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We report a beam-shaping technique whereby the output power from a high-power laser-diode stack is efficiently coupled, reconfigured, and transmitted to a thin-disk laser by means of a compact optical fiber bundle. By using this technique, the power density is increased by a factor of 2 when compared to direct coupling with a octagonal fused silica rod while the numerical aperture is kept constant. Transmission efficiency of 80% was measured for the beam shaper without antireflection coating. The top-hat distribution is numerically calculated at the thin-disk laser crystal. OCIS codes: 140.0140, 140.3300, 140.3460, 140.3480.

Ubiquitous radar systems look everywhere at all times and require both parallel radar processors and parallel beamformers. Current systems operate with subgigahertz bandwidths and produce a handful of angle-of-arrival (AOA) beams. We present an electro-optic radar processor that combines the multigigahertz wideband capabilities of a spectral hole burning correlator with wideband Doppler processing and the thousands of parallel channels available from an electro-optical beamformer. Preliminary experiments demonstrate 150 MHz bandwidth range correlations across 20 AOA beams. [c] 2010 Optical Society of America OCIS codes: 090.4220, 280.5110, 070.4340, 070.4550, 070.0070.

Normally, fly's eye condensers are used to homogenize light. However, in the case of fully coherent light, a fly's eye condenser, in connection with some simple optical elements, such as a diffractive axicon, a grating, and a telescope, can be used as a quite flexible beam shaping system, forming arrays of rings, parts of rings, or other structures with varying diameters. We present the principle, some simulation results, and some first experimental results. OCIS codes: 050.1970, 220.2560, 350.3950.

The applicability of layers of ion-implanted polymethyl methacrylate (PMMA) for beam splitting of laser light at the telecommunications wavelength of 1.55 [micro]m is examined. Bulk PMMA is studied, subjected to low-energy (50 keV) silicon ion implantation at various ion fluences in the range from [10.sup.14] to [10.sup.17] [cm.sup.-2]. The formed ultrathin near-surface ion-implanted layer of a thickness of about 100 nm, buried in a depth of ~100nm, can be used to split (or combine) laser beams at 1.55 [micro]m with a low absorption loss. OCIS codes: 130.1750, 230.1360, 240.1485.

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.

A metal slit array arranged along a semicircular surface achieving subwavelength optical beam focusing along the lateral direction is proposed. Taking into consideration surface plasmon polaritons that pass through a metal slit array, we design the array with a curvature. By use of a genetic algorithm, the size of the metal slit and the corresponding curvature are to be determined. Based on our metal slit array configuration, the full width at half-maximum can be achieved on a subwavelength scale. OCIS codes: 240.6680, 230.3120.

We report the focusing of a normally incident plane wave of 405 nm through a Ag/dielectric annular ring structure, using finite-difference time domain analysis. We first study the dependency of the focusing efficiency on slit width when the incident wave is transmitted through a single ring whose slit is filled with a dielectric. Then, light focusing by the multiple-ring structure is investigated as a function of the dielectric thickness. It is observed that the focusing is tunable between near-field and quasi-far-field regimes in the Ag/dielectric layered annular ring structure. Also, the focal intensities are remarkably enhanced by the addition of the dielectric layer, showing a Fabry--Perot-like resonance with respect to the thickness of the dielectric layer. The controllable near-field and far-field focusing offers more flexibility for applications of future nano-optic devices. [c] 2010 Optical Society of America OCIS codes: 240.6680, 240.0240.

We present the design and fabrication of a novel dual-function subwavelength fused-silica grating that can be used as a polarization-selective beam splitter. For TM polarization, the grating can be used as a two-port beam splitter at a wavelength of 1550 nm with a total diffraction efficiency of 98%. For TE polarization, the grating can function as a high-efficiency grating, and the diffraction efficiency of the-1st order is 95% under Littrow mounting. This dual-function grating design is based on a simplified modal method. By using the rigorous coupled-wave analysis, the optimum grating parameters can be determined. Holographic recording technology and inductively coupled plasma etching are used to manufacture the fused-silica grating. Experimental results are in agreement with the theoretical values. OCIS codes: 050.1950, 230.1360, 230.5440, 050.6624, 060.4510..

