Focal Length

An ultrasonic propagation imaging (UPI) system consisted of a Q-switched Nd-YAG pulsed laser and a galvanometer laser mirror scanner was developed. The system which requires neither reference data nor fixed focal length could be used for health monitoring of curved structures. If combined with a fiber acoustic wave PZT (FAWPZT) sensor, it could be used to inspect hot target structures that present formidable challenges to the usage of contact piezoelectric transducers mainly due to the operating temperature limitation of transducers and debonding problem due to the mismatch of coefficient of thermal expansion between the target, transducer and bonding material. The inspection of a stainless steel plate with a curvature radius of about 4 m, having 2mm×1mm open-crack was demonstrated at 150°C using a FAWPZT sensor welded on the plate. Highly-curved surfaces scanning capability and adaptivity of the system for large laser incident angle up to 70° was demonstrated on a stainless steel cylinder with 2mm×1mm open-crack. The imaging results were presented in ultrasonic propagation movie which was a moving wavefield emerged from an installed ultrasonic sensor. Damages were localized by the scattering wavefields. The result images enabled easy detection and interpretation of structural defects as anomalies during ultrasonic wave propagation.

A new approach for the design and fabrication of a miniaturized Hyperspectral imager is described. A unique and compact instrument has been developed by taking advantage of light propagation within bonded solid blocks of fused silica. The resulting microHSI is a VNIR hyperspectral sensor capable of operating in the 400-1000 nm wavelength range developed, patented, and built by NovaSol. The microHSI spectrograph weighs 12.4 oz from slit input to camera output. The microHSI can accommodate either custom foreoptics or C-mount input lenses to adapt to a wide range of fields-of-view (FOV). The prototype microHSI uses a telecentric F2.8 foreoptic, with 36 mm focal length, to cover a 15 degree FOV. It can resolve 960 spatial pixels, resulting in a 280 murad IFOV for this particular foreoptics implementation. With a 1 nm/unbinned pixel dispersion, the spectrometer spectral resolution is 3.5 nm. Results of field and laboratory testing of the prototype microHSI are presented and show that the sensor consistently meets technical performance predictions. The prototype microHSI employs a holographic diffraction grating embedded within the optical blocks resulting in a 19% diffraction efficiency. Future units are anticipated to incorporate a blazed grating for improved throughput and SNR. The microHSI concept can be extended to operation over other wavelength regions. Designs are nearing completion for a SWIR version of the device, and a miniaturized LWIR microHSI sensor is currently at the conceptual design stage.

ABSTRACT There has been a recent surge in interest in hosted and rideshare payloads that would launch aboard commercial communications satellites. Much of this interest originates with the satellite customers themselves as a way to sell excess mass and power margins that exist at launch. In 2008, NASA selected GOLD (Global-scale Observations of the Limb and Disk) as a mission of opportunity to fly as its first hosted payload experiment on a geosynchronous commercial communications satellite, a STAR-2 bus satellite built by Orbital Sciences. CHIRP (Commercially Hosted Infrared Payload), a hosted payload to test infrared sensors for the Air Force, is also being developed for a STAR-2 bus communications satellite. The mass limitation on a STAR-2 bus hosted payload is roughly 50 - 60 kg and the volume is roughly constrained to a 25" x 30" x 28" box on the nadir deck. Telescope apertures are therefore limited is size to about 50 cm in diameter. The diffraction limit for visible (much less IR) imaging missions barely improves upon ground-based image performance, but UV missions can achieve better than 0.1" resolution. There is at least one family of optical designs that (a) provide the necessary focal length and (b) are light and compact enough to fit within the STAR-2 bus mass and volume constraints. These designs also afford opportunities to maintain 0.05" pointing accuracy through a combination of a fine steering mirror and an orthogonal transfer CCD.

Pupil plane encoding has shown to be a useful technique to extend the depth of field of optical systems. Recently, further studies have demonstrated its potential in reducing the impact of other common focus-related aberrations (such as thermally induced defocus, field curvature, etc) which enables to employ simple and low-cost optical systems while maintaining good optical performance. In this paper, we present for the first time an experimental application where pupil plane encoding alleviates aberrations across the field of view of an uncooled LWIR optical system formed by F/1, 75mm focal length germanium singlet and a 320x240 detector array with 38-micron pixel. The singlet was corrected from coma and spherical aberration but exhibited large amounts of astigmatism and field curvature even for small fields of view. A manufactured asymmetrical germanium phase mask was placed at the front of the singlet, which in combination with digital image processing enabled to increase significantly the performance across the entire field of view. This improvement is subject to the exceptionally challenging manufacturing of the asymmetrical phase mask and noise amplification in the digitally restored image. Future research will consider manufacturing of the phase mask in the front surface of the singlet and a real-time implementation of the image processing algorithms.

