Abstract
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. To the best of our knowledge, these are the most precise and highest resolution spectral measurements performed with a broadband spectrometer, either comb-based or non-comb-based. This result pushes the limits of broadband comb-based spectroscopy to Hz-level regime. As a demonstration of these capabilities, we perform simultaneous cavity-enhanced measurements of molecular absorption and dispersion, deriving the gas spectra from cavity mode widths and positions. Such approach is particularly important for gas metrology and was made possible by the Hz-level resolution of the system. The presented method should be especially applicable to monitoring of chemical kinetics in, for example, plasma discharges or measurements of narrow resonances in cold atoms and molecules.
Highlights
In cavity ringdown spectroscopy (CRDS)26, sample absorption is derived from decay time constant of the light leaking from the cavity, which shortens with increasing absorption
We report measurements of 15 times narrower cavity modes with 900 times narrower instrumental function, resulting in few-Hz precision of cavity mode width and position determination and demonstrating the most exact application of the optical frequency comb (OFC) frequency precision in a broadband spectroscopic system
The optical frequency comb (OFC) spanning 1.52– 1.59 μm wavelength range is generated by an Er:fiber laser (Menlo FC1500) emitting pulses with the repetition rate frep of 250 MHz
Summary
In its most straightforward form the sample absorption is determined by directly measuring attenuation of the probe laser by the sample This technique has been successfully combined with OFCs leading to broadband and highly sensitive measurements. Its Fourier inverse, cavity mode-width spectroscopy (CMWS), and cavity mode-dispersion spectroscopy (CMDS) depend on the ability to precisely measure shapes and positions of narrow cavity modes, trading the requirement of high-speed operation of the detection system for relative frequency stability of the laser and the cavity. While the CMWS technique utilizes broadening of cavity modes to determine sample absorption, CMDS makes use of the fact that cavity modes are shifted by sample dispersion In the latter case, as measurements are based purely on frequency determination of mode centers, they are less susceptible to systematic errors in intensity measurements caused, for example, by detector nonlinearity. The careful analysis of molecular lineshapes did not reveal any distortions, verifying that the spectrometer fully resolved the cavity resonances without influence of any instrumental effects and that brodband comb-based systems can be successfully applied to measurements of sub-kHz spectral features
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
