Testing a Parabolic Mirror with a Compact Interferometer

Parabolic mirrors are well suited to a number of imaging and illumination applications. In the case of an imaging application, the form accuracy of the parabola can introduce significant wavefront error. While reflective optics are free of chromatic aberration, care must also be taken to minimize degradation due to mounting distortion. This paper describes the measurement of a 300 mm diameter f/8 parabolic mirror with a compact, phase-shifting interferometer. Read in full

Optical measurement of materials and lens assemblies at specific or varied temperatures

Optical materials and lens assemblies are specified for use at various operating temperatures. Ophthalmic lenses such as intra-ocular (IOLs), rigid gas permeable (RGP), and soft contact lenses must be verified at a single well-controlledtemperature to ensure correct performance. In comparison, lens assemblies for UAVs (unmanned aerial vehicles) and other “outdoor” applications demand performance over a substantial range of temperatures. Both applications demandthe ability to integrate temperature monitoring or control with optical measuring instruments. A common practice is to thermally soak the material or lens assembly and then attempt measurement before the object under evaluation returns to ambient room temperature. We are reporting on the utilization of a NIST-traceable temperature device combined with wavefront sensing technology for faster integrated measurement capability. The temperature sensor is currently capable of 0.01 and 0.1 degree C resolution and accuracy; respectively for an operating range of 0 to 100 degrees C. Efforts are underway to extend the temperature measurement range down to -30 C. The wavefront measurement device is a Shack-Hartmann sensor (SHS) operating at 5 to 15 Hz with simultaneous gauging of temperature. The SHS can be operated with a choice of wavelengths from 400 to 1,000 nm. It also supports both single and double-pass configurations. Thesingle-pass arrangement was chosen for these experiments due to the simpler, more compact set-up. The dynamic range of the wavefront sensor is first utilized to evaluate the temperature chamber. Results are then presented for two lens assemblies intended for commercial UAVs. Read in full

Reflectance confocal endomicroscope with optical axial scanning for in vivo imaging of the oral mucosa (Jabbour et al. 2014)

This paper presents the design and evaluation of a reflectanceconfocal laser endomicroscope using a miniature objective lens within arigid probe in conjunction with an electrically tunable lens for axialscanning. The miniature lens was characterized alone as well as in theendoscope across a 200 μm axial scan range using the tunable lens. Theability of the confocal endoscope to probe the human oral cavity isdemonstrated by imaging of the oral mucosa in vivo. The results indicatethat reflectance confocal endomicroscopy has the potential to be used in aclinical setting and guide diagnostic evaluation of biological tissue. Read in full

LSST Detector Module and Raft Assembly Metrology Concepts (Takacs et al. 2006)

The LSST camera focal plane array will consist of individual Si sensor modules, each 42x42mm2 in size, that are assembled into 3x3 "raft" structures, which are then assembled into the final focal plane array. It is our responsibility at Brookhaven National Lab (BNL) to insure that the individual sensors provided by the manufacturer meet the flatness requirement of 5pm PV and that the ssembled raft structure be within the 6.5pm PV flatness tolerance. These tolerances must be measured with the detectors operating in a cryogenic nvironment at -lOOC in a face-down configuration. Conventional interferometric techniques for flatness testing are inadequate to insure that edge discontinuities between detector elements are within the tolerances because of the quarter-wave phase ambiguity problem. For this reason we have chosen a combination of metrology techniques to solve the discontinuity ambiguity problem that include both a full aperture interferometer and a scanning confocal distance microscope. We will discuss concepts for performing flatness metrology testing with these instruments under these conditions and will present preliminary results of measurement sensitivity and repeatability from tests performed on step height artifacts. Read in full

Sample Imaging with a Compact Twyman-Green Interferometer

Sample illumination properties of interferometers utilized for surface and transmitted wavefront testing of precision components and optical assemblies are well known. This paper addresses the sometimes overlooked aspect of proper sample imaging. Read in full