Dynamic high-speed spatial manipulation of cold atoms using acousto-optic and spatial light modulation.

We demonstrate an experimental technique for high-resolution, high-speed spatial manipulation of atom clouds. By combining holographically engineered laser beams from a spatial light modulator with off-axis shear mode acousto-optic deflectors, we manipulate 1 x 3 arrays of cold atoms with individual site addressability. Additionally, we demonstrate smooth 2-dimensional motion of atomic ensembles, and the ability to guide multiple atomic ensembles independently.

Cold atom guidance using a binary spatial light modulator.

We have guided cold (85)Rb atoms in a blue-detuned, high-order hollow laser beam generated by a binary spatial light modulator. The binary holograms written to the modulator produce smooth hollow laser beams with steep intensity walls that can be updated with a 1.6 kHz refresh rate. We analyze the guiding laser beams numerically and experimentally, and show that the atoms are exposed to an average intensity that is ~2% of the maximum intensity of the guide at a laser detuning of 1 GHz and 2 mW of optical power.

Side-illuminated hollow-core optical fiber for atom guiding.

We demonstrate a technique for coupling guiding light into hollow-core optical fibers for atom guiding. Microprisms embedded into a multimode, double-clad hollow fiber, allow light to be coupled into the fiber at multiple locations along the length of the fiber. The technique offers significant advantages over end-pumped configurations.

Two-dimensional synthetic aperture imaging in the optical domain.

In scan-mode synthetic aperture imaging radar, spatial resolution in a range is given by a frequency-swept waveform, whereas resolution in the orthogonal direction is derived from the record of phase as the beam footprint executes linear motion over the object. We demonstrate here what is to our knowledge the first two-dimensional imaging that uses exactly this process in the optical domain for a 1 cm x 1 cm object with 90 mumx170 mum resolution.

Statistics and reduction of speckle in optical coherence tomography.

Studies have shown that optical coherence tomography (OCT) is useful in imaging microscopic structures through highly scattering media. Because spatially coherent light is used in OCT, speckle in the reconstructed image is unavoidable, resulting in degradation of the quality of the OCT images and impaired ability to differentiate subsurface structures. Therefore speckle reduction is an important issue in OCT imaging. We develop speckle statistics that are appropriate to the OCT measurements and demonstrate a simple and practical speckle-reduction technique.

Speckle photography using optically addressed multiple quantum well spatial light modulators.

We demonstrate speckle photography using an optically addressed multiple quantum well spatial light modulator. An optical Fourier transform is used to allow real-time displacement measurements.

Introduction.

Finding defects in materials using optics has a long and glorious history. The very first optical detection method used by humans was, of course, based on simple visual inspection. After the invention of the microscope (possibly the greatest optical invention ever), material inspection techniques took a great leap forward. In recent decades, with the invention of the laser and other advances in science and technology, there have been dramatic improvements in existing optical inspection techniques and the creation of many new ones. In this issue, we have collected four papers from different areas of optics that highlight important advances that have been made in material inspection techniques.

Subsurface defect detection in materials using optical coherence tomography.

We have used optical coherence tomography to study the internal structure of a variety of non-biological materials. In particular, we have imaged internal regions from a commercial grade of lead zirconate titanate ceramic material, from a sample of single-crystal silicon carbide, and from a Teflon-coated wire. In each case the spatial positions of internal defects were determined.

Characteristics of a Yb-doped superfluorescent fiber source for use in optical coherence tomography.

We have used a newly developed Yb-doped high-power fiber source in an optical coherence tomography (OCT) apparatus. We have analyzed various properties of interest for OCT measurements such as spectral shape, related gate width, central wavelength, bandwidth, and power output.

Subsurface defect detection in ceramics by high-speed high-resolution optical coherent tomography.

We use optical coherence tomography with a new configuration to determine the size and location of subsurface defects in solid ceramic and composite ceramic materials. Cross-sectional subsurface regions either parallel or perpendicular to the surface were examined. We present experimental results showing that the size and distribution of small subsurface defects can be determined with depth and lateral resolutions of 10 and 4 microm, respectively.

Generation of high-contrast narrow-band subpicosecond correlations from broadband stochastic fields.

We demonstrate that two broadband stochastic fields generated by use of either parametric frequency conversion or stimulated Raman scattering can be mixed in a nonlinear crystal to produce an output spectrum with a pronounced narrow-band feature. This narrow-band feature, which we show is due to the phase-correlated nature of the beams, is present when the two broadband beams are delayed less than a coherence length relative to each other. We apply this technique to a novel measurement of the field cross-correlation function between two broadband stochastic fields with different center frequencies.

Coherently amplified Raman polarization gate for imaging through scattering media.

We demonstrate a new nonlinear optical field cross-correlation technique for two-dimensional imaging through scattering media. The technique, the coherently amplified Raman polarization gate, relies on both the polarization and coherence sensitivity of broadband stimulated Raman amplification to produce a high-contrast gate with temporal resolution of the order of the inverse bandwidth of the pump.

Nonlinear-optical field cross-correlation techniques for medical imaging with lasers.

We show that certain resonant nonlinear-optical processes are capable of producing a cross-correlation function of the incident fields. This property can be used for time-gating purposes. Using a coherent anti-Stokes Raman scattering process as a time gate, we reproduce an image of an object obscured by a scattering medium.

Fiber Bragg reflectors prepared by a single excimer pulse.

Narrow-line, permanent Bragg reflection gratings have been created in Ge-doped silica-core optical fibers by interfering beams of a single 20-ns pulse of KrF excimer laser light. Of the fibers studied, the highest reflectance value of ~2% was observed with a linewidth (FWHM) of 0.1 nm, which corresponds to a 2-mm grating length with an index modulation of ~3 x 10(-5).