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A newly developed nonlinear crystal belonging to the borate family, lithium tetraborate Li2B4O7 (LB4), has excellent properties below 180 nm and allows the generation of wavelengths down to 170 nm with an all-solid state laser system. This was gleaned from a characterization of the newly grown crystal by the Czochralski method. A comparison with a lithium triborate sample showed that it performs better in the vacuum ultraviolet spectral region below 180 nm. Its effective nonlinearity is maximized under the conditions of 90 degree-phase matching.

We propose a model for a magnetic recording channel to estimate the influences of the nonlinear distortion of an MR head on the performance of the PRML system, using a superposition of a magnetic field and a transfer curve obtained by a micro-magnetic model. A readback signal was simulated using a nonlinear model. The simulated signal was compared with an actual readback signal in the analysis of the isolated pulse, frequency response, and extracted dipulse response. We found that the nonlinear model represents actual MR head output satisfactorily, and that the performance of the PR4ML system was affected by the nonlinear distortion of the MR head for a 5% loss of the amplitude margin when the asymmetry was within 10%.

A new chemiluminescence procedure was established that eliminates the need to use a separate oxidant such as hydrogen peroxide for chemiluminescence detection reactions. In the procedure called optically pumped chemiluminescence (OPC), red light energy is used by a photosensitive dye to oxidize luminol and generate blue light. By puising the excitation light and measuring chemiluminescence during the off time, light scattering background was eliminated and sensitivity enhanced 10-fold. The OPC reaction mechanism was determined to be type I (direct reaction of excited dye with substrate), and the dye catalyst is recycled in the reaction. Of the popular photosensitive dyes tested, methylene blue showed the best detection limit in the OPC system. A methylene blue dye derivative was synthesized and covalently attached to protein. Antibody proteins were labeled with up to 16 dyes per antibody. An [alpha]-fetoprotein immunoassay was developed having a detection limit of 17 pg. This assay had sensitivity of 1.5 ng of alphafetoprotein/mL of plasma and showed good correlation (R = 0.98). The OPC catalysts are more stable and less temperature sensitive than enzyme catalysts, and the substrate solution needed is very stable. Thus, OPC may be valuable in applications where convenience and reagent stability are important., The possibility of utilizing photoactive dyes as chemiluminscence catalysts for diagnostic assays is discussed. This optically pumped chemiluminescence (OPC) technique was used to irradiate a highly acidic luminol concentration and to detect the presence of the photoactive dye catalyst from the luminol chemiluminescence. The resulting alpha-fetoprotein imunoassay was applied on blood samples. The utility of the OPC method was demonstrated.

In this work, we consider narrow band partial response (NBPR) systems for (1, 7) RLL code. As a new type of (1, 7) PRML system, a PR(1, 1.5, 0, -1.5, -1) system called a modified MEEPR4 (MMEEPR4) which contains a spectral null below the Nyquist frequency is proposed. We compared the performances of 8/9 (0, 4, 4) PR4, (1, 7) EEPR4, (1, 7) MEEPR4 and (1, 7) MMEEPR4 in recording systems with both electronic and medium noise characterized by Thurlings' model. Medium noise power was corrected using the code magnetic transition probability. Thus the average medium noise power for code-2/3 (1, 7) was at a 20% smaller than that of code-8/9 (0, 4, 4). To verify the practical use of this system, we defined the broader constraints and calculated the error propagation. It is clear that the (1, 7) MEEPR4 system does not satisfy the broader constraints because it generates no quasi-catastrophic trellis sequence. Simulation results indicate that the narrow-band (1, 7) MMEEPR4 system provides a significant improvement over 8/9 (0, 4, 4) PR4 and (1, 7) EEPR4 and avoids the signal band extension for a 2/3 code-rate without a loss in performance.

A high areal density of 5 Gb/[in.sup.2] (7.75 Mbit/[mm.sup.2]) has been demonstrated with narrow track NiFe/[Co.sub.90][Fe.sub.10] spin-valve read heads on low-noise CoCrTaPt/CrMo-alloy thin-film disks. The MFM measurements clearly showed the write track width to be 1.2 [[micro]meter] on the Co[Cr.sub.17][Pt.sub.5][Ta.sub.4] thin-film media. This corresponds to 19.5 kTPI (768 track/mm) including a guard band of 0.1 [[micro]meter]. The error rate performance was tested using a PR4ML channel with write precompensation. At a data rate of 3.3 MB/s, a practical error rate of 9.0x[10.sup.-6] was obtained without error correction at a linear density as high as 257 kBPI (10.1 kbit/mm). At a linear density of 217 kBPI (8.5 kbit/mm), we obtained an error rate of less than [10.sup.-8] without error correction. With a 192-bit Reed-Solomon error correcting code, we can expected an error rate of 1.0x[10.sup.-14].

Cr-Fe heterogeneous alloy films sputter-deposited on heated substrates record large negative magnetoresistance (MR). The highest MR, 37.3% at 4.2 K and 14 T, occurs near the Fe concentration of 20 atomic weight %. MR does not change with substrate temperature when the Fe concentration is greater than 20 atomic weight %, while at Fe concentrations less than 20 atomic weight %, MR records a marked substrate temperature dependence.