Modern lithographic simulation engines1 are quite capable of determining the detrimental impact of source and lens
aberrations on low k1 lithographic metrics - given the proper input2. Circuit designers, lithographic engineers, and
manufacturing facilities would seem to be the beneficiaries of the predictive power of lithographic simulators; however,
in-situ methods for accurately determining lens aberrations and source metrology maps have only rather recently been
accepted3 and integrated into practice4. For this work, we introduce several new methods for characterizing scanner
performance including a high accuracy source metrology tool and integrated simulation engine5. We focus attention on
the combined detrimental effects of lens aberrations, source non-ideality, distortion, synchronization error, and transmission error on deep sub-wavelength lithographic metrics such as: H-V bias, feature-shift, and ΔCD. After a brief theoretical discussion, we describe a matrix of simulation case studies and present results. Finally, we discuss potential applications for the simulation performance framework and its potential impact to industry.
We seek to examine near-IR photometric signatures for geosynchronous earth orbit (GEO) communication satellites. To this end, we present a set of high quality photometric measurements for a sample of ten GEOs. The observations were made with a standard set of broad band astronomical filters (Johnson filters), using the 3.6 meter telescope at the Air Force Research Laboratory (AFRL) Directed Energy Directorate Starfire Optical Range, Kirtland AFB, NM. The results indicate that near-IR photometric signatures can be used to distinguish among different satellite classes. Other uses of the data, e.g. anomaly resolution and health status, are discussed.
The use of liquid crystal devices for wavefront control has been suggested and implemented by several authors. Our group has been at the forefront of the development of this technology. In this paper we report some preliminary experimental results on the use of Nematic based liquid crystal devices. Several experimental efforts have been carried out in the past few months. One of the main aims was to characterize a new devices that uses dual frequency nematic material.
For many years, the United States Air Force Research Laboratory (AFRL) has developed algorithms and researched methods for optical tracking and imaging space objects. This effort has been partly limited by the lack of a calibrated on- orbit 'proof' object that can be used to reliably compare predictions to observations. In 1996, AFRL scientists began discussing this problem with the Scientific Research Institute for Precision Device Engineering of the Space Device Engineering Corporation (SDEC), Moscow, Russia. SDEC's own research in this area has been similarly limited. As a result of these discussions, and as a spin-off from related research conducted under AFRL contract, SDEC has constructed a small instrument that can fulfill the role of a non-orbit proof instrument. This free-flying passive satellite, named REFLECTOR, is designed using 32 corner cube retro-reflectors on a simple aluminum frame to ensure reliable return when illuminated from any angle. It is approximately 2 m high and 1 m wide at the base with a mass of only 6 kg. The REFLECTOR satellite has been built and is scheduled for launch as a secondary payload in December 1999. Once deployed, into its near sun-synchronous orbit, it will be observable from any location on Earth. It will be possible to passively acquire and track the satellite (using reflected sunlight) with a telescope as small as 10 cm in diameter. Because the retro- reflectors on the satellite return a large signal, laser tracking and imaging experiments can be done from the ground using small, laboratory-sized lasers. REFLECTOR will provide a 'proof instrument' that will allow the U.S. Air Force and others to test various atmospheric correction techniques.
Gone are the days of unfettered government spending. An affordable, high performance alternative to multi-million dollar adaptive optics systems is required by the scientific and industrial communities. We have constructed and now give early performance specifications for the 1 St ofthree low cost Adaptive Optics systems for the University of Puerto Rico Imaging Interferometer. Built in months, not years, our in-house subsystem developments include (1) a photon counting ICCD Shack-Hartmann wavefront sensor; (2) a zero latency analog wavefront reconstructor; (3) a precision 2D geometry interpolator; (4) a 700Hz bandwidth beamsteering mirror system with photon counting tracker; and (5)adata acquisition, monitoring and deformable mirror control computer. Key to the control system is a 37-element MEM electrostatic membrane deformable mirror purchased from OKO Technologies. Every element of this system is innovative in the sense of exceptionally high performance at low cost. We will discuss the applicability of using several unique 2D liquid crystal spatial light modulators as correcting elements. We will discuss feedback vs. feed-forward implementations of control law, as well as many practical considerations of full implementation. Other possible medical, industrial, and scientific applications of this affordable, high performance AO technology will be presented.
KEYWORDS: Wavefront sensors, Analog electronics, CCD cameras, Cameras, Wavefronts, Signal to noise ratio, Sensors, Quantum efficiency, Data acquisition, Charge-coupled devices
The contradiction inherent in high temporal bandwidth adaptive optics wavefront sensing at low-light-levels (LLL) has driven many researchers to consider the use of high bandwidth high quantum efficiency (QE) CCD cameras with the lowest possible readout noise levels. Unfortunately, the performance of these relatively expensive and low production volume devices in the photon counting regime is inevitably limited by readout noise, no matter how arbitrarily close to zero that specification may be reduced. Our alternative approach is to optically couple a new and relatively inexpensive Ultra Blue Gen III image intensifier to an also relatively inexpensive high bandwidth CCD camera with only moderate QE and high rad noise. The result is a high bandwidth broad spectral response image intensifier with a gain of 55,000 at 560 nm. Use of an appropriately selected lenslet array together with coupling optics generates 16 X 16 Shack-Hartmann type subapertures on the image intensifier photocathode, which is imaged onto the fast CCD camera. An integral A/D converter in the camera sends the image data pixel by pixel to a computer data acquisition system for analysis, storage and display. Timing signals are used to decode which pixel is being rad out and the wavefront is calculated in an analog fashion using a least square fit to both x and y tilt data for all wavefront sensor subapertures. Finally, we present system level performance comparisons of these new concept wavefront sensors versus the more standard low noise CCD camera based designs in the low-light-level limit.
