Microfabrication is required to process glass materials in order to locally assign the desired optical properties. The authors have proposed a new microfabrication technique to form a metal sphere and manipulate the sphere inside glass. When a continuous-wave (CW) laser was illuminated from the glass side to a metal attached to the glass, a metal sphere was formed. The metal sphere was moved towards a light source with laser illumination in the glass. When the sphere migrates, it is accompanied by the diffusion of submicron metal particles. Hence, this technique allows the creation of doped regions of fine particles in the shape of a sphere’s trajectory. Controlling the shape of the particle-doped area to transform into arbitrary shapes enables the design of more flexible optical devices. The Soret effect could be one of the keys to satisfying these requirements. The Soret effect is a material transport phenomenon driven by temperature gradients in multiple components. However, to the best of our knowledge, there have been no studies on the Soret effect on metal particles in glass. Herein, we show that iron particles are transported inside silica glass as a result of temperature gradient. Metal-sphere migration produces a local particle-doped area in the glass. A temperature gradient was formed by laser heating the sphere under conditions that prevented it from moving. In situ observations revealed that particles migrated toward the metal sphere at a maximum speed of 0.56 μm/s.
Ultrashort-pulsed laser illumination focused inside a diamond converts sp3-bonded diamond to sp2-bonded amorphous carbon in the vicinity of the focal point and changes the color to black. A wire-shaped modified region is fabricated by scanning the laser focus toward the laser source in the diamond. Volumetric expansion by converting diamond to amorphous carbon forms cracks around the modified region. In this study, diamond slicing was attempted by using cracks formed around the modified region. A near-infrared picosecond laser was focused inside a high-temperature, high-pressure diamond. The cracks fabricated under various laser conditions were observed. The plane crack was formed by lining up the wire-shaped modified regions next to each one. During the fabrication, a high-speed polarization camera was used to observe the stress distribution around the modified region and in the adjacent wire-shaped modified region. The crack propagation was estimated by observing the stress distribution in situ. The kerf loss in the slicing process was estimated by observing the cross section of the cracks from multiple directions. These results demonstrate that plane cracks suitable for slicing the diamond were fabricated. Diamond separation was performed by applying an external force to the plane cracks.
Several applications of glass nanofibers have been proposed for the past years. We found a new method for production of nanofibers with a diameter of 100 nm order from thin glass plates by irradiation with nanoseconds pulsed UV laser (wavelength is 355 nm). Although the generation of nanofibers from the back surface of a glass plate is convenient for continuous laser irradiation and collection of fibers, the details of the mechanism have not been elucidated yet. In this paper, we focused on the dynamics of ejection of glass melts that results in the formation of nanofibers, and investigated the mechanism of nanofiber generation. Based on the observation by a high-speed camera, we found that voids inside of the glass plate propagated in the laser propagation direction shot by shot, then, the void pushed the molten glass near the back surface. We also confirmed that the molten glass was ejected from the back surface of plates at a speed of 10-100 m/s. We assumed that the driving force is "recoil pressure", and compared the estimated pressure value from this experiment with that shown in the references. The value estimated by the relationship between pressure and momentum was 1.3 MPa, which was close to that reported in the past.
Glass nanofibers are prospective material, because they have the potential to function as biomedical tissues, optical components, or catalysts. Now, precise control of synthesis method is necessary for a variety of glass nanofiber applications. We found that glass nanofibers were generated from the back surface of a substrate during a drilling experiment using a nanosecond pulsed UV laser. In this report, we investigated the generation process. To understand the process, we set up an optical system for generating nanofibers, which is capable of moving a sample linearly using an XY stage, and monitored around the laser spot using a CCD camera. A non-alkaline, thin glass substrate was irradiated with a laser beam of wavelength 355 nm and pulse width 40 ns. As a result, when the scanning speed and focusing position were favorable, glass nanofibers were generated. According to the in situ observation, microparticles were found on the tip of the nanofibers. Also, the glass substrate was modified in a wider range compared with the laser spot size. Thus, we considered that glass nanofibers were generated when the particles were ejected resulting from local heating. Additionally, glass nanofibers could be generated in combination with a galvano scanning system. The generation of glass nanofibers from the back surface of a substrate is advantageous in terms of their collection owing to the reduced interaction with the laser beam.
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