We developed a new one-beam detection method with changeable multi division patterns, pairing with tangential spot size detection (SSD) method for focusing error detection. The changeable multi division patterns are realized by the active device, which consists of a non-polarizing HOE for tangential SSD method, liquid crystal (LC) active rotator and two different division patterns of layered polarizing blazed HOEs. The LC active rotator properly acts as the mode selector and an R/RE mode pattern for one-beam push-pull method and a ROM mode pattern for differential phase detection (DPD) method can be selected only changing the applied voltage. The newly developed system can derive one-beam push-pull signal, DPD signal, wobble signal and RF signal from the output only from five common
photo detectors. Sufficient quality of these signals is experimentally confirmed. The one-beam push-pull signal is hardly affected by the stray light from other layers. The traversing noise of its focusing error signal is stably low even with high push-pull media and possibly large astigmatism. Its focusing error signal turns out to be much more stable and less influenced by groove traverses. In addition, we present a vision for next-generation slim and compact integrated optics with dual LC cells, which consist of the LC attenuator, laser noise reduction technology, and the LC mode selector, as explained above.
troduction The scalar diffraction theory represented by the Hopkins’ method has been widely used for simulating the readout signals from optical pickups. This method is based on the partially coherence theory, and was well improved by previous works, for example the classification into the two types of scanning microscopes,2< extension for MO pickups, and so on. Furthermore, various super-resolution techniques and the crosstalk reduction technique were analyzed theoretically by using this scalar diffraction theory. On the use of this theory, the light amplitude distribution on the exit pupil of the objective lens or the modulation transfer function (MTF) is usually employed for the explanation of the functions of optics. Meanwhile, the method we present here is based on the work by Velzel. His method is basically an approximation of the scalar theory and concentrates on the point spread function (PSF) of the illumination optics in the pickup. And it provides a simple and practical way for computations and understanding of the readout process. For example, Kubota presented in his study the influences of wave front aberrations on the readout characteristics by using jitter calculations, in which the readout signal was calculated as a convolution of the pits on the disk and the PSF. In this paper, we present a method using an extended point spread function (EPSF) that can be applied for the case when the detector has an arbitrary shape and information pits are recorded on a groove. After that, two examples, differential phase detection (DPD) method and jitter analysis of the readout signal from pits on a groove, will be shown. Although our method is also an approximation, physical and intuitive considerations will be acquired even under such complex cases.
A two-dimensional multi-lens array of 350 mm in diameter with 37 pieces of spherical element lenses is tested for improving the irradiation uniformity of the ICF target. Circular and hexagonal shapes of element lens aperture have been examined. The circular aperture is chosen for eliminating azimuthally asymmetric intensity distribution in the beam pattern. An approximate flat-top intensity distribution has been obtained at the focus of the principal lens. Beam patterns of coherent laser and partially coherent light (PCL) with the random phase plate (RPP) and the multi-lens array (MLA) have been measured at GEKKO XII glass laser system. The irradiation non uniformity of MLA on a spherical target is calculated from the measured beam patterns.
An aspherical lens for the control of the intensity distribution on the target has been designed and fabricated. The diffraction from the edge of the element lens was eliminated with an edge- shaped plate. The beam profile on the target was measured, and it was in good agreement with the calculated profile by the diffraction code with the aspherical lens shape.
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