A general overview of adhesive bonding for optical elements addresses all the relevant parameters and properties. An
extensive listing of references is associated with many of the critical topics. Technical literature addressing optical
bonding has been difficult to find. This paper has conducted a search to aid engineers trying to solve these bonding
problems. The user must first look at his/her options for fastening the optical element. Next, he/she must consider all
the parameters that influence its cure, performance and survival. If an adhesive represents a good solution, the type of
adhesive must be selected. Throughout this selection process, it is important to maintain priorities on critical parameters.
Compromises must always be made and assigning priority levels will aid in making these decisions. Future work will
establish a selection matrix weighing relevant factors in making the adhesive selection more logical.
This paper provides a case study for identifying radius measurement uncertainty on a commercially-available optical bench using a homogeneous transformation matrix (or HTM)-based formalism. In this approach, radius is defined using a vector equation, rather than relying solely on the recorded displacement between the confocal and cat's eye null positions (i.e., the projection of the true displacement between these positions on the transducer axis). The vector-based approach enables the stage error motions, as well as other well-known error sources, to be considered through the use of HTMs. An important aspect of this mathematical radius definition is the intrinsic correction for measurement biases, such as cosine error (i.e., misalignment between the stage motion and displacement transducer axis) which would lead to an artificially small radius value if the traditional projection-based radius measurand were employed. Experimental results and measurement techniques are provided for the stage error motions, which are then combined with the setup geometry to determine the radius of curvature for a spherical artifact. Comparisons are shown between the vector-based radius calculation, traditional radius computation, and independent measurements using a coordinate measuring machine. The measurement uncertainty for the vector-based approach is determined using Monte Carlo simulation and is compared to experimental results.
Traceable radius of curvature measurements are critical for precision optics manufacture. An optical bench measurement of radius is very repeatable and is the preferred method for low-uncertainty applications. On an optical bench, the displacement of the optic is measured as it is moved between the cat's eye and confocal positions, each identified using a figure measuring interferometer. Traceability requires connection to a basic unit (the meter, here) in addition to a defensible uncertainty analysis, and the identification and proper propagation of all uncertainty sources in this measurement is challenging. Recent work has focused on identifying all uncertainty contributions; measurement biases have been approximately taken into account and uncertainties combined in an RSS sense for a final measurement estimate and uncertainty. In this paper we report on a new mathematical definition of the radius measurand, which is a single function that depends on all uncertainty sources, such as error motions, alignment uncertainty, displacement gauge uncertainty, etc. The method is based on a homogeneous transformation matrix (HTM) formalism, and intrinsically defines an unbiased estimate for radius, providing a single mathematical expression for uncertainty propagation through a Taylor-series expansion.
We present a high-speed silicon wafer metrology tool capable of resolving surface features in the nanometer height range. This tool uses a high performance Shack-Hartman sensor to analyze the wavefront of a beam of light reflected from a silicon wafer surface. By translating the wafer to analyze small portions of the wafer in each camera frame and then continuously piecing the frames together, we can retain sub-millimeter spatial resolution while rapidly analyzing large apertures. This tool is particularly effective for resolving features near the wafer edge. We will describe the measures required to obtain this level of resolution. We also compare data taken with this device to that taken with the National Institute of Standards and Technology X-ray optics Calibration Interferometer (XCALIBIR). Finally, we show measurements of a variety of typical and atypical 200 mm diameter wafer samples.
The radius of curvature of spherical surfaces may be determined using the well-known radius, or optical, bench. In this method, a figure measuring interferometer is employed to identify the null positions at the center of curvature (confocal) and surface (cat's eye) of the test optic. A linear slide provides motion between these positions and one or more displacement transducers is used to record the displacement between the cat's eye and confocal positions and, hence, the radius of curvature. Measurements of a polished Zerodur sphere have been completed on the X-ray Optics Calibration Interferometer (XCALIBIR) using both Twyman-Green and Fizeau configurations. Mechanical measurements of the spherical artifact have also been completed using a coordinate measuring machine (CMM). Recorded disagreement between the individual transmission sphere measurements and CMM measurements under well-controlled environmental conditions is larger than the limits predicted from a traditional uncertainty analysis based on a geometric measurement model. Additional uncertainty sources for the geometric model, as well as a physical optics model of the propagation of light, are therefore suggested. The expanded uncertainty analysis is described.
Conventional interferometric testing of the flatness of photomask substrates is rendered difficult by the long coherence length of the HeNe laser sources typically used in commercially available phase measuring interferometers appropriate for flatness testing. The Ritchey-Common configuration allows testing of flats in a spherical wavefront; this paper shows that, under appropriate conditions, high resolution surface flatness maps of photomask substrates may be obtained using instrumentation currently available in many optical shops.
The basic goal of the Advanced Optics Metrology program in NIST's Manufacturing Engineering Laboratory is to help industry ensure that their measurement results of optical figure and wavefront are traceable. This paper underscores the importance of traceability and reviews the facilities and projects dedicated to achieving that objective.
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