| 1. |
- Mølster, Kjell Martin, 1992-, et al.
(author)
-
Highly efficient, high average power, narrowband, pump-tunable BWOPO
-
Other publication (other academic/artistic)abstract
- We demonstrate a continuously tunable mid-infrared source that produces narrowband radiation at 1981 nm and 2145 nm based on a tunable Yb-based hybrid MOPA pump and backward-wave optical parametric oscillator (BWOPO). The BWOPO employs PPRKTP crystal with 580 nm domain periodicity. The BWOPO has a record-low oscillation threshold of 19.2 MW/cm2 and generates mJ-level output with efficiency exceeding 70%, reaching average power of 5.65W at the repetition rate of 5 KHz. The system is mechanically robust and optical cavity-free, making it suitable for spectroscopic systems on mobile platforms. The MIR signal frequency is tuned by pump tuning with a linear pump-to-signal frequency translation rate of 1-to-1.001 Hz/Hz. The tuning range of 10 GHz is demonstrated only limited by choice of the seed laser in the Yb-based MOPA system.
|
|
| 2. |
- Mølster, Kjell Martin, 1992-, et al.
(author)
-
Highly efficient, high average power, narrowband, pump-tunable BWOPO
- 2023
-
In: Optics Letters. - : Optica Publishing Group. - 0146-9592 .- 1539-4794. ; 48:24, s. 6484-6487
-
Journal article (peer-reviewed)abstract
- We demonstrate a continuously tunable mid-infrared source that produces narrowband radiation at 1981 nm and 2145 nm based on a tunable Yb-based hybrid MOPA pump and a backward-wave optical parametric oscillator (BWOPO). The BWOPO employs a PPRKTP crystal with 580 nm domain periodicity. The BWOPO has a record-low oscillation threshold of 19.2 MW/cm2 and generates mJ level output with an overall efficiency exceeding 70%, reaching an average power of 5.65W at the repetition rate of 5 kHz. The system is mechanically robust and optical cavity-free, making it suitable for spectroscopic systems on mobile platforms. The mid-infrared signal frequency is tuned by pump tuning with a linear pump-to-signal frequency translation rate close to the predicted 1 to 1.001 Hz/Hz.
|
|
| 3. |
- Mølster, Kjell Martin, 1992-, et al.
(author)
-
Low-threshold Highly Efficient Backward Wave OPO
- 2022
-
In: Nonlinear Photonics, NP 2022. - : Optica Publishing Group (formerly OSA).
-
Conference paper (peer-reviewed)abstract
- Cavity-free, precision-tunable source of a nanosecond, mJ-level, pulses consisting of backward optical parametric oscillator pumped by diode-seeded laser amplifier shows a record threshold of 19 MW/cm2 and an optical-to-optical efficiency exceeding 70%.
|
|
| 4. |
|
|
| 5. |
- Mølster, Kjell Martin, 1992-, et al.
(author)
-
Pump Tunable Mirrorless OPO : an Innovative Concept for Future Space IPDA Emitters
- 2023
-
In: International Conference on Space Optics, ICSO 2022. - : SPIE-Intl Soc Optical Eng.
-
Conference paper (peer-reviewed)abstract
- A highly efficient mirrorless OPO tunable in the mid-infrared around 2 μm has been developed and characterized in an original pumping configuration comprising a tunable high power hybrid Ytterbium laser MOPA (Master Oscillator Power Amplifier) in the nanosecond regime. The hybrid pump laser is based on a fiber laser seeder continuously tunable over several GHz at 1030 nm, which is shaped in the time domain with acousto-optic modulators (AOM), and power amplified in a dual stage Ytterbium doped fiber amplifiers, followed by two Yb:YAG bulk amplifiers. The pump delivers up to 3.5 mJ of energy within narrowband 15 ns pulses with a 5 kHz repetition rate. The output was focused into Periodically Poled KTP (PPKTP) crystals with a quasi-Phase Matching (QPM) period of 580 nm, producing Backward Optical Parametric Oscillation (BWOPO), with a forward signal wave at 1981 nm and a backward traveling idler at 2145 nm. We report significant optical to optical efficiencies exceeding 70 % depending on crystal length and input power. As theoretically expected, the forward wave could be continuously tuned over 10 GHz following the pump frequency sweep, while the backward wave remains almost stable, both being free from mode hops. These properties obtained from an optical arrangement without free-space cavities are attractive for future space Integrated Path Differential Absorption (IPDA) Lidar applications, which require robust and efficient tunable frequency converters in the mid-infrared.
|
|
| 6. |
- Abercrombie, Daniel, et al.
