The optical system of an imaging spectrometer working on a geostationary earth orbit (GEO) covering a full optical spectrum of 0.3–12.5 μm is analyzed and designed. It enables a ground coverage of 400 × 400 km by internal scanning and achieves a high spatial resolution of 25 m. The full spectrum is divided into five sub-bands, and each band adopts four spectrometers to splice in the field of view to achieve the ultra-long slit required by the wide swath. The total length of the slit is up to 241.3 mm. This paper focuses on compact spectrometers with long slits that can meet the splicing requirements and points out that low spectral distortions, low stray light, high signal-to-noise ratio, and uniform spectral response are necessary for high-fidelity performance. The Offner and Wynne–Offner high-fidelity spectrometers based on convex blazed gratings are designed, and prototypes of each band are developed as well. The properties of long slits and convex blazed gratings are presented. The maximum length of a single slit is 61.44 mm. The groove density of gratings for five bands ranges from 8.8 lp/mm to 312.1 lp/mm, and the peak efficiency is up to 86.4%. The alignment and test of the spectrometers are introduced. Results show that the developed spectrometers have high fidelity and fulfill all requirements.

Hypericin tautomerization that involves the migration of the labile protons is believed to be the primary photophysical process relevant to its light-activated antiviral activity. Despite the difficulty in isolating individual tautomers, it can be directly observed in single-molecule experiments. We show that the tautomerization of single hypericin molecules in free space is observed as an abrupt flipping of the image pattern accompanied with fluorescence intensity fluctuations, which are not correlated with lifetime changes. Moreover, the study can be extended to a λ/2 Fabry–Pérot microcavity. The modification of the local photonic environment by a microcavity is well simulated with a theoretical model that shows good agreement with the experimental data. Inside a microcavity, the excited state lifetime and fluorescence intensity of single hypericin molecules are correlated, and a distinct jump of the lifetime and fluorescence intensity reveals the temporal behavior of the tautomerization with high sensitivity and high temporal resolution. The observed changes are also consistent with time-dependent density functional theory calculations. Our approach paves the way to monitor and even control reactions for a wider range of molecules at the single molecule level.

Video preserves valuable raw information. Understanding these data and then recognizing objects and tagging them are crucial to intelligent planning and decision making. Deep learning provides us an effective way to understand big data with a human-level. As traffic video is characterized by crowded scene and low definition, it will be non-effective to deal with the whole image once. An alternative way is to separate image and determine a small window for each moving object. A Q-learning based moving object recognition approach, which firstly finds out moving object region and then uses a Q-learning based optimization method to determine the most compact region that contain the moving object, is proposed. The algorithms enable to detect the most compact rectangle around the moving object at near real-time speed. After that, a deep neural network is used to semantic tag the recognized objects. The experiment results show the algorithms work effectively.

The structure of a grating polarizer in common 1053 nm lasers was optimized for high power laser systems. The diffraction characteristics and extinction ratio of the grating polarizer were investigated by using rigorous coupled-wave theory. The results show when the grating period, duty cycle and the groove depth of the grating are 600 nm, 0.535-0.55 and 1 395-1 420 nm at a wavelength of 1053 nm, respectively, the extinction ratio could be more than 1500, and the optical transmittance of the TM-polarized wave could be over 95%. Based on the above analysis, a high quality photoresist grating mask was made by holographic lithography. Then, it was transferred to the fused silica substrate by tilted rotating ion beam etching and reactive ion beam etching to fabricate a grating polarizer with the period of 600 nm, bottom duty cycle of 0.54 and the groove depth 1 400 nm. Experimental measurements on the grating polarizer show that the optical transmittance is 92.9% and the extinction ratio is 160. Compared with other fabricating methods for the grating polarizer, the proposed method only requires a single layer of photoresist grating mask, which simplifies the fabricating process, enjoys low costs and guarantees the high damage threshold of the grating. As the method can fabricate large scale gratings, it is suitable for applications to the high power laser systems.