) a history of periodontitis. Clinical and radiographic examinations were performed at 5-year recall appointments.Implants respectively placed in PP and NPP were: 35.68% and 42.50% in 8.0 mm-length group, 33.33% and 36.67% in 6.0 mm-length group, and 30.99% and 20.83% in 5.0 mm-length group. Implant-based survival after 5 years of follow-up was 95.77% for PP and 96.67% for NPP (p = 0.77). Regarding crestal bone level variations, average crestal bone loss was statistically different (p = 0.04) among PP (0.74 mm) and NPP (0.61 mm). Implants presenting signs of mucositis were 6.86% in PP and 7.76% in NPP (p = 0.76). Setting the threshold for excessive bone loss at 1 mm after 60 months, peri-implantitis prevalence was 7.84% in PP and 2.59% in NPP (p = 0.08). Overall implant success was 92.16% and 97.41%, respectively, for PP and NPP.Under strict maintenance program, five-year outcomes suggest that short and ultra-short locking-taper implants can be successfully restored with single crowns in the posterior jaws both in PP and NPP.

Published
2022

5. The development of an ultra-short, maternal mental health screening tool in South Africa

Author

T. van Heyningen, L. Myer, M. Tomlinson, S. Field, and S. Honikman

Subjects
Antenatal screening, common perinatal mental disorders, low- and middle-income countries, ultra-short, Neurosciences. Biological psychiatry. Neuropsychiatry, RC321-571
Abstract

Purpose.The burden of common perinatal mental disorders (CPMD) in low-and-middle-income countries is substantially higher than high-income countries, with low levels of detection, service provision and treatment in resource-constrained settings. We describe the development of an ultra-short screening tool to detect antenatal depression, anxiety disorders and maternal suicidal ideation.Methods.A sample of 376 women was recruited at a primary-level obstetric clinic. Five depression and anxiety symptom-screening questionnaires, demographics and psychosocial risk questionnaires were administered. All participants were assessed with the Mini-International Neuropsychiatric Interview (MINI), a structured, diagnostic interview. Screening tool items were analysed against diagnostic data using multiple logistic regression and receiver operating curve (ROC) analysis.Results.The prevalence of MINI-defined major depressive episode (MDE) and/or anxiety disorders was 33%. Overall, 18% of participants expressed suicidal ideation and behaviour, 54% of these had no depression or anxiety diagnosis. Multiple logistic regression identified four screening items that were independently predictive of MDE and anxiety disorders, investigating depressed mood, anhedonia, anxiety symptoms and suicidal ideation. ROC analysis of these combined items yielded an area under the curve of 0.83 (95% CI 0.78–0.88). A cut-off score of 2 or more offered a sensitivity of 78% and specificity of 82%.Conclusion.This novel screening tool is the first measure of CPMD developed in South Africa to include depressed mood, anxiety symptoms and suicidal ideation. While the tool requires further investigation, it may be useful for the early identification of mental health symptoms and morbidity in the perinatal period.

Published
2019
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6. The development of an ultra-short, maternal mental health screening tool in South Africa.

Author

van Heyningen, T., Myer, L., Tomlinson, M., Field, S., and Honikman, S.

Subjects
*MENTAL health screening, *MENTAL illness, *MATERNAL health, *SUICIDAL ideation, *SYMPTOMS
Abstract