(author)
-
Dark Matter benchmark models for early LHC Run-2 Searches : Report of the ATLAS/CMS Dark Matter Forum
- 2020
-
In: Physics of the Dark Universe. - : Elsevier BV. - 2212-6864. ; 27
-
Journal article (peer-reviewed)abstract
- This document is the final report of the ATLAS-CMS Dark Matter Forum, a forum organized by the ATLAS and CMS collaborations with the participation of experts on theories of Dark Matter, to select a minimal basis set of dark matter simplified models that should support the design of the early LHC Run-2 searches. A prioritized, compact set of benchmark models is proposed, accompanied by studies of the parameter space of these models and a repository of generator implementations. This report also addresses how to apply the Effective Field Theory formalism for collider searches and present the results of such interpretations.
|
|
| 7. |
- Ademuyiwa, Adesoji O., et al.
(author)
-
Determinants of morbidity and mortality following emergency abdominal surgery in children in low-income and middle-income countries
- 2016
-
In: BMJ Global Health. - : BMJ Publishing Group Ltd. - 2059-7908. ; 1:4
-
Journal article (peer-reviewed)abstract
- Background: Child health is a key priority on the global health agenda, yet the provision of essential and emergency surgery in children is patchy in resource-poor regions. This study was aimed to determine the mortality risk for emergency abdominal paediatric surgery in low-income countries globally.Methods: Multicentre, international, prospective, cohort study. Self-selected surgical units performing emergency abdominal surgery submitted prespecified data for consecutive children aged <16 years during a 2-week period between July and December 2014. The United Nation's Human Development Index (HDI) was used to stratify countries. The main outcome measure was 30-day postoperative mortality, analysed by multilevel logistic regression.Results: This study included 1409 patients from 253 centres in 43 countries; 282 children were under 2 years of age. Among them, 265 (18.8%) were from low-HDI, 450 (31.9%) from middle-HDI and 694 (49.3%) from high-HDI countries. The most common operations performed were appendectomy, small bowel resection, pyloromyotomy and correction of intussusception. After adjustment for patient and hospital risk factors, child mortality at 30 days was significantly higher in low-HDI (adjusted OR 7.14 (95% CI 2.52 to 20.23), p<0.001) and middle-HDI (4.42 (1.44 to 13.56), p=0.009) countries compared with high-HDI countries, translating to 40 excess deaths per 1000 procedures performed.Conclusions: Adjusted mortality in children following emergency abdominal surgery may be as high as 7 times greater in low-HDI and middle-HDI countries compared with high-HDI countries. Effective provision of emergency essential surgery should be a key priority for global child health agendas.
|
|
| 8. |
- Deyra, Loïc, et al.
(author)
-
High power single-crystal fiber CW 946 nm laser and blue generation based on Rubidium-doped PPKTP
- 2013
-
In: 2013 Conference on Lasers and Electro-Optics Europe and International Quantum Electronics Conference. - : IEEE conference proceedings.
-
Conference paper (peer-reviewed)abstract
- Blue lasers have numerous applications in spectroscopy, underwater communication and material processing. Direct emission in the blue region can be achieved with laser diodes, with powers up to the watt level [1]. Higher powers require efficient laser operating around 950 nm to be frequency doubled to the blue spectrum, which usually suffer from a lower gain than conventional 1μm lasers. Generally, intracavity frequency doubling set-ups and pulsed operation are used to increase the second harmonic generation efficiency, with output powers up to 4 W in cw[2] and 1.3W in pulsed regime [3]. In the past few years, both lasers materials and non linear crystals have progressed enough to allow the very simple extracavity frequency doubling of continuous wave lasers in periodically poled materials to acceptable powers[4].
|
|
| 9. |
- Dherbecourt, Jean Baptiste, et al.
