arXiv subjects

Nicolas Forget

Publications and source records attributed to Nicolas Forget.

13 recordsLinked to original sources

arXiv2026

Broadband heterodyne interferometry with a chirped femtosecond laser in the H-band

Infrared heterodyne interferometry offers a scalable alternative to direct interferometry for long-baseline telescope arrays. However, at near-infrared wavelengths, its sensitivity is limited by the electronic detection bandwidth and shot noise from the optical reference. Parallel detection via spectral multiplexing has long been identified as a potential means to increase the signal-to-noise ratio of heterodyne interferometers. We propose a new heterodyne detection architecture based on highly dispersed broadband pulses from a mode-locked laser, fast photoreceivers, and numerical correlation. This enables straightforward spectral multiplexing with commercial components to increase the SNR, while extending instantaneous wavelength coverage to simultaneous J- and H-band operation. The scheme also supports high-resolution spectroscopic imaging ($R \simeq 10^{3}-10^{4}$). We derive the SNR of a two-arm heterodyne interferometer based on balanced photodetection and apply the model to the proposed scheme, using measurements from a single-spectral-channel, all-fiber interferometer operating at 1.56 micrometer over an 8 nanometer bandwidth. We experimentally demonstrate an SNR exceeding 2 for a spectral flux density of 188 pW/nm, with an integration time of 0.4 ms. Scaling the integration time and number of spectral channels suggests that fringe visibility of the brightest H-band stars could be achieved with 1 m$^2$ telescopes within the typical atmospheric coherence time. These results represent a significant step toward broadband, scalable heterodyne interferometers, demonstrating the potential of ultrafast laser and telecommunications technologies for astronomical interferometry in the J+H bands. By combining broadband spectral multiplexing with numerical correlation, the architecture also opens a route to direct spectro-imaging without an additional spectrometer.

astro-ph.IM↗

arXiv2026

Swept-source heterodyne detection for interferometry in the H band

It is well established that direct-detection interferometry outperforms heterodyne interferometry in terms of signal-to-noise ratio at optical wavelengths, not only because of the limited electronic bandwidth of photodetectors (typically <100 GHz), but also due to the shot-noise contribution of the optical local oscillator. The large-scale production of high-quality and cost-effective telecom components in the J+H band, and more recently in the K band, may open new schemes for the heterodyne signal detection and processing (e.g. correlation) as well as for the transport, distribution and control of the local oscillator. We describe how high-repetition-rate frequency-swept sources and telecom components could be exploited to parallelize, at reasonable cost, a large number of coherent detectors to expand the spectral coverage. We also present a first laboratory single-channel proof of concept that achieves a signal-to-noise ratio (SNR) probably sufficient for observing the brightest stars in the H band with telescopes of ~1 m2 at short integration time (<100 ms).

astro-ph.IM↗

arXiv2026

All-optical control of second-harmonic generation in $\beta$-BaB$_2$O$_4$ via coherent, terahertz-driven acentric lattice displacement

Dynamical control of the nonlinear optical properties of solids -- with light itself -- will be essential for future ultrafast photonic technologies. Previously, methods to modulate nonlinear processes including second-harmonic generation (SHG) have relied primarily on non-resonant light-matter interaction or photo-generation of hot electrons in nanoscale materials. However, these approaches are typically constrained by limited interaction lengths and the initial frequency conversion is relatively weak under equilibrium conditions. Here, an approximately 30\% modulation of efficient phase-matched SHG in bulk beta-barium borate (beta-BaB2O4) is achieved through transient lattice deformation by intense terahertz (THz) pulses that are tuned to resonance with an infrared-active phonon mode. The effect originates from modification of the index of refraction ellipsiod and the corresponding nonlinear phase-matching conditions, rather than from direct modulation of the nonlinear susceptibility through THz-mediated chi^(3) processes. This mechanism, of resonant selective lattice excitation, points toward novel THz-control schemes to tune the nonlinear optical response in materials.

physics.optics↗

arXiv2025

Phase noise properties of supercontinuum generation in all-normal dispersion fibers

