The two stilbazolium derivatives, 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) and 4-dimethylamino-N-methyl-4-stilbazolium p-chlorobenzenesulfonate (DASC), are organic ionic nonlinear optical materials that have a tendency to form bulk crystals when grown in a mixed solvent of methanol and acetonitrile. We observed the generation of broadband high-power terahertz (THz) waves from the bulk crystals of DASC. DASC crystals have superior transmission characteristics in the THz band than DAST crystals, and it is expected that the THz waves generated using DASC crystals will have higher power than those generated using DAST crystals.
An inexpensive and practical mastering technology was developed using a blue-laser optical system with a wavelength of 405 nm and numerical aperture (NA) of 0.95 comprising an inorganic photoresist. The resist system showed a higher resolution for a successful 130 nm pit patterning than that obtained by an ordinary organic photoresist system. Based on this technology, a read only memory (ROM) disc with a recording capacity of 25.2 GB on a 120-mm-diameter surface was mastered at a high recording speed of 4.92 m/s. The disc showed a reasonable jitter value of 8.0% using a conventional equalizer, 4.6% using a limit equalizer and a push-pull signal using a conventional readout optical system of ¼ 405 nm and NA ¼ 0:85.
We have demonstrated volumetric optical recording using an all-semiconductor picosecond laser, which generated optical pulses with a duration of 3 ps and a maximum peak power of 100 W at a wavelength of 404 nm and a repetition frequency of 1 GHz. This pulsed laser system efficiently induced multiphoton absorption in the recording media due to its high peak power and high repetition rate. The recording marks were formed as submicrometer voids inside a single thick recording layer by multiphoton absorption. A clear readout signal was obtained from the recorded marks.
Conventional CMOS image sensors widely used in products currently on the market are mainly equipped with a rolling exposure function. This rolling exposure causes so-called "Jell-o effect" distortion when capturing a moving target. CMOS image sensors with a global-shutter function are one of the solutions to avoid this distortion. An in-pixel storage node is required to create a global-shutter CMOS image sensor. A floating diffusion and an additional capacitor can be used as an in-pixel storage node [1,2]. The light sensitivity of the in-pixel storage node is specified by the parasitic light sensitivity (PLS), which is the ratio of the light sensitivity of an in-pixel storage node and the light sensitivity of a photodiode. The PLS should be small enough so that the in-pixel storage is not lightsensitive. Artifacts are captured in an image from bright moving objects during read-out if the PLS is not small enough. The PLS of reported global-shutter CMOS image sensors is around -100dB. That would be small enough to use those image sensors in fields where the light source can be controlled. However, for DSC usage, users can easily encounter scenes with bright objects (e.g. sunlight or car headlights). Even if the in-pixel storage node is light-shielded, it is difficult to perfectly protect the in-pixel storage node from photo-generated carriers, as long as the in-pixel storage node and a photodiode are on the same silicon substrate. Meanwhile, 3D stacking technologies have been introduced for image sensors to give them more functionality and improved performance [3,4]. The reported minimum interconnection pitches for image sensors are over 20μm. These technologies do not fit the smaller pixel pitches of the image sensors in recent DSCs. In this paper, we report a rolling-shutter distortion-free 3D stacked image sensor with an in-pixel storage node of -160dB parasitic light sensitivity. The image sensor virtually achieves a global-shutter function using a 4times frame-shutter operation. The image sensor has 2 semiconductor substrates, where 1 substrate has a backside-illuminated photodiode array and the other a storage-node array. The image sensor achieves a PLS level of -160dB. The image sensor has 8.6μm pitched interconnections, and an interconnection yield of over 99.9% is achieved.
We have investigated the generation of THz radiation in lithium ternary compounds LiInSe 2 , LiGaSe 2 , LiInS 2 , LiGaS 2 and characterized these materials by THz time-domain spectroscopy. Using 800 nm femtosecond excitation pulse, all crystals produce THz radiation due to an optical rectification corresponding to the nonlinear optical coefficient d 33 . We have measured refractive indices along the x-axis and the z-axis for all crystals in the range 150-700 μm and fitted them by using Sellmeier equation. With respect to the obtained results, velocity-matching between the incident laser pulse and the generated THz wave cannot be achieved at 800 nm, but for shorter wavelengths. Hence, an enhanced THz generation in Lithium ternary compounds may be observed by using a laser emitting below 800 nm.
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