We report on continuously tunable operation of a diode pumped lasers based on Tm-doped materials, emitting in the 1.8 - 2.mu1 m spectral band. In our study we compare results obtained with three various single crystals doped by Tm3+ ions: Yttrium Aluminum perovskite YAP (YAlO3), Gadolinium orthovanadate GdVO4, and Yttrium Lithium Fluoride YLF (YLiF4). Following samples were available: the 3mm

Small-sized liquid crystal displays are widely used for mobile applications such as cell phones. Electronic control of a viewing angle range is desired in order to maintain privacy for viewing in public as well as to provide wide viewing angles for solitary viewing. Conventionally, a polymer-dispersed liquid crystal (PDLC) panel is inserted between a backlight and a liquid crystal panel. The PDLC layer either transmits or scatters the light from the backlight, thus providing an electronic control of viewing angles. However, such a display system is obviously thick and expensive. Here, we propose to place an electronically-controlled, light-deflecting device between an LED and a light-guide of a backlight. For example, a liquid crystal lens is investigated for other applications and its focal length is controlled electronically. A liquid crystal phase grating either transmits or diffracts an incoming light depending on whether or not a periodic phase distribution is formed inside its liquid crystal layer. A bias applied to such a device will control the angular distribution of the light propagating inside a light-guide. Output couplers built in the light-guide extract the propagating light to outside. They can be V-shaped grooves, pyramids, or any other structures that can refract, reflect or diffract light. When any of such interactions occur, the output couplers translate the changes in the propagation angles into the angular distribution of the output light. Hence the viewing-angle characteristic can be switched. The designs of the output couplers and the LC devices are important for such a backlight system.

The optical properties of the crystalline lenses were studied in a variety of large predatory teleosts (bony fishes) that forage in the open ocean, some of them at considerable depths. We found the first fish lenses that are free of measurable longitudinal spherical aberration, i.e., are perfectly monofocal, in contrast to the multifocal lenses that are typical for smaller fishes living close to the surface. In fact, none of the lenses investigated in this study were clearly multifocal. Most, but not all, of the lenses had long normalized focal lengths (focal length/lens radius) of up to 3.3 lens radii. A monofocal lens of long focal length, combined with spectrally suitably placed cone pigments, may be the optimal solution for vision of high spatial and spectral resolutions in a habitat where the available spectrum of light is limited.

We present microlens arrays consisting of multiple focus-tunable microlenses omnidirectionally fabricated on spherical surfaces, to realize large field of view. Thin flexible polymer bridges connecting adjacent microlenses are designed to reduce the wrapping stress and deformation of the microlens array. Each microlens, formed via water-oil interface, is individually tuned by a thermo-responsive hydrogel actuator. The range of the focal length of each microlens in this array varied from millimeters to infinity. A prototype of optical imaging system based on such a microlens array on a spherical surface, including a charged-coupled device camera, a fiber bundle, and a 3-D rotational stage, is demonstrated as well.

High resolution is in demand for the new applications based on the use of infrared technology. For observation task, high resolution provides more information either under the form of better resolving power or larger field-of-view. Various solutions can be envisioned to achieve high resolution imaging. In this paper, a combination of high resolution detector and microscanning system is proposed. This strategy results in higher resolution and reduced aliasing. A catadioptric configuration is preferred when a microscan is required to increase the spatial sampling frequency. Among the catadioptric configurations, the Schmidt-Cassegrain has wide angle capability due to its aspherical entrance window. However, when the system is used in harsh environment, this compensator window may have to be replaced often. In this case, a flat window would be preferred because it can be removed or easily replaced at reasonable cost. The reduction of the aberrations to an acceptable level without compensator window requires that the mirrors of the telescope be aspherized. In this paper, we present a modified Cassegrain telescope with two aspherical mirrors and one field lens. Due to the large obscuration of the secondary mirror, the effective F/1.05 necessitates a larger working F-number of 0.75. The spectral band ranges from 7.0 to 14.0 microns and the focal length is 50mm. The system is designed for the ULIS UL04171 microbolometer detector with 640 x 480 pixels and 25 microns pixel pitch. With this sensor, the total field of view of the system is 22.6 degrees, which is very large for a catadioptric system. A microscan increases the system maximal spatial sampling frequency from 20 to 40 cycles per millimeter. Despite of the compactness, there is enough room between the field lens and the detector to insert a shutter. A baffle extending ahead of the device is needed in this large field of view design to avoid undesired rays reaching the detector.

We describe a new method of achieving autocalibration that uses a stochastic optimization approach taken from the field of evolutionary comput- ing and we perform a number of experiments on standardized data sets that show the effectiveness of the approach. The basic assumption of this method is that the internal (intrinsic) camera parameters remain constant throughout the image sequence, i.e.

Partially coherent Lorentz-Gauss beams can propagate by remaining spatially localized and non-divergent. The Gaussian beams and after a bit application of Lorentz function, the Lorentz-Gauss beams are a better tool for optical communication. Analytical formulae for spatial complex degree of coherence are derived. In this paper mathematical model of Lorentz-Gauss beams is derived in terms of ABCD parameters. The dependence of spatial complex degree of coherence on beam parameters and coherence length is shown and the role of ABCD parameters is widely discussed. It is observed that focal length plays important role for the performance of Lorentz-Gauss beams.