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The Large Synoptic Survey Telescope uses a unique optomechanical design that places the primary and tertiary mirrors on a single glass substrate. The honeycomb sandwich mirror blank was formed in March 2008 by spin-casting. The surface is currently a paraboloid with a 9.9 m focal length matching the primary. The deeper curve of the tertiary mirror will be produced when the surfaces are generated. Both mirrors will be lapped and polished using stressed laps and other tools on an 8.4 m polishing machine. The highly aspheric primary mirror will be measured through a refractive null lens, and a computer-generated hologram will be used to validate the null lens. The tertiary mirror will be measured through a diffractive null corrector, also validated with a separate hologram. The holograms for the two tests provide alignment references that will be used to make the axes of the two surfaces coincide.

The first of the 8.4 m off-axis segments for the primary mirror of the Giant Magellan Telescope is being manufactured at the Steward Observatory Mirror Lab. In addition to the manufacture of the segment, this project includes the development of a complete facility to make and measure all seven segments. We have installed a new 28 m test tower and designed a set of measurements to guide the fabrication and qualify the finished segments. The first test, a lasertracker measurement of the ground surface, is operational. The principal optical test is a full-aperture interferometric test with a null corrector that includes a 3.75 m spherical mirror, a smaller sphere, and a computer-generated hologram. We have also designed a scanning pentaprism test to validate the measurement of low-order aberrations. The first segment has been cast and generated, and is in the process of loose-abrasive grinding.

The first of the two Gregorian Adaptive Secondary Mirror (ASM) units for the Large Binocular Telescope (LBT) has been fully integrated and tested for laboratory acceptance. The LBT unit represents the most advanced ASM device existing in hardware. The unit has 672 electro-magnetic force actuators to change the shape of the 1.6mm-thick and 911mm-diameter Zerodur shell. The actuators control the mirror figure using the position feedback from the internal metrology provided by co-located capacitive sensors. The on-board real-time control electronics has a parallel computational power of 163Gflop/s providing not only the internal control of the unit with a 72kHz loop but also the wavefront reconstruction for the 1kHz Adaptive Optics loop. The paper describes the final configuration of the system and reports the results of the characterization and optimization process together with the results of the laboratory acceptance tests.

We report on the current status of production of the thin shells for the LBT adaptive secondary mirrors. These shells are made of Zerodur and have a front (optical) surface highly aspherical whereas the other (rear) surface is spherical. They have a 910mm diameter and an average thickness of 1.6mm. The manufacturing of these shells starts with a thick blank of Zerodur and follows the steps of: 1) optical surface figuring, 2) blank thinning, 3) rear surface grinding and polishing, 4) edges machining and 5) rear surface aluminizing. Of the three (two plus a spare) shells planned for LBT the first shell was completed and shipped to Italy for integration with magnets and the second is in advanced state of production. The third shell (spare) is planned to start production soon. In the paper we report details of production of these shells as well as the 'as built' characteristics. Details concerning the operations that follow the production, i.e. surface aluminum coating as well as handling and shipping fixtures are also reported.

Deterministic subaperture finishing technologies, such as Magnetorheological Finishing (MRF(R)) are becoming the industry standard for finishing high precision optics with complex shapes, such as aspheres. However, astronomical or very large optics were beyond the scale of existing capabilities and relied on traditional, artisan-based methods of manufacture. It is not uncommon for these critical parts to spend a year or more in production. Recent developments from QED Technologies(R) have expanded MRF technology to enable the manufacture of meter-scale aspheric optics. QED, in conjunction with the Steward Observatory Mirror Laboratory (SOML) at the University of Arizona, demonstrated the fabrication of an 840 mm diameter convex asphere with 1.3 mm of aspheric departure from a best-fit sphere. Long-trace profilometry scans were initially performed at SOML to characterize the surface. A first figure correction polishing iteration was conducted at QED Technologies in Rochester, NY on a meter-class MRF machine (Q22-950F). The correction improved the surface to within the capture range of a full aperture interferometric test performed at the Mirror Lab. A final polishing iteration at QED improved the surface to meet the optic specifications.

We describe the manufacture of thin shells for the deformable secondary mirrors of the LBT adaptive optics system. The secondary mirrors are thin shells, 910 mm in diameter and 1.6 mm thick. Each mirror will have its shape controlled by 672 voice-coil actuators. The main requirement for manufacture of the shell is smoothness on scales too small to be adjusted by the actuators. An additional requirement is that the rear surface match the reference body within 30 μm peak-to-valley. A technique was developed for producing smooth surfaces on the very aspheric surfaces of the shells. We figure the optical surfaces on a thick disk of Zerodur, then turn the disk over and thin it to 1.6 mm from the rear surface. Figuring is done primarily with a 30 cm diameter stressed lap, which bends actively to match the local curvature of the aspheric surface. For the thinning operation, the mirror is blocked with pitch, optical surface down, onto a granite disk with a matching convex surface. Because the shell may bend during the blocking operation and as its thickness is reduced to 1.6 mm, figuring of the rear surface is guided by precise thickness measurements over the surface of the shell. This method guarantees that both surfaces of the finished shell will satisfy their requirements when corrected with small actuator forces. Following the thinning operation, we edge the shell to its final dimensions, remove it from the blocking body, and coat the rear surface with aluminum to provide a set of conductive plates for capacitive sensors.

