This paper presents refinements to the design of the TMT primary mirror segment passive-support system that are
effective in reducing gravity print-through and thermal distortion effects. First, a novel analytical method is presented
for tuning the axial and lateral support systems in a manner that results in improved optical performance when subject to
varying gravity fields. The method utilizes counterweights attached to the whiffletrees to cancel astigmatic and comatic
errors normally resulting when the lateral support system resists transverse loads induced by gravity. Secondly, several
central diaphragm designs are presented and analyzed to assess lateral-gravity and thermal distortion performance: 1) a
simple flat diaphragm, 2) a stress-relieving diaphragm having a slotted outer rim and a circumferential convolution near
the outside diameter, and 3) a flat diaphragm having a slotted outer rim. The latter design is chosen based on results from
analytical studies which show it to have better overall optical performance in the presence of gravity and thermal
The Space Interferometry Mission (SIM) requires the control of the optical path of each interferometer with picometer
accuracy. Laser metrology gauges are used to measure the path lengths to the fiducial corner cubes at the siderostats.
Due to the geometry of SIM a single corner cube does not have sufficient acceptance angle to work with all the gauges.
Therefore SIM employs a double corner cube. Current fabrication methods are in fact not capable of producing such a
double corner cube with vertices having sufficient commonality. The plan for SIM is to measure the non-commonalty of
the vertices and correct for the error in orbit. SIM requires that the non-common vertex error (NCVE) of the double
corner cube to be less than 6 μm. The required accuracy for the knowledge of the NCVE is less than 1 μm. This paper
explains a method of measuring non-common vertices of a brassboard double corner cube with sub-micron accuracy.
The results of such a measurement will be presented.
We have built and field tested a multiple guide star tomograph with four Shack-Hartmann wavefront sensors. We predict the wavefront on the fourth sensor channel estimated using wavefront information from the other three channels using synchronously recorded data. This system helps in the design of wavefront sensors for future extremely large telescopes that will use multi conjugate adaptive optics and multi object adaptive optics. Different wavefront prediction algorithms are being tested with the data obtained. We describe the system, its current capabilities and some preliminary results.
We describe the current performance of an adaptive optics testbed for free space optical communication. This adaptive optics system allows for simulation of night and day-time observing on a 1 meter telescope with a 97 actuator deformable mirror. In lab-generated seeing of 2.1 arcseconds (at 0.5μm) the system achieves a Strehl of 21% at 1.064μm (210nm RMS wavefront). Predictions of the system's performance based on real-time wavefront sensor telemetry data and analytical equations are shown to agree with the observed image performance. We present experimentally measured gains in communications performance of 2-4dB in the received signal power when AO correction is applied in the presence of high background and turbulence at an uncoded bit error rate of 0.1. The data source was a 100Mbps on-offkeyed signal detected with an IR-enhanced avalanche photodiode detector as the receiver.
The Space Interferometry Mission (SIM) PlanetQuest is managed by the Jet Propulsion Laboratory for the National Aeronautics and Space Administration. SIM requires, among other things, high precision double cube-corner retroreflectors. A test device has recently been fabricated for this project with demanding specifications on the optical surfaces and gold reflective coatings. Several gold deposition techniques were examined to meet the stringent specifications on uniformity, optical properties, micro-roughness and surface quality. We report on a comparative study of optical performance of gold films deposited by resistive and e-beam pvaporation, including measurements of the scattering from the coated surfaces. The effects of oxygen bombardment and titanium under-layer on optical properties and adhesion were evaluated. The influence of surface preparation on the optical properties was examined also.
Recent work done at CSIRO's Australian Centre for Precision Optics has pushed the fabrication limits on optical retroreflectors. To achieve dihedral angle errors well below an arcsecond, the measurement accuracy was required to be 0.1 arcsec or better. On this level, the error introduced by the interferometer's instrument function is not negligible. So-called "collimation errors", or more generally, wavefront aberrations, can significantly falsify the angle measurements. This paper describes and demonstrates the basic concepts for interferometric measurement of dihedral angle errors in retroreflectors from a practical point of view. We discuss obvious and subtle stumbling blocks, summarize practical experiences, and show some results of the recent joint work between JPL and CSIRO.
The design of a novel wavefront sensor is presented. The wavefront sensor is an extension of the classical Hartmann wavefront sensor. Analogous to the operation of the classical Hartmann wavefront sensor, each lenslet forms an image of the object, but shifted by an amount proportional to the average tilt across its subaperture. An optical information processor system is used to compute the location of each image relative to each other formed by the lenslets.
The multi-spectral sensor calibration system (MSSCS) is a highly automated calibration system designed around an optical table. It consists of several instruments and sources mounted on two translating tables and placed at the focus of an off-axis parabolic collimating mirror. These instruments and sources are linked to a control computer via the IEEE-488 buss. Sophisticated system control software consists of interlinked programs that provide: (1) instrument control and data acquisition, (2) automated calibration and data analysis, and (3) automated report generation. The MSSCS is used to calibrate several of NASA's airborne multi-spectral sensor systems currently in use to provide remote sensing data. These systems include the CAMS (calibrated airborne multi-spectral sensor), the ATLAS (airborne terrestrial applications sensor) and TIMS (thermal infrared multi-spectral scanner). We begin by briefly describing the overall system design with an emphasis on the objectives of the design and the capabilities provided by the complete system. This is followed by a description of how the system is aligned with the unit under test. Examples of data produced by the system are presented, and how this data was certified correct. We conclude with how the system's data products were validated.