Using an ultrashort pulse laser, photon energy of which is smaller than the band gap energy of silicon, machining of
substances located at back of a silicon plate should be achievable. To realize this possibility, machining of a silicon
substrate as well as machining of gold film on it was carried out using femtosecond laser pulses, wavelength of which
lay between 1.5 to 2.5 μm. It is demonstrated that the rare surface of the silicon substrate and the gold film placed at the
back of the silicon substrate can be machined with no detectable change on its front surface. Frequency adjustment of
crystal oscillator sealed in a silicon package is tried and up-conversion of the frequency is achieved by removing small
amount of thin gold film on the crystal with irradiation of 1.5 μm laser pulses through the silicon lid.
A thin metal electrode tip instantly changes its shape into a sphere or a needlelike shape in a single electrical discharge of
high current. These changes occur within several hundred microseconds. To observe these high-speed phenomena in a
single discharge, an imaging system using a high-speed video camera and a high repetition rate pulse laser was
constructed. A nanosecond laser, the wavelength of which was 532 nm, was used as the illuminating source of a newly
developed high-speed video camera, HPV-1. The time resolution of our system was determined by the laser pulse width
and was about 80 nanoseconds. The system can take one hundred pictures at 16- or 64-microsecond intervals in a single
discharge event. A band-pass filter at 532 nm was placed in front of the camera to block the emission of the discharge
arc at other wavelengths. Therefore, clear images of the electrode were recorded even during the discharge. If the laser
was not used, only images of plasma during discharge and thermal radiation from the electrode after discharge were
observed. These results demonstrate that the combination of a high repetition rate and a short pulse laser with a high
speed video camera provides a unique and powerful method for high speed imaging.
Organic light emitting diode (OLED) is now in practical use and also a subject of active research and development. In
industrial production of OLED displays, one of the key technologies is patterning of electrodes, especially a metal
cathode, which is usually made on a thin layer of organic electro-luminescence (OEL) compounds. Difficulties in
machining of the OLED come from the fact that the OLED has multi-layered structures consisted from very thin layers
of different materials, one of which is a highly heat- and chemical-sensitive organic material. The typical OLED sample
has indium tin oxide (ITO) electrode of about 150 nm thick at the bottom. The organic electro-luminescence material of
less than 200 nm is deposited on it and the top is aluminum electrode of 100 to 150 nm thickness. We have constructed
a fabrication system of the OLED by using an ultrashort fiber laser in the patterning of aluminum electrode and
fabricated a display panel successfully. The system has several advantages comparing to other methods currently used.
To investigate the process in detail, we have constructed two ultra-fast photography systems, with either sub-picoseconds
or nanoseconds time resolution, and carried out the time-resolved observation of the process. It is found
that the underlying layer affects much to the machinability of the top metal layer. The ITO layer seems to enhance the
machining efficiencies of the aluminum electrode: the ablated spot size becomes larger for that on ITO, even though the
laser pulse energy is kept constant.
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