The spectrum of N₂ from 4,500 to 15,700 cm⁻¹ revisited with PGOPHER

International audienceUsing a reference molecular atlas to ensure self-consistency of wavelength calibration is widespread practice. Boesch & Reiners (Astronomy & Astrophysics 582 A43 (2015)) reported a line list from a discharge of molecular nitrogen from 4500 to 11000 cm −1 for this purpose. With a hollow-cathode discharge source, we have extended the experimental spectrum up to 15700 cm −1 , to include the range of Ti:sapphire lasers, since the density of N 2 lines is greater than atomic atlases in common use. Recognizing that experimental conditions can vary, we have also analysed the spectra (comprising several B ³Π g-A ³Σ u + , B' ³Σ u −-B ³Π g , and W ³Δ u-B ³Π g N 2 bands) with standard Hamiltonians, so that any part of the discharge spectrum 4500-15700 cm −1 can be simulated. Parameters are given to do this with the spectral simulation and analysis package PGOPHER. (C. Western, J. Quant. Spectrosc. Rad. Transf., 186, 221 (2016)). The analysis also included high-level ab initio calculations of potential energy curves, transition moments and spin-orbit coupling constants and these were used in preparing the model, extending the potential range of applicability. The results are available in a variety of formats to suit possible applications, including the experimental spectrum in ASCII, a detailed line list with positions and Einstein A coefficients, and a PGOPHER input file to synthesize the spectrum at selectable temperature and resolution.

Axion Search by Laser-based Experiment OSQAR

International audienceLaser-based experimentOSQAR in CERN is aimed to the search of the axions by twomethods. The photon regeneration experiment is using two LHC dipole magnets of the length 14.3 m and magnetic field 9.5 T equipped with an optical barrier at the end of the first magnet. It looks as light shining through the wall. No excess of events above the background was detected at this arrangement. Nevertheless, this result extends the exclusion region for the axion mass. The second method wants to measure the ultra-fine Vacuum Magnetic Birefringence for the first time. An optical scheme with electro-optical modulator has been proposed, validated and subsequently improved. Cotton-Mouton constant for air was determined in this experiment setup

Progress of the Laser-based Experiment OSQAR

International audienceOSQAR experiment at CERN is based on two laser methods for search of axions and scalar particles. The light shining through the wall experiment has been using two LHC dipole magnets with an optical barrier, argon laser, and cooled 2D CCD detector for the measuring of expected regenerated photons. The second method wants to measure the Vacuum Magnetic Birefringence. An optical set-up with electro-optical modulator has been proposed, validated and subsequently improved in collaborating institutes. Cotton-Muton effect in nitrogen was measured by this method. Prototype of a one-meter long laser cavity was developed for this experiment

Shot-noise-limited measurement of sub-parts-per-trillion birefringence phase shift in a high-finesse cavity

International audienceWe report on a promising approach to high-sensitivity anisotropy measurements using a high-finesse cavity locked by optical feedback to a diode laser. We provide a simple and effective way to decouple the weak anisotropy of interest from the inherent mirror's birefringence whose drift may be identified as the key limiting parameter in cavity-based techniques. We demonstrate a shot-noise-limited phase shift resolution previously inaccessible in an optical cavity, readily achieving the state-of-the-art level of 3×10-13 rad

Mid-infrared continuous-filtering Vernier spectroscopy using a doubly resonant optical parametric oscillator

We present a continuous-filtering Vernier spectrometer operating in the 3.15–3.4 µm range, based on a femtosecond doubly resonant optical parametric oscillator, a cavity with a finesse of 340, a grating mounted on a galvo scanner, and two photodiodes. The spectrometer allows acquisition of one spectrum spanning 250 nm of bandwidth in 25 ms with 8 GHz resolution, sufficient to detect molecular lines at atmospheric pressure. An active lock ensures good frequency and intensity stability of the consecutive spectra and enables continuous signal acquisition and efficient averaging. The relative frequency scale is calibrated using a Fabry–Perot etalon or, alternatively, the galvo scanner position signal. We measure spectra of a calibrated CH4 gas sample as well as dry and laboratory air and extract CH4 and H2O concentrations by multiline fitting of model spectra. The figure of merit of the spectrometer is 1.7 × 10−9 cm−1 Hz−1/2 per spectral element and the minimum detectable concentration of CH4 is 360 ppt Hz−1/2, averaging down to 90 ppt after 16 s

Feasibility of dual comb spectroscopy in the UV range using a free-running, bidirectional ring titanium sapphire laser

We show that our developed free-running, bidirectional ring Ti:Sa laser cavity meets the requirements for Dual Comb Spectroscopy in the UV range (UV-DCS). Two counter-propagative frequency combs with slightly different repetition rate are generated in such a cavity and we show quantitatively that this repetition rate difference can be explained by the self-steepening effect. Molecular absorption lines of the O2 A-band centered around 760~nm are measured with a 1,5 GHz spectral resolution, demonstrating that the mutual coherence of the two combs allows GHz-resolution DCS measurements. Moreover, we demonstrate that the generated output peak power allows for efficient second harmonic generation (SHG), in the scope of developing laboratory and open-path UV-DCS experiments

Cavity-Enhanced Continuous-Filtering Vernier Spectroscopy at 3.3 mu m using a Femtosecond Optical Parametric Oscillator

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