This work investigates the influence of light coherence on speckle imaging through a scattering layer. A focused laser is incident on a rotating ground glass (RGG). By changing the distance from the focus to the RGG, the degree of coherence of partially spatially coherent light can be controlled. Speckle correlation technique with iterative phase-retrieval algorithm and deconvolution method using point spread function are employed, and their results indicate that the lower the spatial coherence of the light, the higher the quality of the reconstructed object. Moreover, similar conclusions are obtained using an LED as light source. The results suggest that the coherence of light source should be carefully examined and selected to achieve high-quality speckle imaging through scattering layers.

The ultra-stable laser is a key component of the optical frequency standard system, where one of the primary limitations on its secondary stability index arises from thermal noise. This makes it essential to maintain the laser cavity within an extremely stable thermal environment. We develop and validate experimentally a thermal model for a typical Fabry–Pérot cavity for accuracy. To improve the thermal stability of the design, a machine learning–assisted optimization design method is proposed, which includes a deep neural network surrogate model, sensitivity analysis, and multi-objective optimization based on the Pareto front. The primary optimization targets are minimizing temperature fluctuations and system weight. A case study demonstrates the efficacy of this approach, showing that the thermal response time constant increased from 97 h before optimization to 190 h after optimization, with only a minimal weight cost. Furthermore, under an external temperature fluctuation of 1 mK, the silicon crystal’s temperature fluctuation is reduced to 0.46 μK—an improvement over the 6μK fluctuation reported in previous studies. We provide crucial guidance for the thermal design of ultra-stable laser cavities, enhancing their accuracy and performance in optical systems.

The solar occultation flux Fourier transform infrared spectrometer boasts advantages such as high resolution, broadband analysis, non-contact measurement, fast response, flexibility, and visualization, making it an indispensable and important tool for monitoring unorganized emissions from vehicles in mobile monitoring systems. However, factors such as uneven road surfaces and fast cornering can cause sunlight to jitter, which not only leads to jitter in the interference signal detected by the infrared detector but also results in an expanded angle of incidence, causing spectral broadening and wavelength shift. These effects directly influence the line shape function of the instrument. To address this issue, we propose a method for correcting interferogram jitter. This method incorporates a Savitzky–Golay filter into the interferogram processing workflow to precisely determine the baseline of the interferogram. It then corrects the jitter caused by vehicle movement, environmental vibrations, and other factors, ensuring the baseline is zeroed out. Following this correction, the standard interferogram data processing (apodization, phase correction, etc.), the same spectral conversion workflow, and the gas concentration inversion method are applied. To verify the effectiveness of our method, we compared the results processed with the calibration algorithm to those without it. The experimental results demonstrate that our correction algorithm effectively eliminates interferogram jitter, enhances the spectral signal-to-noise ratio, increases the stability of the spectral baseline, and successfully retains more affected spectral data. This ensures consistency in the retrieval of atmospheric composition, providing robust support for the application of vehicle-mounted solar occultation flux Fourier transform spectrometer technology in mobile monitoring systems. It fully meets the demand for spectral data processing in such systems.

The characteristics of photonic nanojets (PNJs) generated by layered semi-elliptical microcolumns are numerically simulated based on the 2D finite-difference time-domain method. The simulation results demonstrate that compared with the semi-elliptical microcolumn, the full width half maximum (FWHM) (230 nm) of the layered semi-elliptical microcolumn is narrower, whereas its focal length and effective length L (∼66λ) are longer, which is four times that of the semi-elliptical microcolumn. Furthermore, we investigate the effects of shell-to-core ratio, refractive index contrast, and wavelength on PNJ regulation. The findings indicate that a thin-shell semi-elliptical microcolumn exhibits superior performance in generating PNJs. Finally, the properties of PNJs produced by semi-elliptical microcolumns with gradient refractive index distribution are studied, and the effects of refractive index gradient and stratification number on the control of PNJs are systematically investigated. The results show that with the increase in the number of layers, the FWHM of the photonic nanojet can be further reduced. We study the effect of stratification and refractive index distribution on the optimal control of PNJ. This will provide a reference for the application of layered semi-elliptical microcolumns in the fields of high-resolution optical imaging, biophotonics, far-field lithography, and optical data storage.