High-Spectral-Resolution Imaging Spectroscopy with a Dual-Comb Interferometer

Abstract

Imaging absorption spectroscopy with laser frequency combs simultaneously measures 64 spectra at 250-MHz resolution over a span of 4 nm, within 3 seconds. At 1000 s averaging, the high signal-to-noise ratio reaches 250 per pixel.

Advances in Digital Holographic Interferometry

“…The usage of an interferometer based on two frequency ranges with slightly different repetition frequencies and a camera sensor without a lens allows for recording time-varying spatial interference patterns that generate spectral hypercubes of complex holograms, revealing the amplitudes and phases of scattered wave fields for each frequency of the comb line [ 3 , 11 ]. A similar method is used by other authors [ 12 ]. They exploit the high-resolution spectroscopy with the spectra in the form of frequency combs, which simultaneously measure 64 spectra with a resolution of 250 MHz in the 4 nm range during 3 s. When averaging 1000 s, the signal-to-noise ratio reaches 250 per pixel.…”

“…At the same time, for example, the recording of holograms at three wavelengths with subsequent reconstruction of their multiplex is used to further expand the range of the measured relief Δ z [ 40 , 41 , 42 , 43 ]. It is also possible to use two frequency comb generators for recording holograms [ 12 ]. This allows you to expand the range of the measured relief almost indefinitely without increasing the level of phase noise.…”

Dual-comb hyperspectral digital holography

“…We therefore resort to modulator-based combs with fewer than 100 comb lines, but excellent passive mutual coherence [27,28]. The few previous experiments combining detector matrices and dual-comb interferometers have all made use of a double acousto-optic-frequency-shifter scheme [17][18][19][20], where the two combs are shifted by a slightly different radio-frequency, enabling to center the down-converted comb at frequencies on the order of tens of Hz. To increase the effective spectral span, we actually employ two sub-combs in each frequency comb, separated in frequency by several hundred GHz, as has been done before in spectrally-tailored dual-comb spectroscopy with thin-film lithium-niobate-oninsulator electro-optic micro-rings [24].…”

“…With a set-up which seemingly involves merely the same simple hardware as that harnessed for dual-comb hyperspectral imaging [17][18][19][20] -two frequency-comb generators and a detector matrix-, we take a new route to lens-less scan-free 3D-profiling, suited to dimensional metrology of macroscopic and microscopic objects and to advanced optical sensing that combines spatial and spectral information.…”

“…For instance, if the object absorbs or if an absorber is in the beam path, the amplitude of the reconstructed images additionally reveals its spectral absorption map, enabling identification and quantification. Unlike dualcomb hyperspectral imaging [17][18][19][20], dual-comb digital holography provides 4D information (3D spatial and spectral dimensions). Beside hyperspectral imaging, our technique might also be reminiscent -to readers familiar with frequency combs-of the single-photodetector dual-comb ranging technique which combines time-of-flight (LIDAR) and interferometric distance measurements [23].…”