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Optical disks in digital audio
Published in John Watkinson, An Introduction to Digital Audio, 2013
Figure 11.17 shows a Sony laser head used in early consumer players. The cylindrical-lens focus method is used, requiring a four-quadrant sensor. Since this method has a small capture range, a focus-search mechanism is necessary. When a disk is loaded, the objective lens is ramped up and down looking for a zero crossing in the focus error. The three-spot method is used for tracking. The necessary diffraction grating can be seen adjacent to the laser diode. Tracking error is derived from side-spot sensors (E, F). Since the side-spot system is sensitive to angular error, a parallel-tracking laser head traversing a disk radius is essential. A cost-effective linear motion is obtained by using a rack-and-pinion drive for slow, coarse movements, and a laterally moving lens in the light path for fine rapid movements. The same lens will be moved up and down for focus by the so-called two-axis device, which is a dual-moving coil mechanism. In some players this device is not statically balanced, making the unit sensitive to shock, but this was overcome on later heads designed for portable players. Some designs incorporate a prism to reduce the height of the pickup above the disk.
Digital audio in optical disks
Published in John Watkinson, The Art of Digital Audio, 2013
Figure 12.24 shows a Sony laser head used in consumer players. The cylindrical-lens focus method is used, requiring a four-quadrant sensor. Since this method has a small capture range, a focus-search mechanism is necessary. When a disk is loaded, the objective lens is ramped up and down looking for a zero crossing in the focus error. The three-spot method is used for tracking. The necessary diffraction grating can be seen adjacent to the laser diode. Tracking error is derived from side-spot sensors (E, F). Since the side-spot system is sensitive to angular error, a parallel-tracking laser head traversing a disk radius is essential. A cost-effective linear motion is obtained by using a rack-and-pinion drive for slow, coarse movements, and a laterally moving lens in the light path for fine rapid movements. The same lens will be moved up and down for focus by the so-called two-axis device, which is a dual-moving coil mechanism. In some players this device is not statically balanced, making the unit sensitive to shock, but this was overcome on later heads designed for portable players. Figure 12.25 shows a later Sony design having a prism which reduces the height of the pickup above the disk.
Optical disks in digital audio
Published in John Watkinson, The Art of Sound Reproduction, 2012
Figure 11.16 shows a Sony laser head used in consumer players. The cylindrical-lens focus method is used, requiring a four-quadrant sensor. Since this method has a small capture range, a focus-search mechanism is necessary. When a disk is loaded, the objective lens is ramped up and down looking for a zero crossing in the focus error. The three-spot method is used for tracking. The necessary diffraction grating can be seen adjacent to the laser diode. Tracking error is derived from side-spot sensors (E, F). Since the side-spot system is sensitive to angular error, a parallel-tracking laser head traversing a disk radius is essential. A cost-effective linear motion is obtained by using a rack-and-pinion drive for slow, coarse movements, and a laterally moving lens in the light path for fine rapid movements. The same lens will be moved up and down for focus by the so-called two-axis device, which is a dual-moving coil mechanism. In some players this device is not statically balanced, making the unit sensitive to shock, but this was overcome on later heads designed for portable players. Figure 11.17 shows a later Sony design having a prism which reduces the height of the pickup above the disk.
Enhanced outer peaks in turbulent boundary layer using uniform blowing at moderate Reynolds number
Published in Journal of Turbulence, 2022
Gazi Hasanuzzaman, Sebastian Merbold, Vasyl Motuz, Christoph Egbers
Two channel, single point, noninvasive LDA technique in back scattering mode was used for the measurement. LDA setup consists of the followings: an Argon-ion continuous wave laser (Ion laser technology) was used as the laser source. At all cross sections along the laser beam, the intensity has a Gaussian distribution, and the width of the beam is usually defined by the edge-intensity being of the core-intensity. The transmitting optics includes beam splitter where a coherent light beam of wavelength λ is split equally. One beam passes through a 40-MHz bragg cell where frequency of one beam is decreased by the shift frequency . Different optical paths of shifted and unshifted beam are compensated through cylindrical lens by allowing the unshifted beam to pass through it. Finally, monochromatic lens installed within the transmitting optics focuses both the splitted beams at same focal length using a beam expander (expander ratio () = 1.98) so that they intersect with the angle θ. Simultaneously the aperture of optical receiver was adjusted to a greater value (95 mm) so that it receives more of the reflected light from the particles. Therefore, focal length of the front lens from transmitting optics () was obtained at % mm.