arXiv subjects

Paul Chevalier

Publications and source records attributed to Paul Chevalier.

12 recordsLinked to original sources

arXiv2026

A swept-source dual-comb spectrometer on a chip

Dual-comb spectroscopy (DCS) enables high-speed, high-resolution spectroscopy by down-converting optical spectra to the radio-frequency (RF) domain through the interference of two mutually detuned frequency combs. Accurately resolving narrow molecular absorption features requires closely spaced comb lines generated by large laser cavities with long round-trip times, thereby hindering the miniaturization of high-resolution spectrometers. Here, we circumvent this limitation by demonstrating a swept-source dual-comb spectrometer using two unidirectional racetrack semiconductor lasers integrated on the same chip. The traveling-wave frequency combs are generated by strong RF injection at the laser cavity round-trip frequency of 14.3~GHz and are continuously tuned in frequency by varying the laser drive currents. This enables continuous spectral sampling over a 32~cm$^{-1}$ range centered near 8~\textmu m, with an effective sampling interval of approximately 80~MHz. The outputs of both combs are coupled into the same monolithically integrated light coupler, providing automatic collinear alignment before the combined beam interrogates the sample. We benchmark the spectrometer against an external-cavity tunable laser and validate its performance using HITRAN simulations for 1.25\% nitrous oxide. Finally, the unidirectional comb architecture suppresses the detrimental effects of optical feedback, yielding comparable residuals even under deliberately introduced strong feedback. More broadly, the benefits of miniaturization extend beyond reduced footprint: chip-scale integration enables new forms of electrical and optical control that can fundamentally change how dual-comb spectrometers are operated.

physics.optics↗

arXiv2026

A scalable platform for nanometer-scale quantum confinement

Overcoming the limitations of current nanofabrication techniques to achieve nanoscale feature sizes is essential for achieving new regimes of light-matter interactions at extreme frequencies and length scales. Here, we demonstrate a scalable nanofabrication platform capable of producing in-plane feature sizes down to 1.75 nm, pushing the boundaries of current top-down nanofabrication techniques. Using precise thickness control of atomic layer deposition (ALD) and employing widely spaced oxide nanofins, we transform conventional ALD into a surface structuring method that produces nanolaminates with sub-10 nm periodicities over large areas. The resulting nanostructures can be used as a one-dimensional gate array to control charge carriers in two-dimensional materials. As an initial demonstration, we integrate the platform with graphene and perform electron transport measurements. In the presence of the gate array enabled by the nanolaminate, we observe satellite Dirac peaks consistent with band-structure modulation, suggestive of quantum-confinement effects. Our platform paves the way for exploring previously inaccessible regimes of nanoscale light-matter interactions, holding significant promise for applications in short wavelength optics, electronics, and polaritonics.

physics.optics↗

arXiv2021

Multi-line lasing in the broadly tunable ammonia quantum cascade laser pumped molecular laser

Gaseous ammonia has previously been demonstrated as a compelling gain medium for a quantum cascade laser pumped molecular laser (QPML), exhibiting good power efficiency but limited tunability. Here we explore the potential of the ammonia QPML to produce powerful, broadly tunable terahertz frequency lasing on rotational and pure inversion transitions. After theoretically predicting possible laser frequencies, pump thresholds, and efficiencies, we experimentally demonstrate unprecedented tunability -- from 0.762 to more than 4.5 THz -- by pumping Q- and R-branch infrared transitions with widely tunable quantum cascade lasers. We additionally demonstrate two types of multi-line lasing: simultaneous pure inversion and rotation-inversion transitions from the same pumped rotational state, and cascaded lasing involving transitions below the pumped rotational state. We report single frequency power levels as great as 0.33 mW from a low volume laser cavity.

