Magnetic and magneto-optic (MO) properties are investigated for (Nd,Pr)Gd/FeCo multilayer films (MLFs) prepared by means of rf magnetron sputtering. Perpendicularly magnetized films with a good square Kerr hysteresis loop, which is necessary for high density magnetic recording media, are prepared by adjusting the composition as well as the thickness of each layer and bilayer period. Within the frame of this work, the best result is obtained for conditions of approximately 33% Nd, approximately 10% Co, bilayer period of 1 nm, and bilayer thickness ratio of 1. The figure of merit for the Kerr read out in MO memory is found to be 0.36 deg at 400 nm, which is about 30% larger than that for Tb-FeCo.

Magnetic and magneto-optical properties of MnBi films doped with rare earth (RE) elements (RE equals Ce, Pr, Nd, Sm, Tb, Dy, and Ho) have been studied. It was found that MnBiRE (RE equals Ce, Pr, and Sm) films have larger Kerr rotation angle than that of MnBiRE (Nd, Tb, Dy, and Ho) films. When the RE component doped is in the range from x equals 0.02 to 0.25, the Kerr rotation angle can reach from 2 degree(s) to approximately 2.5 degree(s) at the wavelength 633 nm and zero magnetic field at room temperature. Large enhancement of Kerr effect can be explained by using the inter-band transition of the 3d - 6p electrons in MnBiRE alloys.

The rare earth-transition metal (RE-TM) alloys are widely accepted as the most suitable material for magneto-optical (MO) recording. The magnetic and optical properties of the recording media, hence the read-write-erase characteristics of the disk, are crucially dependent on the composition of the RE-TM films. Tailoring the composition of the films to meet the requirements in various magneto-optical recording applications is, therefore, important. In-line sputtering is the most common method for RE-TM film coating in disk production process. There are two common methods for fabricating sputter target; one is powder-sintering, the other is melt-casting. The former method yields a target composed of mixtures of pure element phases and certain percentage of intermetallic compound phases, the latter method yields a target composed of 100% intermetallic compound phases. The sputtering of RE-TM target often gives nonuniform composition distribution on the disk based on past experiences. This problem motivated us to study the sputtered atom distribution of the targets which were fabricated by different methods.

The exchange-coupled magnetic films of amorphous rare earth-transition metal alloys have large potentiality for improvement in the characteristics and the function of magneto-optical disks. The studies of the exchange-coupled magnetic films are reviewed and the recent progress in its technology are reported.

The recording domain sizes of amorphous DyFeCo thin films are compared with those of films with addition of Nd element. It is shown that NdDyFeCo films possess smaller domain sizes than DyFeCo films do under the same recording conditions. These results may be explained by the temperature dependence of coercivity of the thin films. The addition of Nd element to DyFeCo films plays a role of increasing the coercivity of thin films at high temperature, which has influence on the recording domain sizes.

The laser-induced crystallization and annealing-induced crystallization of amorphous TbFeCo magneto-optical films have been investigated by TEM. The film was prepared by FTMS system. It was found that the crystallization occurred when a powerful laser irradiated the medium. The size was related to the irradiating power and time. The area took the shape of circularity. The electron diffraction pattern showed that there was a clear boundary between the amorphous and the crystallized regions. On the other hand, under annealing the crystallization started at 300 degree(s)C. The HREM of the film annealed at 400 degree(s)C showed the crystallization occurred at different areas simultaneously. There was no clear boundary between the amorphous and the crystallized areas. The lattice image of the film indicated that there was not any compositional modulation in the film.

The aging properties of TbFeCo film have been investigated with TEM, XPS, and AES. It was found that the absorption, migration, and combination of oxygen are considerable factors. Lower density boundary regions of the columnar microstructure accelerate the diffusion of oxygen. A model about oxidation is provided to explain the layered structure in the film.

The influence of domain walls on magneto-optic effect of the double-layered films is investigated. A method to cut the domain walls into a set of parallel thin-limit layers is introduced.Thus, the problems of light reflected by and transmitting through the domain walls are equivalent to those by thin-limit multilayer systems. The equation of Kerr rotation angle induced by domain walls is deduced. It is found that the Kerr rotation angle depends on the thickness of domain walls in the double-layered films.

Cu-doped Bi, Ga:DyIG and Bi, Al:DyIG films on glass substrates have been prepared by pyrolysis method, and the coercive force (H_c) and the compensation temperature (T_comp) were investigated. For Cu-doped Bi, Ga:DyIG and Bi, Al:DyIG films, high H_c values of 13 kOe and 7 kOe were obtained, respectively. The extremely high H_c values were attributed to Cu entering the lattice sites.