The University ofPuerto Rico, Mayaguez, in conjunction with the Deep Space Surveillance Branch (DEBS) ofthe USAF Research Laboratory (AFRL) Phillips Site (PL) in Albuquerque, NM is initiating an Adaptive Optics (AO) Interferometry program. The program will begin with four projects. We currently have finding for a three element optical interferometer, described in this paper, using Technology developed at DEBS, for a new wavefront sensor and a Liquid Crystal (LC) wavefront compensator being presented at this meeting'9.and a Low Light Level Fringe Tracker (LLLFT)"6'1"24 Michelson: Interferometer. We are also developing a program to put a similarly configured inexpensive two-element interferometer test-bed in orbit. The interferometer would have optical elements on a 10-meter boom. It will use Aperture Synthesis by rotation and motion ofthe elements along the booms. The third project under development would incorporate the initial 3-element interferometer into a larger array with the additional collaboration ofNew Mexico Tech and New Mexico State University at a 10,600' site near Socorro, NM. As part ofthe ground based interferometry effort we are trying to develop inexpensive meter class telescopes. The 0.75meter telescopes we are building for our small interferometer will serve as prototypes and system test-beds. The telescopes will be robotic, remotely operable, essentially self-orienting, and portable. We hope to produce such systems for commercial distribution for approximately $250K each. All ofthe ground-based interferometric systems will be configured for remote operation and independent use ofsub-arrays while upgrades and repairs are underway. The major thrust ofthe UPR effort will be to develop inexpensive interferometers for diverse applications with the low light level capabilities and the LC adaptive optics developed at the Phillips Site. Particular applications will be for high-resolution astronomy and satellite imaging. The adaptive optics will be such that they can be placed on the individual telescopes and are not part ofthe interferometer. They will then serve as templates fbr AO systems ofgeneral interest. As an additional part ofall ofthese projects we will try to develop the use ofoptical fibers for several applications. We would like to couple the telescopes with fiber if we can develop an efficient way to couple the output signal from the telescope to the fibers. in addition we hope to use fiber stretchers for optical path compensation to replace expensive conventional optical delay lines. Key words; adaptive optics, interferometer, Liquid Crystal wavefront compensation
A two multi-ro telescope interferometer was built at Air Force Research Lab in Albuquerque New Mexico as a development testbed. The principal objective of this testbed is to develop existing techniques and to test novel low-cost technologies for applications in future interferometers. These technologies include a tip/tilt piston mirror that has a 500-Hz bandwidth with a 200-wave adjustable piston capability at 633nm. This type of mirror has been installed on both telescopes and is used to track objects and scan for fringes. The data obtained on these objects will be used to determine algorithms for measuring fringe visibility at low light level. Additional technologies include liquid crystal devices that have been used to correct static aberrations in the optical system and will be used with a new wavefront sensing technique to correct low order atmospheric aberrations. The new wavefront sensor currently being developed in-house uses a GEN III intensifier optically coupled to a Dalsa camera to provide atmospheric correction on faint extended objects. The testbed will also be utilized to test single mode fiber optics as a replacement to traditional recombining optics. This will potentially reduce the cost and simplify the alignment of multi telescope interferometers.
The Air Force Phillips Laboratory is testing the feasibility of developing a long-path, CO2 laser-based DIAL system for remote sensing applications from an airborne platform. The validity of DIAL system performance simulations for long slant-range paths is being established by means of well-characterized field experiments in which the contributions of atmospheric transmission and atmospheric-turbulence-induced beam spreading and scintillation are being independently measured concurrently with DIAL system radiometric performance. Initial measurements were performed with both diffuse and specular targets using a 3.2 km path located at the Phillips Laboratory Starfire Optical Range. Measurements reported herein were performed using a slant-range path of 21.3 km originating at the Phillips Laboratory AMOS facility on Maui, Hawaii. The latter location offers a slant-range propagation path from 3.04 km above sea level (ASL) to near sea level. The DIAL system under test utilized a 4-joule class laser coupled to 61 cm aperture beam director telescope. Measurements were performed with the laser operating on the C13 isotope in order to increase the atmospheric transmission with respect to a laser operating at C12O216 wavelengths. Concurrent atmospheric optical characterization measurements were performed with an infrared scintillometer operating over the same path and at the same wavelength as the DIAL system. Results of atmospheric propagation characterization measurements are described in this paper and results of DIAL system performance and comparisons to simulations are described in accompanying papers.
A laser long range remote sensing (LRS) program is being conducted by the United States Air Force Phillips Laboratory (AF/PL). As part of this program, AF/PL is testing the feasibility of developing a long path CO2 laser-based DIAL system for remote sensing. In support of this program, the AF/PL has recently completed an experimental series using a 21 km slant- range path (3.05 km ASL transceiver height to 0.067 km ASL target height) at its Phillips Laboratory Air Force Maui Optical Station (AMOS) facility located on Maui, Hawaii. The dial system uses a 3-joule, 13C isotope laser coupled into a 0.6 m diameter telescope. The atmospheric optical characterization incorporates information from an infrared scintillometer co-aligned to the laser path, atmospheric profiles from weather balloons launched from the target site, and meteorological data from ground stations at AMOS and the target site. In this paper, we report a description of the experiment configuration, a summary of the results, a summary of the atmospheric conditions and their implications to the LRS program. The capability of such a system for long-range, low-angle, slant-path remote sensing is discussed. System performance issues relating to both coherent and incoherent detection methods, atmospheric limitations, as well as, the development of advanced models to predict performance of long range scenarios are presented.
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