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Philippe Vallée

Publications and source records attributed to Philippe Vallée.

6 recordsLinked to original sources
arXiv2026

ANDES, the high-resolution spectrograph for the ELT: design and performance analysis of the YJH spectrograph

The ArmazoNes high Dispersion Echelle Spectrograph (ANDES) is a powerful second-generation high-resolution spectroscopic instrument for the Extremely Large Telescope (ELT). The UBV, RIZ, and YJH modules comprise fibre-fed spectrographs of the ANDES baseline design and will offer continuous wavelength coverage of 0.35-1.8 $μ$m, with the addition of a K-band channel providing coverage up to 2.4 $μ$m. Coupled with a spectral resolution of $\sim$100,000, ANDES must deliver the required wavelength calibration stability of 1 m/s over 24 hours, with a goal of 0.02 m/s across 10 years. These requirements establish the framework for the infrared module of ANDES, the YJH Spectrograph, leading to what will likely be the largest cryogenic, ultra-stable, high-resolution spectrograph ever built, and will offer the unique ability to observe in both seeing- and diffraction-limited modes interchangeably. We present the current design and performance analysis of the ANDES YJH Spectrograph, outlining the engineering challenges encountered alongside the corresponding strategies adopted to navigate them. In particular, we detail the technology development of the primary dispersing element, an echelle grating mosaic that will span over a metre in length.

astro-ph.IM↗
arXiv2023

On-sky demonstration at Palomar Observatory of the near-IR, high-resolution VIPA spectrometer

A near-IR high-resolution, R=80000 spectrometer has been developed at IPAG to directly characterize the atmosphere of exoplanets using adaptive optics (AO) assisted telescopes, and a single-mode fiber-injection unit. A first technical test with the 200' Hale telescope at Palomar Observatory occurred in March 2022 using the PALM3000 AO system offered by this telescope. Observations have also been made at the same time with the PARVI spectrometer so that a direct comparison can be made between the two instruments. This spectrometer uses a virtually imaged phased array (VIPA) instead of an echelle grating, resulting in a very compact optical layout that fits in a 0.25m3 cryostat. Using a quarter of an H2RG detector, the spectrometer analyses the middle part of the H-band, from 1.57 to 1.7 microns for 2 sources whose light is transferred from the telescope to the spectrometer using single-mode fibers. By design, the transmission of the spectrometer is expected to be 40-50%, which is 2-3 times higher than the transmission of current high-resolution spectrometers such as CRIRES+ and NIRSPEC. A damaged cross-disperser limited it to 21%, however. A replacement grating with a correct, twice as high efficiency has been procured after the on-sky demonstration. In addition to recalling the main specifications of the VIPA spectrometer, this paper presents the control software, the calibration process, and the reduction pipeline that have been developed for the instrument. It also presents the results of the on-sky technical test with the Hale telescope, as well as measurements of the effective resolution and transmission, along with a comparison of a spectrum of the sun obtained with the spectrometer with the BASS2000 reference spectrum. Planned modifications are also discussed. That includes the integration of a new dedicated H2RG detector, and of K-band optics.

astro-ph.IM↗
arXiv2014

SPIRou: the near-infrared spectropolarimeter/high-precision velocimeter for the Canada-France-Hawaii telescope

SPIRou is a near-IR échelle spectropolarimeter and high-precision velocimeter under construction as a next-generation instrument for the Canada-France-Hawaii-Telescope. It is designed to cover a very wide simultaneous near-IR spectral range (0.98-2.35 μm) at a resolving power of 73.5K, providing unpolarized and polarized spectra of low-mass stars at a radial velocity (RV) precision of 1m/s. The main science goals of SPIRou are the detection of habitable super-Earths around low-mass stars and the study of how critically magnetic fields impact star / planet formation. Following a successful final design review in Spring 2014, SPIRou is now under construction and is scheduled to see first light in late 2017. We present an overview of key aspects of SPIRou's optical and mechanical design.

astro-ph.IM↗
arXiv2005

Raman Scattering of Water and Photoluminescence of Pollutants Arising from Solid-Water Interaction

Systematic Raman experiments performed on water and water-ethanol samples, stored in different containers (fused silica, polypropylene, soda-lime glass type III) for several hours, have shown that the luminescence contribution to the Raman signal fluctuations is directly related to the container composition. Intensity fluctuations as large as 98%, have been observed in the spectral regions corresponding to the both water intramolecular and intermolecular vibrations, despite the fact that the wavenumbers of the modes remained unchanged. We undoubtedly attribute these fluctuations to a luminescence phenomenon on the basis of : i) the absence of such effect in the anti-Stokes domain, ii) its dependence on the excitation laser wavelength, iii) other relevant photoluminescence experiments. This luminescence is attributed to pollutants at ultra-low concentration coming from the different containers.

physics.chem-ph↗
arXiv2005

Effects of pulsed low frequency electromagnetic fields on water using photoluminescence spectroscopy: role of bubble/water interface

The effects of a pulsed low frequency electromagnetic field were investigated on photoluminescence of well characterized water and prepared under controlled conditions (container, atmospheric, electromagnetic, and acoustic environments). When reference water samples were excited at 260 nm, two wide emission bands centered at 345 nm (3.6 eV) and 425 nm (2.9 eV) were observed. By contrast under 310 nm excitation, only one band appeared at 425 nm. Interestingly, electromagnetic treatment (EMT) induced, at both excitation wavelengths, a decrease (around 70%) in the 425 nm band relative photoluminescence intensity. However, no difference between reference and treated sample was observed in the 345 nm band. Other experiments, performed on outgassed samples (reference and treated), show that the emission bands (position, shape, intensity) under excitation at 260 nm and 310 nm were similar and close to the corresponding bands of the treated nonoutgassed samples. Similar effects were observed on photoluminescence excitation of water samples. Two excitation bands monitored at 425 nm were observed at 272 nm and 330 nm. After EMT and/or outgassing, a decrease (> 60%) was observed in the intensity of these two bands. Altogether, these results indicate that electromagnetic treatment and/or outgassing decrease in a similar fashion the photoluminescence intensity in water samples. They also suggest that this effect is most likely indirectly attributed to the presence of gas bubbles in water. The possible role of hydrated ionic shell around the bubbles in the observed extraluminescence is discussed.

physics.chem-ph↗