ABSTRACT
An etched calcite square-wave retarder is designed, fabricated, and demonstrated as an illuminator for an interlaced polarization computer-generated hologram (PCGH). The calcite square-wave retarder enables alternating columns of orthogonal linear polarizations to illuminate the interlaced PCGH. Together, these components produce a speckled, tangentially polarized PCGH diffraction pattern with a measured ratio of polarization of 84% and a degree of linear polarization of 0.81. An experimental alignment tolerance analysis is also reported.
ABSTRACT
An interlaced polarization computer-generated hologram (PCGH) is designed to produce specific irradiance and polarization states in the image plane. The PCGH produces a tangentially polarized annular pattern with correlated speckle, which is achieved by a novel application of the diffuser optimization method. Alternating columns of orthogonal linear polarizations illuminate an interlaced PCGH, producing a ratio of polarization of 88% measured on a fabricated sample. The demonstrated technique can be applied to designs for arbitrary irradiance and polarization states in the image plane.
ABSTRACT
We present the results of crystallization and amorphization studies on a thin-film sample of Ge(2)Sb(2.3)Te(5), encapsulated in a quadrilayer stack as in the media of phase-change optical disk data storage. The study was conducted on a two-laser static tester in which one laser, operating in pulsed mode, writes either amorphous marks on a crystalline film or crystalline marks on an amorphous film. The second laser, operating at low power in the cw mode, simultaneously monitors the progress of mark formation in terms of the variations of reflectivity both during the write pulse and in the subsequent cooling period. In addition to investigating some of the expected features associated with crystallization and amorphization, we noted certain curious phenomena during the mark-formation process. For example, at low-power pulsed illumination, which is insufficient to trigger the phase transition, there is a slight change in the reflectivity of the sample. This is believed to be caused by a reversible change in the complex refractive index of the Ge(2)Sb(2.3)Te(5) film in the course of heating above the ambient temperature. We also observed that the mark-formation process may continue for as long as 1 mus beyond the end of the write laser pulse. This effect is especially pronounced during amorphous mark formation under high-power, long-pulse illumination.
ABSTRACT
We develop a theory of the crystallization dynamics of Ge(2)Sb(2.3)Te(5) thin films that shows good qualitative agreement with experimental reflectivity results from a two-laser static tester. The theory is adapted from the nucleation theory of liquid droplets from supersaturated vapor and elucidates the physics underlying the amorphous-to-crystalline phase transformation under short-pulse excitation. In particular, the theory provides a physical picture in which crystalline islands, or basic embryos, are thermally activated in the amorphous material and subsequently grow as stable nuclei are formed.
ABSTRACT
We have designed and built a static tester around a commercially available polarized light microscope. This device employs two semiconductor laser diodes (at 643- and 680-nm wavelengths) for the purpose of recording small marks on various media for optical data storage and for the simultaneous monitoring of the recording process. We use one of the lasers in the single-pulse mode to write a mark on the sample and operate the other laser in the cw mode to monitor the recording process. The two laser beams are brought to coincident focus on the sample through the objective lens of the microscope. The reflected beams are sent through a polarizing beam splitter and thus divided into two branches, depending on whether they are p or s polarized. In each branch the beam is further divided into two according to the wavelength. The four beams thus produced are sent to four high-speed photodetectors, and the resulting signals are used to monitor the reflectance as well as the polarization state of the beam on reflection from the sample. We provide a comprehensive description of the tester's design and operating principles. We also report preliminary results of measurements of phase-change, dye-polymer, and magneto-optical samples, which are currently of interest in the areas of writable and rewritable optical data storage.
