Eigenmode Analysis in Plasmonics: Application to Second Harmonic Generation and Electron Energy Loss Spectroscopy

Eigenmodes are central to the study of resonant phenomena in all areas of physics. However, their use in nano-optics seems to have been hindered and delayed for various reasons. First, due to their small size, the response of nanostructures to a far-field optical excitation is mainly dipolar. Thus, preliminary studies of nanosystems through optical methods meant that only very few eigenmodes of the system were probed, and a complete eigenmode theory was not required. Second, rigorously defining eigenmodes of an open and lossy cavity is far from trivial. Finally, only few geometries allow for an analytical solution of Maxwellâs equations that can be expressed in terms of modes, rendering the use of numerical methods mandatory to study non-trivial shapes. On the other hand, modern spectroscopy techniques based on fast electron excitation, instead of optical excitation, allow going beyond the above-mentioned dipolar regime and enable the observation of high order modes. In addition, the generation of second harmonic light (SHG) by nanoparticles permits revealing higher order modes that weakly couple to planewave far-field probing. Thus, to be able to analyze the data collected with such experimental methods and comprehend them in order to make appropriate nanostructure designs, one needs to develop suitable numerical tools for the computation of eigenmodes. This is the focus of this thesis, where eigenmodes are used throughout to analyze and understand experimental and numerical results. First, different approaches used to define and compute eigenmodes are presented in details together with the surface integral equation method used in this manuscript. The second chapter presents the use of eigenmodes to study the SHG in plasmonic nanostructures. A single mode is used as an SHG source to disentangle the modal contributions from different SHG channels. For three different nanostructures, the dipolar mode gives a pure quadrupolar second harmonic (SH) response. Then, the interplay of dipolar and quadrupolar SH radiations in nanorods of different sizes is revealed through a multipolar analysis, explaining the experimental observation of the flip between forward and backward maximum SH emissions. Finally, the dynamics of the SHG from a silver nanorod generated by short pulses is investigated. By tuning the spectral position and width of the pulses, the dynamics of a single mode is observed, both in the linear and SH responses, and fits extremely well with a harmonic oscillator model. The last chapter presents the utilization of the eigenmodes to interpret electron energy loss spectroscopy (EELS) measurements. An alternative approach to compute EELS signal is presented, revealing the different paths through which the energy of the electron is dissipated. Instead of computing the work done by the electron against the scattered electric field, the Ohmic and the radiation losses are evaluated. Then, heterodimers with several shapes and compositions are studied. A rich variety of modes is found, due to the additional degree of freedom associated with the different metals. Dolmen shaped nanostructures are also investigated in great details. A rigorous analysis of the eigenmode evolution when the central horizontal nanorod is moved is performed. Finally, we study the EELS for three iterations of a Koch snowflake nanoantenna. The evolution of the modes with the iteration of the fractal is analysed and the modes are linked to the experimental EELS ma

X-ray Emission from Young Stellar Objects in the \epsilon Chamaeleontis Group: the Herbig Ae Star HD 104237 and Associated Low-Mass Stars

We present Chandra-HETGS observations of the Herbig Ae star HD 104237 and the associated young stars comprising lower mass stars, in the 0.15-1.75\msol mass range, in their pre-main sequence phase. The brightest X-ray source in the association is the central system harboring the Herbig Ae primary, and a K3 companion. Its X-ray variability indicates modulation possibly on time scales of the rotation period of the Herbig Ae star, and this would imply that the primary significantly contributes to the overall emission. The spectrum of the Herbig Ae+K3 system shows a soft component significantly more pronounced than in other K-type young stars. This soft emission is reminiscent of the unusually soft spectra observed for the single Herbig Ae stars HD 163296 and AB Aur, and therefore we tentatively attribute it to the Herbig Ae of the binary system. The HETGS spectrum shows strong emission lines corresponding to a wide range of plasma temperatures. The He-like triplet of MgXI and NeIX suggest the presence of plasma at densities of about $10^{12}$ cm$^{-3}$, possibly indicating accretion related X-ray production mechanism. The analysis of the zero-order spectra of the other sources indicates X-ray emission characteristics typical of pre-main sequence stars of similar spectral type, with the exception of the T Tauri HD104237-D, whose extremely soft emission is very similar to the emission of the classical T Tauri star TW Hya, and suggests X-ray production by shocked accreting plasma.Comment: accepted for publication on the Astrophysical Journa

Case Reports1. A Late Presentation of Loeys-Dietz Syndrome: Beware of TGFβ Receptor Mutations in Benign Joint Hypermobility

