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We have achieved high-precision laser beam shaping by using a binary-amplitude spatial light modulator, a digital micromirror device (DMD), followed by an imaging telescope that contains a pinhole low-pass filter (LPF). An error diffusion algorithm was used to design the initial DMD pixel pattern based on the measured input beam profile. This pattern was iteratively refined by simulating the optically low-pass filtered DMD image and changing DMD pixels to lift valleys and suppress peaks. We noted the gap between the experimental result of 1.4% root-mean-square (RMS) error and the simulated result for the same DMD pattern of 0.3% RMS error. Therefore, we deemed it necessary to introduce iterative refinement based on actual measurements of the output image to further improve the uniformity of the beam. Using this method, we have demonstrated the ability to shape raw, non-spatially filtered laser beams (quasi-Gaussian beams) into beams with precisely controlled profiles that have an unprecedented level of RMS error with respect to the target profile. We have shown that our iterative refinement process is able to improve the light intensity uniformity to around 1% RMS error in a raw camera image for both 633 and 1064 nm laser beams. The use of a digital LPF on the camera image is justified in that it matches the performance of the pinhole filter in the experimental setup. The digital low-pass filtered results reveal that the actual optical beam profiles have RMS error down to 0.23%. Our approach has also demonstrated the ability to produce a range of target profiles as long as they have similar spatial-frequency content (i.e., a slowly varying beam profile). Circular and square cross-section flat-top beams and beams with a linear intensity variation within a circular and square cross section were produced with similarly low RMS errors. The measured errors were about twice the ultimate limit of 0.1% RMS error based on the number of binary DMD pixels that participate in the beam-formation process. OCIS codes: 070.6120, 140.3300, 230.6120.

We demonstrate a digital micromirror device (DMD)-based optical system that converts a spatially noisy quasi-Gaussian to an eighth-order super-Lorentzian flat-top beam. We use an error-diffusion algorithm to design the binary pattern for the Texas Instruments DLP device. Following the DMD, a telescope with a pinhole low-pass filters the beam and scales it to the desired sized image. Experimental measurements show a 1% root-mean-square (RMS) flatness over a diameter of 0.28 mm in the center of the flat-top beam and better than 1.5% RMS flatness over its entire 1.43 mm diameter. The power conversion efficiency is 37%. We develop an alignment technique to ensure that the DMD pattern is correctly positioned on the incident beam. An interferometric measurement of the DMD surface flatness shows that phase uniformity is maintained in the output beam. Our approach is highly flexible and is able to produce not only flat-top beams with different parameters, but also any slowly varying target beam shape. It can be used to generate the homogeneous optical lattice required for Bose--Einstein condensate cold atom experiments. OCIS codes: 140.3300, 070.6120.

The experimental model for the deposition of silver lines and films via the impaction of a silver nanoparticle aerosol delivered through a supersonic jet is described. It is found that, for a given gas type, the size of the grains and morphological features within the impacted films were similar to the size of the nanoparticles from which the films were formed.

Nonuniformity in the thickness of thin films can severely distort their transmission spectra as compared with those of flat, smooth films. Methods that extract properties such as refractive index, thickness, and extinction coefficient of such films can suffer inaccuracies when they are applied to wedged or nonuniformly thick films. To accurately extract optical properties of nonuniform films, we have developed a novel numerical method and efficient constitutive relations that can determine film properties from just the transmission spectrum for films that are locally smooth with negligible scattering loss. This optimum parameter extraction (OPE) method can accommodate films with two-dimensional thickness variation that would result in significant errors in the values of refractive index and film thickness if not considered. We show that for carefully chosen test cases and for actual pulsed-laser-deposition A1N thin films, properties such as refractive index, extinction coefficient, and film thickness were very accurately determined by using our OPE method. These results are compared with previous techniques to determine the properties of thin films, and the accuracy of and applicable conditions for all these methods are discussed. OCIS codes: 310.6860, 310.3840, 240.0310.

The optical cross correlation of an image with another image that was spatial-frequency shifted in one dimension was demonstrated in a photorefractive VanderLugt correlator. The first image was stored as a Fourier-transform hologram in a photorefractive [Bi.sub.12] Si[O.sub.20] crystal (BSO) and was successively correlated with different spatial-frequency-shifted versions of a second image. We implemented the spatial-frequency shift by rotating a galvanometer mirror in an image plane, causing the Fourier transform to be shifted laterally in the BSO. We verified that the resulting operation in the BSO was an accurate complex multiplication of the shifted and the stored Fourier transforms. As many as 20 successive readouts were conducted without measurable erasure of the stored hologram. The dynamic range, saturation behavior, and other performance parameters were measured and are discussed. OCIS codes: 070.4550, 070.6020, 160.5320, 070.4340.

