Linear dual-comb interferometry at high power levels.

Detector non-linearity is an important factor limiting the maximal power and hence the signal-to-noise ratio (SNR) in dual-comb interferometry. To increase the SNR without overwhelming averaging time, photodetector non-linearity must be properly handled for high input power. Detectors exhibiting nonlinear behavior can produce linear dual-comb interferograms if the area of the detector's impulse response does not saturate and if the overlap between successive time-varying impulse responses is properly managed.

Correcting spectral baseline fluctuations in dual-comb interferometry.

A method to measure and correct for spectral baseline fluctuations in dual-comb interferometry is presented. Fluctuations can be measured from the amplitude of beat notes between combs and a continuous wave laser or from a separate measurement of the combs' repetition rates, filtered around the spectral region of interest. Amplitude-dependent spectral variations are characterized using low-resolution Fourier transforms around the centerburst of several interferograms, and a nonstationary filter is applied to properly account for the combs' variations during the measurement.

Correcting photodetector nonlinearity in dual-comb interferometry.

Photodetector nonlinearity, the main limiting factor in terms of optical power in the detection chain, is corrected to improve the signal-to-noise ratio of a short-time measurement in dual-comb spectroscopy. An iterative correction algorithm minimizing out-of-band spectral artifacts based on nonlinearity correction methods used in classical Fourier-transform spectrometers is presented. The exactitude of the nonlinearity correction is validated using a low power linear measurement.

Toward free-running operation of dual-comb fiber lasers for methane sensing.

The phase information provided by the beat note between frequency combs and two continuous-wave lasers is used to extrapolate the phase evolution of comb modes found in a spectral region obtained via nonlinear broadening. This thereafter enables using interferogram self-correction to fully retrieve the coherence of a dual-comb beat note between two independent fiber lasers. This approach allows the $ f - 2f $f-2f self-referencing of both combs, which is a significant simplification.

External serrodyne modulation for the suppression of low-frequency noise in quadrature interferometry.

In interferometry, reaching a high signal-to-noise ratio at low frequencies can be challenging when the additive noise is nonstationary. Although this problem is typically solved by inserting a frequency shifter into one of the arms, in some cases, the interferometer cannot or should not be modified in this way. This Letter presents an alternative solution, based on external serrodyne frequency modulation, which is comparable to the typical approach in terms of complexity and performance yet does not require the modification of a passive interferometer.

An open and flexible digital phase-locked loop for optical metrology.

This paper presents an open and flexible digital phase-locked loop optimized for laser stabilization systems. It is implemented on a cheap and easily accessible FPGA-based digital electronics platform (Red Pitaya) running a customizable open-source firmware. A PC-based software interface allows controlling the platform and optimizing the loop parameters remotely.