We report on an experimental realization of polarization-holographic optical elements (PHOEs) for laser beam shaping. The PHOEs were written into an azobenzene polymer layer by illumination with linearly polarized, focused light with spatially varying orientation. We propose a noniterative design method for the calculation of PHOEs that transform laser beams into arbitrary rotationally symmetric or separable intensity distributions such as flattop or ring profiles. The experimentally observed intensity distributions are compared with those predicted by numerical simulations based on the Fresnel diffraction approximation. Diffraction efficiencies up to 79% were determined experimentally. OCIS codes: 050.1970, 090.1760, 220.4000.

Laser beam shaping is an important subject for industrial and medical applications since different applications may require different laser intensity distributions. We present an all-fiber beam-shaping device that could transform a Gaussian-shaped laser beam into an intensity uniform beam in the 1.0 [micro]m wavelength region using a long-period grating (LPG). The device can be used to shape the beam of a Yb-doped high-power fiber laser. The mode structure of the LPGs made of HI1060 fiber is analyzed. The design parameters that affect the beam shaping are discussed, and the results of the beam shaping using two cladding modes, [LP.sub.03] and [LP.sub.04], are presented. OCIS codes: 060.2340, 060.2310, 140.3300, 230.2285.

We report a quantum random number generator based on the photon-number--path entangled state that is prepared by means of two-photon quantum interference at a beam splitter. The randomness in our scheme is truly quantum mechanical in origin since it results from the projection measurement of the entangled two-photon state. The generated bit sequences satisfy the standard randomness test. OCIS codes: 270.5585, 030.5260, 190.7110.

A new technique for external measurement of dihedral right angles is presented. An expanded, collimated, and linearly polarized He--Ne laser beam (632.8 nm) from a Fizeau interferometer is launched into a cyclic path optical configuration (CPOC) in which the counterpropagating p and s polarization components traverse the same optical path in opposite directions. A right-angled component (RAC), with its plane surfaces forming the right angle, is set to externally reflect the counterpropagating p and s components of the CPOC in nearly the same directions but with a lateral separation. In a plane normal to the right-angle edge of the RAC, the laterally separated collimated beams have angular separation, which is equal to twice the error in the dihedral right angle. Another CPOC setup is used to recombine the beams by reducing the lateral shear to zero. Error in right angle is calculated from the spacing of the resulting two-beam Fizeau fringes. Methods for overcoming the restriction of measurement accuracy due to beam aperture limitation and the effects of the positional tilt of the RAC have been discussed. Results of validation experiments are presented. OCIS codes: 230.5480, 220.4610, 120.3180, 220.4840.

We discuss the theoretical and experimental investigation of acousto-optic dispersive tunable filters, based on quasi-collinear geometry of light-sound interaction in a tellurium dioxide single crystal. The geometry uses the effect of strong acoustic anisotropy in the paratellurite as well as peculiarities of acoustic wave reflections at the free boundary of the crystal. A mathematical concept for determination of optical, electrical, and constructional parameters of the filters is developed. Different experimental acousto-optic filters intended for femtosecond pulse shaping are designed and tested. Preliminary experiments are performed in a subpetawatt optical parametric chirped pulse amplification laser system. The experimental data conform completely with the predicted data. OCIS codes: 230.1040, 140.7090, 190.4970.

The laser-jamming effectiveness of combined fiber lasers for airborne defense systems is analyzed in detail. Our preliminary experimental results are proof of the concept of getting a high-power laser through a beam combination technique. Based on combined fiber lasers, the jamming effectiveness of four-quadrant guidance and imaging guidance systems are evaluated. The simulation results have proved that for a four-quadrant guidance system, the tracking system takes only two seconds to complete tracking, and the new tracking target is the jamming laser; for the imaging guidance system, increasing the power of the jamming laser or the distance between the target and the jamming laser are both efficient ways to achieve a successful laser jamming. OCIS codes: 140.3510, 350.4600.

