Time-domain mid-infrared frequency-comb spectrometer

Abstract

A novel type of Fourier-transform infrared spectrometer (FTIR) is demonstrated. It is based on two Ti:sapphire lasers emitting femtosecond pulse trains with slightly different repetition frequencies. Two mid-infrared beams-derived from those lasers by rectification in GaSe-are superimposed upon a detector to produce purely time-domain interferograms that encode the infrared spectrum. The advantages of this spectrometer compared with the common FTIR include ease of operation (no moving parts), speed of acquisition (100 micros demonstrated), and not-yet-shown collimated long-distance propagation, diffraction-limited microscopic probing, and electronically controllable chemometric factoring. Extending time-domain frequency-comb spectroscopy to lower (terahertz) or higher (visible, ultraviolet) frequencies should be feasible.

Coherent dual-comb spectroscopy at high signal-to-noise ratio

“…Also visible at 14 ps is a weak ringing containing absorption information from an HCN gas sample. (d) The equivalent frequency domain description of the coherent dual-comb spectrometer [1,2]. In the frequency domain each comb creates an array of discrete teeth.…”

“…1, the basic approach of dual comb spectroscopy is to interfere two combs with repetition periods differing slightly by f r . If the two combs are combined before the sample, the system is analogous to traditional FTS [1,2,7] and yields the intensity absorption spectrum only. Alternatively, as is done here and in [3,6,8], the source comb passes through the sample and afterwards be combined with a local oscillator (LO) comb.…”

“…The use of free-running combs, i.e. femtosecond lasers, is certainly the simplest method and was used in a pioneering demonstration of dual comb spectroscopy [1]; however such an approach provides no absolute frequency accuracy, has limited frequency resolution and coherent averaging is challenging (although coherent averaging has been achieved in the far-IR where carrier phase is less of a problem [3]). In an intermediate approach, the carrier frequency of each comb is phase-locked to a common reference cw laser, and the pulse repetition rates are monitored [40,41].…”

“…The use of an optical filter is not absolutely necessary [1,2,7,8] and might at first seem unwanted. On one hand the filter reduces the power on the detector and requires multiple measurements to reconstruct the spectrum.…”

Frequency comb assisted diode laser spectroscopy for measurement of microcavity dispersion

“…Within the last decade, the invention of the optical frequency comb has revolutionized the field of spectroscopy and allowed measurements with previously unattainable precision [1,2,3]. However, despite significant advances [4,5,6,7,8], the use of frequency combs for precise broadband spectroscopy has remained challenging owing to low optical power per comb line and the difficulty to resolve features that are smaller than the combs free spectral range.Here, we present a novel and easy-to-use scheme for fast, broadband and precise spectroscopy combining the accuracy of an optical frequency comb with the broad bandwidth, high power and tunability of a mode-hopfree external cavity diode laser. We achieve sub-MHzresolution over a bandwidth exceeding 4 THz in the 1550-nm range at scanning speeds up to 1 THz per second.…”