Common organic modification of metal superhydrophobic surface has these problems such as serious environmental pollution, high thermal resistance, low processing efficiency, and easy to fall off. A chemical-free direct laser selective texturing technology is proposed to enhance condensation heat transfer performance on stainless steel surface. A micro-textured steel plate was processed by nanosecond pulsed laser to obtain a superhydrophilic surface of a square grid groove-convex structure. After heat treatment, the superhydrophilic surface changed to be superhydrophobic. The superhydrophobic surface was then laser selective textured to get a wedge-shaped superhydrophilic-superhydrophobic surface. Surface morphology, chemical composition and three-dimensional profile were analyzed. By comparing the superhydrophobic and superhydrophilic surfaces, the back-surface temperature and the average detached diameter of the condensed droplets was measured. Furthermore, the surface condensation heat transfer coefficient of samples was calculated according to the relevant condensing heat transfer theory. At the same time, samples with different area ratios of laser textured superhydrophilic-superhydrophobic were designed for heat transfer analysis. Condensation results showed that the heat transfer coefficient of the selective-textured surfaces was enhanced compared to the full laser textured superhydrophobic surface. After the condensed droplet grew to the superhydrophobic boundary of the laser selected area, it was restricted to grow and merge quickly and then was removed by self-transport in the wedge-shaped superhydrophilic area. The laser textured patterns showed a smaller detachment diameter than the fully superhydrophobic surface and had enhanced condensation heat transfer coefficient, as laser textured superhydrophilic-superhydrophobic areas are equal.
Based on the beam propagation method, a compact 1 × 16 polymeric optical splitter with center wavelength ∼1550 nm is designed for electro-optical printed circuit board (EOPCB). The length of the optical splitter is 20,000 μm. Spacing between each output port is 127 μm. The cross section of the optical splitter is 10 μm × 10 μm. The silicon glass is chosen as a substrate material of the optical splitter, the cladding material of the optical splitter is air, and the core material of the optical splitter is SU8 polymer. It is fabricated for a 1 × 16 chip-to-chips optical interconnect by femtosecond laser. The testing results show that average insertion loss per channel for the optical splitter is IL ≤ 20 dB and the uniformity for the optical splitter is Cu ≈ 1.42 dB. It is very suitable for the optical interconnection of EOPCB.
Diffractive telescope technology is an innovation solution in construction of large light-weight space telescope. However, the nondesign orders of diffractive optical elements (DOEs) may affect the imaging performance as stray light. To study the stray light characteristics of a diffractive telescope, a prototype was developed and its stray light analysis model was established. The stray light characteristics including ghost, point source transmittance, and veiling glare index (VGI) were analyzed. During the star imaging test of the prototype, the ghost images appeared around the star image as the exposure time of the charge-coupled device improving, consistent with the simulation results. The test result of VGI was 67.11%, slightly higher than the calculated value 57.88%. The study shows that the same order diffraction of the diffractive primary lens and correcting DOE is the main factor that causes ghost images. The stray light sources outside the field of view can illuminate the image plane through nondesign orders diffraction of the primary lens and contributes to more than 90% of the stray light flux on the image plane. In summary, it is expected that these works will provide some guidance for optimizing the imaging performance of diffractive telescopes.
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