The spectral coherence properties of supercontinuum generation in polarization-maintaining all-normal dispersion fibers are investigated. Stochastic phase noise induced by energy fluctuations, along with spectrally-resolved intensity-to-phase transfer coefficients, are quantitatively analyzed, confirming the high coherence of the generated supercontinuum. Our results show that the nonlinear process is fundamentally deterministic with ultra-low spectral phase noise, yet exhibits significant intensity-to-phase coupling.

physics.optics↗

arXiv2024

Hyperspectral acquisition with ScanImage at the single pixel level: Application to time domain coherent Raman imaging

We present a comprehensive strategy and its practical implementation using the commercial ScanImage software platform to perform hyperspectral point scanning microscopy when a fast time dependent signal varies at each pixel level. In the proposed acquisition scheme the scan along the X axis is slowed down while the data acquisition is maintained at high pace to enable the rapid acquisition of the time dependent signal at each pixel level. The ScanImage generated raw 2D images have a very asymmetric aspect ratio between X and Y, the X axis encoding both for space and time acquisition. The results are X axis macro-pixel where the associated time depend signal is sampled therefore providing an hyperspectral information. We exemplified the proposed hyperspectral scheme in the context of time domain coherent Raman imaging where a pump pulse impulsively excites molecular vibrations that are subsequently probed by a time delayed probe pulse. In this case the time dependent signal is a fast acousto-optics delay line that can scan a delay of 4.5ps in 25$\mu$s, at each pixel level. We this acquisition scheme we demonstrate ultra-fast hyperspectral vibrational imaging in the low frequency range [10$cm^{-1}$, 150 $cm^{-1}$] over a 500 $\mu m$ field of view in 14ms (7 frames/s). The proposed acquisition scheme can be readily extended to other applications requiring to acquired a fast evolving signal at each pixel level.

physics.optics↗

arXiv2023

Compressed Sensing of Field-resolved Molecular Fingerprints Beyond the Nyquist Frequency

Ultrashort time-domain spectroscopy and field-resolved spectroscopy of molecular fingerprints are gold standards for detecting samples' constituents and internal dynamics. However, they are hindered by the Nyquist criterion, leading to prolonged data acquisition, processing times, and sizable data volumes. In this work, we present the first experimental demonstration of compressed sensing on field-resolved molecular fingerprinting by employing random scanning. Our measurements enable pinpointing the primary absorption peaks of atmospheric water vapor in response to terahertz light transients while sampling beyond the Nyquist limit. By drastically undersampling the electric field of the molecular response at a Nyquist frequency of 0.8 THz, we could successfully identify water absorption peaks up to 2.5 THz with a mean squared error of 12 * 10^-4. To our knowledge, this is the first experimental demonstration of time-domain compressed sensing, paving the path towards real-time field-resolved fingerprinting and acceleration of advanced spectroscopic techniques.

physics.optics↗

arXiv2023

Ultralow-Noise Optical Parametric Amplifier for Stimulated Raman Scattering Imaging

We present a 40-MHz ultrafast optical parametric amplifier (OPA), tunable from 0.8 to 1 $\mu$m, with a relative intensity noise (RIN) matching the shot-noise floor (-160 dB/Hz) above 2 MHz. The OPA is pumped by a 20-W Kerr-lens mode-locked Ytterbium laser and seeded by a a supercontinuum generated in an all-normal-dispersion (ANDi) fiber. With an average output power >1.5 W, this compact and simple scheme is an attractive alternative to synchronously-pumped optical parametric oscillators, especially within the context of stimulated Raman scattering (SRS) imaging. To illustrate the latter, we perform chemical imaging of vinegar droplets in oil by SRS microscopy.

physics.optics↗

arXiv2022

Enhancing Branch-and-Bound for Multi-Objective 0-1 Programming

In the bi-objective branch-and-bound literature, a key ingredient is objective branching, i.e. to create smaller and disjoint sub-problems in the objective space, obtained from the partial dominance of the lower bound set by the upper bound set. When considering three or more objective functions, however, applying objective branching becomes more complex, and its benefit has so far been unclear. In this paper, we investigate several ingredients which allow to better exploit objective branching in a multi-objective setting. We extend the idea of probing to multiple objectives, enhance it in several ways, and show that when coupled with objective branching, it results in significant speed-ups in terms of CPU times. We also investigate cut generation based on the objective branching constraints. Besides, we generalize the best-bound idea for node selection to multiple objectives and we show that the proposed rules outperform the, in the multi-objective literature, commonly employed depth-first and breadth-first strategies. We also analyze problem specific branching rules. We test the proposed ideas on available benchmark instances for three problem classes with three and four objectives, namely the capacitated facility location problem, the uncapacitated facility location problem, and the knapsack problem. Our enhanced multi-objective branch-and-bound algorithm outperforms the best existing branch-and-bound based approach and is the first to obtain competitive and even slightly better results than a state-of-the-art objective space search method on a subset of the problem classes.