Purpose.: The burden of common perinatal mental disorders (CPMD) in low-and-middle-income countries is substantially higher than high-income countries, with low levels of detection, service provision and treatment in resource-constrained settings. We describe the development of an ultra-short screening tool to detect antenatal depression, anxiety disorders and maternal suicidal ideation. Methods.: A sample of 376 women was recruited at a primary-level obstetric clinic. Five depression and anxiety symptom-screening questionnaires, demographics and psychosocial risk questionnaires were administered. All participants were assessed with the Mini-International Neuropsychiatric Interview (MINI), a structured, diagnostic interview. Screening tool items were analysed against diagnostic data using multiple logistic regression and receiver operating curve (ROC) analysis. Results.: The prevalence of MINI-defined major depressive episode (MDE) and/or anxiety disorders was 33%. Overall, 18% of participants expressed suicidal ideation and behaviour, 54% of these had no depression or anxiety diagnosis. Multiple logistic regression identified four screening items that were independently predictive of MDE and anxiety disorders, investigating depressed mood, anhedonia, anxiety symptoms and suicidal ideation. ROC analysis of these combined items yielded an area under the curve of 0.83 (95% CI 0.78–0.88). A cut-off score of 2 or more offered a sensitivity of 78% and specificity of 82%. Conclusion.: This novel screening tool is the first measure of CPMD developed in South Africa to include depressed mood, anxiety symptoms and suicidal ideation. While the tool requires further investigation, it may be useful for the early identification of mental health symptoms and morbidity in the perinatal period. [ABSTRACT FROM AUTHOR]

Published
2019
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7. Assessment of Peri-Implant Soft Tissues Conditions around Short and Ultra-Short Implant-Supported Single Crowns: A 3-Year Retrospective Study on Periodontally Healthy Patients and Patients with a History of Periodontal Disease

Author

Mauro Marincola, Pier Francesco Nocini, Giorgio Lombardo, and Annarita Signoriello

Subjects
Male, Peri-implantitis, Health, Toxicology and Mutagenesis, Radiography, Peri, periodontal disease, Alveolar Bone Loss, lcsh:Medicine, Dentistry, survival, Single-Tooth, Article, 03 medical and health sciences, 0302 clinical medicine, Dental Implants, Single-Tooth, Periodontal disease, bone loss, Mucositis, medicine, Prevalence, Humans, success, Periodontal Diseases, 030304 developmental biology, Retrospective Studies, short, Dental Implants, 0303 health sciences, Crowns, business.industry, lcsh:R, Public Health, Environmental and Occupational Health, Soft tissue, Retrospective cohort study, 030206 dentistry, medicine.disease, mucositis, single crown, Female, Implant, business, ultra-short, peri-implantitis, Follow-Up Studies
Abstract

The aim of this retrospective study was to evaluate implant survival, marginal bone loss and peri-implant complications in 326 short and ultra-short implants. Implants were placed in the maxillary and mandibular posterior regions of 140 patients with (PP) and without (NPP) a history of periodontal disease. Clinical and radiographic examinations were performed at 3-year recall appointments. The 8.0, 6.0 and 5.0 mm-length implants placed in PP and NPP were respectively 43.75% and 38.46%, 35.10% and 34.19%, 21.15% and 27.35%, 325 implants (one early failure) were rehabilitated with single crowns in 139 patients. Overall implant survival after 3 years of follow-up was 97.55%, 98.08% and 96.61% for PP and NPP (p = 0.46). Crestal bone level variations were not statistically different among PP and NPP, 15.41% of implants presented signs of mucositis, 14.71% and 16.67% in PP and NPP (p = 0.64). Setting the threshold for bone loss at 2 mm after 36 months, peri-implantitis prevalence was 2.2%, 1.96% and 2.63% in PP and NPP (p = 0.7). Overall implant success was 82.39%, 83.33% and 80.7% for PP and NPP (p = 0.55). Short-term outcomes suggest that short and ultra-short locking-taper implants can successfully be restored with single crowns in the posterior jaws both in PP and NPP.

Published
2020

8. Spinopelvic alignment predicts disc calcification, displacement, and Modic changes: Evidence of an evolutionary etiology for clinically-relevant spinal phenotypes

Author

Dino Samartzis, Rebecca J. Crawford, Cora Bow, William W. Lu, Keith D. K. Luk, Jason Pui Yin Cheung, and Uruj Zehra