Al and Ga-substituted Bi:DyIG films have been prepared on glass substrates by pyrolysis method. The magnetic and magneto-optical properties of Al or Ga-substituted garnet films have been investigated in detail. Al or Ga-substituted Bi:DyIG films have high coercive force and good Faraday hysteresis loops. At the wavelength of 510 nm, the Faraday rotation angle was about 8 degree(s)/micrometers for the optimum Al or Ga content of 1 or 0.7, respectively. For optimum Al and Ga content, the crystallization temperatures were about 700 and 675 degree(s)C, respectively. X-ray diffraction pattern showed that the film was polycrystalline garnet phase without preferred crystal orientation.

Cu-doped polycrystalline BiGa:HoIG films were prepared on glass substrate by rf sputtering and post annealing. The addition of 1.8% Cu was very effective to increase the coercivity from 130 Oe to more than 10 kOe, whereas the Faraday rotation angle does not decrease.

An analytical calculation is applied for temperature distribution in a garnet disk with bilayer structure. An optimized structure is designed to lower the writing power and obtain good read- out performance and the influence of writing conditions on temperature distribution is discussed.

A new method to improve the structure and the magnetic-optical (MO) properties of sputtered bismuth garnet films for MO storage has been studied. The method employs high temperature ramp-up rate recurrent annealing as well as quenching in air environment. It results in small grain size (43.0 nm to approximately 30.0 nm), smooth surface, and less bubbles in the garnet film than those with conventional annealing. We discovered that the sample with more recurrent annealing only appeared in garnet phase, and its counterpart with fewer recurrent annealing appeared in garnet phase as well as DyFeO₃ phase. Meanwhile the Farady angle and the coercivity increase with the recurrent number due to the increase of volume transitional rate of crystal phase in the film. Using this new method, garnet film has been successfully crystallized with a grain size of about 30.0 nm with excellent magnetic and MO properties.

In stoichiometric GeTe-Sb₂Te₃ films, reversible phase change optical recording materials, Sb addition is used widely to improve the data retention time and the repetition cycles, but its mechanism is not clear. To clarify the effect of excess Sb, the effects of Te and Ge addition were also investigated in the compositions from the stoichiometry Ge₂Sb₂Te₅ toward the vertices in the Ge-Te-Sb triangle. By DSC measurements, it was found that a retention ability for amorphous (`write') states related to the increase of repetition cycles is larger in the Sb addition than in the Te and Ge addition. By XRD measurements, it was understood that an optimum ratio of (Sb,Te)(beta) /GeTe(111), about 0.5 was necessary to static repetition cycles approximately 10⁶ in the laser annealed film of 1000 angstroms thick.

A series of Ge-Sb-Te system films with good write/erase properties are prepared by the co- sputtering method. Both within 75 to approximately 200 ns pulse widths, the writing and erasing powers are 15 to approximately 22 mW and 6 to approximately 10 mW, respectively. Under these conditions, high write/erase cycles up to 10⁵ are obtained in some film samples among the above system. Furthermore, the refractive indices are calculated according to the IR-spectra and the thickness of the film. The multilayer films with optimal recording properties can be designed by using the erasable phase change materials with suitable refractive indices and film thickness.

In stoichiometric GeTe-Sb₂Te₃ films, reversible phase change optical recording materials, Sb addition is used widely in order to improve the crystallization speed, the data retention time, and the stability of cyclic operation, but its mechanism is not clear. V-VI compounds (GeTe, SnTe) are well known as compounds in which the ferroelectric structural phase transition occurs. The dielectric constant (epsilon) ₀ changes largely due to a change in the short-range order of weakly bound nearest neighbors in the crystal to more strongly bound nearest neighbors in the amorphous phase. Therefore, it is necessary to discuss the effect of Sb addition in the stoichiometric GeTe-Sb₂Te₃ composition upon the dynamic properties of crystallization and the dielectric constant change (Delta) (epsilon) ₀ based on the ferroelectric phase transition.

The microstructure of sputtered amorphous magneto-optic media TbFeCo is observed by self- designed scanning tunneling microscopy (STM), and tracks in phase-change media are recorded. GeSbTe is also investigated by atomic force microscopy.

Using a novel organic dye-phthalocyanine compound, organic dye media for write-once optical recording were obtained by vacuum sublimation. The new media exhibited satisfactory optical recording characteristics and provided write-in power < 8 mW, write-in pulse duration equals 150 ns, the signal contrast > 20%, and the ratio of carrier to noise > 45%.

Langmuir-Blodgett (LB) films of tetra-neopentoxy phthalocyanine zinc and tetra-nonyl phthalocyanine copper are prepared. Their structures, optical properties, and temperature dependencies are investigated. Static optical recording tests by He-Ne laser are done in these LB films and the experimental results demonstrate that phthalocyanine derivates are useful for phase change type erasable data storage media.

Persistent spectral hole burning (PSHB) was performed for several porphyrin molecules imbedded in polymer hosts and rare-earth ion Sm²⁺ doped in BaFCl_0.5Br_0.5 matrix. Power saturation and broadening effects for hole depth and width were observed. The dynamical process of hole formation was measured and explanation by population rate equations was given. Quantum efficiency of photochemical hole burning was investigated. For BaFCl_0.5Br_0.5:Sm²⁺ the capacity of data storage was estimated according to the result of multiple hole burning.

