Mechanism and characterization of nanosecond laser rust-removal on AH36 steel

In this paper,the effects of different laser powers,repetition rates,and spot overlaps on the surface roughness,micromorphology,and Vickers hardness of rusted AH36 steel were researched in the rust removal experiment of fiber pulse laser on the marine steel surface.Then,the mechanical properties,corrosion resistance,and metallographic microstructure of the surface of samples after laser cleaning were analyzed.The experimental results show that when the processing parameters were the laser power of 40 W,the repetition rate of 110 k Hz,and the spot overlap of 50%,the rust removal effect on AH36 steel was the best,and it met the cleanliness standard of marine steel coating.Moreover,its Vickers hardness,mechanical properties,corrosion resistance,and repainting properties were superior to those of the original substrate.

Design and implementation of a jellyfish otolith-inspired MEMS vector hydrophone for low-frequency detection

Detecting low-frequency underwater acoustic signals can be a challenge for marine applications.Inspired by the notably strong response of the auditory organs of pectis jellyfish to ultralow frequencies,a kind of otolith-inspired vector hydrophone(OVH)is developed,enabled by hollow buoyant spheres atop cilia.Full parametric analysis is performed to optimize the cilium structure in order to balance the resonance frequency and sensitivity.After the structural parameters of the OVH are determined,the stress distributions of various vector hydrophones are simulated and analyzed.The shock resistance of the OVH is also investigated.Finally,the OVH is fabricated and calibrated.The receiving sensitivity of the OVH is measured to be as high as−202.1 dB@100 Hz(0 dB@1 V/μPa),and the average equivalent pressure sensitivity over the frequency range of interest of the OVH reaches−173.8 dB when the frequency ranges from 20 to 200 Hz.The 3 dB polar width of the directivity pattern for the OVH is measured as 87°.Moreover,the OVH is demonstrated to operate under 10 MPa hydrostatic pressure.These results show that the OVH is promising in low-frequency underwater acoustic detection.

Fabrication of sapphire rib waveguides using a femtosecond laser

We demonstrate a method for fabricating sapphire rib waveguides with femtosecond laser micromachining technology. Finite difference beam propagation method(FD-BPM) is applied to design sapphire rib waveguides. We explore the process of etching on a sapphire substrate surface via direct laser ablation. Rib waveguides that satisfies the dimensions of our design were fabricated. Actual light propagation performance is tested, and with the cut-back method, the insertion loss of 2.9±0.5 dB/cm is measured.

Fabricating lifted Haar transform image compression optical chip based on femtosecond laser

In this paper,a lifted Haar transform(LHT)image compression optical chip has been researched to achieve rapid image compression.The chip comprises 32 same image compression optical circuits,and each circuit contains a 2×2 multimode interference(MMI)coupler and aπ/2 delay line phase shifter as the key components.The chip uses highly borosilicate glass as the substrate,Su8 negative photoresist as the core layer,and air as the cladding layer.Its horizontal and longitudinal dimensions are 8011μm×10000μm.Simulation results present that the designed optical circuit has a coupling ratio(CR)of 0:100 and an insertion loss(IL)of 0.001548 d B.Then the chip is fabricated by femtosecond laser and testing results illustrate that the chip has a CR of 6:94 and an IL of 0.518 d B.So,the prepared chip possesses good image compression performance.