Subjects
sacral slope, medicine.medical_specialty, Lordosis, Population, Urology, Context (language use), Scoliosis, Modic, ultra‐short, lordosis, tilt, Lumbar, lcsh:Orthopedic surgery, medicine, Orthopedics and Sports Medicine, pelvic, education, Research Articles, lumbar, Sciatica, education.field_of_study, business.industry, Modic changes, medicine.disease, Spondylolisthesis, lcsh:RD701-811, spinopelvic alignment, incidence, UTE, medicine.symptom, business, Research Article, MRI
Abstract

Lumbar disc‐displacement, Modic changes (MCs), and UTE Disc Sign (UDS) on MRI are clinically relevant spinal phenotypes that can lead to sciatica/LBP. Not all degenerated discs result in disc‐displacement, MCs and UDS, suggesting varied etiologies. Spinopelvic parameters have been implicated in various spinal disorders. Pelvic incidence (PI) is “fixed parameter” since skeletal maturity. No study has addressed disc‐displacement, MCs and UDS in context of spinopelvic parameters. Therefore, the aim of study was to determine if spinopelvic parameters are associated and predict clinically‐relevant MRI‐phenotypes. One hundred and eight population‐based subjects (mean age: 52.3 years) were recruited. Spondylolisthesis and scoliosis individuals were excluded. Lumbar lordosis (LL), PI, sacral slope (SS), and pelvic tilt (PT) were assessed on lateral plain radiographs. Disc degeneration was assessed and summated, and presence or not of disc‐displacement and MCs were noted on T2W MRI. UDS was detected on UTE. Following exclusion criteria, 95 subjects were assessed. Disc‐displacement (82.1%), MCs (52.6%), and UDS (37.9%) were associated with lower PI, SS, LL, and LL/PI index. On multivariate analyses, lower PI was significantly related to development of these MRI phenotypes (adjusted OR range:0.95‐0.92; P, Our findings suggest a strong biomechanical influence of spinopelvic morphometry on clinically meaningful anterior column spinal phenotypes, which may have an etiological foundation in spinal evolution secondary to permanent bipedalism. Our results improve the understanding of spinal phenotypes, contributing additional steps toward personalized spine care.

Published
2019

10. Reliability of heart-rate-variability features derived from ultra-short ECG recordings and their validity in the assessment of cardiac autonomic neuropathy.

Author

Wehler, D., Jelinek, H.F., Gronau, A., Wessel, N., Kraemer, J.F., Krones, R., and Penzel, T.

Subjects
FREQUENCY-domain analysis, ELECTROCARDIOGRAPHY, NEUROPATHY, CURVES, HEART beat
Abstract

Our research aimed at providing methodologically strong evidence for the reliability of HRV analysis of ultra-short (10–150 s) ECGs compared to the benchmark of 300 s. Furthermore, we evaluated the retainment of HRV differences between participants with definite cardiac autonomic neuropathy (dCAN) and controls as ECG recording length was reduced to 10 s. Pre-processed ECG recordings from 11 individuals with dCAN and 76 healthy controls were used to determine SDNN, RMSSD, Low Frequency (LF) and High Frequency (HF) and assess whether the reliability of HRV features remains comparable for ultra-short ECG time series. For frequency domain analysis, the Lomb-Scargle-Periodogram (LSP) and Fast-Fourier-Transform (FFT) approaches were compared. Nonparametric areas under the curve (AUCs) were estimated to examine the overall ability of ultra-short HRV to classify dCAN from ECGs of 10–300 s. RMSSD and HF were reliable and retained significant differences between control and dCAN from ECGs down to 10 s. SDNN and LF could be considered reliable in recordings of at least 30 s. LSP and FFT yielded comparable results. Most prevalent group differences were found for LF between 60 and 300 s. RMSSD and HF were reliable HRV features showing excellent potential for the classification of dCAN from 10-s ECG strips. For recordings longer than one minute, LF proved to be reliable and yielded best discrimination results. The current research indicated that ultra-short HRV analysis has the potential to become a time-efficient and accurate diagnostic tool for dCAN in clinical practice. [ABSTRACT FROM AUTHOR]

Published
2021
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12. Assessment of Peri-Implant Soft Tissues Conditions around Short and Ultra-Short Implant-Supported Single Crowns: A 3-Year Retrospective Study on Periodontally Healthy Patients and Patients with a History of Periodontal Disease.