Background: Thoracic aortic aneurysms (TAA) and dissections are not uncommon causes of sudden death in young adults. Loeys-Dietz syndrome (LDS) is a rare, recently described, autosomal dominant, connective tissue disease characterized by aggressive arterial aneurysms, resulting from mutations in the transforming growth factor beta (TGFβ) receptor genes TGFBR1 and TGFBR2. Mean age at death is 26.1 years, most often due to aortic dissection. We report an unusually late presentation of LDS, diagnosed following elective surgery in a female with a long history of joint hypermobility. Methods: A 51-year-old Caucasian lady complained of chest pain and headache following a dural leak from spinal anaesthesia for an elective ankle arthroscopy. CT scan and echocardiography demonstrated a dilated aortic root and significant aortic regurgitation. MRA demonstrated aortic tortuosity, an infrarenal aortic aneurysm and aneurysms in the left renal and right internal mammary arteries. She underwent aortic root repair and aortic valve replacement. She had a background of long-standing joint pains secondary to hypermobility, easy bruising, unusual fracture susceptibility and mild bronchiectasis. She had one healthy child age 32, after which she suffered a uterine prolapse. Examination revealed mild Marfanoid features. Uvula, skin and ophthalmological examination was normal. Results: Fibrillin-1 testing for Marfan syndrome (MFS) was negative. Detection of a c.1270G > C (p.Gly424Arg) TGFBR2 mutation confirmed the diagnosis of LDS. Losartan was started for vascular protection. Conclusions: LDS is a severe inherited vasculopathy that usually presents in childhood. It is characterized by aortic root dilatation and ascending aneurysms. There is a higher risk of aortic dissection compared with MFS. Clinical features overlap with MFS and Ehlers Danlos syndrome Type IV, but differentiating dysmorphogenic features include ocular hypertelorism, bifid uvula and cleft palate. Echocardiography and MRA or CT scanning from head to pelvis is recommended to establish the extent of vascular involvement. Management involves early surgical intervention, including early valve-sparing aortic root replacement, genetic counselling and close monitoring in pregnancy. Despite being caused by loss of function mutations in either TGFβ receptor, paradoxical activation of TGFβ signalling is seen, suggesting that TGFβ antagonism may confer disease modifying effects similar to those observed in MFS. TGFβ antagonism can be achieved with angiotensin antagonists, such as Losartan, which is able to delay aortic aneurysm development in preclinical models and in patients with MFS. Our case emphasizes the importance of timely recognition of vasculopathy syndromes in patients with hypermobility and the need for early surgical intervention. It also highlights their heterogeneity and the potential for late presentation. Disclosures: The authors have declared no conflicts of interes

Maternal outcomes and risk factors for COVID-19 severity among pregnant women.

Pregnant women may be at higher risk of severe complications associated with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which may lead to obstetrical complications. We performed a case control study comparing pregnant women with severe coronavirus disease 19 (cases) to pregnant women with a milder form (controls) enrolled in the COVI-Preg international registry cohort between March 24 and July 26, 2020. Risk factors for severity, obstetrical and immediate neonatal outcomes were assessed. A total of 926 pregnant women with a positive test for SARS-CoV-2 were included, among which 92 (9.9%) presented with severe COVID-19 disease. Risk factors for severe maternal outcomes were pulmonary comorbidities [aOR 4.3, 95% CI 1.9-9.5], hypertensive disorders [aOR 2.7, 95% CI 1.0-7.0] and diabetes [aOR2.2, 95% CI 1.1-4.5]. Pregnant women with severe maternal outcomes were at higher risk of caesarean section [70.7% (n = 53/75)], preterm delivery [62.7% (n = 32/51)] and newborns requiring admission to the neonatal intensive care unit [41.3% (n = 31/75)]. In this study, several risk factors for developing severe complications of SARS-CoV-2 infection among pregnant women were identified including pulmonary comorbidities, hypertensive disorders and diabetes. Obstetrical and neonatal outcomes appear to be influenced by the severity of maternal disease

Rheumatoid arthritis - treatment: 180. Utility of Body Weight Classified Low-Dose Leflunomide in Japanese Rheumatoid Arthritis