Laser ablation of microparticles before nanoparticle generation is investigated using time resolved optical shadow images and Schlieren images.

We measured the functional degradation of silicon CCD photodetector arrays when subjected to Nd:YAG laser irradiation at 1.06 [mu]m by 10-ns pulses. Operational tests such as dark leakage, point-spread function, and modulation transfer function were developed for testing individual pixels and applied to the testing of locally laser-damaged CCD arrays. Testing revealed that the primary failure mechanism was the spreading of the point-spread function in the direction of clocked charge motion that resulted from a decreased depth of potential wells within the laser-damaged spot. Lesser degradation was observed at pixels near the damaged spot that were served by clock lines that traversed the damage spot. This damage behavior was correlated with decreased breakdown voltage and increased leakage current between adjacent clock lines. Subsequent morphological and TEM examination of similarly constructed chips indicated that laser heating of the polysilicon clock lines led to degradation of the adjacent isolation oxide between clock lines. Functional damage occurred at locations where two clock lines were very close to each other, and the thin oxide layer separating them was subjected to high temperatures that resulted from melting of the neighboring polysilicon. Key words: Laser damage, CCD arrays, sensor damage.

We employed the rigorous vector coupled-wave theory [J. Opt. Soc. Am. 73, 1105 (1983)] to analyze the electromagnetic scattering from two dimensional (2-D) surface-relief dielectric gratings. A shoot-back method was developed for the numerical solution of the resulting coupled differential equations. This method allowed numerical solutions to be found for grating structures of arbitrary profiles and relatively deep grooves. It was most suitable where the grating medium refractive index was not too large and where only a small number of propagating orders existed. Experiments confirmed the numerically predicted reflectivities for 2-D surface-relief dielectric sinusoidal gratings. Reflectivity measurements were made on 2-D sinusoidal gratings fabricated on photoresist and on polycarbonate. The grating periodicities were of the order of 3000 lines/mm such that only the zero-order diffracted waves were propagating in the incident region, and possibly a few forward orders in the transmission region. The embossing technique that was used for replicating the grating patterns from photoresist onto polycarbonate proved to be a feasible method for the production of such gratings. Key words: Scattering, two-dimensional surface-relief gratings, embossed gratings.

A hybrid optical-digital Processor has been developed that computes both the magnitude and phase of the bispectrum for wide bandwidth (10 MHz to 1 GHz) rf signals. The overall optical architecture is that of a modified Mach-Zehnder interferometer that contains three acousto-optic modulators and appropriate transforming lenses. The intensity distribution in the output plane of the interferometer contains an interference term that represents the real part of the bispectrum multiplied by a spatial carrier (the interference fringes). To isolate the bispectrum information, the output image is digitized and digitally filtered. The imaginary part of the bispectrum is obtained by Hilbert transforming the real part, and then computing the bispectrum magnitude and phase. The processor is tested with four different combinations of rf test signals. Each signal has a bandwidth of either 6 or 12 MHz. Test results that illustrate the performance of the processor in the recovery of magnitude and phase information for the bispectrum of quadratically related signals are presented., An optical-digital processor computes both the bispectrum magnitude and phase for 10 MHz to one GHz radio frequency signals and has a modified Mach-Zehnder interferometer architecture with three acousto-optic modulators and transforming lenses. The processor performs well in the magnitude and phase information recovery tests using several combinations of radio frequency test signals with a bandwidth of 6 or 12 MHz each.

We describe a new method for producing ultrafine magnetic particles that employs pulsed-laser particle ablation. Pulsed-laser radiation with wavelength of 248 nm was used to ablate 1 to 10 [[micro]meter] diameter permalloy microparticles under normal atmospheric conditions. The ejected nano-particles were collected on silicon substrates for further analysis. Scanning electron micrographs of the samples were analyzed by computer aided image processing to determine the effect of laser fluence on the particle size distribution. Results showed that mean particle diameters were in the range from 60 to 90 nm, and that the particle size distributions were closely log-normal.

Silver nanostructured films are produced by supersonic jet deposition of nanoparticles, which are generated by laser ablation of microparticle aerosols (LAMA). The analysis has shown that increases in conductivity during annealing at temperatures less than 400 degree centigrade has resulted from grain size coarsening rather than densification.