Author

Lombardo G, Signoriello A, Marincola M, and Nocini PF

Subjects
Female, Follow-Up Studies, Humans, Male, Prevalence, Retrospective Studies, Alveolar Bone Loss epidemiology, Alveolar Bone Loss etiology, Crowns standards, Crowns statistics & numerical data, Dental Implants, Single-Tooth adverse effects, Dental Implants, Single-Tooth standards, Dental Implants, Single-Tooth statistics & numerical data, Periodontal Diseases complications
Abstract

The aim of this retrospective study was to evaluate implant survival, marginal bone loss and peri-implant complications in 326 short and ultra-short implants. Implants were placed in the maxillary and mandibular posterior regions of 140 patients with (PP) and without (NPP) a history of periodontal disease. Clinical and radiographic examinations were performed at 3-year recall appointments. The 8.0, 6.0 and 5.0 mm-length implants placed in PP and NPP were respectively 43.75% and 38.46%, 35.10% and 34.19%, 21.15% and 27.35%; 325 implants (one early failure) were rehabilitated with single crowns in 139 patients. Overall implant survival after 3 years of follow-up was 97.55%, 98.08% and 96.61% for PP and NPP ( p = 0.46). Crestal bone level variations were not statistically different among PP and NPP; 15.41% of implants presented signs of mucositis, 14.71% and 16.67% in PP and NPP ( p = 0.64). Setting the threshold for bone loss at 2 mm after 36 months, peri-implantitis prevalence was 2.2%, 1.96% and 2.63% in PP and NPP ( p = 0.7). Overall implant success was 82.39%, 83.33% and 80.7% for PP and NPP ( p = 0.55). Short-term outcomes suggest that short and ultra-short locking-taper implants can successfully be restored with single crowns in the posterior jaws both in PP and NPP.

Published
2020
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13. A Novel Sloped Field Plate-Enhanced Ultra-Short Edge Termination Structure

Author

Yang, Wentao, Feng, Hao, Fang, Xiangming, Onozawa, Yuichi, Tanaka, Hiroyuki, Sin, Johnny Kin On, Yang, Wentao, Feng, Hao, Fang, Xiangming, Onozawa, Yuichi, Tanaka, Hiroyuki, and Sin, Johnny Kin On

Abstract

A novel sloped field plate (FP)-enhanced ultra-short edge termination structure is proposed and experimentally demonstrated. The structure features a benzocyclobutene dielectric filled trench, and is fabricated along with a high-voltage p-i-n diode. In addition, a sloped FP is put inside the trench and connected to the anode electrode. The fabricated device shows a breakdown voltage of 755 V, and is confirmed as the ideal planar junction breakdown voltage of the p-i-n diode. The proposed edge termination structure has a total width of 35 mu m, which is similar to 1/5 the size of a conventional termination structure using the guard rings approach.

Published
2016

14. Ionization of argon by two-color laser pulses with coherent phase control

Author

Nicolas Camus, Diego G. Arbó, Thomas Pfeifer, Lutz Fechner, Stefan Nagele, Andreas Krupp, S. D. López, Joachim Burgdörfer, Christoph Lemell, and R. Moshammer

Subjects
Physics, Física Atómica, Molecular y Química, Ultra-Short, Ionization, Argon, Ciencias Físicas, chemistry.chemical_element, Laser, purl.org/becyt/ford/1.3 [https], Two-Color, Atomic and Molecular Physics, and Optics, law.invention, Atmospheric-pressure laser ionization, X-ray laser, purl.org/becyt/ford/1 [https], chemistry, law, Atomic physics, Phase control, Pulses, CIENCIAS NATURALES Y EXACTAS, Óptica
Abstract

