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We demonstrate the use of a two-channel cavity ring-down (CRD) technique for simultaneously measuring/mapping the reflectance R, transmittance T and optical loss L (absorption plus scattering losses) of highly reflective (HR) and anti-reflective (AR) laser components. High reflectance/transmittance of HR/AR components is measured with the ring-down time of CRD signals, while the low residual transmittance/ reflectance of HR/AR components is determined by the amplitude ratio of two CRD signals, and the optical loss is then determined via L = 1-R-T. Experiments are performed to measure and map R, T, and L of HR mirrors with different transmittance levels from below 1ppm to about 70 ppm (part-per-million) and of one AR window at 635nm. For a 4 ppm-transmittance HR mirror, the measured R, T, and L at one position are 99.99821 ± 0.00004%, 4.042 ± 0.008 ppm and 13.9 ± 0.4 ppm, respectively. For the AR sample, the measured T, R, and L at one position are 99.99279 ± 0.00004%, 50.0 ± 0.7 ppm and 22.0 ± 0.4 ppm, respectively. The sub-ppm standard deviations for R, T, and L indicate the high accuracy of the two-channel CRD technique for the simultaneous measurements of reflectivity, transmittance and optical loss of HR and AR components. High-resolution mappings of R, T, and L of both HR and AR samples are demonstrated. The simultaneous measurements/mappings of reflectance, transmittance, and optical loss with sub-ppm accuracy are of great importance to the preparation of high-performance laser optics for applications such as gravitational-wave detection and laser gyroscopes.

Current optical differentiators are generally limited to realizing a single differential function once fabricated. Herein, a minimalist strategy in designing multiplexed differentiators (1st‐ and 2nd‐order differentiations), implemented with a Malus metasurface consisting of single‐sized nanostructures is proposed, thus improving the functionality of optical computing devices without the cost of complex design and nanofabrication. It is found that the proposed meta‐differentiator exhibits excellent differential‐computation performance and can be used for simultaneous outline detection and edge positioning of objects, corresponding to the functions of the 1st‐ and 2nd‐order differentiations respectively. Experiments with biological specimens showcase that boundaries of biological tissues can not only be identified, but also the edge information for realizing high‐precision edge positioning is highlighted. The study provides a paradigm in designing all‐optical multiplexed computing meta‐devices, and initiates tri‐mode surface morphology observation by combining meta‐differentiator with optical microscopes, which can find their applications in advanced biological imaging, large‐scale defect detection, and high‐speed pattern recognition, etc.