Search

We present the inscription of narrow-linewidth fiber Bragg gratings (FBGs) into different types of multicore fibers (MCFs) using ultrashort laser pulses and the phase mask technique, which can act as notch filters. Such filters are required, e.g., to suppress light emitted by hydroxyl in the Earth’s upper atmosphere, which disturbs ground-based observation of extraterrestrial objects in the near infrared. However, the inscription into a commercially available seven-core fiber showed a quite large core-to-core deviation of the resonance wavelength of up to 0.45 nm. Two options are presented to overcome this: first, we present the photo-treatment of the FBGs to tune the resonance wavelength, which allows for sufficient resonance shifts. Second, adapted MCFs containing 12 cores, arranged on a circle, are fabricated. For this, two different fabrication procedures were investigated, namely, the mechanical drilling of the preform for a rod-in-tube version as well as a stack-and-draw approach. Both adapted MCFs yielded significant improvements with core-to-core wavelength variations of the FBGs of only about 0.18 nm and 0.11 nm, respectively, sufficient to fulfill the requirements for astronomical filter applications as discussed above.

Recently, we developed a new ghost imaging (GI) detection concept based on the superposition of object and reference beams with subsequent photon statistics evaluation by using one single photon counting detector (PS-GI). Here, we derive analytical expressions for the spatial correlations of this mixed light GI concept considering the mode properties of the speckles of an illuminating classical pseudothermal source. This model supports the first experimental results of PS-GI in [Opt. Lett.41, 2863–2866 (2016)OPLEDP0146-959210.1364/OL.41.002863] and explains deviating characteristic features in comparison to state-of-the-art GI detection, such as maximum and minimum ghost image signals as well as the visibility performance. Furthermore, the model also explains the higher order correlations, which have been experimentally obtained by using a single detector. The overall good agreement between theory and experiment provides physical insight into the functional principle of mixed light GI, thus fostering PS-GI as a real alternative to established GI technologies.

The optical aberrations induced by imaging through skin can be predicted using formulas for Seidel aberrations of a plane-parallel plate. Knowledge of these aberrations helps to guide the choice of numerical aperture (NA) of the optics we can use in an implementation of Gabor domain optical coherence microscopy (GD-OCM), where the focus is the only aberration adjustment made through depth. On this basis, a custom-designed, liquid-lens enabled dynamic focusing optical coherence microscope operating at 0.2 NA is analyzed and validated experimentally. As part of the analysis, we show that the full width at half-maximum metric, as a characteristic descriptor for the point spread function, while commonly used, is not a useful metric for quantifying resolution in non-diffraction-limited systems. Modulation transfer function (MTF) measurements quantify that the liquid lens performance is as predicted by design, even when accounting for the effect of gravity. MTF measurements in a skinlike scattering medium also quantify the performance of the microscope in its potential applications. To guide the fusion of images across the various focus positions of the microscope, as required in GD-OCM, we present depth of focus measurements that can be used to determine the effective number of focusing zones required for a given goal resolution. Subcellular resolution in an onion sample, and high-definition in vivo imaging in human skin are demonstrated with the custom-designed and built microscope.

A major advantage of fiber-optic beam delivery in laser materials processing is the ability to guide the laser power to the location where it is needed, leaving the laser itself remote and protected from the process. This is of special importance if the processing is to be performed in a hazardous environment. Particular problems are faced by the nuclear industry where weld repair and surface treatment work are required inside radioactive installations. By use of fiber beam delivery, only part of the delivery system and effector optics become contaminated, but the expensive laser system does not. However, in many cases the region where repair is required is not only radioactive but has only limited physical access, e.g., inside tubes or into corners, which prevents use of standard effector optics. We present a new design to deal with such constraints of a 2-mm outer diameter employing a hollow waveguide and gas shielding. This design is optically characterized and its performance assessed in welding and surface treatment applications. The potential of this compact effector optics in limited physical access situations is clearly demonstrated.

Laser beam characteristics are altered during propagation through large-core optical fibers. The distribution of modes excited by the input laser beam is modified by means of mode coupling on transmission through the fiber, leading to spatial dispersion of the profile and, ultimately and unavoidably, to degradation in the quality of the delivered beam unless the beam is spatially filtered with consequent power loss. Furthermore, a mismatch between the intensity profile of a typical focused high-power laser beam and the profile of the step-index fiber gives rise to additional beam-quality degradation. Modern materials processing applications demand ever higher delivered beam qualities (as measured by a parameter such as M^2) to achieve greater machining precision and efficiency, a demand that is currently in conflict with the desire to utilize the convenience and flexibility of large-core fiber-optic beam delivery. We present a detailed experimental investigation of the principal beam-quality degradation effects associated with fiber-optic beam delivery and use numerical modeling to aid an initial discussion of the causes of such degradation.