We present a joint experimental and theoretical study of ionization of argon atoms by a linearly polarized two-color laser field (800 nm, 400 nm). Changing the relative phase between the two colors, the forward-backward asymmetry of the doubly differential momentum distribution of emitted electrons can be controlled. We nd excellent agreement between the measurements and the solution of the time-dependent Schrodinger equation in the single-active electron approximation. Surprisingly, we also nd good agreement between the quantum and classical calculations of electron momentum distributions generated by lasers at optical wavelengths. Fil: Arbo, Diego. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Lemell, C.. Vienna University of Technology; Austria Fil: Nagele, S.. Vienna University of Technology; Austria Fil: Camus, N.. Max-Planck-Institut fur Kernphysik; Alemania Fil: Fechner, L.. Max-Planck-Institut fur Kernphysik; Alemania Fil: Krupp, A.. Max-Planck-Institut fur Kernphysik; Alemania Fil: Pfeifer, T.. Max-Planck-Institut fur Kernphysik; Alemania Fil: López, Sebastián David. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Moshammer, R.. Max-Planck-Institut fur Kernphysik; Alemania Fil: Burgdörfer, J.. Vienna University of Technology; Austria

Published
2015

15. Experimental observation for new polymorphs of silicon formed through ultrafast-laser-induced microexplosion

Author

Rapp, L., Haberl, Bianca, Pickard, Chris, Bradby, J. E., Gamaly, E. G., Williams, J. S., Rode, A. V., Rapp, L., Haberl, Bianca, Pickard, Chris, Bradby, J. E., Gamaly, E. G., Williams, J. S., and Rode, A. V.

Abstract

Intense ultrafast laser pulses tightly focused in the bulk of transparent material produce plasma in the extreme conditions similar to those in the cores of planets. The plasma generates strong shock waves in such confined geometry, thus inducing a laser-ignited microexplosion. This new method of compression of matter by ultra-short laser induced micro-explosion generates pressures in excess of Terapascals, leaving all the pressure/temperature-affected material confined inside the bulk of pristine crystal for the further investigations

Published
2014

16. Comparing field ionization models in simulations of laser-matter interaction

Author

Garten, M., Prof. Dr. Cowan, Thomas, Prof. Dr. Schramm, Ulrich, and Dr. Bussmann, Michael

Subjects
atomic physics, ionization, field ionization, atomic physics, high-power ultra-short lasers, plasma physics, Physics::Atomic Physics, ultra-short, lasers, high-power
Abstract

Field ionization plays an important role in modeling the interaction of high-power, ultra-short laser pulses with matter. Many field ionization models exist that have predictive capability at non-relativistic laser intensities and for laser pulse durations much longer than the atomic time scales. Most existing models take a quasi-static approach to the laser field on atomic dimensions and time scales. Yet, with pulses as short as a few ~10 to ~100 as and intensities of 1021 W/cm2 the feasibility of these approximations becomes questionable. Still, the exploration of plasma effects in relativistic laser matter interaction requires to test the boundaries of validity for these models. This thesis will take a step to point out the difficulties to be considered when existing ionization models are applied to such extreme cases.

Published
2013
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17. Two-phase Zirconium Boride thin film obtained by ultra-short Pulsed Laser Ablation of a ZrB12 target

Author

Julietta V. Rau, Takahiro Mori, L. Medici, Antonio Santagata, Alessandro Latini, Roberto Teghil, and A. De Bonis

Subjects
Materials science, microRaman, Scanning electron microscope, Zirconium dodecaboride, Analytical chemistry, General Physics and Astronomy, chemistry.chemical_element, Pulsed laser deposition, law.invention, Coatings and Films, chemistry.chemical_compound, law, Boride, Two-phase thin film, Two-phase thin film microRaman, Ultra-short PLA, Thin film, Spectroscopy, Zirconium, Laser ablation, Ultra-short, Surfaces and Interfaces, General Chemistry, PLA, Surfaces, Coatings and Films, Condensed Matter Physics, Laser, Surfaces, chemistry
Abstract

Two-phase zirconium boride thin films have been obtained by ultra-short pulsed laser ablation (PLA) of a zirconium dodecaboride (ZrB 12 ) target performed in vacuum. The ablation source was a frequency doubled ( λ = 527 nm) Nd:glass laser with a pulse duration of 250 fs. Laser induced plasma has been studied by ICCD imaging and time and space resolved optical emission spectroscopy (OES), whereas the deposited films have been characterized by atomic force microscopy, scanning electron microscopy, X-Ray diffraction and micro-Raman spectroscopy. The film morphology and composition have been interpreted on the basis of the laser ablation mechanism.