(author)
-
Injection-Free and Cavity Free Parametric Sources for Future Spaceborne DIAL Based on Periodically Poled Nonlinear Materials
- 2024
-
In: Springer Aerospace Technology. - : Springer Nature. ; , s. 363-371
-
Book chapter (other academic/artistic)abstract
- We present new parametric source architectures for future spaceborne Differential Absorption Lidar (DIAL). This work focalizes on the developments performed during LEMON H2020 project using periodically poled nonlinear crystals. Such phase matching configuration offers the possibility to go towards more simple and robust set-ups for future space operation. We investigated injection-free optical parametric oscillator OPO set-ups, such as the Nested Cavity OPO–which allows a broad tuning range and thus can address several gas species with a single OPO—and also propose an injection and cavity free OPO solution using the counter-propagating phase matching configuration (Backward wave OPO). Moreover, we studied the implementation of high efficiency optical parametric amplifiers, to investigate the possibility to scale the output energies to several tens of mJ in the 2 µm region, and performed radiation testing on the specifically developed, large aperture, periodically poled KTP crystals.
|
|
| 10. |
- Johansson, Sandra, 1974-
(author)
-
Concepts for compact solid-state lasers in the visible and UV
- 2006
-
Doctoral thesis (other academic/artistic)abstract
- In many fields, scientific or industrial, optical devices that can be tailored in terms of spectral qualities and output power depending on the application in question are attractive. Nonlinear optics in combination with powerful laser sources provide a tool to achieve essentially any wavelength in the electromagnetic spectrum, and the advancement of material technology during the last decade has opened up new possibilities in terms of realising such devices. The main part of the thesis deals with the development of compact functional lasers based on nonlinear interaction utilising diode-pumped solid-state lasers and also laser diodes. Efficient frequency conversion into the visible and ultraviolet part of the electromagnetic spectrum has been achieved, using both Nd:YAG and Nd:YVO4 lasers as well as a semiconductor laser as the fundamental light sources. For the nonlinear conversion, periodically poled potassium titanyl phosphate (PPKTP), bismuth triborate (BiBO) and beta barium borate (BBO) have been employed. In the search for compact and reliable light sources emitting in the visible part of the spectrum, two different approaches have been explored. First, a scheme based on sum-frequency mixing of a diode-pumped solid-state laser and a laser diode of good beam quality. The idea of this approach is to take advantage of the individual strength of each device, which would be the flexibility in terms of wavelength for the laser diode and the possibility to reach high output power from the diode-pumped solid-state laser. Second, by mixing two different solid-state lasers substantially more output power could be generated albeit at a cost of less freedom in the choice of spectral output. As these two light sources had their central wavelength at 492 nm and 593 nm, respectively, they are highly interesting in biomedical applications since they correspond to the peak absorption of several popular fluorophores. In applications such as lithography, material synthesis and fibre grating fabrication, laser sources emitting in the deep-UV spectrum are desired. An all solid-state 236 nm laser source with 20 mW of average power have been designed and constructed, by frequency-quadrupling a passively Q-switched Nd:YAG laser lasing on a quasi-three level transition. Also, a novel concept for miniaturising solid-state lasers has been examined. Using a heat-conductive polymer carrier, a generic approach especially suited for mass-production of functional laser devices is presented. Finally, it has been proven that GRIN lenses can provide a very compact beam shaping solution to standard laser diodes based on the beam twisting approach. This method offers several advantages such as compactness of the beam shaping system, automated assembly in solid-state laser manufacturing due to the shape of these lenses and polarisation preservation of the laser diode output.
|
|
| 11. |
- Kudrnovsky, Josef, et al.
