| 1. |
- Berne, Olivier, et al.
(author)
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PDRs4All : A JWST Early Release Science Program on Radiative Feedback from Massive Stars
- 2022
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In: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 134:1035
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Journal article (peer-reviewed)abstract
- Massive stars disrupt their natal molecular cloud material through radiative and mechanical feedback processes. These processes have profound effects on the evolution of interstellar matter in our Galaxy and throughout the universe, from the era of vigorous star formation at redshifts of 1-3 to the present day. The dominant feedback processes can be probed by observations of the Photo-Dissociation Regions (PDRs) where the far-ultraviolet photons of massive stars create warm regions of gas and dust in the neutral atomic and molecular gas. PDR emission provides a unique tool to study in detail the physical and chemical processes that are relevant for most of the mass in inter- and circumstellar media including diffuse clouds, proto-planetary disks, and molecular cloud surfaces, globules, planetary nebulae, and star-forming regions. PDR emission dominates the infrared (IR) spectra of star-forming galaxies. Most of the Galactic and extragalactic observations obtained with the James Webb Space Telescope (JWST) will therefore arise in PDR emission. In this paper we present an Early Release Science program using the MIRI, NIRSpec, and NIRCam instruments dedicated to the observations of an emblematic and nearby PDR: the Orion Bar. These early JWST observations will provide template data sets designed to identify key PDR characteristics in JWST observations. These data will serve to benchmark PDR models and extend them into the JWST era. We also present the Science-Enabling products that we will provide to the community. These template data sets and Science-Enabling products will guide the preparation of future proposals on star-forming regions in our Galaxy and beyond and will facilitate data analysis and interpretation of forthcoming JWST observations.
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| 2. |
- Mølster, Kjell Martin, 1992-, et al.
(author)
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Highly efficient, high average power, narrowband, pump-tunable BWOPO
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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.
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| 3. |
- Mølster, Kjell Martin, 1992-, et al.
(author)
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Highly efficient, high average power, narrowband, pump-tunable BWOPO
- 2023
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In: Optics Letters. - : Optica Publishing Group. - 0146-9592 .- 1539-4794. ; 48:24, s. 6484-6487
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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.
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| 4. |
- Mølster, Kjell Martin, 1992-, et al.
(author)
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Low-threshold Highly Efficient Backward Wave OPO
- 2022
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In: Nonlinear Photonics, NP 2022. - : Optica Publishing Group (formerly OSA).
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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%.
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| 5. |
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| 6. |
- Mølster, Kjell Martin, 1992-, et al.
(author)
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Pump Tunable Mirrorless OPO : an Innovative Concept for Future Space IPDA Emitters
- 2023
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In: International Conference on Space Optics, ICSO 2022. - : SPIE-Intl Soc Optical Eng.
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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.
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| 7. |
- Schulz, Rita, et al.
(author)
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Comet 67P/Churyumov-Gerasimenko sheds dust coat accumulated over the past four years
- 2015
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In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 518:7538, s. 216-218
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Journal article (peer-reviewed)abstract
- Comets are composed of dust and frozen gases. The ices are mixed with the refractory material either as an icy conglomerate, or as an aggregate of pre-solar grains (grains that existed prior to the formation of the Solar System), mantled by an ice layer. The presence of water-ice grains in periodic comets is now well established. Modelling of infrared spectra obtained about ten kilometres from the nucleus of comet Hartley 2 suggests that larger dust particles are being physically decoupled from fine-grained water-ice particles that may be aggregates, which supports the icy-conglomerate model. It is known that comets build up crusts of dust that are subsequently shed as they approach perihelion. Micrometre-sized interplanetary dust particles collected in the Earth's stratosphere and certain micrometeorites are assumed to be of cometary origin. Here we report that grains collected from the Jupiter-family comet 67P/Churyumov-Gerasimenko come from a dusty crust that quenches the material outflow activity at the comet surface. The larger grains (exceeding 50 micrometres across) are fluffy (with porosity over 50 per cent), and many shattered when collected on the target plate, suggesting that they are agglomerates of entities in the size range of interplanetary dust particles. Their surfaces are generally rich in sodium, which explains the high sodium abundance in cometary meteoroids. The particles collected to date therefore probably represent parent material of interplanetary dust particles. This argues against comet dust being composed of a silicate core mantled by organic refractory material and then by a mixture of water-dominated ices. At its previous recurrence (orbital period 6.5 years), the comet's dust production doubled when it was between 2.7 and 2.5 astronomical units from the Sun, indicating that this was when the nucleus shed its mantle. Once the mantle is shed, unprocessed material starts to supply the developing coma, radically changing its dust component, which then also contains icy grains, as detected during encounters with other comets closer to the Sun.
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