Silicon, Regression Analysis, statistical analysis, Measurement by laser beam, adaptive optics, chemical sensors, elemental semiconductors, infrared detectors, infrared spectra, laser noise, light interference, light interferometry, light reflection, optical sensors, optical waveguides, organic compounds, photodetectors, Allan-variance analysis, fringe subtraction models, dynamic etalon fitting-routine, on-chip silicon waveguide, time-varying etalon drifts, light reflections, nonlinear regression model, high index contrast waveguide-based laser absorption spectrometers, long-term stability improvement, adaptive etalon suppression technique, absorption sensor, on-chip sensor embodiment, Gaussian-noise limited performance, stochastic line-edge roughness imperfections, near-infrared methane absorption spectroscopy, spectral baseline recalibration interval, etalon spectral background, line-scanned optical absorption spectrometers, size 10.0 cm, Si