(author)
-
Exchange interactions and critical temperatures in diluted magnetic semiconductors
- 2004
-
In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 16:48, s. S5571-S5578
-
Journal article (peer-reviewed)abstract
- A first-principles approach to magnetic properties of diluted magnetic semiconductors (DMS) is presented that is based on the local spin-density approximation (LSDA) as implemented in the framework of the tight-binding linear muffin-tin orbital method, while the effect of randomness is described by the coherent potential approximation. Application of a real-space Green-function formalism yields the exchange pair interactions between distant magnetic atoms that are needed for quantitative studies of magnetic excitations including the Curie temperatures. We have found that the pair exchange interactions exhibit a strong directional dependence and are exponentially damped with increasing distance between magnetic atoms due to disorder and the half-metallic character of the DMS. As a case study we consider (Ga, Mn) As, (Ga, Mn)N, and (Zn, Cr)Te alloys. The calculations demonstrate that inclusion of disorder and, in particular, realistic distances among magnetic impurities, are needed to obtain critical temperatures which are in good agreement with available experiments.
|
|
| 12. |
- Kunder, Andrea, et al.
(author)
-
THE RADIAL VELOCITY EXPERIMENT (RAVE) : FIFTH DATA RELEASE
- 2017
-
In: The Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 153:2
-
Journal article (peer-reviewed)abstract
- Data Release 5 (DR5) of the Radial Velocity Experiment (RAVE) is the fifth data release from a magnitude-limited (9 < I < 12) survey of stars randomly selected in the Southern Hemisphere. The RAVE medium-resolution spectra (R ∼ 7500) covering the Ca-triplet region (8410-8795 A) span the complete time frame from the start of RAVE observations in 2003 to their completion in 2013. Radial velocities from 520,781 spectra of 457,588 unique stars are presented, of which 255,922 stellar observations have parallaxes and proper motions from the Tycho-Gaia astrometric solution in Gaia DR1. For our main DR5 catalog, stellar parameters (effective temperature, surface gravity, and overall metallicity) are computed using the RAVE DR4 stellar pipeline, but calibrated using recent K2 Campaign 1 seismic gravities and Gaia benchmark stars, as well as results obtained from high-resolution studies. Also included are temperatures from the Infrared Flux Method, and we provide a catalog of red giant stars in the dereddened color - (J Ks) 0 interval (0.50, 0.85) for which the gravities were calibrated based only on seismology. Further data products for subsamples of the RAVE stars include individual abundances for Mg, Al, Si, Ca, Ti, Fe, and Ni, and distances found using isochrones. Each RAVE spectrum is complemented by an error spectrum, which has been used to determine uncertainties on the parameters. The data can be accessed via the RAVE Web site or the VizieR database.
|
|
| 13. |
|
|
| 14. |
- Sestito, Federico, et al.
(author)
-
The Pristine survey – X. A large population of low-metallicity stars permeates the Galactic disc
- 2020
-
In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 497:1, s. L7-L12
-
Journal article (peer-reviewed)abstract
- The orbits of the least chemically enriched stars open a window on the formation of our Galaxy when it was still in its infancy. The common picture is that these low-metallicity stars are distributed as an isotropic, pressure-supported component since these stars were either accreted from the early building blocks of the assembling Milky Way (MW), or were later brought by the accretion of faint dwarf galaxies. Combining the metallicities and radial velocities from the Pristine and LAMOST surveys and Gaia DR2 parallaxes and proper motions for an unprecedented large and unbiased sample of 1027 very metal poor stars at [Fe/H] ≤ −2.5 dex, we show that this picture is incomplete. We find that 31 per cent of the stars that currently reside spatially in the disc (|Z|≤3kpc) do not venture outside of the disc plane throughout their orbit. Moreover, this sample shows strong statistical evidence (at the 5.0σ level) of asymmetry in their kinematics, favouring prograde motion. The discovery of this population implies that a significant fraction of stars with iron abundances [Fe/H] ≤ −2.5 dex merged into, formed within, or formed concurrently with the MW disc and that the history of the disc was quiet enough to allow them to retain their disc-like orbital properties, challenging theoretical and cosmological models.
|
|
| 15. |
- Vaccarella, Salvatore, et al.