An erasable and rewritable electron-trapping optical-storage material SrS:Eu, Sm was synthesized. Using the SrS:Eu, Sm-PMMA film, the image-recording experiment was performed. After the picture information is written on the film by the frequency doubled (532 nm) output of a Nd:YAG laser, a clearly discernible red image can be created by using 1.064 nm laser output of proper intensity (0.1 mJ/cm²) to irradiate the film. The written information can be maintained for tens of days in darkness, and one can write, read, and erase the information almost innumerable times.

This paper proposes a new interferometer to measure the roughness of optical disk substrates, which applies the principle of shearing interferometry and uses a Faraday modulator to detect the phase between two polarized beams. The instrument can produce surface probe and other statistical data with a height sensitivity of 2 nm and a lateral resolution of 1.2 micrometers . It has excellent stability even under vibration conditions, and rapid and noncontact measurements can be made without a special reference surface.

Theoretical and experimental profiles of pregrooved cross-section in coated photoresist layers with a thickness of 470 nm and 150 nm on glass substrates are given. The experiment has been performed on the photoresist cutting machine using focused argon laser beam and AZ-1350 photoresist. The results from scanning tunneling microscope (STM) and scanning electron microscope (SEM) images are also discussed.

This paper describes the application of a frequency-locked servo system in the control system of a laser cutting machine of optical disks for servo grooves and pre-formatted information. The stability of the angular velocity of the spindle is up to 5 X 10^-6 and the accuracy of the track pitch is 1.6 micrometers +/- 0.03 micrometers .

By combining the practical mechanical transmission system with the laser cutting machine of optical disks, a high precision dynamic measurement system of round to long mechanical transmission link is designed. The working principle and system errors are described. Our experiments have proved that the measurement system is completely competent for the measuring task. The special computer interface board and the practical computer software are designed with advantages of fast data collecting and high processing ability. The mechanical transmission link error can be obtained after processing the data.

According to the image relay concept in the optical amplification system, submicrometer resolution of a digital image processing system has been given in this paper. The accuracy and precision of the system has been examined by using a standard identification reticle, and some measurement results of a small focal spot through a computer generated holographic lens have been given.

Comparison of three common focus error detection methods is made on a unified theoretical background. New mathematical models are built up on physical optics. The compared items are theoretical optical gain, adjustment factors, etc., and the theoretical and experimental results are given.

A fully separated optical head means that the carrier and the actuator are separated completely. It causes the mass of the carrier to be less than 10 grams, or even less. It can increase the access rate greatly and avoid the cross interference between two stage seekings.

A simple and precise mathematical model of critical-angle focus error detection method is proposed in this paper. Factors which affect the focus error signals are analyzed and the curve of focus error signals with different parameters are given. The improvement of optical gain is also discussed.

A real time non-contact dynamic testing method for an optical disk is proposed in this paper. The axial run-out and the tilt of the optical disk are measured by two quadrant detectors when the disk is turning at high speed in the drive. The analysis of the results is given with a brief discussion on the error in measurement.

In this paper, holographic optical elements (HOEs) used in optical disk systems are discussed. HOEs have been used to form several beams for detecting focusing and tracking error, as a beam splitter and a formatter of wavefront. It can also be used as an objective lens in the future.

A test unit is described which includes an automatic focusing device and a displacement sensor for lens movement. The resolution of the unit is 20 nm in the range of +/- 40 micrometers . In addition, a technique for ensuring the focal spot using the character of the laser diode is presented. This measurement principle can be widely used in the areas of precision manufacture, optical industry, and soft materials testing.

A key problem in the fast seeking process of optical disk drive is to measure the radial velocity of light spot on disk quickly and accurately. This paper proposes a measuring method with high accuracy and simple circuit design.

A fast software algorithm is used to compute the remainder of interleaved Reed-Solomon ECC in order to get the error location of read data. By using the erasable-programmable-logic- device (EPLD) together with Winchester controller chips, we built a so-called optical/buffer controller. An algorithm may be introduced to solve the write-after-erase problem of MO disk drives.

In order to make the laser diode of an optical disk drive work reliably and stably, this paper proposes a driving and protecting circuit and a laser power feedback control system which can almost eliminate the influence of component parameter change and power voltage fluctuation.

We have developed three types of green solid state lasers pumped by laser diodes. A green laser outputs up to 24.5 mW at 532 nm with Nd:YAG/KTP crystal, the second outputs up to 19 mW with Nd:YVO₄/KTP crystal and the third up to 29 mW with LNYAB crystal. The experiments setups and results are discussed. Comparison of these three kinds of lasers are presented.

In this paper a scheme increasing raster images stored in a WORM is studied. A two- dimensional coding method improved from the CCITT (Comite Consultatif Interationale Telegraphie et Telephonie) is used to compress the image data. And a means of saving image to the WORM in batches is taken to increase the WORM space utilization ratio.