255 research outputs found
Periodically domain−structured KTiOPO4 crystals grown from high temperature solution
International audiencePeriodically-poled ferroelectric crystals proved to be the most promising technique for exploiting at the best nonlinear optical frequency conversion properties of materials using quasi-phase matching (QPM). Until now the common method for obtaining periodically-poled ferroelectric crystals is by electric-field poling. In this technique local inversion of the spontaneous polarization is produced in a single-domain crystal by applying an electric field on a periodic electrode deposited on the crystal surface. The poling technology for nonlinear crystals like KTiOPO4, LiNbO3 and LiTaO3 is by now reliable to produce QPM gratings with periods down to about 8 µm. But the thickness of the periodically poled slabs is restricted to 1 mm for these gratings periods, which limits their use to low- and medium- power applications
Bulk PPKTP by crystal growth from high temperature solution
International audiencePeriodically-poled ferroelectric crystals show unprecedented efficiency and properties otherwise impossible to obtain. Unfortunately, the sample thickness obtainable today limits their use to low and moderate power application. With the aim of increasing the size of periodically domain-structured crystals with a controlled and regular grating period, we proposed an epitaxial growth process using seeds made of thin plates domain engineered by electric field poling. We demonstrated this process with the ferroelectric crystal KTiOPO4 (KTP) which is one of the most promising candidate materials for that purpose. The poling step requires a sample exhibiting (001) and (00 (1) over bar) faces, so that the growth step has to be performed onto these faces. This constraint is a difficulty to circumvent as these faces are not present in the standard equilibrium morphology. It is then necessary to find the growth conditions enabling to work below the roughening temperature of these faces. By using a high temperature solution method, the so-called "flux method", and by choosing an appropriate chemical composition of the flux solution, we obtained periodically domain-structured KTP layers with thicknesses up to 800 mu m and regular periodicity onto (001) and (00 (1) over bar) faces of the initial PPKTP seeds
Template-growth of periodically domain-structured KTiOPO4
International audienceWe performed the first growth, from a high temperature solution, of a 38.86 μm-periodicity PPKTP crystal of good optical quality over a thickness of more than 800 μm onto each of the two faces perpendicular to the c direction of a PPKTP substrate previously obtained by electric field poling. The quasi-phase matched second harmonic generation properties in the grown layer and substrate are similar and in accordance with calculation
Effect of the cooling rate on encapsulant's crystallinity and optical properties, and photovoltaic modules' lifetime
Since the renewable energy thrive, performances and lifetime of photovoltaic (PV) modules have been one of the big international concern. The mechanical bonding between the different components and the materials' choice can significantly improve both performances and lifetime of PV modules. The manufacturing process plays also a significant part in the modules lifetime [G. Oreski, B. Ottersböck, A. Omazic, Degradation Processes and Mechanisms of Encapsulants, in Durability and Reliability of Polymers and Other Materials in Photovoltaic Modules (Elsevier, 2019), pp. 135–152]. This work deals with the controlled cooling part of the manufacturing process. The aim is to characterize its influence on an encapsulant properties, and its influences on modules degradation. This work is a part of improving both performances and lifetime of PV modules. First, the work focuses on describing the real temperature seen by a thermoplastic polyolefin encapsulant during the lamination process. A multi-chamber R&D laminator is used and studied in order to better know the industrial equipment. Results show that the cooling process reduces the time to cool down by a factor of ∼5 compared to natural air convection. Secondly, the material's micro-structure is analysed by Differential Scanning Calorimetry (DSC). The impact of the process is quantified. It does have an influence on the encapsulant crystallites' size distribution without modifying the total crystallinity. Thirdly, the impact of the cooling process on optical properties is investigated. Using spectrophotometry and haze-metry optical characterization, coupled with a known light spectrum, the light intensity coming out from the material is analysed. Results show that the cooling process does not have any influence on transmittance nor reflectance. However, a 34% reduction in the haze factor is recorded when using the industrial laminator cooling process. Fourthly, mechanical bond strength between glass and encapsulant is characterized over ageing. Normalized 10 mm width strips are used to estimate the bond strength. It demonstrates that applying pressure during cooling does not influence the bond strength between glass and encapsulant after 1000 h of damp heat ageing. Finally, impact of the cooling process over ageing on PV modules is discussed. Two accelerating ageing methods, 300 Thermal Cycles and 1000 h damp heat, are used to speed up ageing processes. The electrical components of the PV modules are analysed and used to assess the modules' degradation. Modules manufactured with the cooling process are more sensitive to damp heat after 500 h than modules cooled by natural convection. No significant differences were found in thermal cycling ageing
: Gender differences in STEMI
International audienceBACKGROUND: Gender differences in presentation, management and outcome in patients with ST-segment elevation myocardial infarction (STEMI) have been reported. AIM: To determine whether female gender is associated with higher inhospital mortality. METHODS: Data from ORBI, a regional STEMI registry of 5 years' standing, were analysed. The main data on presentation, management, inhospital outcome and prescription at discharge were compared between genders. Various adjusted hazard ratios were then calculated for inhospital mortality (women versus men). RESULTS: The analysis included 5000 patients (mean age 62.6±13 years), with 1174 women (23.5%). Women were on average 8 years older than men, with more frequent co-morbidities. Median ischaemia time was 215 minutes (26 minutes longer in women; P<0.05). Reperfusion strategies in women less frequently involved fibrinolysis, coronary angiography, radial access and thrombo-aspiration. Female gender, especially in patients aged<60 years, was associated with poorer inhospital prognosis (including higher inhospital mortality: 9% vs. 4% in men; P<0.0001), and underutilization of recommended treatments at discharge. Moreover, excess female inhospital mortality was independent of presentation, revascularization time and reperfusion strategy (hazard ratio for women 1.33, 95% confidence interval 1.01-1.76; P=0.04). CONCLUSIONS: One in four patients admitted for STEMI was female, with significant differences in presentation. Female gender was associated with less-optimal treatment, both in the acute-phase and at discharge. Efforts should be made to reduce these differences, especially as female gender was independently associated with an elevated risk of inhospital mortality
PDRs4All IV. An embarrassment of riches: Aromatic infrared bands in the Orion Bar
(Abridged) Mid-infrared observations of photodissociation regions (PDRs) are
dominated by strong emission features called aromatic infrared bands (AIBs).
