Beam-shaped femtosecond laser printing of quasi-capsule-shaped holographic terahertz metasurfaces.

Terahertz (THz) metasurfaces have opened up a new avenue for the THz wavefront modulation. However, high-efficient and low-cost fabrication of THz metasurfaces remains a great challenge today. Here, quasi-capsule-shaped polarization-multiplexed holographic THz metasurfaces were printed by a beam-shaped femtosecond laser. The laser beam was spatially modulated by holograms of optimized cylindrical lens loaded on a spatial light modulator (SLM). The size of quasi-capsule apertures can be exquisitely and flexibly controlled by adjusting the focal length in holograms, pulse energy, and pulse number. Based on near-field diffraction and Burch encoding, an array of 100 × 100 basic unit apertures were initially designed, and a polarization-multiplexed THz metasurface was finally printed with a dimension of 8 mm × 8 mm. The function of polarization multiplexing was demonstrated, by which two kinds of images were reconstructed in response to X and Y-polarization THz waves, respectively. The present work highlights a great leap in fabrication method for THz metasurfaces and hopefully stimulates the development of miniaturized and integrated THz systems.

[Comparison of the efficacy of TiRobot orthopaedic robot assisted F screw technique and inverted triangle parallel nail internal fixation in the treatment of unstable femoral neck fractures].

OBJECTIVE: To compare the effectiveness of TiRobot assisted F screw technique and inverted triangle parallel nail internal fixation in the treatment of unstable femoral neck fractures. METHODS: A retrospective analysis was conducted on 72 patients with unstable femoral neck fractures who were treated with percutaneous cannulated screw fixation assisted with TiRobot Orthopaedic robot from December 2019 to April 2021. Among them, 37 patients were treated with F screw internal fixation, including 16 males and 21 females, aged 47 to 64 years old with an average of （53.87±5.28） years old；According to Pauwels classification, there were 1 case of type Ⅰ, 19 cases of type Ⅱ, 17 cases of type Ⅲ；8 cases of combined medical diseases；17 cases of falling, 8 cases of traffic accident and 12 cases of falling from height；The time from injury to operation was 29 to 49 hours with average of （35.00±7.34） hours. Another 35 cases used internal fixation with an inverted triangle parallel nail, including 13 males and 22 females with an average age of 46 to 63 years old （52.36±5.05） years old；According to the Pauwels injury classification：there were 2 cases of type Ⅰ, 21 cases of type Ⅱ, 12 cases of type Ⅲ；6 cases of medical diseases, 15 cases of falling injury, 9 cases of traffic accident, 11 cases of falling injury；The time from injury to operation was 30 to 45 hours with an average of （33.00±6.83） h. The intraoperative blood loss, operation time, intraoperative fluoroscopy times, follow-up time, fracture healing time, postoperative complications were observed and compared between the two groups. The hip joint function was evaluated by Harris score at 6 months and 12 months after operation. RESULTS: There was no significant difference in operation time, intraoperative blood loss, intraoperative fluoroscopy times and other intraoperative data between two groups（P>0.05）. Both groups were followed up regularly, and the follow-up time was 12 to 16 months. The fracture healing time and Harris score of the F screw internal fixation group were better than those of the inverted triangle parallel nail internal fixation group （P<0.05）. There was 1 case of femoral neck shortening in the F screw internal fixation group, 1 case of nonunion, 1 case of nail withdrawal, and 1 case of lower extremity deep vein thrombosis in the inverted triangle internal fixation group. The incidence of complications in the F screw internal fixation group was lower than that in the inverted triangle parallel nail internal fixation group（P<0.05）. CONCLUSION: Percutaneous cannulated F screw technique using Tirobot navigation positioning system is a safe and effective treatment for patients with unstable femoral neck fractures. It can significantly shorten the fracture healing time, reduce the incidence of postoperative complications, significantly improve hip joint function, and improve the quality of life.

Tunable color generation in CdTe-doped silicate glass enabled by ultrashort laser pulses: interior coloring and multilevel encryption.