Published
2013

18. Development of an ultra-short, carrier-to-envelope phase-stable, high-contrast laser source for high repetition rate relativistic optics

Author

Ricci, A. and Ricci, Aurélien

Subjects
[PHYS.PHYS.PHYS-OPTICS] Physics [physics]/Physics [physics]/Optics [physics.optics], Contraste temporel, Femtoseconde, Ultra-short, Femtosecond, Temporal contrast, Laser, High repetition rate, Haute cadence, Plasma, Cycle optique, Few-cycle, XPW, Ultra-court, IR, Infra-rouge
Abstract

Laser-plasma interaction at high intensities (I " 1015 W/cm2) with ultra-short pulses ( t " 100 fs) is a booming research domain as it offers the opportunity to study increasingly short phenomena, comprised under the trivial name " attosecond science ". Laser-plasma interaction also bears the promise to achieve new light sources for the generation of energetic particle beams and X-rays. Our approach focuses on the generation of attosecond pulses from plasma mirrors using few-cycle laser pulses ( 5 fs at 800 nm) at high repetition rate (1 kHz) and with fine control of laser parameters. The generation and spatio-temporal control of high-order harmonics emission in the non-relativistic regime has recently been demosntrated by our group. The following objective is to reach the relativistic regime thanks to higher intensities on target. This thesis pursued the goals of improving the existing laser chain performances in termes of energy and temporal contrast, while preserving, at least, all the other key parameters. Meeting these requirements was achieved while developing a laser architecture based on chirped-pulse amplification (CPA) delivering 5 mJ, 5 fs pulses at 1 kHz, with a temporal contrast C = 1011 and an absolute phase (CEP) stabilized down to 200 mrad rms. Contrast improvement by cross-polarized wave (XPW) generation is at the centre of this dissertation. An extensive study of the mechanism was carried out. It allowed to confront experimental results and theoretical developments in " extremes " regimes such as the generation at very high efficiency and few-cycle pulse filtering. Besides, a new energy-scalable scheme was proposed to filter efficiently (20%) a wide range of pulse energies (from 100 μJ to 10 mJ). Pulse compression by a factor larger than two was also demonstrated. The new laser chain includes such filter in a double-CPA configuration delivering pulses of 10 mJ, 20 fs, C = 1011 and CEP = 200 mrad rms. A detailed study was carried out to develop a new stretcher/compressor scheme achieving highly stretched pulses (50 ps) while remaining compact to preserve CEP stability. The chosen configuration consists of a bulk stretcher, an acousto-optic programmable dispersive filter and a grisms compressor. The manuscript finally presents the perspectives of post-compression in a rare-gas filled hollow-core fibre in order to achieve pulses of 5 mJ, 5 fs, C = 1011, CEP = 200 mrad rms at 1 kHz., L'interaction laser-plasma à très haute intensité (I " 1015 W/cm2) avec des impulsions ultra-courtes ( t " 100 fs) est un domaine en plein essor car il offre l'opportunité d'étudier des phénomènes physiques toujours plus brefs, regroupés sous l'appellation " science attoseconde ". L'interaction laser-plasma promet aussi l'avènement de nouvelles sources pour la génération de faisceaux de particules et de rayonnement X très énergétiques. Notre démarche se concentre sur la génération d'impulsions attosecondes sur miroir plasma à partir d'impulsions de quelques cycles optiques ( 5 fs à 800 nm), à haut taux de répétition (1 kHz) et avec un contrôle fin des paramètres laser. La génération et le contrôle temporel et spatial de l'émission d'harmoniques d'ordres élevés dans le régime non-relativiste ont récemment été démontrés par le groupe. L'objectif suivant est d'atteindre le régime relativiste, qui nécessite une intensité sur cible plus élevée. Ce travail de thèse s'inscrit donc dans la logique d'améliorer les performances de la chaine existante en termes d'énergie et de contraste temporel, tout en préservant les autres paramètres clés. Pour répondre à ces défis, l'objectif a été de mettre au point une architecture laser basée sur l'amplification à dérive de fréquence (CPA) délivrant des impulsions de 5 mJ, 5 fs à 1 kHz, avec un contraste temporel C = 1011 et une phase absolue (CEP) stabilisée à 200 mrad rms. La problématique de l'amélioration du contraste par la technique de génération de polarisation croisée (XPW) occupe une place centrale dans ce mémoire. Une étude extensive du mécanisme XPW a été menée. Elle a permis de confronter résultats expérimentaux et développements théoriques dans les régimes dits " extrêmes " tels que la génération à très haut rendement et le filtrage d'impulsions de quelques cycles optiques. En outre, un nouveau schéma de filtrage adaptable sur une large gamme d'énergie (de 100 μJ à 10 mJ) et efficace (20%) a été réalisé. La compression des impulsions d'un facteur supérieur à deux avec ce schéma a également été démontrée. La nouvelle chaine laser inclut un tel filtre dans une configuration en double CPA dont les performances finales visées sont les suivantes : 10 mJ, 20 fs, C = 1011 et CEP = 200 mrad rms. Le schéma d'étirement/compression a fait l'objet d'une étude détaillée pour permettre un étirement élevé (50 ps) tout en restant compact pour préserver la stabilité CEP. La configuration adoptée consiste en un étireur verre, un filtre acousto-optique dispersif programmable et un compresseur "grismes". Le mémoire présente enfin les perspectives de post-compression dans une fibre creuse remplie d'un gaz rare pour obtenir des impulsions de 5 mJ, 5 fs, C = 1011, CEP = 200 mrad rms à 1 kHz.

