A dynamic-mode-decomposition-based acceleration method for unsteady adjoint equations at low Reynolds numbers

The computational cost of unsteady adjoint equations remains high in adjoint-based unsteady aerodynamic op-timization.In this letter,the solution of unsteady adjoint equations is accelerated by dynamic mode decomposi-tion(DMD).The pseudo-time marching of every real-time step is approximated as an infinite-dimensional linear dynamical system.Thereafter,DMD is utilized to analyze the adjoint vectors sampled from these pseudo-time marching.First-order zero frequency mode is selected to accelerate the pseudo-time marching of unsteady adjoint equations in every real-time step.Through flow past a stationary circular cylinder and an unsteady aerodynamic shape optimization example,the efficiency of solving unsteady adjoint equations is significantly improved.Re-sults show that one hundred adjoint vectors contains enough information about the pseudo-time dynamics,and the adjoint dominant mode can be precisely predicted only by five snapshots produced from the adjoint vectors,which indicates DMD analysis for pseudo-time marching of unsteady adjoint equations is efficient.

Reflective ultrathin light-sheet microscopy with isotropic 3D resolutions

Light-sheet fluorescence microscopy(LSFM)has played an important role in bio-imaging due to its advantages of high photon efficiency,fast speed,and long-term imaging capabilities.The perpendicular layout between LSFM excitation and detection often limits the 3D resolutions as well as their isotropy.Here,we report on a reflective type light-sheet microscope with a mini-prism used as an optical path reflector.The conventional high NA objectives can be used both in excitation and detection with this design.Isotropic resolutions in 3D down to300 nm could be achieved without deconvolution.The proposed method also enables easy transform of a conventional fluorescence microscope to high performance light-sheet microscopy.

Detour-phased perovskite ultrathin planar lens using direct femtosecond laser writing

Perovskite-enabled optical devices have drawn intensive interest and have been considered promising candidates for integrated optoelectronic systems.As one of the important photonic functions,optical phase modulation previously was demonstrated with perovskite substrate and complex refractive index engineering with laser scribing.Here we report on the new scheme of achieving efficient phase modulation by combining detour phase design with 40 nm ultrathin perovskite films composed of nanosized crystalline particles.Phase modulation was realized by binary amplitude patterning,which significantly simplifies the fabrication process.Perovskite nanocrystal films exhibit significantly weak ion migration effects under femtosecond laser writing,resulting in smooth edges along the laser ablated area and high diffractive optical quality.Fabrication of a detour-phased perovskite ultrathin planar lens with a diameter of 150μm using femtosecond laser scribing was experimentally demonstrated.A high-performance 3D focus was observed,and the fabrication showed a high tolerance with different laser writing powers.Furthermore,the high-quality imaging capability of perovskite ultrathin planar lenses with a suppressed background was also demonstrated.