RESUMEN
We demonstrate mid-infrared time-domain optical coherence tomography (OCT) with an orientation-patterned GaP optical parametric oscillator. Instantaneous broadband mid-infrared spectra provide reduced scattering for OCT applications including cultural heritage, quality assurance, and security. B-scan calibrations performed across the wavelength tuning range show depth resolutions of 67â µm at 5.1â µm and 88â µm at 10.5â µm. Volumetric imaging inside a plastic bank card is demonstrated at 5.1â µm, with a 1â Hz A-scan rate that indicates the potential of stable broadband OPO sources to contribute to mid-infrared OCT.
RESUMEN
Spectrally-resolved imaging provides a spectrum for each pixel of an image that, in the mid-infrared, can enable its chemical composition to be mapped by exploiting the correlation between spectroscopic features and specific molecular groups. The compatibility of Fourier-transform interferometry with full-field imaging makes it the spectroscopic method of choice, but Nyquist-limited fringe sampling restricts the increments of the interferometer arm length to no more than a few microns, making the acquisition time-consuming. Here, we demonstrate a compressive hyperspectral imaging strategy that combines non-uniform sampling and a smoothness-promoting prior to acquire data at 15% of the Nyquist rate, providing a significant acquisition-rate improvement over state-of-the-art techniques. By illuminating test objects with a sequence of suitably designed light spectra, we demonstrate compressive hyperspectral imaging across the 700-1400â cm-1 region in transmission mode. A post-processing analysis of the resulting hyperspectral images shows the potential of the method for efficient non-destructive classification of different materials on painted cultural heritage.
RESUMEN
A multi-GHz frequency comb (astrocomb) is typically realized by filtering modes of a sub-GHz frequency comb (source comb) in a Fabry-Pérot etalon, which can lead to ambiguities in determining which subset of source comb modes has been filtered. Here we demonstrate a broadband Fourier-transform spectrometer (FTS) with a resolving power of R = 430,000 at 550 nm, and apply it to the identification of comb subsets from a filtered 1GHz supercontinuum. After apodization the FTS demonstrated an instrument line shape width of 1.26 GHz which enabled individual comb-line positions to be identified with an uncertainty of 17.6 MHz, a relative precision of 5 × 10-8. Correcting for air dispersion allowed the instrument to determine the comb-mode spacing to an accuracy of 300 Hz and filtered subsets of source comb modes to be uniquely distingished across the entire comb bandwidth from 550 to 900 nm. The inherently broadband design of the FTS makes it suitable in future applications for calibrating ultra-broadband astrocombs employed by instruments such as ELT HIRES.
RESUMEN
A new regime of precision radial-velocity measurements in the search for Earth-like exoplanets is being facilitated by high-resolution spectrographs calibrated by laser frequency combs. Here we review recent advances in the development of astrocomb technology, and discuss the state of the field going forward.