physics.optics↗

arXiv2021

A quantum cascade laser-pumped molecular laser tunable over 1 THz

By introducing methyl fluoride (CH$_3$F) as a new gain medium for a quantum cascade laser-pumped molecular laser (QPML), we demonstrate continuous-wave lasing from more than 120 discrete transitions spanning the frequency range 0.25 to 1.3 THz. The unprecedented degree of spectral tuning achieved with CH$_3$F also confirms the universality of the QPML concept: for all polar gas molecules, lasing can be induced on any dipole-allowed rotational transition by sufficient pumping of a related roto-vibrational transition using a continuously tunable quantum cascade laser.

physics.optics↗

arXiv2020

Response to Comment on Widely tunable compact terahertz gas lasers

We recently demonstrated a widely tunable THz molecular laser and reported mathematical formulas and a table for comparing how various molecules would perform as such lasers (Chevalier et al., Science, 15 November 2019, p. 856-860). Here we correct the value of a single parameter used to calculate the table (see Erratum for Chevalier et al.), thereby eliminating the concerns raised by Lampin and Barbieri (Lampin et al., arXiv:2004.04422). We also show that our simplified model for the output THz power is a better approximation than the alternative one proposed in the technical comment.

physics.app-ph↗

arXiv2019

Laser radio transmitter

Since the days of Hertz, radio transmitters have evolved from rudimentary circuits emitting around 50 MHz to modern ubiquitous Wi-Fi devices operating at gigahertz radio bands. As wireless data traffic continues to increase there is a need for new communication technologies capable of high-frequency operation for high-speed data transfer. Here we give a proof of concept of a new compact radio frequency transmitter based on a semiconductor laser frequency comb. In this laser, the beating among the coherent modes oscillating inside the cavity generates a radio frequency current, which couples to the electrodes of the device. We show that redesigning the top contact of the laser allows one to exploit the internal oscillatory current to drive an integrated dipole antenna, which radiates into free space. In addition, direct modulation of the laser current permits encoding a signal in the radiated radio frequency carrier. Working in the opposite direction, the antenna can receive an external radio frequency signal, couple it to the active region and injection lock the laser. These results pave the way to new applications and functionality in optical frequency combs, such as wireless radio communication and wireless synchronization to a reference source.

physics.app-ph↗

arXiv2018

In-water chemical sensing by fiber-optic evanescent waves spectroscopy using mid-infrared quantum cascade lasers

The ability of detecting harmful chemicals is an important safety requirement for drinking water systems. An apparatus for in-water chemical sensing based on the absorption of evanescent waves generated by a quantum cascade laser array propagating in a silver halide optical fiber immersed into water is demonstrated. We present a theoretical analysis of the sensitivity of the system and experimentally characterize its real-time response and spectroscopic detection for injection of a sample chemical (ethanol) in a tube containing water.

physics.app-ph↗

arXiv2018

Watt-level widely tunable single-mode emission by injection-locking of a multimode Fabry-Perot quantum cascade laser

Free-running Fabry-Perot lasers normally operate in a single-mode regime until the pumping current is increased beyond the single-mode instability threshold, above which they evolve into a multimode state. As a result of this instability, the single-mode operation of these lasers is typically constrained to few percents of their output power range, this being an undesired limitation in spectroscopy applications. In order to expand the span of single-mode operation, we use an optical injection seed generated by an external-cavity single-mode laser source to force the Fabry-Perot quantum cascade laser into a single-mode state in the high current range, where it would otherwise operate in a multimode regime. Utilizing this approach we achieve single-mode emission at room temperature with a tuning range of $36 \, \mathrm{cm}^-1$ and stable continuous-wave output power exceeding 1 W. Far-field measurements show that a single transverse mode is emitted up to the highest optical power indicating that the beam properties of the seeded Fabry-Perot laser remain unchanged as compared to free-running operation.

physics.optics↗

arXiv2017

Mid infrared two-photon absorption in a room-temperature extended-wavelength InGaAs photodetector