The most prominent AIBs are found at 3.3, 6.2, 7.7, 8.6, and 11.2 m. The
most sensitive, highest-resolution infrared spectral imaging data ever taken of
the prototypical PDR, the Orion Bar, have been captured by JWST. We provide an
inventory of the AIBs found in the Orion Bar, along with mid-IR template
spectra from five distinct regions in the Bar: the molecular PDR, the atomic
PDR, and the HII region. We use JWST NIRSpec IFU and MIRI MRS observations of
the Orion Bar from the JWST Early Release Science Program, PDRs4All (ID: 1288).
We extract five template spectra to represent the morphology and environment of
the Orion Bar PDR. The superb sensitivity and the spectral and spatial
resolution of these JWST observations reveal many details of the AIB emission
and enable an improved characterization of their detailed profile shapes and
sub-components. While the spectra are dominated by the well-known AIBs at 3.3,
6.2, 7.7, 8.6, 11.2, and 12.7 m, a wealth of weaker features and
sub-components are present. We report trends in the widths and relative
strengths of AIBs across the five template spectra. These trends yield valuable
insight into the photochemical evolution of PAHs, such as the evolution
responsible for the shift of 11.2 m AIB emission from class B in
the molecular PDR to class A in the PDR surface layers. This
photochemical evolution is driven by the increased importance of FUV processing
in the PDR surface layers, resulting in a "weeding out" of the weakest links of
the PAH family in these layers. For now, these JWST observations are consistent
with a model in which the underlying PAH family is composed of a few species:
the so-called 'grandPAHs'.Comment: 25 pages, 10 figures, to appear in A&
PDRs4All III: JWST's NIR spectroscopic view of the Orion Bar
(Abridged) We investigate the impact of radiative feedback from massive stars
on their natal cloud and focus on the transition from the HII region to the
atomic PDR (crossing the ionisation front (IF)), and the subsequent transition
to the molecular PDR (crossing the dissociation front (DF)). We use
high-resolution near-IR integral field spectroscopic data from NIRSpec on JWST
to observe the Orion Bar PDR as part of the PDRs4All JWST Early Release Science
Program. The NIRSpec data reveal a forest of lines including, but not limited
to, HeI, HI, and CI recombination lines, ionic lines, OI and NI fluorescence
lines, Aromatic Infrared Bands (AIBs including aromatic CH, aliphatic CH, and
their CD counterparts), CO2 ice, pure rotational and ro-vibrational lines from
H2, and ro-vibrational lines HD, CO, and CH+, most of them detected for the
first time towards a PDR. Their spatial distribution resolves the H and He
ionisation structure in the Huygens region, gives insight into the geometry of
the Bar, and confirms the large-scale stratification of PDRs. We observe
numerous smaller scale structures whose typical size decreases with distance
from Ori C and IR lines from CI, if solely arising from radiative recombination
and cascade, reveal very high gas temperatures consistent with the hot
irradiated surface of small-scale dense clumps deep inside the PDR. The H2
lines reveal multiple, prominent filaments which exhibit different
characteristics. This leaves the impression of a "terraced" transition from the
predominantly atomic surface region to the CO-rich molecular zone deeper in.
This study showcases the discovery space created by JWST to further our
understanding of the impact radiation from young stars has on their natal
molecular cloud and proto-planetary disk, which touches on star- and planet
formation as well as galaxy evolution.Comment: 52 pages, 30 figures, submitted to A&
PDRs4All II: JWST's NIR and MIR imaging view of the Orion Nebula
The JWST has captured the most detailed and sharpest infrared images ever
taken of the inner region of the Orion Nebula, the nearest massive star
formation region, and a prototypical highly irradiated dense photo-dissociation
region (PDR). We investigate the fundamental interaction of far-ultraviolet
photons with molecular clouds. The transitions across the ionization front
(IF), dissociation front (DF), and the molecular cloud are studied at
high-angular resolution. These transitions are relevant to understanding the
effects of radiative feedback from massive stars and the dominant physical and
chemical processes that lead to the IR emission that JWST will detect in many
Galactic and extragalactic environments. Due to the proximity of the Orion
Nebula and the unprecedented angular resolution of JWST, these data reveal that
the molecular cloud borders are hyper structured at small angular scales of
0.1-1" (0.0002-0.002 pc or 40-400 au at 414 pc). A diverse set of features are
observed such as ridges, waves, globules and photoevaporated protoplanetary
disks. At the PDR atomic to molecular transition, several bright features are
detected that are associated with the highly irradiated surroundings of the
dense molecular condensations and embedded young star. Toward the Orion Bar
PDR, a highly sculpted interface is detected with sharp edges and density
increases near the IF and DF. This was predicted by previous modeling studies,
but the fronts were unresolved in most tracers. A complex, structured, and
folded DF surface was traced by the H2 lines. This dataset was used to revisit
the commonly adopted 2D PDR structure of the Orion Bar. JWST provides us with a
complete view of the PDR, all the way from the PDR edge to the substructured
dense region, and this allowed us to determine, in detail, where the emission
of the atomic and molecular lines, aromatic bands, and dust originate
- …