To achieve highly efficient observatory operations requires continuous evaluation and improvement of facility and instrumentation metrics. High quality metrics requires a foundation of robust and complete observatory telemetry. At the Large Binocular Telescope Observatory (LBTO), a variety of telemetry-capturing mechanisms exist, but few tools have thus far been created to facilitate studies of the data. In an effort to make all observatory telemetry data easy to use and broadly available, we have developed a suite of tools using in-house development and open source applications. This paper will explore our strategies for consolidating, parameterizing, and correlating any LBTO telemetry data to achieve easily available, web-based two- and three-dimensional time series data visualization.
The Large Binocular Telescope (LBT) is built around two 8.4 m-diameter primary mirrors placed with a centerline separation of 14.4 m in a common altitude/azimuth mount. Each side of the telescope can utilize a deployable prime focus instrument; alternatively, the beam can be directed to a Gregorian instrument by utilizing a deployable secondary mirror. The direct-Gregorian beam can be intercepted and redirected to several bent-Gregorian instruments by utilizing a deployable tertiary mirror. Two of the available bent-Gregorian instruments are interferometers, capable of coherently combining the beams from the two sides of the telescope. Active optics can utilize as many as 26 linearly independent degrees of freedom to position the primary, secondary and tertiary mirrors to control optical collimation while the telescope operates in its numerous observing modes. Additionally, by applying differential forces at 160 locations on each primary mirror, active optics controls the primary mirror figure. The authors explore the challenges associated with collimation and primary mirror figure control at the LBT and outline the ongoing related development aimed at optimizing image quality and preparing the telescope for interferometric operations.
The LBTO software and IT group was originally responsible for development of the Telescope Control System (TCS) software, and build-out of observatory Information Technology (IT) infrastructure. With major construction phases of the observatory mostly completed, emphasis is transitioning toward instrument software handover support, IT infrastructure obsolescence upgrades, and software development in support of efficient operations. This paper discusses recent software and IT group activities, metrics, issues, some lessons learned, and a near-term development road-map for support of efficient operations.
The Large Binocular Telescope (LBT) has eight Acquisition, Guiding, and wavefront Sensing Units (AGw units). They provide guiding and wavefront sensing capability at eight different locations at both direct and bent Gregorian focal stations. Recent additions of focal stations for PEPSI and MODS instruments doubled the number of focal stations in use including respective motion, camera controller server computers, and software infrastructure communicating with Guiding Control Subsystem (GCS). This paper describes the improvements made to the LBT GCS and explains how these changes have led to better maintainability and contributed to increased reliability. This paper also discusses the current GCS status and reviews potential upgrades to further improve its performance.
Over the last several years the primary mirror cell systems for the Large Binocular Telescope have been upgraded to
improve on-sky performance and observing efficiency. We describe improvements made to the support actuators and
mirror positioning system and explain how those changes have led to better performance and contributed to increased
reliability. Both systems have been substantially redesigned and remanufactured to allow the LBT primary mirror
systems to meet extremely precise performance requirements over a very broad temperature range. We also discuss the
mirror ventilation and thermal monitoring system and review its current status and potential upgrades to improve its
The Adaptive Optics System at the Large Binocular Telescope Observatory consists of two
Adaptive Secondary (ASM) mirrors and two Pyramid Wavefront sensors. The first
ASM/Pyramid pair has been commissioned and is being used for science operation using the NIR
camera PISCES on the right side of the binocular telescope. The left side ASM/Pyramid system
is currently being commissioned, with completion scheduled for the Fall of 2012.
We will discuss the operation of the first Adaptive Optics System at the LBT Observatory
including interactions of the AO system with the telescope and its TCS, observational modes,
user interfaces, observational scripting language, time requirement for closed loop and offsets and
LINC-NIRVANA will employ four wave front sensors to realize multi-conjugate correction on both arms of a Fizeau interferometer for LBT. Of these, one of the two ground-layer wave front sensors, together with its infrared test camera, comprise a stand-alone test platform for LINC-NIRVANA. Pathfinder is a testbed for full LINC-NIRVANA intended to identify potential interface problems early in the game, thus reducing both technical, and schedule, risk. Pathfinder will combine light from multiple guide stars, with a pyramid sensor dedicated to each star, to achieve ground-layer AO correction via an adaptive secondary: the 672-actuator thin shell at the LBT. The ability to achieve sky coverage by optically coadding light from multiple stars has been previously demonstrated; and the ability to achieve correction with an adaptive secondary has also been previously demonstrated. Pathfinder will be the first system at LBT to combine both of these capabilities.
Since reporting our progress at A04ELT2, we have advanced the project in three key areas: definition of specific goals for Pathfinder tests at LBT, more detail in the software design and planning, and calibration. We report on our progress and future plans in these three areas, and on the project overall.
We describe the design and performance of an improved hardpoint for the primary mirror cell of the Large Binocular
Telescope. Six hardpoints define the position and orientation of the primary mirror and are key elements of the active
optics system. After several years of operation, various undesirable characteristics of the original hardpoints were
identified. A new deign was developed that provides higher stiffness, greater repeatability, and better overall
performance. We describe the design features and present preliminary performance data from lab testing and initial
operation in the telescope.