Published
2013

19. Ultracompact and broadband polarization beam splitter utilizing the evanescent coupling between a hybrid plasmonic waveguide and a silicon nanowire

Author

Guan, Xiaowei, Wu, Hao, Shi, Yaocheng, Wosinski, Lech, Dai, Daoxin, Guan, Xiaowei, Wu, Hao, Shi, Yaocheng, Wosinski, Lech, and Dai, Daoxin

Abstract

An ultracompact polarization beam splitter (PBS) is proposed based on an asymmetrical directional coupler consisting of a silicon hybrid plasmonic waveguide (HPW) and a silicon nanowire. The widths of the two coupling waveguides are chosen so that the phase-matching condition is satisfied for TE polarization only while the phase mismatch is significant for TM polarization. A sharply bent silicon HPW is connected at the thru port to play the role of polarizer by utilizing its polarization-dependent loss. With the present principle, the designed PBS has a footprint as small as only similar to 1.9 mu m x 3.7 mu m, which is the shortest PBS reported until now, even when large waveguide dimensions (e. g., the waveguide widths w(1,2) = similar to 300 nm and the gap width w(gap) = similar to 200 nm) are chosen to simplify the fabrication process. The numerical simulations show that the designed PBS has a very broad band (similar to 120 nm) with an extinction ratio >12 dB and a large fabrication tolerance to allow a waveguide width variation of similar to 30 nm., QC 20130909

Published
2013
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20. Kluge et al. Reply

Author

Kluge, T., Cowan, T. E., Debus, A., Schramm, U., Zeil, K., Bussmann, M., Kluge, T., Cowan, T. E., Debus, A., Schramm, U., Zeil, K., and Bussmann, M.

Abstract

A Reply to the Comment by C. Thaury et al.