cs.DS↗

arXiv2022

Nonlinear chirped Doppler interferometry for \c{hi}(3) spectroscopy

Four-wave mixing processes are ubiquitous in ultrafast optics and the determination of the coefficients of the $\chi^{(3)}$ tensor is thus essential. We introduce a novel time-resolved ultrafast spectroscopic method to characterize the third-order nonlinearity on the femtosecond time-scale. This approach, coined as "nonlinear chirped Doppler interferometry", makes use of the variation of the optical group delay of a transmitted probe under the effect of an intense pump pulse in the nonlinear medium of interest. The observable is the spectral interference between the probe and a reference pulse sampled upstream. We show that the detected signal is enhanced when the pulses are chirped, and that, although interferometric, the method is immune to environmental phase fluctuations and drifts. By chirping adequately the reference pulse, the transient frequency shift of the probe pulses is also detected in the time domain and the detected nonlinear signal is enhanced. Nonlinear phase shifts as low as 10\,mrad, corresponding to a frequency shift of 30\,GHz, i.e. 0.01\% of the carrier frequency, are detected without heterodyne detection or active phase-stabilization. The diagonal and/or non-diagonal terms of reference glasses (SiO$_2$) and crystals (Al$_2$O$_3$, BaF$_2$, CaF$_2$) are characterized. The method is finally applied to measure the soft vibration mode of KTiOAsO$_4$ (KTA).

physics.optics↗

arXiv2022

Spectral coherence properties of continuum generation in bulk crystals

The stability of the phase difference between two white-light continua, generated from the same 180-fs pulses at 1035\,nm, is assessed by a modified Bellini-Hansch interferometer. Mutual spectral stability is studied as a function of several parameters: position of the nonlinear crystal with respect to the beam waist, interaction length, and pulse energy. Intensity-to-phase coupling coefficients are measured and stability regions are identified.

physics.optics↗

arXiv2019

Shot noise limited high speed stimulated Raman microscopy

We report a shot noise limited high speed stimulated Raman microscopy platform allowing to acquire molecular vibrational spectra over \SI{200}{\per \cm} in \SI{12}{\micro \second} at a scan rate of 40kHz. Using spectral focusing together with optimized acousto-optics programmable dispersive filters the designed low noise imaging platform performs chemical imaging of dynamical processes such as Mannitol crystal hydratation and reaches a signal to noise ratio sufficient to perform label free histological imaging on frozen human colon tissue slides.

physics.optics↗

arXiv2018

Rapid-scan acousto-optical delay line with 34 kHz scan rate and 15 attosecond precision

An optical fast-scan delay exploiting the near-collinear interaction between a train of ultrashort optical pulses and an acoustic wave propagating in a birefringent crystal is introduced. In combination with a femtosecond Er:fiber laser, the scheme is shown to delay few-fs pulses by up to 6 ps with a precision of 15 as. A resolution of 5 fs is obtained for a single sweep at a repetition rate of 34 kHz. This value can be improved to 39 as for multiple scans at a total rate of 0.3 kHz.

physics.ins-det↗

arXiv2018

Carrier-envelope-phase stable, high-contrast, double chirped-pulse-amplification laser system

We present the first carrier-envelope phase stable chirped pulse amplifier (CPA) featuring high temporal contrast for relativistic intensity laser-plasma interactions at 1 kHz repetition rate. The laser is based on a double-CPA architecture including XPW filtering technique and a high-energy grism-based compressor. 8 mJ, 22 fs pulses are produced with 10-11 temporal contrast at -20 ps and a CEP drift of 240 mrad RMS.

physics.optics↗