A deep-etched polarization-independent binary fused-silica phase grating as a three-port beam splitter is designed and manufactured. The grating profile is optimized by use of the rigorous coupled-wave analysis around the 785 nm wavelength. The physical explanation of the grating is illustrated by the modal method. Simple analytical expressions of the diffraction efficiencies and modal guidelines for the three-port beam splitter grating design are given. Holographic recording technology and inductively coupled plasma etching are used to manufacture the fused-silica grating. Experimental results are in good agreement with the theoretical values. OCIS codes: 050.1950, 050.1960, 230.1360, 220.4000.

We propose a miniature pulse compressor that can be used to compensate the group velocity dispersion that is produced by a commercial femtosecond laser cavity. The compressor is composed of two identical highly efficient deep-etched transmissive gratings. Compared with prism pairs, highly efficient deep-etched transmissive grating pairs are lightweight and small. With an optimized groove depth and a duty cycle, 98% diffraction efficiency of the -1 transmissive order can be achieved at a wavelength of 800 nm under Littrow conditions. The deep-etched gratings are fabricated in fused silica by inductively coupled plasma etching. With a pair of the fabricated gratings, the input positively chirped 73.9fs pulses are neatly compressed into the nearly Fourier transform-limited 43.2 fs pulses. The miniature deep-etched grating-based pulse compressor should be of interest for practical applications. OCIS codes: 320.5520, 050.0050.

Synthetic radar image recognition is an area of interest for military applications including automatic target recognition, air traffic control, and remote sensing. Here a dynamic range compression two-beam-coupling joint transform correlator for detecting synthetic aperture radar targets is utilized. The joint input image consists of a prepower-law, enhanced scattering center of the input image and a linearly synthesized power-law-enhanced scattering center template. Enhancing the scattering center of both the synthetic template and the input image furnishes the conditions for achieving dynamic range compression correlation in two-beam coupling. Dynamic range compression (a) enhances the signal-to-noise ratio, (b) enhances the high frequencies relative to low frequencies, and (c) converts the noise to high frequency components. This improves the correlation-peak intensity to the mean of the surrounding noise significantly. Dynamic range compression correlation has already been demonstrated to outperform many optimal correlation filters in detecting signals in severe noise environments. The performance is evaluated via established metrics such as peak-to-correlation energy, Homer efficiency, and correlation-peak intensity. The results showed significant improvement as the power increased. OCIS codes: 100.5010, 070.4550, 100.6740.

Spatial engineering of polarization as a new method of beam shaping is analyzed by using scalar diffraction theory. For the one-dimensional case, it is shown that the smallest flattop far-field distribution can be obtained by adopting a linear polarization that changes direction as a linear function of location in the pupil plane. The resulting light field is functionally equivalent to a cosinusoidal function modulation of the wavefront but maintains high efficiency. This polarization beam shaping technique proves to be highly useful in applications where diffraction effects need to be taken into account. The extension of this technique to two-dimensional beam shaping is also demonstrated. OCIS codes: 260.5430, 260.1960, 140.3300, 220.2560, 220.2740, 070.2580.

The design principle for a nonpolarizing beam splitter based on the Brewster condition in a cube is introduced. Nonpolarizing beam splitters in an asymmetrical glass cube are proposed and theoretically investigated, and applied examples are given. To realize 50% reflectance and 50% transmittance at specified wavelengths for both polarization components with an error of less than 2%, two measurements are taken by adjusting the refractive index of the substrate material and optimizing the thicknesses of each film in the design procedures. The simulated results show that the targets are achieved using the method reported here. OCIS codes: 310.6860, 230.1360, 260.5430.