Irsweep Ag

Eth Zurich

Empa Eidgenossische Materialprufungs-Und Forschungsanstalt

Andreas Hugi

Pierre Brochard

Stéphane Schilt

Kenichi Komagata

Giulio Terrasanta

Jérôme Faist

Lukas Emmenegger

Markus Mangold

Michele Gianella

Akshay Nataraj

Gustavo Filipe Ferreira Villares

Kenich Komagata

A dual-comb spectrometer comprising two lasers outputting respective frequency combs having a frequency offset between their intermode beat frequencies. One laser acts as a master and the other as a follower. Although the master laser is driven nominally with a DC drive signal, the current on its drive input line nevertheless oscillates with an AC component that follows the beating of the intermode comb lines lasing in the driven master laser. This effect is exploited by tapping off this AC component and mixing it with a reference frequency to provide the required frequency offset, the mixed signal then being supplied to the follower laser as the AC component of its drive signal. The respective frequency combs in the optical domain are thus phase-locked relative to each other in one degree of freedom, so that the electrical signals obtained by multi-heterodyning the two optical signals are frequency stabilized.

Dual-comb spectroscopy

A dual-comb spectrometerwith two lasersserving as a local oscillator and an interrogator. The lasers output light beams with respective frequency combs C, Cof defined free spectral range, FSR. A detectorcan detect heterodyne mixing of the combined beams to detect an RF frequency comb C. Respective control signals are supplied to the lasers which have functional forms configured to cause the frequencies of the lasers' frequency combs C, Cto tune over a defined fraction of their FSR. This enables a reduction of the effective spectral sampling period by a factor equal to the ratio of the FSR to the spectral resolution of the spectrometer, which will typically be several orders of magnitude, so that the spectral sampling period can be reduced from the GHz to the MHz range, which in turn enables a gapless spectrum to be obtained in a short time.

A heterodyne detection spectrometer setup comprises an optical path with at least a first cavity able to emit a first laser beam; a second cavity able to emit a second laser beam; and at least one combining and/or reflecting element. The cavities are connected to current drivers for stimulating laser emission, which shows increased signal-to-noise ratios of the heterodyne signal and an increased dynamic range. This can be reached if at least the second cavity comprises an active medium connected to a heterodyne signal extraction element and a (multi-) heterodyne signal processing unit, which is simultaneously usable for laser light generation and as detector element, comprising an active medium introduced in the optical path in order that the first and/or second laser beam can enter the respective other cavity. At least one reference path is established between the two cavities in the optical path with at least two combining and/or reflecting elements.

(Multi-) heterodyne detection spectrometer setup

A method for optical and electrical signal processing of a multi-heterodyne signal generated by a multi-mode semi-conductor laser, for a system comprising two laser sources and an sample interaction unit. At least the beam of one of the laser passes through said sample interaction unit before being combined on a detector. The first laser is tuned () by an amount keeping the tuning result within the available detector bandwidth (). Then the second laser is roughly tuned by the same amount as the tuning of the first laser to bring back the signal to the vicinity () of the original place in the RF-domain and within the bandwidth () of the detector. The tuning steps are repeated with different value of mode spacing for reconstructing the sample spectrum and provide a high resolution image of the dip () absorption line ().

Method for optical and electrical signal processing of a multi-heterodyne signal generated by a multi-mode semi-conductor laser and detection device utilizing that method

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Zurich, Switzerland

Andreas Hugi