Absorption line shape recovery beyond the detection bandwidth limit: application to the precision spectroscopic measurement of the Boltzmann constant

22 pagesInternational audienceA theoretical model of the influence of detection bandwidth properties on observed line shapes in laser absorption spectroscopy is described. The model predicts artificial frequency shifts, extra broadenings and line asymmetries which must be taken into account in order to obtain accurate central frequencies and other spectroscopic parameters. This reveals sources of systematic effects most probably underestimated so far potentially affecting spectroscopic measurements. This may impact many fields of research, from atmospheric and interstellar physics to precision spectroscopic measurements devoted to metrological applications, tests of quantum electrodynamics or other fundamental laws of nature. Our theoretical model is validated by linear absorption experiments performed on H2O and NH3 molecular lines recorded by precision laser spectroscopy in two distinct spectral regions, near- and mid-infrared. Possible means of recovering original line shape parameters or experimental conditions under which the detection bandwidth has a negligible impact, given a targeted accuracy, are proposed. Particular emphasis is put on the detection bandwidth adjustments required to use such high-quality molecular spectra for a spectroscopic determination of the Boltzmann constant at the 1 ppm level of accuracy

Comb-assisted mercury spectroscopy in the deep-ultraviolet: towards the development of a new primary thermometer

We report on the development of a new primary thermometer based upon high-precision spectroscopy of mercury vapors in the deep-ultraviolet region for the practical realization of the new kelvin. The line profile of the (6s2)1S0 > (6s6p)3P1 intercombination transition of the 200Hg bosonic isotope is observed with a high spectral fidelity using a coherent radiation source at 253.7 nm. This latter consists of a near-IR external cavity diode laser followed by a double-stage second-harmonic generation apparatus. Metrology grade UV spectroscopy is demonstrated by locking the diode laser to a self-referenced optical frequency comb synthesizer

frequency metrology in the near infrared spectrum of h217o and h218o molecules testing a new inversion method for retrieval of energy levels

An extensive Doppler-free spectroscopic investigation of the near-infrared absorption spectrum of the H218O molecule was performed, for the first time, with absolute frequency calibration by using a GPS-disciplined fiber-based optical frequency comb. The investigated line pairs belong to the ν1+ν3 band and have been chosen in the wavelength range from 1.38 to 1.41μm with a lambda scheme, so as to share the excited energy level and allow an accurate determination of the rotational energy separations of the fundamental vibrational state. The measurement of the sub-Doppler line-center frequencies, also extended to the H217O spectrum, has been performed with an overall uncertainty of ~30 kHz, i.e. about three orders of magnitude lower than the HITRAN data set. The retrieved energy separations agree, by less than 80 kHz, with recent findings provided by the so-called MARVEL procedure for spectral data inversion, thus yielding a very stringent test of its accuracy

Quantum cascade laser frequency stabilisation at the sub-Hz level

Quantum Cascade Lasers (QCL) are increasingly being used to probe the mid-infrared "molecular fingerprint" region. This prompted efforts towards improving their spectral performance, in order to reach ever-higher resolution and precision. Here, we report the stabilisation of a QCL onto an optical frequency comb. We demonstrate a relative stability and accuracy of 2x10-15 and 10-14, respectively. The comb is stabilised to a remote near-infrared ultra-stable laser referenced to frequency primary standards, whose signal is transferred via an optical fibre link. The stability and frequency traceability of our QCL exceed those demonstrated so far by two orders of magnitude. As a demonstration of its capability, we then use it to perform high-resolution molecular spectroscopy. We measure absorption frequencies with an 8x10-13 relative uncertainty. This confirms the potential of this setup for ultra-high precision measurements with molecules, such as our ongoing effort towards testing the parity symmetry by probing chiral species

Erratum: Doppler-limited precision spectroscopy of HD at 1.4 μm: An improved determination of the R (1) center frequency (Physical Review A (2021) 103 (022828) DOI: 10.1103/PhysRevA.103.022828)

There is a mistake in the updated determination of the center frequency of the R(1) line of the HD 2-0 band. In fact, the blueshift due to the recoil effect is present in linear absorption spectroscopy and it is not negligible in a light molecule such as hydrogen deuteride. This shift amounts to 34.6 kHz. Therefore, the corrected position of the R(1) line is 217?105?181.901 MHz with a global uncertainty of 76 kHz. The uncertainty budget, all discussions, and concluding remarks remain unaltered

Absolute frequency stabilization of an extended-cavity diode laser by means of noise-immune cavity-enhanced optical heterodyne molecular spectroscopy

We implemented an optical frequency standard based on noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) at 1.39 μm. The emission frequency of an extended-cavity diode laser was actively stabilized against the center of the 44;1 → 44;0 transition of the H2 18O ν1 ν3 band, under optical saturation conditions. The nonlinear regime of laser-gas interaction was reached by using an optical cavity with a finesse of about 8700. By filling it with an 18O-enriched water sample at a pressure of a few Pa, the Lamb dip could be observed with a full width at half-maximum of about 2 MHz. Absolute frequency stabilization was obtained by locking the cavity resonance to the center of the sub-Doppler signal, which was provided by the NICE-OHMS technique under the dispersion regime of operation. An Allan deviation analysis demonstrated a relative frequency stability of ∼5 × 10−13 for an integration time of 1 s. For longer integration times, the flicker frequency noise floor set the stability at the level of 4 × 10−14

Characterization of the frequency stability of an optical frequency standard at 1.39 μm based upon noise-immune cavity-enhanced optical heterodyne molecular spectroscopy

Frequency fluctuations of an optical frequency standard at 1.39 µm have been measured by means of a highly-sensitive optical frequency discriminator based on the fringe-side transmission of a high finesse optical resonator. Built on a Zerodur spacer, the optical resonator exhibits a finesse of 5500 and a cavity-mode width of about 120 kHz. The optical frequency standard consists of an extended-cavity diode laser that is tightly stabilized against the center of a sub-Doppler H218O line, this latter being detected by means of noise-immune cavity-enhanced optical heterodyne molecular spectroscopy. The emission linewidth has been carefully determined from the frequency-noise power spectral density by using a rather simple approximation, known as β-line approach, as well as the exact method based on the autocorrelation function of the laser light field. It turns out that the linewidth of the optical frequency standard amounts to about 7 kHz (full width at half maximum) for an observation time of 1 ms. Compared to the free-running laser, the measured width corresponds to a line narrowing by a factor of ~220

Absolute frequency stabilization of an extended-cavity diode laser against Doppler-free H217O absorption lines at 1.384 μm

We report the frequency stabilization of a cw extended-cavity diode laser against saturated absorption lines of the H217O isotopologue of water vapor at around 1.384 μm. The saturation of rotovibrational transitions is achieved by filling a high-finesse optical resonator with H2 O at low pressure and by locking the laser frequency to the resonator by using the Pound-Drever-Hall technique. Absolute frequency stabilization is obtained, locking the cavity resonance to the center of the sub-Doppler line by means of the wavelength modulation method. A relative frequency stability of σy (τ)= 10-18(0. 1τ-2 + 0.9)1/2 is demonstrated for integration times in the range 4 ms< τ<30 S. © 2009 Optical Society of America