Hubble Imaging Michelson Spectrometer (HIMS), a proposed instrument currently completing its definition phase, is designed to provide background-limited imaging capability and to exploit the diffraction-limited imaging capability of the Hubble Space Telescope (HST) in the wavelength range extending from 1000 to 2500 nanometers. The HIMS instrument also provides spectral resolution with resolving power [λ/Δλ] from 1 to 104. The basic opto-mechanical characteristics and design considerations for the instrument are described.
A five-axis system was designed to automate the alignment of single mode fibers to optical sources such as laser diodes. This system combines 0.01 micron positioning resolution for maximizing the coupling efficiency into single mode fibers with a closed optical feedback loop to compensate for thermal and mechanical drift.
A two-beams interference technique developed to test the wedge of a lens (Ref. 1) has been applied to precision mounting of optical systems. When an optical system requires very high centration and tolerates very little tilt for each of its optical elements, one way of achieving that goal is to mount each individual lens well-aligned in a sub-cell, and the sub-cells are made press-fit to the main lens housing. The main housing and sub-cells are made with high mechanical precision. A twelve lenses optical system for a laser scanner has been assembled that way, the whole optical system achieves diffraction limited quality.
Optical wafer steppers are extremely precise instruments with some very stringent demands placed upon them. They include three-shift production operation, submicron resolution and overlay and high wafer throughput. Registration, a component of overlay, is dependent on the stability of the alignment system and its relationship to the optical axis of the reduction lens. Baseline, the distance between the alignment system and the optical axis, must be stable to for proper operation of the system. Baseline stability in the DSW Wafer Stepper® system has been a issue for a very long time. A large component of this drift has been traced to a high thermal sensitivity of a flexure in the focus motion actuator. This thermal sensitivity, coupled with the Abbe offset in the alignment microscope and the proximity of the voice coil motor to the flexure, causes a rotation of the optical column. Because of the Abbe offset, this rotation causes a shift in the baseline, which has been previously attributed to other unrelated items. Remedies for this problem are quite simple once the phenomenon is understood. They include: proper setup of the instrument to minimize the heat generated at the voice coil motor; thermal isolation of the flexure from the voice coil motor with low thermal conductivity materials; redesign of the voice coil motor for higher efficiency; and active control of the motor temperature. Later designs of the focus motion assembly eliminate the baseline drift problem through the use of high efficiency motors and mechanical design symmetry.
Surface defect measurements are important in several industries. In semiconductor manufacturing, surface defect measurements are made during final inspection by the slice vendor, at incoming inspection by the circuit fabricator and before certain key operations. The principal requirements of the inspection systems are a low defect diameter detection threshold, good repeatability, high throughput and that they add very few particles of critical diameter. These functional requirements lead to sometimes conflicting design requirements for the optical measuring subsystems. We examine the key design requirements for future inspection equipment, and compare approaches used in commercially available equipment.
This paper discusses the design and manufacture of an optical system used in a portable wear metal analyzer (PWMA). The PWMA was developed for the United States Air Force to analyze used aircraft engine of for wear metal contents in the parts per million range. The PWMA uses the graphite furnace atomic absorption technique to detect nine wear metals simultaneously. The instrument has to perform in the field where environmental conditions are particularly challenging. The operating thermal environment spans 75 degrees C and the instrument must withstand a 30 g shock without degradation in performance afterwards. Weight and volume of this stand-alone analytical instrument are limited to what can be carried by one man.
A symmetric Inline Hologram Interferometer is designed to verify and measure the straigthness in a travel distance of 10mm., for a transversal movement from 2.μm up to 20.μm. In this type of hologram interferometer the light source illuminating the object, the object itself, the hologram and the optical viewing system are aligned. As an object a transmitting diffuser plate is used. The diffuser plate is placed on the translation stage that will be moving in the direction of the optical axis of the viewing system. In order to define the parameters of this instrument, an analysis of the visibility function and the optical path difference is made. Experimental results are presented.
This paper discusses the design and testing of a new accelerometer calibrator that will be used to calibrate United States Primary Standard Transducers at the U.S. National Bureau of Standards, Gaithersburg Maryland. Accelerometers are currently calibrated by mounting them to the moving coil of an electrodynamic exciter and driving it with a sinusoidal signal of known frequency. The amplitude of oscillation is measured using laser interferometry techniques. Knowing the frequency and amplitude of oscillation, the acceleration can be determined and the sensitivity calculated. The uncertainty of the existing system at the NBS is ±1.0%, the double amplitude displacement is 7.4 mm (1 7/8 in), and the bandwidth is 2 to 49 Hz. In this paper, the design evolution and component selection reasoning for a new calibrator is presented. A new calibrator was designed and built using the following components: linear air bearing with 0.5 m (20 in) travel, linear brushless DC motor, and laser interferometer transducer system with 2.5 nm (0.1 pin) resolution and maximum allowable slew rate of 1.8 m/s (70 in/s). The new design has the following characteristics: 0.4 m (16 in) double amplitude displacement, 0.8g peak acceleration, 1.3 m/s (50 in/s) peak velocity and 20 Hz bandwidth.
The alignment camera for the Keck Observatory uses a modified Shack-Hartmann test to phase the 36 segments of the primary mirror. The camera also has the capability to do direct imaging (and therefore image stacking), and to perform simple image quality measurements on individual segments. In this paper we motivate several of the design considerations for the alignment camera and describe the overall design.
