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Nature Communications 11(1), 4164 (2020). doi:10.1038/s41467-020-17908-9, Photo-acoustic spectroscopy (PAS) is one of the most sensitive non-destructive analysis techniques for gases, fluids and solids. It can operate background-free at any wavelength and is applicable to microscopic and even non-transparent samples. Extension of PAS to broadband wavelength coverage is a powerful tool, though challenging to implement without sacrifice of wavelength resolution and acquisition speed. Here we show that dual-frequency comb spectroscopy (DCS) and its potential for unmatched precision, speed and wavelength coverage can be combined with the advantages of photo-acoustic detection. Acoustic wave interferograms are generated in the sample by dual-comb absorption and detected by a microphone. As an example, weak gas absorption features are precisely and rapidly sampled; long-term coherent averaging further increases the sensitivity. This novel approach of dual-frequency comb photo-acoustic spectroscopy (DCPAS) generates unprecedented opportunities for rapid and sensitive multi-species molecular analysis across all wavelengths of light., Published by Nature Publishing Group UK, [London]

Optics letters 45(24), 6583 - 6586 (2020). doi:10.1364/OL.410762, Hyperspectral imaging provides spatially resolved spectral information. Utilizing dual-frequency combs as active illumination sources, hyperspectral imaging with ultra-high spectral resolution can be implemented in a scan-free manner when a detector array is used for heterodyne detection. Here, we show that dual-comb hyperspectral imaging can be performed with an uncooled near-to-mid-infrared detector by exploiting the detector array’s high frame rate, achieving 10 Hz acquisition in 30 spectral channels across 16,384 pixels. Artificial intelligence (AI) enables real-time data reduction and imaging of gas concentration based on characteristic molecular absorption signatures. Owing to the detector array’s sensitivity from 1 to 5 µm wavelength, this demonstration lays the foundation for real-time versatile imaging of molecular fingerprint signatures across the infrared wavelength regime with high temporal resolution., Published by OSA

A light pulse source (100), being adapted for generating repetitive optical pulses, comprises a continuous wave (cw) laser (10) being arranged for providing cw laser light, an optical microresonator (20) being made of a resonator material, which has a third order (Kerr) nonlinearity and an anomalous resonator dispersion, wherein the cw laser (10) is arranged for coupling the cw laser light into the optical microresonator (20), which, at a predetermined relative detuning of the cw laser (10) and the optical microresonator (20), is capable of including a light field in a soliton state, wherein soliton shaped pulses can be coupled out of the optical microresonator (20) for providing the repetitive optical pulses, and a tuning device (30) being arranged for creating and maintaining the predetermined relative detuning of the cw laser (10) and the optical microresonator (20); based on a tuning time profile being selected in dependency on a thermal time constant of the optical microresonator (20) such that the soliton state is achieved in a thermal equilibrium state of the optical microresonator (20). Furthermore, a method of generating repetitive optical pulses is described based on soliton shaped pulses coupled out of an optical microresonator (20) is described.

Astronomical spectroscopy allows detection of exoplanets and their atmospheres, and gives insights into variability of physical constants. Astronomical spectrographs require suitable wavelength reference to provide precise and accurate measurements. Laser frequency combs have been recognised as an invaluable tool in spectrograph calibration. This thesis reports on the development and on-site test of two laser frequency combs operating in the near-infrared wavelength range. Both systems, the electro-optic frequency comb and Kerr frequency comb, are based on technologies providing directly high repetition rate (>10 GHz) operation and a calibration precision at the level of tens of cm/s. Furthermore, a novel technique for frequency comb generation in the visible wavelength range is demonstrated, which relies on triple-sum frequency generation in a nonlinear optical waveguide. This thesis contributes to the development of astronomical spectroscopy by offering perspectives for the improvement of existing and future extreme precision astronomical spectrographs.