Recent improvements in design have made it possible to build Nd:YAG lasers with both high pulse energy and high beam quality. These lasers are particularly suited for percussion drilling of holes of as much as 1-mm diameter thick (a few millimeters) metal parts. An example application is the production of cooling holes in aeroengine components for which 1-ms duration, 30-J energy laser pulses produce holes of sufficient quality much more efficiently than with a laser trepanning process. Fiber optic delivery of the laser beam would be advantageous, particularly when one is processing complex three-dimensional structures. However, lasers for percussion drilling are available only with conventional bulk-optic beam delivery because of laser-induced damage problems with the small-diameter (approximately 200–400-µm) fibers that would be required for preserving necessary beam quality. We report measurements of beam degradation in step-index optical fibers with an input beam quality corresponding to an M^2 of 22. We then show that the laser-induced damage threshold of 400-µm core-diameter optical fibers can be increased significantly by a CO_2 laser treatment step following the mechanical polishing routine. This increase in laser-induced damage threshold is sufficient to propagate 25-J, 1-ms laser pulses with a 400-µm core-diameter optical fiber and an output M^2 of 31.

We describe an off-axis design for a 6.5-m astronomical telescope optimized for low scattered light and low emissivity. This is part of a new concept for an instrument that we call the New Planetary Telescope. We show how the geometric optical performance can equal that of an on-axis conventional telescope while the diffractive performance fundamentally surpasses conventional telescopes because of the absence of pupil obstruction. The decentered concept also allows wide-field and versatile instrumentation configurations that are not possible with more-conventional designs.

The patent number, date of issuance by the U.S. Patent Office, and classification are shown on the first line. The filing date is that of the first application (although some patents may derive from earlier applications with earlier claim dates). Any opinions expressed are those of the reviewers and do not reflect the opinions of the organizations with which they are associated, the Optical Society of America, or this journal. Printed copies of these patents may be ordered from the Commissioner of Patents, Washington, DC 20231: telephone (703) 557-3158, URL http://patents.uspto.gov. Inquiries about patents should be addressed to the Patents Office, not to this journal or to OSA.

The patent number, date of issuance by the U.S. Patent Office, and classification are shown on the first line. The filing date is that of the first application (although some patents may derive from earlier applications with earlier claim dates). Any opinions expressed are those of the reviewers and do not reflect the opinions of the organizations with which they are associated, the Optical Society of America, or this journal. Printed copies of these patents may be ordered from the Commissioner of Patents, Washington, DC 20231: telephone (703) 557-3158, URL http://patents.uspto.gov. Inquiries about patents should be addressed to the Patents Office, not to this journal or to OSA.

The patent number, date of issuance by the U.S. Patent Office, and classification are shown on the first line. The filing date is that of the first application (although some patents may derive from earlier applications with earlier claim dates). Any opinions expressed are those of the reviewers and do not reflect the opinions of the organizations with which they are associated, the Optical Society of America, or this journal. Printed copies of these patents may be ordered from the Commissioner of Patents, Washington, DC 20231: telephone (703) 557-3158, URL http://patents.uspto.gov. Inquiries about patents should be addressed to the Patents Office, not to this journal or to OSA.

The patent number, date of issuance by the U.S. Patent Office, and classification are shown on the first line. The filing date is that of the first application (although some patents may derive from earlier applications with earlier claim dates). Any opinions expressed are those of the reviewers and do not reflect the opinions of the organizations with which they are associated, the Optical Society of America, or this journal. Printed copies of these patents may be ordered from the Commissioner of Patents, Washington, DC 20231: telephone (703) 557-3158, URL http://patents.uspto.gov. Inquiries about patents should be addressed to the Patents Office, not to this journal or to OSA.

We describe here an off-axis design for a 4.0-m astronomical telescope. We show that the geometric optical performance of this configuration can equal that of an on-axis conventional configuration while the diffractive performance fundamentally surpasses conventional telescopes because of the absence of pupil obstruction. The specific optical design described here uses a single off-axis primary mirror to obtain three distinct final focus ports: an f/10 port (with corrector) for wide-field imaging and spectroscopy with a field of view (FOV) of 15 arc min; a small-field, 2-reflection f/10 port suitable for polarimetry and coronagraphy; and a slower, f/16 (3-reflection) port with a 7 arc min FOV. For general astronomical observations requiring high optical throughput and low scattered light, this design is superior to conventional Ritchey–Chretien optical configurations.

Ongoing research on a system for the automated evaluation of digitized images of histopathologic sections is described. The system comprises an ultrafast laser scanner microscope capable of recording image data at 64 Mhz in each of two wavelength channels, and a multiprocessor computer containing thirty-six Motorola 68000 processing elements. The operating system allows an image-data-driven dynamic reconfiguration of the computer architecture; this reconfiguration is based on prior knowledge of the histopathologic sections to be processed. Knowledge engineering methods are used extensively as development tools in the development of an expert system-controlled scene segmentation, processing task scheduling, in the diagnostic expert system module, and its validation procedures.

The first experimental results, to our knowledge, for an optical modulator that makes use of an electro-optic polymer located between two thin silver films are presented. The methods used to fabricate the modulator are discussed. Initial results show 18.5% modulation in the intensity of the light reflected off of the modulator at a wavelength of 6328 Å.

Calculations of radiative through and resulting ir cooling of cloud forms is certainly more difficult than observations. Based on observations, a radiative transfer model has been developed for absorption in clouds employing an observationally determined volume absorption coefficient, ranging from 0.0005 to 0.0007 cm^−1. This model does not require any assumption of cloud blackness or thickness and permits clouds to remain partially transparent or opaque as their thickness and absorption dictate. Agreement within a standard deviation of 12.0 W m^−2 between observation and calculation has been maintained in approximately twenty profiles through clouds. The standard deviation was determined from some 140 observations.