Published
2013

21. Interaction of ultra-short laser pulses with metal surfaces: Impulsive jelliun-Volkov approximation versus the solution of the time-dependent Schrödinger equation

Author

Marisa Noemi Faraggi, Dario Marcelo Mitnik, and Maria Silvia Gravielle

Subjects
Física Atómica, Molecular y Química, Ultra-Short, Ciencias Físicas, Jellium, Laser, Spectral line, Schrödinger equation, law.invention, Metal, purl.org/becyt/ford/1 [https], symbols.namesake, Ultrashort laser, law, Quantum mechanics, Pulso, Physics, Valence (chemistry), purl.org/becyt/ford/1.3 [https], Atomic and Molecular Physics, and Optics, visual_art, symbols, visual_art.visual_art_medium, Atomic physics, CIENCIAS NATURALES Y EXACTAS
Abstract

Electron emission coming from the valence band of metal surfaces due to grazing incidence of high frequency ultrashort laser pulses is studied. We introduce a distorted-wave method, named impulsive jellium-Volkov (IJV) approximation, in which the surface is represented by the jellium model while the interaction with the laser field is described by means of the Volkov phase. With the purpose of examining the proposed approach, we compare IJV results with values derived from the numerical solution of the corresponding time-dependent Schrödinger equation (TDSE). For Al(111) surfaces, double and single differential probability spectra are calculated considering different duration of the laser pulse. Very good agreement between IJV and TDSE results was found. The total probability dependence on the intensity and carrier-envelope phase of the pulse is also investigated. Fil: Faraggi, Marisa Noemi. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Gravielle, Maria Silvia. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Mitnik, Dario Marcelo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina

Published
2007

22. Photoelectron emission from metal surfaces by ultrashort laser pulses

Author

Vyacheslav M. Silkin, Marisa Noemi Faraggi, and Maria Silvia Gravielle

Subjects
Ciencias Físicas, chemistry.chemical_element, ULTRA-SHORT, Electron, ELECTRON EMISSION, Otras Ciencias Físicas, law.invention, purl.org/becyt/ford/1 [https], Metal, LASER PULSE, law, Aluminium, Electric field, Electronic band structure, Plasmon, Physics, Valence (chemistry), purl.org/becyt/ford/1.3 [https], Laser, Atomic and Molecular Physics, and Optics, METAL SURFACE, chemistry, visual_art, visual_art.visual_art_medium, Atomic physics, CIENCIAS NATURALES Y EXACTAS
Abstract

Electron emission from metal surfaces produced by short laser pulses is studied within the framework of the distorted-wave formulation. The proposed approach, named surface-Volkov (SV)approximation, makes use of the band-structure based (BSB)model and the Volkov phase to describe the interaction of the emitted electron with the surface and the external electric field, respectively. The BSB model provides a realistic representation of the surface, based on a model potential that includes the main features of the surface band structure. The SV method is applied to evaluate the photoelectron emission from the valence band of Al(111). Angular and energy distributions are investigated for different parameters of the laser pulse, keeping in all cases the carrier frequency larger than the plasmon one. Fil: Faraggi, Marisa Noemi. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Gravielle, Maria Silvia. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Silkin, V. M.. Donostia International Physics Center; España

Published
2006

23. Electron bunch length measurements from laser-accelerated electrons using single-shot THz time-domain interferometry

Author

Debus, A., Bussmann, M., Schramm, U., Sauerbrey, R., Karsch, S., Debus, A., Bussmann, M., Schramm, U., Sauerbrey, R., and Karsch, S.

Abstract

Laser-plasma wakefield based electron accelerators are expected to deliver ultrashort electron bunches with unprecedented peak currents. However, their actual pulse duration has never been directly measured in a single-shot experiment. We present measurements of the ultrashort duration of such electron bunches by means of THz time-domain interferometry. With data obtained using a 0.5J, 45fs, 800nm laser and a ZnTe-based electro-optical setup we demonstrate the duration of laser-accelerated, quasi-monoenergetic electron bunches at a best fit of 32fs (FWHM) with a 90% upper confidence level of 38fs.

Published
2010

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