(author)
-
Socioeconomic inequalities in cancer mortality between and within countries in Europe : a population-based study
- 2023
-
In: The Lancet Regional Health. - : Elsevier. - 2666-7762. ; 25
-
Journal article (peer-reviewed)abstract
- BACKGROUND: Reducing socioeconomic inequalities in cancer is a priority for the public health agenda. A systematic assessment and benchmarking of socioeconomic inequalities in cancer across many countries and over time in Europe is not yet available.METHODS: Census-linked, whole-of-population cancer-specific mortality data by socioeconomic position, as measured by education level, and sex were collected, harmonized, analysed, and compared across 18 countries during 1990-2015, in adults aged 40-79. We computed absolute and relative educational inequalities; temporal trends using estimated-annual-percentage-changes; the share of cancer mortality linked to educational inequalities.FINDINGS: Everywhere in Europe, lower-educated individuals have higher mortality rates for nearly all cancer-types relative to their more highly-educated counterparts, particularly for tobacco/infection-related cancers [relative risk of lung cancer mortality for lower- versus higher-educated = 2.4 (95% confidence intervals: 2.1-2.8) among men; = 1.8 (95% confidence intervals: 1.5-2.1) among women]. However, the magnitude of inequalities varies greatly by country and over time, predominantly due to differences in cancer mortality among lower-educated groups, as for many cancer-types higher-educated have more similar (and lower) rates, irrespective of the country. Inequalities were generally greater in Baltic/Central/East-Europe and smaller in South-Europe, although among women large and rising inequalities were found in North-Europe (relative risk of all cancer mortality for lower- versus higher-educated ≥1.4 in Denmark, Norway, Sweden, Finland and the England/Wales). Among men, rate differences (per 100,000 person-years) in total-cancer mortality for lower-vs-higher-educated groups ranged from 110 (Sweden) to 559 (Czech Republic); among women from approximately null (Slovenia, Italy, Spain) to 176 (Denmark). Lung cancer was the largest contributor to inequalities in total-cancer mortality (between-country range: men, 29-61%; women, 10-56%). 32% of cancer deaths in men and 16% in women (but up to 46% and 24%, respectively in Baltic/Central/East-Europe) were associated with educational inequalities.INTERPRETATION: Cancer mortality in Europe is largely driven by levels and trends of cancer mortality rates in lower-education groups. Even Nordic-countries, with a long-established tradition of equitable welfare and social justice policies, witness increases in cancer inequalities among women. These results call for a systematic measurement, monitoring and action upon the remarkable socioeconomic inequalities in cancer existing in Europe.FUNDING: This study was done as part of the LIFEPATH project, which has received financial support from the European Commission (Horizon 2020 grant number 633666), and the DEMETRIQ project, which received support from the European Commission (grant numbers FP7-CP-FP and 278511). SV and WN were supported by the French Institut National du Cancer (INCa) (Grant number 2018-116). PM was supported by the Academy of Finland (#308247, # 345219) and the European Research Council under the European Union's Horizon 2020 research and innovation programme (grant agreement No 101019329). The work by Mall Leinsalu was supported by the Estonian Research Council (grant PRG722).
|
|
| 16. |
- Woithe, Julia, et al.
(author)
-
Higgs in a Box : Investigating the Nature of a Scientific Discovery
- 2022
-
In: The Physics Educator. - 2661-3395. ; 4:4
-
Journal article (peer-reviewed)abstract
- The discovery of the Higgs boson by the ATLAS and CMS collaborations in 2012 concluded the longest search for a particle in the history of particle physics and was based on the largest and most complex physics experiments ever conducted, involving thousands of scientists and engineers from around the world. It provided crucial evidence for a theory developed in the 1960s that describes the existence of the invisible Brout-Englert-Higgs field and the effects of this field on the mass of elementary particles. After the discovery, the work on the theoretical prediction was awarded the Nobel Prize in Physics 2013. This discovery provides a prime example of modern science in the making and a fantastic opportunity to discuss important aspects of Nature of Science (NoS) in the classroom. In this article, we draw connections between (a) milestones in the discovery of the Higgs boson, (b) important aspects of NoS, and (c) hands-on activities with mystery boxes, which are an effective tool to enable students to experience elements of scientific discovery and explicitly reflect on NoS. We hope that this supports educators in bringing lively discussions about modern physics research into their classrooms.
|
|
| 17. |
- Abbafati, Cristiana, et al.
(author)
-
- 2020
-
Journal article (peer-reviewed)
|
|
