Flattop beams are in high demand for a variety of applications, including uniform surface treatment, interference laser processing, repairing and skin therapy. In this experiment, we optimized the direction of phase grating to spatially separate the beam into extracted and residual components in the Fourier plane, and spatially filtered the components to form a square or hexagonal flattop beam with no wave-like structure inside and high edge steepness.

Low molecular weight silicones were ejected from silicone rubber target irradiated by a 193 nm ArF excimer laser through the photo-desorption. The ejected silicones were successfully deposited on a fused silica glass substrate in air. An approximately 0.3 mm of the target-substrate distance was required for the deposition. The deposited silicones became a thin film, showing an interference color when the ArF excimer laser was irradiated for a long time. Chemical bonding state of the formed thin films was analyzed by the Fourier transform infrared spectroscopy. The thin films were slightly different from the original silicone rubber structure, still it was composed of Si-O-Si bonds and Si-CH₃ bonds. Also, OH bonds were clearly produced in the silicone thin films. As a result, contact angle of water on the silicone thin films was measured to be approximately 20 degrees, indicating a hydrophilic property.

We have demonstrated that 7-fs, ~810-nm laser pulses can produce a much finer periodic nanostructure on a diamond-like carbon (DLC) film than that formed with 100-fs, ~800-nm laser pulses through ablation in air. The minimum period size is ~60 nm, corresponding to ~1/13 of the center wavelength. We report the physical mechanism responsible for finer nanostructuring. It has been found that the thickness of bonding structural changes with 7-fs pulses is much thinner than that with 100-fs pulses. The results show that the 7-fs pulses with high peak power density at low fluence create a few-nm-thick layer with high-density electrons and excite short-range surface plasmon polaritons, which have a large wave number around the layer and induce the plasmonic near-field nanoablation. The period size estimated by using a model target reproduces well the observed size of nanostructures.

Laser processing has great potential for precision microfabrication of various materials including hard-to-machine materials, and has a high affinity for digital transformation. The productivity and quality of laser micromachining depend on multiple laser parameters. For those optimizations, the quick survey of laser parameters in wide range is vital. Recently, we have developed Yb-doped fiber chirped-pulse amplification system that can control various laser parameters in a wide range (pulse duration: 0.4 to 400 ps, repetition: single shot to 1 MHz, etc.). In this work, using this laser system, percussion micro-drilling of glass materials, such as silica glass and alkali-free boro-aluminosilicate glass, was investigated with pulse duration and fluence as wide-range variables. The repetition rate and number of shots were fixed at 1 MHz and 100. The ablation was observable when the pulse duration was below 30 ps and 50 ps for silica glass and alkali-free boro-aluminosilicate glass, respectively. From the ablation volume dependence on laser fluence, the ablation threshold of silica glass was much higher than that of alkali-free boro-aluminosilicate glass. The fast and comprehensive survey of ultrafast laser ablation of glass materials was demonstrated.

Co patterns were fabricated by using femtosecond laser pulse-induced thermochemical reduction of glyoxylic acid Co complex. Glyoxylic acid Co complex was synthesized by mixing CoSO₄·7H₂O and glyoxylic acid, following that the complex was dissolved in 2-aminoethanol/ethanol. Femtosecond laser pulses were focused and irradiated to the glyoxylic acid Co complex films spin-coated on glass substrates to form patterns. The minimum line width was 4 µm, which was larger than the focal spot diameter, indicating that the precipitation was induced by thermochemical reduction. The crystal structures of the patterns which were fabricated at high scanning speed, 10 and 20 mm/s, exhibited Co(fcc), suggesting that the precipitated Co nanoparticles from glyoxylic acid Co complex were sintered without the phase transition to Co(hcp). In contrast, CoO patterns were formed at low scanning speed, 1 mm/s. These results suggested that precipitated Co was oxidized by ambient oxygen in air by irradiating excess laser pulse energy. The metal Co direct writing technique is useful for printing of various microdevices.

Adaptive optics for compensating wavefront aberrations is important because the aberrations cause focal spot distortion leading to loss of resolution in laser processing. In this paper, femtosecond laser processing with adaptive optics based on machine learning was demonstrated. The aberrations existing in the laser processing system were continuously predicted by the trained neural network with an update period of 36 ms and were compensated by a liquid crystal spatial light modulator. In the experiment, the machine learning-based adaptive optics reduced the wavefront error in the laser processing system to most one-ninth. Furthermore, parallel laser processing by a computer-generated hologram displayed on the spatial light modulator was also demonstrated while dynamically compensating the aberrations in the system.

This paper analyzes security strength of Iseki & Hayashi's secure computation which is valid for computation of polynomial as for real numbers, and proposes a new method to improve its security strength. First we derive the fact that Iseki & Hayashi's secure computation is deciphered if the value of single input variables of the computation is known. This implies that the security strength of Iseki & Hayashi's secure computation is bounded by the length of bits which can be inputted to this single variable. To improve this bound to be more secured, we propose a technique to repeat steps of Iseki & Hayashi's secure computation until its security strength becomes sufficiently powerful. A simple relationship about security strength between Iseki & Hayashi's secure computation and our proposal is found, and it shows security strength becomes quickly powerful with the increase of number of repetitions. Finally, numerical examples are demonstrated to show the effectiveness of our proposal.

In recent years, various user interfaces have been developed to meet the diverse needs of physically disabled persons. In this paper, we developed a method to identify gazing and facial movements based on gaze time and eye/face information and developed an electric wheelchair that can be operated with the user’s "natural gazing and facial movements. This intention estimation model is composed of 1DCNN and LSTM layers. First, 1DCNN is used to extract features from gaze and face information, and then the extracted features are input to LSTM to estimate the user’s intentions regarding movement. The evaluation experiments suggest that the combination of gaze and face information improves the estimation accuracy and contributes to the classification. Furthermore, it was confirmed that adding a convolutional filter layer to the LSTM layer improved the accuracy.

Drones, or unmanned aerial vehicles (UAVs), have the potential to considerably reduce the cost and time required to deliver parcels. This paper addresses a parcel delivery scheduling problem, which is to find the optimal assignment of customers to the drones and their takeoff points. In this problem, depending on the number of the drones, the optimal solution changes. We propose a genetic algorithm to find near-optimal solutions simultaneously for multiple different numbers of the drones. The performance of the proposed method is evaluated through conducting experiments.