Frequency comb spectroscopy

Abstract

A laser frequency combs is a broad spectrum composed of equidistant narrow lines. Initially invented for frequency metrology, such combs enable new approaches to spectroscopy over broad spectral bandwidths, of particular relevance to molecules. With optical frequency combs, the performance of existing spectrometers, such as Michelson--based Fourier transform interferometers or crossed dispersers, involving e.g. virtual imaging phase array (VIPA) étalons, is dramatically enhanced. Novel types of instruments, such as dual--comb spectrometers, lead to a new class of devices without moving parts for accurate measurements over broad spectral ranges. The direct self-calibration of the frequency scale of the spectra within the accuracy of an atomic clock and the negligible contribution of the instrumental line--shape will enable determinations of all spectral parameters with high accuracy for stringent comparisons with theories in atomic and molecular physics. Chip--scale frequency--comb spectrometers promise integrated devices for real--time sensing in analytical chemistry and biomedicine. This review article gives a summary of advances in the emerging and rapidly advancing field of atomic and molecular broadband spectroscopy with frequency combs. Frequency comb spectroscopy N. Picqué, T. W. Hänsch Preprint version of Nature Photonics 13, 146--157 (2019). /27Frequency comb spectroscopy N. Picqué, T. W. Hänsch Preprint version of Nature Photonics 13, 146--157 (2019). /27 3 assisted precision spectroscopy, frequency comb spectroscopy began to attract the interest of a few research groups 12--20 . Stimulated by a number of intriguing proof--of--principle demonstrations, the field has grown to a hot research topic and, with new research groups constantly getting involved, novel clever and unforeseen applications emerge. Most of the time, frequency comb spectroscopy implies spectroscopy over a broad spectral bandwidth, of particular relevance to molecular spectroscopy.Frequency comb spectroscopy N. Picqué, T. W. Hänsch Preprint version of Nature Photonics 13, 146--157 (2019). /27 4 2. Frequency--comb light sources for spectroscopy. 2.1 General characteristics. Often, a comb is generated by a mode--locked laser system. In the time domain (Fig. 1a), a train of ultrashort pulses is emitted at the output of the cavity. The period of the envelope of the pulses, 1/frep= L/vg , corresponds to the round--trip time inside a laser cavity of round--trip length L and group velocity of the light vg. Due to dispersion inside the cavity, a pulse--to--pulse phase--shift Δφ between the carrier and the envelope of the electric field of the pulses is observed. In the frequency domain, the associated spectrum is composed of a discrete set of evenly spaced narrow lines with frequencies fn that can be written fn= n frep + f0, where n is a large integer, frep is the repetition frequency of the envelope of the pulses and f0 is the carrier--envelope offset frequency, related to the phase--shift Δφ by the relationship f0 = frep Δφ/2π (Fig. 1a). In ...

Generation of ultralow power phononic combs

“…Photonic frequency combs generators are an important tool used for many scientific applications allowing to couple distant parts of frequency spectrum 1 . Amongst others, these important applications include ultra stable clocks and frequency metrology [2][3][4] and spectroscopy 5,6 . All of these system are photonic mostly utilising a carrier signal at an optical frequency and RF or microwave repetition rates.…”

Opportunities for photonic integrated circuits in optical gas sensors

“…Figure 6 illustrates the two different approaches. With frequency combs and modelocked lasers, the benefits of both approaches can be harvested [6,[25][26][27]. Mode-locked lasers feature very well defined emission lines over a wide wavelength span, and can be considered an optical ruler.…”

On-chip mid-infrared and THz frequency combs for spectroscopy

“…The radio-frequency comb of line spacing Dfrep, formed by the beat signals is easily measurable by standard electronics tools. Details may be found in the review article [7]. Besides spectroscopy, the dualcomb technique proves also useful for characterizing frequency comb generators and for other applications of interferometry.…”