Background: In Japan, more than 20 rheumatoid arthritis (RA) patients died of interstitial pneumonia (IP) caused by leflunomide (LEF) were reported, but many of them were considered as the victims of opportunistic infection currently. In this paper, efficacy and safety of low-dose LEF classified by body weight (BW) were studied. Methods: Fifty-nine RA patients were started to administrate LEF from July 2007 to July 2009. Among them, 25 patients were excluded because of the combination with tacrolimus, and medication modification within 3 months before LEF. Remaining 34 RA patients administered 20 to 50 mg/week of LEF were followed up for 1 year and enrolled in this study. Dose of LEF was classified by BW (50 mg/week for over 50 kg, 40 mg/week for 40 to 50 kg and 20 to 30 mg/week for under 40 kg). The average age and RA duration of enrolled patients were 55.5 years old and 10.2 years. Prednisolone (PSL), methotrexate (MTX) and etanercept were used in 23, 28 and 2 patients, respectively. In case of insufficient response or adverse effect, dosage change or discontinuance of LEF were considered. Failure was defined as dosages up of PSL and MTX, or dosages down or discontinuance of LEF. Last observation carried forward method was used for the evaluation of failed patients at 1 year. Results: At 1 year after LEF start, good/ moderate/ no response assessed by the European League Against Rheumatism (EULAR) response criteria using Disease Activity Score, including a 28-joint count (DAS28)-C reactive protein (CRP) were showed in 14/ 10/ 10 patients, respectively. The dosage changes of LEF at 1 year were dosage up: 10, same dosage: 5, dosage down: 8 and discontinuance: 11 patients. The survival rate of patients in this study was 23.5% (24 patients failed) but actual LEF continuous rate was 67.6% (11 patients discontinued) at 1 year. The major reason of failure was liver dysfunction, and pneumocystis pneumonia was occurred in 1 patient resulted in full recovery. One patient died of sepsis caused by decubitus ulcer infection. DAS28-CRP score was decreased from 3.9 to 2.7 significantly. Although CRP was decreased from 1.50 to 0.93 mg/dl, it wasn't significant. Matrix metalloproteinase (MMP)-3 was decreased from 220.0 to 174.2 ng/ml significantly. Glutamate pyruvate transaminase (GPT) was increased from 19 to 35 U/l and number of leukocyte was decreased from 7832 to 6271 significantly. DAS28-CRP, CRP, and MMP-3 were improved significantly with MTX, although they weren't without MTX. Increase of GPT and leukopenia were seen significantly with MTX, although they weren't without MTX. Conclusions: It was reported that the risks of IP caused by LEF in Japanese RA patients were past IP history, loading dose administration and low BW. Addition of low-dose LEF is a potent safe alternative for the patients showing unsatisfactory response to current medicines, but need to pay attention for liver function and infection caused by leukopenia, especially with MTX. Disclosure statement: The authors have declared no conflicts of interes

Mortality and pulmonary complications in patients undergoing surgery with perioperative SARS-CoV-2 infection: an international cohort study

Background: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods: This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings: This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (74·0%) had emergency surgery and 280 (24·8%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (26·1%) patients. 30-day mortality was 23·8% (268 of 1128). Pulmonary complications occurred in 577 (51·2%) of 1128 patients; 30-day mortality in these patients was 38·0% (219 of 577), accounting for 81·7% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 1·75 [95% CI 1·28–2·40], p\textless0·0001), age 70 years or older versus younger than 70 years (2·30 [1·65–3·22], p\textless0·0001), American Society of Anesthesiologists grades 3–5 versus grades 1–2 (2·35 [1·57–3·53], p\textless0·0001), malignant versus benign or obstetric diagnosis (1·55 [1·01–2·39], p=0·046), emergency versus elective surgery (1·67 [1·06–2·63], p=0·026), and major versus minor surgery (1·52 [1·01–2·31], p=0·047). Interpretation: Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding: National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research

Modes interplay controls the second harmonic generation dynamics of plasmonic nanostructures

A large amount of experimental and theoretical works deals with the second harmonic generation from different plasmonic geometries. Since they often consider relatively long optical pulses, many of these studies are focused on the investigation of a quasi-monochromatic response of the system and can be understood through the excitation of one, possibly two, optical modes. On the other hand, when the excitation pulse duration is short (say, below several tens of fs), the excitation spectrum becomes broader and a very interesting dynamics emerges from the interplay between several optical modes. In this work, the dynamics of modes at the second harmonic frequency for two silver spheres of different diameters and a nanorod is investigated numerically and shown to be quite different. For the pulsed illumination with length close to the modes lifetime, apart from different relative contributions of dipolar and quadrupolar multipoles in the far-field, we have been able to observe and explain non constant phase difference between multipoles, which is not accessible in continuous wave regime. Short pulse durations also allow us to observe only one mode, while another one has already decayed. For the case of the nanorod we also perform an eigenmode analysis, which allows to understand the modes interplay that explains the observed spectra. In the paper, we also show a method allowing a significant reduction of required computational steps to find the response of a plasmonic nanostructure to a pulsed illumination with arbitrary frequency-domain method

New numerical methods for the design of efficient nonlinear plasmonic sources of light and nanosensors

During the last decade, important attention has been devoted to the observation of nonlinear optical processes in plasmonic nanosystems, giving rise to a new field of research called nonlinear plasmonics. The cornerstone of nonlinear plasmonics is the use of the large field enhancement associated with the excitation of localized surface plasmon resonances to reach high nonlinear conversion yields. Among all the nonlinear optical processes, second harmonic generation (SHG), the process whereby two photons at the fundamental frequency are converted into one photon at the second harmonic frequency, is undoubtedly the most studied one due to the relative simplicity of its experimental observation. However, the physical origin of SHG from plasmonic nanostructures hides a lot of subtleties, which are mainly related to its particular behavior upon inversion symmetry. In order to catch all the peculiarities of SHG, it is mandatory to develop dedicated numerical methods able to accurately describe all the underlying physical processes and the influence of the initial assumptions needs to be well-characterized. In this presentation, we discuss and compare different methods (namely full-wave computations based on the surface integral equations method, mode analysis, the Miller’s rule, and the effective nonlinear susceptibility method) proposed for the evaluation of the SHG from plasmonic nanoparticles emphasizing their limitations and advantages. In particular, the design of double resonant antennas for efficient nonlinear conversion at the nanoscale is addressed in detail