Dual-comb cavity ring-down spectroscopy.

Cavity ring-down spectroscopy is a ubiquitous optical method used to study light-matter interactions with high resolution, sensitivity and accuracy. However, it has never been performed with the multiplexing advantages of direct frequency comb spectroscopy without significantly compromising spectral resolution. We present dual-comb cavity ring-down spectroscopy (DC-CRDS) based on the parallel heterodyne detection of ring-down signals with a local oscillator comb to yield absorption and dispersion spectra.

Frequency-based dispersion Lamb-dip spectroscopy in a high finesse optical cavity.

Frequency-based cavity mode-dispersion spectroscopy (CMDS), previously applied for Doppler-limited molecular spectroscopy, is now employed for the first time for saturation spectroscopy. Comparison with two intensity-based, cavity-enhanced absorption spectroscopy techniques, i.e.

Intensity noise optimization of a mid-infrared frequency comb difference-frequency generation source.

We experimentally demonstrate in a difference-frequency generation mid-infrared frequency comb source the effect of temporal overlap between pump and signal pulses on the relative intensity noise (RIN) of the idler pulse. When scanning the temporal delay between our 130 fs long signal and pump pulses, we observe a RIN minimum with a 3 dB width of 20 fs delay and a RIN increase of 20 dB in 40 fs delay at the edges of this minimum. We also demonstrate active long-term stabilization of the mid-infrared frequency comb source to the temporal overlap setting corresponding to the lowest RIN operation point by an online RIN detector and active feedback control of the pump-signal pulse delay.

Ultrahigh finesse cavity-enhanced spectroscopy for accurate tests of quantum electrodynamics for molecules.

We report the most accurate, to the best of our knowledge, measurement of the position of the weak quadrupole S(2) 2-0 line in $ {{\rm D}_2} $D. The spectra were collected with a frequency-stabilized cavity ringdown spectrometer (FS-CRDS) with an ultrahigh finesse optical cavity ($ {\cal F} = 637 000 $F=637000) and operating in the frequency-agile, rapid scanning spectroscopy (FARS) mode. Despite working in the Doppler-limited regime, we reached 40 kHz of statistical uncertainty and 161 kHz of absolute accuracy, achieving the highest accuracy for homonuclear isotopologues of molecular hydrogen.

High-accuracy and wide dynamic range frequency-based dispersion spectroscopy in an optical cavity.

A spectroscopic method free from systematic errors is desired for many challenging applications of gas detection. Although existing cavity-enhanced techniques exhibit very high precision, their accuracy strongly depends on propagation of the light amplitude through an optical system and its detection. Here, we demonstrate that the frequency-based molecular dispersion spectroscopy, involving sub-Hz-level precision in frequency measurements of optical cavity resonances, leads to sub-per-mille accuracy and a wide dynamic range, both previously unattainable by any other spectroscopic technique.

Broadband Optical Cavity Mode Measurements at Hz-Level Precision With a Comb-Based VIPA Spectrometer.

Optical frequency comb spectrometers open up new avenues of investigation into molecular structure and dynamics thanks to their accuracy, sensitivity and broadband, high-speed operation. We combine broadband direct frequency comb spectroscopy with a dispersive spectrometer providing single-spectrum acquisition time of a few tens of milliseconds and high spectral resolution. We interleave a few tens of such comb-resolved spectra to obtain profiles of 14-kHz wide cavity resonances and determine their positions with precision of a few hertz.

Absolute frequency and isotope shift measurements of mercury S-P transition.

We report the measurement of the absolute frequencies of the 6s S-6s6p P transition (253.7 nm) and the relevant isotope shifts in five mercury isotopes  Hg,  Hg,  Hg,  Hg, and  Hg. The Doppler-free saturated absorption measurements were performed in an atomic vapour cell at room temperature with a four-harmonic generated (FHG) continuous-wave (cw) laser digitally locked to the atomic transition.

Response of an optical cavity to phase-controlled incomplete power switching of nearly resonant incident light.

The response of an optical cavity to incomplete extinction of nearly resonant incident light was experimentally examined. Measurements were performed using a Pound-Drever-Hall-locked frequency-stabilized cavity ring-down spectrometer (CRDS) that allowed the laser frequency detuning from the cavity resonance center to be controlled at Hz-level resolution. It is shown that an insufficient laser light extinction ratio combined with a phase shift and frequency detuning may lead to non-exponential cavity pumping and decay signals.

Conjugating precision and acquisition time in a Doppler broadening regime by interleaved frequency-agile rapid-scanning cavity ring-down spectroscopy.

We propose a novel approach to cavity-ring-down-spectroscopy (CRDS) in which spectra acquired with a frequency-agile rapid-scanning (FARS) scheme, i.e., with a laser sideband stepped across the modes of a high-finesse cavity, are interleaved with one another by a sub-millisecond readjustment of the cavity length.

Self-referenced, accurate and sensitive optical frequency comb spectroscopy with a virtually imaged phased array spectrometer.

We present a cavity-enhanced direct optical frequency comb spectroscopy system with a virtually imaged phased array (VIPA) spectrometer and either a dither or a Pound-Drever-Hall (PDH) locking scheme used for stable transmission of the comb through the cavity. A self-referenced scheme for frequency axis calibration is shown along with an analysis of its accuracy. A careful comparison between both locking schemes is performed based on near-IR measurements of the carbon monoxide ν=3←0 band P branch transitions in a gas sample with known composition.

Absolute measurement of the 1S0 - 3P0 clock transition in neutral 88Sr over the 330 km-long stabilized fibre optic link.

We report a stability below 7 × 10(-17) of two independent optical lattice clocks operating with bosonic (88)Sr isotope. The value (429 228 066 418 008.3(1.

One-dimensional frequency-based spectroscopy.

Recent developments in optical metrology have tremendously improved the precision and accuracy of the horizontal (frequency) axis in measured spectra. However, the vertical (typically absorbance) axis is usually based on intensity measurements that are subject to instrumental errors which limit the spectrum accuracy. Here we report a one-dimensional spectroscopy that uses only the measured frequencies of high-finesse cavity modes to provide complete information about the dispersive properties of the spectrum.

Absolute frequency measurement of rubidium 5S-7S two-photon transitions.

We report the absolute frequency measurements of rubidium 5S-7S two-photon transitions with a cw laser digitally locked to an atomic transition and referenced to an optical frequency comb. The narrow, two-photon transition, 5S-7S (760 nm), insensitive to first-order in a magnetic field, is a promising candidate for frequency reference. The performed tests yielded more accurate transition frequencies than previously reported.

Quantum-noise-limited optical frequency comb spectroscopy.

We achieve a quantum-noise-limited absorption sensitivity of 1.7×10(-12) cm(-1) per spectral element at 400 s of acquisition time with cavity-enhanced frequency comb spectroscopy, the highest demonstrated for a comb-based technique. The system comprises a frequency comb locked to a high-finesse cavity and a fast-scanning Fourier transform spectrometer with an ultralow-noise autobalancing detector.

Mid-infrared Fourier transform spectroscopy with a broadband frequency comb.

We present a first implementation of optical-frequency-comb-based rapid trace gas detection in the molecular fingerprint region in the mid-infrared. Near-real-time acquisition of broadband absorption spectra with 0.0056 cm(-1) maximum resolution is demonstrated using a frequency comb Fourier transform spectrometer which operates in the 2100-to-3700-cm(-1) spectral region.