We investigate the nonlinear optical response of a commercial extended-wavelength In$_{0.81}$Ga$_{0.19}$As photodetector. Degenerate two-photon absorption in the mid-infrared range is observed at room temperature using a quantum cascade laser emitting at $\lambda=4.5~\mu$m as the excitation source. From the measured two-photon photocurrent signal we extract a two-photon absorption coefficient $\beta^{(2)} = 0.6 \pm 0.2$ cm/MW, in agreement with the theoretical value obtained from the $E_g^{-3}$ scaling law. Considering the wide spectral range covered by extended-wavelength In$_x$Ga$_{1-x}$As alloys, this result holds promise for new applications based on two-photon absorption for this family of materials at wavelengths between 1.8 and 5.6 $\mu$m.

physics.optics↗

arXiv2017

Single-mode instability in standing-wave lasers: The quantum cascade laser as a self-pumped parametric oscillator

We report the observation of a clear single-mode instability threshold in continuous-wave Fabry-Perot quantum cascade lasers (QCLs). The instability is characterized by the appearance of sidebands separated by tens of free spectral ranges (FSR) from the first lasing mode, at a pump current not much higher than the lasing threshold. As the current is increased, higher-order sidebands appear that preserve the initial spacing, and the spectra are suggestive of harmonically phase-locked waveforms. We present a theory of the instability that applies to all homogeneously broadened standing-wave lasers. The low instability threshold and the large sideband spacing can be explained by the combination of an unclamped, incoherent Lorentzian gain due to the population grating, and a coherent parametric gain caused by temporal population pulsations that changes the spectral gain line shape. The parametric term suppresses the gain of sidebands whose separation is much smaller than the reciprocal gain recovery time, while enhancing the gain of more distant sidebands. The large gain recovery frequency of the QCL compared to the FSR is essential to observe this parametric effect, which is responsible for the multiple-FSR sideband separation. We predict that by tuning the strength of the incoherent gain contribution, for example by engineering the modal overlap factors and the carrier diffusion, both amplitude-modulated (AM) or frequency-modulated emission can be achieved from QCLs. We provide initial evidence of an AM waveform emitted by a QCL with highly asymmetric facet reflectivities, thereby opening a promising route to ultrashort pulse generation in the mid-infrared. Together, the experiments and theory clarify a deep connection between parametric oscillation in optically pumped microresonators and the single-mode instability of lasers, tying together literature from the last 60 years.

physics.optics↗

arXiv2017

Self-starting harmonic frequency comb generation in a quantum cascade laser

Optical frequency combs establish a rigid phase-coherent link between microwave and optical domains and are emerging as high-precision tools in an increasing number of applications. Frequency combs with large intermodal spacing are employed in the field of microwave photonics for radiofrequency arbitrary waveform synthesis and for generation of THz tones of high spectral purity in the future wireless communication networks. We demonstrate for the first time self-starting harmonic frequency comb generation with a THz repetition rate in a quantum cascade laser. The large intermodal spacing caused by the suppression of tens of adjacent cavity modes originates from a parametric contribution to the gain due to temporal modulations of the population inversion in the laser. The mode spacing of the harmonic comb is shown to be uniform to within $5\times 10^{-12}$ parts of the central frequency using multiheterodyne self-detection. This new harmonic comb state extends the range of applications of quantum cascade laser frequency combs.

physics.optics↗

arXiv2014

Giant field enhancement by funneling effect into sub-wavelength slit-box resonators

Inspired by the acoustic Helmholtz resonator, we propose a slit-box electromagnetic nanoantenna able to concentrate the energy of an incident beam into surfaces a thousand times smaller than with a classical lens. This design gives birth to giant field intensity enhancement in hot volume, throughout the slit. It reaches $10^4$ in the visible up to $10^8$ in the THz range even with focused beams thanks to an omnidirectional reception. These properties could target applications requiring extreme light concentration, such as SEIRA, non-linear optics and biophotonics.

physics.optics↗