A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

The Very Large Telescope Survey Telescope (VST) is equipped with an active optics system in order to correct low-order aberrations. The 2.6 m primary mirror is supported both axially and laterally and is surrounded by several safety devices for earthquake protection. We describe the mirror support system and discuss the results of the qualification test campaign.

Active optics primary mirror support system for the 2.6 m VST telescope.

Considering the special characteristics of the removal function with the ring-shaped profile in fluid jet polishing (FJP), we present an effective method called the discrete convolution algorithm to compute the dwell function for controlling the figuring process. This method avoids the deconvolution operation, which usually fails to converge. Then an experimental confirmation of FJP figuring was demonstrated by machining a one-dimensional depth profile on a flat sample. The profile was figured from 0.914lambda(lambda=632.8 nm) peak to valley (PV) to 0.260lambda. This experiment demonstrated the successful implementation of the algorithm to solve the dwell function in optical manufacturing.

Dwell function algorithm in fluid jet polishing

We present scanning Fabry-Perot observations of the planetary nebula NGC 2346 at the near-infrared vibrationally excited line H2 S(1) 1–0 at 2122 μm The kinematics matches a model of two ellipsoids with an outflow velocity proportional to the distance of the gas from the central star and moving radially outward The stronger emission is located in an equatorial torus expanding at 16 km s-1 It is likely that a shock between 6 and 16 km s-1, depending on the assumed velocity of the red giant envelope (0 to 10 km s-1), excites the molecular gas Depending on those limiting values for the shock velocity, the density of the preshock gas falls in the range (03–17) × 104 cm-3, and consequently the mass of the molecular gas in the nebula is estimated to be between 034 and 185 M⊙, much larger than the mass of the ionized gas, and marginally in agreement with the estimate coming from CO observations alone

https://iopscience.iop.org/article/10.1086/324446/pdf

Kinematics of the Molecular Hydrogen from the Planetary Nebula NGC 2346

The different radial support ways for a rotation prism are presented to evaluate the strains and stresses induced by the gravity action and the thermal effects. Due to the large-aperture, non-uniform quality distribution and especially rotation from 0° to 360°, neither the multi-point support way nor the full surface-contact support can well meet the assembly requirements. The paper proposes a novel project of an adjustable partial surface-contact support way to solve this support problem. The maximum strain and stress under this support way both are less than the tolerance limit of the strength assurance regardless of the prism rotating to any position. Meanwhile, the thermally-induced structural analysis is performed to predict some specific work cases, which is much valuable for the improvement of the assembly design.

Radial support analysis for large-aperture rotating wedge prism

We have designed and installed a new set of actuators for the suspension
of the primary mirror of the 2.1-m telescope at San Pedro Martir. This
active optics system has allowed us to correct low-order aberrations
identified by several wave-front analysis techniques.

Active primary mirror support for the 2.1-m telescope at the San Pedro Mártir Observatory.

Previous implementations of the iterative phase shifting method, in which the phase of a test object is computed from measurements using a phase shifting interferometer with unknown positions of the reference, do not provide an accurate way of knowing when convergence has been attained. We present a new approach to this method that allows us to deterministically identify convergence. The method is tested with a home-built Fizeau interferometer that measures optical surfaces polished to λ/100 using the Hydra tool. The intrinsic quality of the measurements is better than 0.5 nm. Other possible applications for this technique include fringe projection or any problem where phase shifting is involved.

Deterministic convergence in iterative phase shifting

HyDRa is a hydrodynamic radial polishing tool ideal for the corrective lapping and fine polishing of diverse materials by means of an accelerated abrasive flux. The roughness of an optical surface is analysed for a continuous manufacturing process, beginning with the basic generation steps up to a finished optical surface. These results were obtained using a Linnik interferometer.

Surface roughness results using a hydrodynamic polishing tool (HyDra)

We report experimental results and analysis about a new hydrodynamic radial tool (HyDra, patent pending), which expels a suspension of water and polishing particles radially on glass. With this method it is possible to locally shape optical surfaces. The depth of material removed by HyDra grows linearly with the time. The removal rate is independent of the velocity between the tool and the glass element. The HyDra has been used to fabricate successfully an optical flat and Schmidt surface.

Polishing TIM mirror segments with HyDra

Seeing and weather observations were conducted at 5 sites within the boundaries of the area reserved for astronomy at the Sierra de San Pedro Martir National Park (SPM), for at least 15 nights at each one of these. Weather variables were measured using a Davis Weather Station and a Metek Ultrasonic Anemometer. Seeing information was collected with a NOAO RoboDIMM unit. Seeing and weather results were compared to those being delivered at the same time by the instrumentation of the Thirty Meter Telescope Project at the Observatorio Astronomico Nacional (OAN) at SPM. Seeing differences are small in most cases. We recommend a long term campaign at the easily accessible site Llano Alto 1, where we found that seeing may be slightly better.

Erika Sohn

Papers

Active primary mirror support for the 2.1-m telescope at the San Pedro Mártir Observatory.

Deterministic convergence in iterative phase shifting

Surface roughness results using a hydrodynamic polishing tool (HyDra)

Polishing TIM mirror segments with HyDra

Site prospection at san pedro mártir