In the past, force measurements were mostly made on constant forces or slowly varying forces. If the forces being measured varied more rapidly with time, not only the sampling rate of the force measurement equipment needed to be increased, the analog filtering of the pre-amplifier must be reduced in order to obtain the true reading of the force being measured. These forces were sometimes mashed by mechanical noise if the analog filtering is reduced and this must be compensated by increasing the digital filtering of these forces. On the other hand, the digital filtering of too many samples can cause an increase in mean error which is a function of time and the mean error will be added to the gauge reading and thus, decreasing the accuracy of the gauge especially capturing the peak force in a test. We have created a technique for designing force measurement gauges that balance the sampling rates, analog and digital filtering. The results of various testing conditions are made with different sampling rates and different analog and digital filtering. These results are compared and analyzed.
Minimizing alignment induced errors between an actuator and bearing so as not to induce wear and error into the system can often be achieved only via the use of kinematic transmission elements. A taught wire attached to the platten and grabbed in the middle by the actuator is the simplest form of a kinematic transmission system and provides the greatest error attenuation of the compliant type kinematic transmissions; however, it is also the most axially compliant. To increase the apparent axial stiffness, one can measure the position of the platten at the points where the wire is attached to the platten and where the actuator is attached to the wire. The stretch of the wire can then be determined and compensated for with the motion of the actuator if the latter has suitable bandwidth.
A computer vision system has been integrated with a modified light-sectioning microscope for the quality control and inspection of a machined part whose critical dimensions are in the range of 30 to 300 μm. Height measurements were determined by analysis of the projected light-section line. Transverse measurements were made using the microscope in a traditional configuration with illumination from selected elements of an external LED ring array. The light section irradiance was under computer control to accommodate the spatial variations in surface reflectance whose dynamic range exceeded that of the vision system. Part features are located by the vision system. Edges and line centers are then measured to sub-pixel resolution with a gray-level analysis algorithm. This paper describes the design and operation of this system. Details of the measurement process and analysis algorithms are provided.
We describe a new electro-optical device being developed to provide precise measurements of the three-dimensional topography of the human cornea. This device, called a digital keratoscope, is intended primarily for use in preparing for and determining the effect of corneal surgery procedures such as laser refractive keratectomy, radial keratotomy or corneal transplant on the refractive power of the cornea. It also may serve as an aid in prescribing contact lenses. The basic design features of the hardware and of the associated computer software are discussed, the means for alignment and calibration are described and typical results are given.
The trend toward fine line geometries coupled with advances in image processing make Automated Optical Inspection of printed wiring boards (PWB) an emerging technology. The inspection of the bare PWB is not a trivial task considering that for an 18 inch by 24 inch panel inspected at half-mil resolution represents a minimum of approximately 1.7 billion pixels that need to be processed. Parallel processing is utilized to push throughput data rates over 60 Mhz in present machines. A PWB inspection system will be described with emphasis on techniques used to preserve the critical pixel placements. Precision laser scanning tecniques form the basis of the image acquisition system. This opto-mechanical system is capable of consistently placing 1 mil spots along the scan line to within .1 mil accuracy in two axes. In order to attain this accuracy the polygon wobble and velocity errors need to be compensated. Several methods of active and passive correction will be evaluated demonstrating where each method is best utilized.
An instrument has been designed and built to measure plane of incidence scatter at multiple wavelengths including .6328μm, from reflective, transmissive, specular, diffuse, flat and curved optics. An extensive software package accompanies the instrument and is used both to control the measurement process and to analyze the measurement data. Techniques employed in the design and development of this instrument are described. An error analysis for the measured BSDF is provided and calibration of the instrument is discussed.
Dynamic Imaging Microellipsometry (DIM) is a fast, high resolution full-field imaging approach to ellipsometry. The testing of the second generation DIM system is described with measurement methodology and system accuracy covered. Relative and absolute errors are discussed separately with analyses of overall accuracy and individual error sources are detailed. Approaches for improving both relative and absolute accuracy are discussed.
Different methods which can be used for boresighting multiple sensors of different or similar wavelengths are described and analyzed. A list and discussion of the various error sources wich affect one's ability to boresight a multisensor system are described. The methods of improving the ability to control error sources and thus, improve one's capability to boresight multiple sensors to a common line are described. Methods of wavelength conversion and different materials for this purpose are discussed.
A portable spectrometer has been designed that measures the transmission of tank periscopes in the field. The purpose of the instrument is to measure optical density to 4.0 over the range from 380 to 1100nm with lnm resolution. A motorized monochromator scans the desired test band. Data is acquired by silicon photodiodes, amplified by a programmable gain amplifier (PGA) and processed using a 12-bit A/D converter. A chopped input beam removes background signal. Ratio detection between measurement and reference arms compensates for input light intensity variation. Innovations in optical, mechanical and signal processing design are described. The precision of measurements made at various wavelengths and angles of incidence is discussed.
This paper outlines the problem, and describes the solution, of developing a means of measuring the beam position of captive production illuminators to allow their use as tooling alignment light sources. The Xerox 9700 Laser Printer, which has a throughput of 120 pages per minute, uses a 25mw argon ion laser as its light source. The laser printer optical assembly is split into two units. 1. The illuminator consists of the laser, beam conditioning optics, modulator, and beam pointing mirrors. This unit is removable from the second half, and is field replaceable. 2. The scanning laser output terminal (SLOT) consisting of the motor polygon assembly, scanning optics, mirrors, scan line detectors, and exit window is a permanently attached assembly to the printing engine frame. The illuminator and slot assemblies are manufactured in two different locations, and the slot is optically aligned utilizing a captive illuminator as a tooling light source. The beam pointing tolerances of the captive tooling illuminators are set to tighter limits than normal production units. In order to align the beam exiting the illuminator, a tool was designed and built which is self-calibrating and has been demonstrated to measure the beam position to an accuracy of 0.0001 an inch, which is sufficient to allow adjustment and verification of the tooling illuminators, reference Figures 1 and 2.