The second 8.4 m primary mirror and its active support system were delivered to the Large Binocular Telescope in September 2005. The mirror was figured to an accuracy of 15 nm rms surface after subtraction of low-order aberrations that will be controlled by the active support. The mirror was installed into its operational support cell in the lab, and support forces were optimized to produce a figure accurate to 20 nm rms surface with no synthetic correction. The mirror was polished on a new 8.4 m polishing machine that gives the Mirror Lab the capacity to process up to four 8.4 m mirrors simultaneously, with each mirror going through a sequence of stations: casting furnace, generating machine, polishing machine, and integration with its support cell. The new polishing machine has two carriages for polishing tools, allowing use of two 1.2 m stressed laps during loose-abrasive grinding and early polishing, followed by final figuring with a stressed lap and a small tool for local figuring.

We have nearly completed the manufacture of a 1.7 m off-axis mirror as part of the technology development for the Giant Magellan Telescope. The mirror is an off-axis section of a 5.3 m f/0.73 parent paraboloid, making it roughly a 1:5 model of the outer 8.4 m GMT segment. The 1.7 m mirror will be the primary mirror of the New Solar Telescope at Big Bear Solar Observatory. It has a 2.7 mm peak-to-valley departure from the best-fit sphere, presenting a serious challenge in terms of both polishing and measurement. The mirror was polished with a stressed lap, which bends actively to match the local curvature at each point on the mirror surface, and works for asymmetric mirrors as well as symmetric aspheres. It was measured using a hybrid reflective-diffractive null corrector to compensate for the mirror's asphericity. Both techniques will be applied in scaled-up versions to the GMT segments.

The two 911mm-diameter adaptive secondary (AS) mirrors for the Large Binocular telescope (LBT) are currently under manufacturing process. Each unit has 672 electro-magnetic force actuators. They control the figure of the Gregorian secondary 1.6mm-thick mirrors with an internal loop using the signal of co-located capacitive sensors. The obtained computational power of the on-board control electronics allows to use it as real-time computer for wavefront reconstruction. We present the progress in manufacturing and assembling of the first telescope unit, the progress in software production, the status of the testing facilities and an update on the latest modification of the design.

Backward-wave oscillators driven by high current relativistic electron beams are capable of producing high power coherent radiation in the ceentimeter and millimeter wavelength regimes. However, the efficiency of these devices is usually limited to 15-20% when a homogeneous slow-wave structure is used. Utilizing a two-section slow wave structure, where the spatial period of the second section is larger than that of the first section, a BWO efficiency of greater than 50% was calculated. A conceptual design of a high efficiency S-band backward-wave oscillator driven by a 500 kV, 5 kA electron beam has been developed and analyzed.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Microwave sources based on backward-wave oscillators (BWOs) driven by relativistic electron beams are capable of producing high power coherent radiation in the cm and mm wavelength region. When the axial magnetic field is used in these devices to confine the electron beam satisfies the condition of cyclotron resonance there is a significant modification in the behavior of BWO due to beam coupling to cyclotron modes. A time-dependent, self-consistent theory of BWOs is developed taking into account a possible cyclotron interaction. The analysis of the system near the cyclotron resonance yields a number of physical effects including the power drop due to the cyclotron absorption observed in many BWO experiments. A series of experiments has been conducted to compare the measured BWO characteristics with the theoretically predicted ones.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Microwave sources based on backward-wave oscillators driven by relativistic electron beams are capable of producing high power coherent radiation in the cm and mm wavelength regime. Although there have been a number of experiments reported over the last decade on this topic, there are only a few publications providing a theoretical description of these devices. Thus, there is a need for theoretical models which can be compared in detail with the experimental data. This work is devoted to filling this need and applied to the University of Maryland backward wave oscillator experiment. It is shown that the theoretical predictions for the threshold current to start the oscillations, the frequency characteristics, and the efficiency of the device compared favorably with the experimental data.

There are many atmospheric trace gas species involved in the three catalytic cycles that contribute to stratospheric ozone depletion. The OH molecule is central to one of this cycles yet its concentration as a function of altitude is very difficult to measure in the stratosphere. The stronger rotational transitions lie at frequencies greater than 1500 GHz, significantly above the realm, of traditional submillimeter heterodyne instruments. Both Fabry-Perot and Fourier transform spectrometers have been used to observe OH in the atmosphere. Due to their inherent lower resolution these instruments can obtain atmospheric profiles only in a limb viewing geometry, thus they must be lofted above the stratosphere via balloons. This significantly constrains their seasonal and geographical survey capabilities. In this paper we Investigate the feasibility of utilizing a far infrared laser heterodyne instrument, operating aboard an aircraft, for the detection of OH and other relevant trace gas species in the stratosphere.