A highly efficient method for splitting the probe beam produced by a scanning low-coherence distance-measuring
interferometer (SLCDI) is presented. The SLCDI is used to measure thicknesses of materials with thicknesses in the
range of 12 microns-50 mm, with a repeatability of 0.1 microns. The measurements are made optically with a beam with
a wavelength of 1.3 microns. The SLCDI is also capable of simultaneous measurement of a stack of multiple films.
Splitting of the beam from the SLCDI probe to create a multi-point probe allows for multiple, simultaneous
measurements to be made at a surface. An advantage of this capability is that it provides the ability of to measure the
surface normal at each of the surfaces that are under test. The operation of the SLCDI will be described along with how
the operation impacts the requirements for the multi-point probe system. The requirements are discussed from the
standpoint of the coherence length of the SLCDI source and the operational usage of the probe. The splitting is achieved
through the use of polarization components. The function and performance of the resulting probe is also discussed.
Conformal windows reduce drag, but introduce optical aberrations. Corrector optics minimize such optical
aberrations, but they feature complex surfaces that cannot presently be measured interferometrically. To address
this problem, ASE Optics has developed a non-contact "Quad-Probe" that measure the position and orientation
of surfaces. By scanning the probe over the surface of the optic, a 3D model of the interior and exterior surfaces
can be built. Furthermore, the Quad-Probe can be used inside a polishing machine, and feedback from the
Quad-Probe can be used to guide the scanner in measuring an unknown part.
Despite increasing demand for freeform optical elements, at present there are no commercial systems to measure
such components. In previously published research we demonstrated that a scanning low-coherence dual-wavelength
interferometer can accurately measure the transmitted wavefront of hemispheric dome optics by
mapping the optical thickness of the dome as a function of probe probe position. To address the issue of more
generalized freeform surfaces, we have developed a new probe for the interferometer. This probe incorporates
a reference surface and simultaneously projects four beams. This allows the instrument to measure both the
position and orientation of the surface with respect to the probe as the probe is scanned over the object. Both the
interior and exterior surfaces can be measured simultaneously. Furthermore, by overlapping the measurement
regions, the redundant data can be used to minimize some forms of measurement error.
We present experimental results for a low-coherence, dual-wavelength metrology system capable of measuring
simultaneously both optical thickness and surface ﬁgure. The system measures optical thicknesses as thin as
12 microns to as wide as 12 mm with an accuracy of 0.1 microns. The current system scans at a resolution of
50 microns, which is limited by the spot-size of the measurement beam. We validate that SLCDI yields results
in agreement with traditional interferometry and demonstrate its ability to measure aspheric “saddle” mirrors
and complex three-dimensional surfaces.
Modern missile domes are up to 7 inches in diameter, subtending an angular aperture of 180 degrees. Quantifying
the transmitted wavefront of these domes is critical for quality control, but such optics are diffcult or impossible
to measure using conventional interferometric techniques. To address this issue, we have developed a non-contact
measurement process that uses a technology similar to optical coherence tomography (OCT) to map the optical
thickness of the dome over its full aperture. The technique has been termed Scanning Low Coherence Dual
Interferometry (SLCDI), and has the unique ability to measure the optical thickness of component layers within
multilayer domes to an accuracy of 0.1 micron. In this paper we demonstrate the capability of SLCDI by
measuring the optical thickness of a seven inch diameter BK7 dome at a sampling resolution of 0.2 mm. SLCDI
yields results comparable to those from a Zygo interferometer, and the two methods agree to within 0.2 micron.
From this we conclude that SLCDI is an effective tool for measuring the optical quality of hemispheric domes.
The Rochester Institute of Technology Multi-Object Spectrometer (RITMOS) utilizes a Texas Instruments Digital Micromirror Device (DMD) for target selection, instead of the fiber bundles or customized slit masks normally used in multi-object spectroscopy. The DMD, which sits at the telescope focal plane, is an 848 x 600 array of 17 micron square mirrors that can individually deflect incident light into one of two output paths: an imaging path or a spectroscopy path. In standard operation, all light is deflected towards the imaging path, consisting of an Offner relay which reimages the DMD onto a CCD detector. The locations of spectroscopic targets are then noted, and the micromirrors corresponding to these targets are then deflected towards the spectroscopy path. This path utilizes a 1200 l/mm transmission grating to disperse images of the micromirror pattern onto a second CCD detector. The spectroscopic parameters (e.g., 0.66 Å/pixel dispersion for a 13.5 micron/pixel detector) were chosen for MK spectral classification. Among the benefits of replacing a fiber bundle or custom slit mask with a DMD are the latter's instantaneous reconfigurability and its aptitude for the study of compact fields. RITMOS is thus suited towards spectral classification surveys of star clusters. We present a description of the instrument, details of its design, and initial measurements, including multi-object stellar spectra.
We have developed a compact laser system capable of amplifying nanosecond-scale pulses form a few picojoules to 20J. The system has a 40-mm clear aperture and a 37-mm working aperture for high-energy output. We measured less than 1 wave phase distortion over full 37-mm aperture for a pulse with 18-J output energy at a shot repetition rate of one shot every 10 min. In experiments with a 30-mm diam beam, a flat-top spatial profile with 4 percent rms over the entire beam diameter was demonstrated for a 1-ns pulse with 20_j output energy. The amplifier has a net gain up to 10<SUP>13</SUP> and fits easily on a 5-ft X 14-ft optical table.
The performance of the National Ignition Facility (NIF), especially in terms of laser focusability, will be determined by several key factors. One of these key factors is the optical specification of the thousands of large aperture optics that will comprise the 192 beamlines. We have previously reported on the importance of the specification of the power spectral density (PSD) on NIF performance. Recently, we have been studying the importance of long spatial wavelength phase errors on focusability. We have concluded that the preferred metric for determining the impact of these long spatial wavelength phase errors is the rms phase gradient. In this paper, we outline the overall approach to NIF optical specifications, detail the impact of the rms phase gradient on NIF focusability, discuss its trade-off with the PSD in determining the spot size, and review measurements of optics similar to those to be manufactured for NIF.
The development ofmodem optical instruments has evolved into a complex multi-disciplinary activity with the explosion of sophisticated applications. For specialized optical systems, the development ofeven a prototype has become a costly exercise. This paper presents a new concept of virtual prototyping for optical systems to minimize the development time, cost and risk. This process employs the computer-aided design and modeling tools to address the broad issues of system layout, optical and optomechanical design, structural and thermal analysis for the real operating environment, tolerance budgeting and optimization procedures. The Center for Applied Optics (CAO) at the University of Alabama in Huntsville (UAH) has developed the necessary computer interfaces between the various stages of optical system design, development and evaluation. As a common thtabase is used for the optical and mechanical design and analyses, the possibility ofa human error is eliminated while minimizing the time and effort required to accomplish these critical tasks. The virtual prototyping concept works in an iterative fashion to achieve the desired system performance at a minimum cost. This technique has been successfully employed in the design and development of several optical instruments for space, military and commercial applications, covering a broad spectrum from Uv to JR The performance specifications and the results of virtual prototyping for some typical systems are also presented.
Keywords: Virtualprototyping, computer-aided design andmodeling, optomechanical design, tolerance analysis, optimization
The purchase of large (15- and 20-cm clear aperture) Brewster-angle laser disks involves the specification of a large number of often conflicting parameters, all of which bear on performance and cost. Furthermore, the laser requirements often approach the state-of-the-art in glass-melting technology and the parameter measurement. This paper enumerates the relevant parameters, the trade-offs made in their selection, and the test procedures and instrumentation required to ensure compliance with the specification.