Rms Figure Error Research Articles

Local tolerance and quality evaluation for optical surfaces

The manufacture of high-precision surfaces is the foundation of building high-performance optical systems. For over 50 years, the tolerance for optical surfaces has been specified by the root-mean-square (rms) or peak-to-valley (PV) value over the entire surface geometry. However, different regions on optical surfaces do not contribute equally to image quality and, thus, can tolerate different levels of errors. A global tolerance described by a single or few parameters cannot precisely provide the manufacturing requirements of each region on the surface, which may result in unnecessary accuracy specifications for surfaces. Furthermore, the components with the same PV or rms figure errors can produce different imaging qualities; however, this difference cannot be distinguished by the conventional figure of merit. To address these problems, a framework that includes a local tolerance model and a quality merit function for optical surfaces is proposed. The local tolerance model can provide an accurate tolerance for each region on the surface so the targeted wave aberration requirements are met during components manufacturing. More importantly, the proposed merit function closely ties the surface figure error to imaging performance, e.g., the findings can explain that the component with lower geometric accuracy may produce better imaging quality. This framework provides new insights into optical design, manufacture, and metrology and especially paves the way for the manufacture of high-precision large-aperture systems.

Possible use of direct silicon-on-silicon bonding for construction of analyzers for inelastic scattering

Bonding of silicon directly to silicon is possible with proper preparation of the two surfaces to be bonded. The advantage of such a method is that a bonding agent is not required, and direct bonding avoids figure errors introduced by thickness variations in a bonding agent. We have succeeded in bonding a 3-inch-diameter diced (1 mm × 1 mm) silicon(111) oriented wafer to a silicon concave spherical form having a 3-m radius. A very good rms figure error of 0.059 millirad over the entire area of the analyzer was measured. The suitability for x-ray inelastic scattering due to introduced strain is, however, still an open question. Whether or not deleterious strain is unavoidably introduced during the bonding process is a question we will answer with availability of photons on sector 3 of the SRI CAT at the Advanced Photon Source.

HIGH-DYNAMIC-RANGE IMAGING USING A DEFORMABLE MIRROR FOR SPACE CORONOGRAPHY

ABSTRACT The need for high dynamic range imaging is crucial in many astronomical fields, such as extra-solar planet direct detection, extra-galactic science and circumstellar imaging. Using a high quality coronograph, dynamic ranges of up to 105 have been achieved. However the ultimate limitations of coronographs do not come from their optical performances, but from scattering due to imperfections in the optical surfaces of the collecting system. We propse to use a deformable mirror to correct these imperfections and decrease the scattering level in local regions called "dark holes." Using this technique will enable imaging of fields with dynamic ranges exceeding 108. We show that the dark-hole algorithm results in a lower scattering level than simply minimizing the RMS figure error (maximum-strehl-ratio algorithm). The achievable scattering level inside the dark-hole region will depend on the number of mirror actuators, the surface quality of the telescope, the single-actuator influence function and the observing wavelength. We have simulated cases with a 37 X 37 deformable mirror using data from the Hubble Space Telescope optics without spherical aberrations and have demonstrated dark holes with rectangular and annular shapes. We also present a preliminary concept of a monolithic, fully-integrated, high-density deformable mirror whih can be used for this type of space application.

Vacuum ultraviolet beam lines at Laboratório Nacional de Luz Síncrotron, the Brazilian synchrotron source

A TGM beamline for the spectral range 12–310 eV is being built at Laboratório Nacional de Luz Síncrotron (LNLS). This beam line consists of safety devices, a condensing mirror, a toroidal grating monochromator, and a refocusing mirror. This beam line has been assembled up to the exit slits. A spherical grating monochromator beam line has been designed for the spectral range 200–1000 eV. The performance is limited by the surface slope error in the gratings. If the rms figure error is 2 μrad, the expected resolving power is better than 3000.

Active Optics Correction Of Thermal Distortion Of A 1.8 Meter Mirror

An active optics system has been built and tested on a prototype 1.8 m lightweight borosilicate glass mirror. Tests of the system have been conducted in two different modes: the system has been used to compensate measured optical surface distortions, and it has been used to correct thermal distortion predicted by computer modeling based on measured mirror temperatures. Both modes were consistently able to reduce rms figure errors on the mirror surface. Test results show that distortions corresponding to astigmatism, coma, spherical aberration, trefoil, and quatrefoil can be effectively countered.

Computer controlled polisher demonstration

A recent effort was conducted to demonstrate the efficiency of the computer controlled polisher process. A computer algorithm was written that predicts the surface figure progress for each polishing cycle. A 1.8-m diam lightweight glass mirror was polished with the computer controlled polisher for four cycles. The prediction program was used to provide an estimate of expected figure improvement for each cycle. The activity used only 72 h of polishing time and improved the mirror surface from an rms figure error of 0.16-0.04 waves, where a wave is 0.633 microm. Even though this figure improvement lagged the predicted improvement due to metrology uncertainty, the rapid error correction demonstrates the computer controlled polisher to be a highly valuable manufacturing tool.