Single-shot frequency-resolved optical gating for retrieving the pulse shape of high energy picosecond pulses.

Accurate characterization of laser pulses used in experiments is a crucial step to the analysis of their results. In this paper, a novel single-shot frequency-resolved optical gating (FROG) device is described, one that incorporates a dispersive element which allows it to fully characterize pulses up to 25 ps in duration with a 65 fs per pixel temporal resolution. A newly developed phase retrieval routine based on memetic algorithms is implemented and shown to circumvent the stagnation problem that often occurs with traditional FROG analysis programs when they encounter a local minimum.

Boron nitride plasma micro lens for high intensity laser pre-pulse suppression.

We demonstrate that amplified spontaneous emission (ASE) and pre-pulses for high power lasers can be suppressed by propagating the pulse through a boron nitride plasma microlens. The microlens is created by ablating a boron-nitride (BN) disk with a central hole using an Nd:YAG laser . The plasma lens produced in the ablation process exhibits different focal lengths for the high intensity main pulse and low intensity pre-pulse that increases the main pulse/pre-pulse contrast ratio by one order of magnitude while maintaining high transmittance of the pulse energy.

Johanson-Blizzard syndrome: clinical spectrum and further delineation of the syndrome.

We report on 2 patients with Johanson Blizzard syndrome and review the literature, in an attempt to further characterize the clinical spectrum of this disorder.

Extended unambiguous range interferometry.

Phase measuring interferometers generally measure phase modulo 2pi. We present a system which uses fringe contrast to help determine the absolute phase in the interference image within the limits of the coherence length of the illumination. This approach obviates the need for phase unwrapping and is unaffected by surface discontinuities or by data dropout. Since the phase is determined on a point-by-point basis, the processing could be pipelined. The system is set up on a microscope interferometer and produces surface profiles over an array of 512 x 512 points. The measurement range is related to the coherence length of the source and can easily be varied from 0.5 to 2.5 microm. The resolution is limited by the 8-bit quantization of the output.

Hypomethylation of DNA derived from purified human erythroid cells correlates with gene activity of the beta-globin cluster.

Analysis of methylation at the beta-globin gene cluster was carried out on DNA derived from nucleated RBCs (orthochromatic normoblasts) isolated from peripheral blood of patients with beta-thalassemia major or other congenital hemolytic anemia after splenectomy. A procedure to separate these normoblasts from the other nucleated cells of the peripheral blood was developed, providing us with a convenient source of DNA for investigating parameters related to human erythroid differentiation. Blood samples were obtained from six adult patients who express their gamma-globin genes at different levels. Inverse correlation between methylation and gene activity was consistently observed for five of the eight sites analyzed. A site 3' to the beta gene was always unmethylated, two sites flanking the epsilon gene were always found to be methylated, and two sites 5' to the two gamma genes, G gamma and A gamma, were hypomethylated in correlation with gamma gene activity of the individual patients. A site 5' to the delta gene was unmethylated in normoblasts as well as in WBC. No apparent relation between hypomethylation and gene activity was observed for two additional sites. The results suggest that methylation at specific chromosomal locations participate in genetic regulation of the beta-like globin genes in humans.

Incoherent optical two-dimensional Fourier transform using the chirp-z algorithm.

An incoherent optical method for computing two-dimensional complex-valued Fourier transforms is described. It is based on implementing the two-dimensional chirp-z algorithm with incoherent optical convolutions and indirect representation of complex-valued functions.

Orthogonal in-plane and out-of-plane fringe maps in holographic interferometry.

A new technique that combines holographic and speckle interferometry in one recording is described. The technique produces two different fringe maps, which correspond to the in-plane and out-of-plane deformation separately. Experimental results demonstrating the feasibility of the technique to determine complex deformations are presented.

Separation of in-plane and out-of-plane motions in holographic interferometry.

A technique for separating the in-plane and out-of-plane motions of a tested object in hologram interferometry is described. In this technique, the object is illuminated with two symmetrically oriented beams, and an image plane hologram is recorded in photoconductor-thermoplastic devices which can be developed in situ and in virtually real time. Then the hologram is read out with the object waves only, thereby reconstructing the reference beam. If the object is moved or deformed during readout, fringes denoting equal in-plane motion appear as long as the motion is less than the speckle size. The exact arrangement is presented along with experimental results, which are compared with conventional holographic interferometry results.

Registration fiducials for automated alignment with optical processing.

Since automated assembly, as well as automated inspection and sorting, usually require prealigned work-pieces, the availability of rapid and simple automatic alignment is a prerequisite to widespread acceptance of such systems. Coherent optical correlators potentially offer the necessary speed, but they have required mechanically coupled image rotation prisms and spatial light modulators and are, therefore, quite complicated and cumbersome. We describe here an alternative approach in which circularly symmetric fiducials are incorporated into the object itself and detected with an incoherent optical correlator. With incoherent correlators there is no need for spatial light modulators; also, the fiducials are so chosen that the correlation is not rotation sensitive. Since several (typically three) identical fiducials are used, their location can provide sufficient information on the object orientation. The approach was tested in the laboratory, and some experimental examples are included.

Low-power phase-conjugate interferometry.

The operation of Mach-Zehnder and Michelson phase-conjugate interferometers is demonstrated. Phase conjugation is obtained by degenerate four-wave mixing in thin films of eosin. High-visibility fringes are observed both in cw and pulsed modes of operation.