The radially polarized beams are modulated by phase-type optical needle modulators can be tightly focused to create needle-like focused beams, which are called optical needles. The use of optical needles with different resolutions and focal depths as direct writing heads for laser direct lithography enables periodic, cross-scale processing of high aspect ratio micro-nano structures with different line widths. The design of the phase-type optical needle modulators is the key to obtain optical needles with different resolutions and focal depths. However, the existing conventional methods for designing phase-type optical needle modulators rely on the physical model for generating optical needles and the defined fitness function, which makes their design time long and not adaptive. Based on the deep learning, a novel phase-type optical needle modulator design (PONMD) approach is proposed in this paper. The results show that the PONMD method takes 0.5526ms to design a phase-type optical needle modulator, and the similarity between the designed and target values is 96.73%. Compared with the conventional methods, the time consumption is reduced by about 8 orders of magnitude, and the similarity is improved by 11.19%. The PONMD approach has the advantages of adaptability, more efficient, less timeconsuming, and less computational resource-consuming.

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A total of 80 invited and contributed talks were presented at the symposium. Topics included fundamentals in CO 2 activation and advanced processes and materials for CO 2 capture, sequestration, conversion, and utilization.Anthropogenic CO 2 emission from fossil energy conversion is one of the major contributors to global climate change. With projected increase in global energy consumption, advanced carbon capture, sequestration, and utilization approaches need to be developed. As a first step for CO 2 mitigation, carbon capture can potentially be achieved, in a cost-effective manner, through new technologies that reduce the energy consumptions for separating diluted CO 2 from conventional power plant flue gas. Alternatively, smart combustion or gasification processes such as oxy-fuel or chemical-looping are capable of producing concentrated CO 2 for easy capture. Successful development and deployment of these aforementioned technologies require breakthroughs in advanced materials as well as innovative reactor concepts and process schemes. Sequestration of captured CO 2 into geological formations such as saline aquifers is the next important step to ensure long term storage of CO 2 . Besides sequestration, a number of emerging ideas have shown promise to recycle and utilize CO 2 as a carbon source for clean energy carriers or chemicals, mainly through catalytic processes. While CO 2 is thermodynamically stable, renewable energy sources like solar can accomplish the challenging task of CO 2 conversion and utilization. For example, it has been demonstrated that nanostructured photocatalysts are capable of converting CO 2 and water into C1 fuels like CO, methane or methanol under solar radiation. Extensive research efforts are underway to enhance the CO 2 conversion efficiency using these novel photocatalytic processes.This AAQR special issue includes ten papers that were selected from the Symposium on CO 2 Capture, Sequestration, Conversion and Utilization. All papers have been peer-reviewed by experts in relevant fields. Among the ten papers, two papers study CO 2 capture by sorbents, and three papers investigate new processes such as chemical-looping combustion and solar thermochemical processes for CO 2 capture. Duan et al. conducted an ab-initio thermodynamic study of CO 2 capture properties by solid sorbents. Thompson et al. investigated the degradation of amine solvents by examining the accumulation of heat stable salts in the solvent in a pilot-scale CO 2 capture experiment. Zhou et al. provided a comprehensive overview of chemical-looping combustion for CO 2 capture in fixed-bed and fluidized-bed reactors with the focus on oxygen carrier utilization and reactor efficiency. Cao et al. studied lanthanum-promoted Copper-based Oxygen Carriers for Chemical Looping Combustion. Reich et al. reported CO 2 capture using calcium oxide looping through a solar thermochemical process and provided a review on the current status of this new technology. One paper in this special issue by Soong et al. reports an experiment...

In this manuscript, a method of generating an ultra-long optical needle (depth-to-width ratio 37.5:1) is proposed and demonstrated by focusing an azimuthally polarized beam. In theory, the action mechanism between the incident beam and the amplitude modulation element, the spiral phase modulation element, the focusing lens were studied based on the Richards and Wolf's theory. The relationship between the intensity distribution of the optical needle and the structure parameter of the element were obtained, thus leading to the complete design model and design standard. In experiment, the annular amplitude modulation element and spiral phase modulation element were fabricated by lithography. The optical needle was obtained based on a custom-designed optical setup in our laboratory. The optical system consists of an annular aperture (3.9-mm inner diameter, 80-µm annular width), a spiral phase plate (topological charge of 1), and an objective lens with numerical aperture of 0.95. Finally, an optical needle with a subwavelength size (0.416λ) and an ultra-long depth of focus (15.6λ) was obtained, showing an excellent agreement with our theoretical model.