The launch of the big data era puts forward challenges for information security. Herein, a new kind of silicate glass system co-doped with CdO and ZnTe, capable of achieving the controllable generation of intrinsic color centers (brown and green) and tiny nuclei of CdTe via direct laser writing (DLW), is developed. The controlled growth of CdTe QDs thermally, leads to a permanent color of orange at the cost of accelerated aging of the color centers of brown and green. On the one hand, going beyond traditional 2D surface coloration, the high transparency of the studied bulk medium makes 3D volumetric interior coloration possible. On the other hand, by encoding ciphertext into the tiny nuclei of CdTe, a strategy of color encryption and heat decryption is established, which brings about the merits of expanded storage capacity and improved information security. The demonstration application confirmed the user-defined multiscale interior coloration and an unprecedented multidimensional color-encryption scheme with a high-security level. The present work highlights a great leap in transparent materials for color encryption and hopefully stimulates the development of new color division multiplexing encryptions.

Femtosecond laser nanoprinting of anisotropic plasmonic surfaces: coloration and anticounterfeiting.

An anisotropic plasmonic surface of nanoellipsoid arrays is successfully fabricated on an Au film using slit-shaping-based femtosecond laser nanoprinting. The size and orientation of the nanoellipsoid can be exquisitely and flexibly controlled by adjusting the width and direction of the slit and the laser pulse energy. By dark-field optical micro-spectroscopy, anisotropic plasmonic color rendering as well as resonant light scattering from the lateral and vertical modes are experimentally and theoretically investigated in the visible spectral range. In addition, prospective use in the fields of steganographic encryption and multidimensional optical multiplexing is also proposed.

Recording, erasing, and rewriting of ripples on metal surfaces by ultrashort laser pulses.

Recording, erasing, and rewriting of ripples are achieved by applying femtosecond laser pulses on tungsten surfaces. Ripples oriented perpendicular to the polarization direction of the writing beam can be recorded on a metal surface by exposing the sample to a series of linearly polarized pulses. When applying the second series of pulses with varied polarization direction on the same place, the original ripples can be erased, and new ripples are rewritten with the orientation perpendicular to the polarization of the second group of pulses. The simulation shows that when original ripples exist, laser intensity is focused above the grooves with polarization parallel to original ripples, which can erase the ripples. However, when the polarization is perpendicular to the existing ripples, laser intensity is almost confined in the grooves, which accelerates the formation of ripples.

Ultrashort pulsed laser induced heating-nanoscale measurement of the internal temperature of dielectrics using black-body radiation.

The nanoscale measurement of temperature in the bulk of dielectrics initiated by a single ultrashort laser pulse was first investigated by black-body radiation. A structureless broad continuum emission has been recorded at an interval delay of 2 ns with a temporal gate of 2 ns and spectral resolution of about 0.137 nm, which provides the highest temporal and spectral precision ever. The temporally resolved emission spectrum was proved to be black-body radiation in nature, and temperature was obtained by fitting the radiation with the Planckian formula. Pulse energy was varied from 110 to 270 µJ at 600 fs and a pulse duration of 0.83 ns was also used. The temperature exhibited a small variation with an increasing pulse energy at 600 fs. However, due to the energy transfer from heated electrons to lattice, the temperature was sharply increased at pulse duration of 0.83 ns. It was estimated that heat accumulation started at 0.42-0.47 MHz for a laser pulse at 600 fs, while it was 0.25 MHz for a laser pulse at 0.83 ns.

Recovery process of optical stopping effect in tin or phosphorus-doped amorphous As2S8 thin-film waveguide.

In this research, the recovery process of the optical stopping effect on an amorphous arsenic sulfide thin-film waveguide is studied, both on the net As(2)S(8) and doping As(2)S(8) waveguide. Based on the experimental results, we analyzed the chemical bond structure of the samples. The hybrid orbital theory and electron energy bandgap theory are applied in order to establish the model of optical stopping and the recovery process. The numerical analysis results are well matched with the experiment data, which indicates that the model properly explains the optical stopping effect phenomenon. The model also can be applied to predict the recovery process of the optical stopping effect.