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.
Progress along the path towards smaller semiconductor feature sizes continually presents new challenges. 157nm technology is a promising new step along this path. The major challenges encountered to date include environmental purging for high transmission and beam alignment in a purged environment at this short wavelength. We present a simple shearing interferometer consisting of two Ronchi phase gratings in series, used on axis. The common path set-up and zero optical path difference between the interfering diffraction orders makes this device both robust and easy to align. Ease of alignment is an added benefit when working remotely in a purged environment with low light levels. If one grating is shifted relative to the other, a phase shift is introduced and phase measurement techniques can be employed for high accuracy characterization of the incident wavefront. Set-ups, measurements and characterization of wavefronts and spatial-coherence at 157nm made with this device are presented.
Full acceptance of 157nm technology for next generation lithography requires that critical optical components and systems be characterized at this wavelength. Some of the challenges inherent in the 157nm test regime include purged beam paths, a partially coherent and astigmatic light source, limitations in reflective and transmissive optical components, and immature CCD detector technology. A Twyman-Green interferometer specially devised for testing lithographic objective lenses and systems at 157nm that addresses these challenges is presented. A description of the design and components used is provided along with test results obtained with the interferometer.
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