The Large Binocular Telescope (LBT) consists of two 8.4-meter primary mirrors on a common mount. When the
telescope is complete, to complement the two primaries there will be two 0.9-meter adaptive secondaries and two tertiary
mirror flats that all work to support a variety of Gregorian focal stations, as well as prime focus. A fundamental goal of
the telescope is to perform interferometric observations, and therefore, there is a critical need for the ability to co-point
the individual telescopes to high precision. Further, a unique aspect of the LBT is the comparatively large range over
which the optics can be adjusted which provides flexibility for the acquisition of targets.
In the most general case, an observer could be performing an observation using different targets, within constraints, with
different instruments on each of the two telescope sides, with different observing duty cycles. As a consequence of the
binocular nature of the telescope and the number of possible observing combinations, there are unique requirements
imposed on the Telescope Control System (TCS), and in particular, on the Pointing Control Subsystem (PCS). It is the
responsibility of the PCS to arbitrate the pointing requests made on the two sides of the telescope by the observers,
incorporate guide updates, and generate tracking trajectories for the mount and the rotators, in conjunction with
providing tip/tilt demands on the subsystem controlling the optical elements, and ensure each target remains on the
specified location (i.e., pointing origin) in the focal plane during an active observation. This paper describes the current
design and implementation of the LBT PCS.
The software group at the Large Binocular Telescope Observatory (LBTO)<sup>1</sup> used logs and telemetry related to telescope
control system behavior to investigate improving the operational efficiency of the telescope. Our investigation unearthed
several surprises of unknown, unexpected, and undesired system behavior. What had been implemented was not always
the same as what we thought had been implemented. A bit of rework using minimal resources would provide an
inexpensive and immediate benefit leading directly to a more efficient operation. Also noted were software resource
usage anomalies that had gone unnoticed and areas where logging and telemetry data was inadequate to answer
fundamental questions. We considered trade-offs regarding what and when to modify configuration parameters,
hardware, and software that when changed, would increase performance. In this paper we statistically examine the raw
data and model system improvements for different implementations when viewed as a system. We also compare the
overall system performance before and after the modifications we have implemented.
The Large Binocular Telescope (LBT) is built around two lightweight borosilicate honeycomb mirrors which, at
8.4 meters in diameter, are the largest operational examples of this technology. Since the mirrors are relatively
stiff, the LBT mirror support system relies on passive position control and active force control. Passive position
control is performed by six extendable hardpoints organized as a truncated hexapod, which may be positioned
as required by the active optics control loop. The hardpoints rely on their axial stiffness to maintain the mirror
position against residual external disturbances. The active force control system minimizes the force exerted by
the hardpoints on the glass. Additionally, the axial component of the nominally uniform active support forces
can be perturbed to distort the mirror as required by the active optics control loop. Because of the relatively
large CTE of borosilicate glass, the differential temperature of the mirror is critical. Thus, the force control
system must support a 16 metric ton mirror using less than 100 Watts of electrical power. The authors present
a description of the primary mirror support system as implemented at the LBT. Initial stability problems made
the mirrors nearly unusable in freezing temperatures. The authors explain the reason for this instability and
describe the solutions implemented. Data demonstrating the current performance of the primary mirror support
system are also presented.
It is now well-known that measurement of field-aberration, and in particular the asymmetric field-astigmatism, is
required to break the degeneracy of tip-induced and
de-centre-induced aberration that exists when only on-axis
misalignment aberrations are considered. This paper discusses the application of the measurement of field-aberrations to
the alignment of LBT optics. This application ranges from the use of wide field out-of-focus images to determine
corrector tip for the red and blue prime-focus correctors, to the use of data acquired by off-axis Shack-Hartman
wavefront sensors to actively reposition the hexapod-mounted primary and secondary mirrors so as to simultaneously
remove both de-centre and tip/tilt such that the only remaining field-astigmatism has rotational symmetry about the
centre of the detector. Also introduced is a novel method to calculate the misalignment aberrations based on an extension
of the plate-diagram analysis. It is shown that this method is readily applicable to the calculation of misalignment
aberrations for systems of three-or-more powered mirrors, with almost no more computational difficulty than that of the
two-mirror case. Results are discussed, as well as work in progress in this area.
The Large Binocular Telescope (LBT) on Mt. Graham in Southeastern Arizona uses two 8.4-meter diameter
primary mirrors mounted side-by-side to produce a collecting area equivalent to an 11.8-meter circular aperture.
We describe our use of active optics with the honeycomb primary mirrors to provide focussing, collimation and
low-order active wavefront correction for the two prime focus cameras now operating on the telescope. We use
a custom IDL program, LBCFPIA, to geometrically analyze extrafocal pupils in order to determine focus and
wavefront corrections through third-order spherical aberration. We also describe that section of the telescope
control system which manages primary mirror collimation and accepts wavefront correction requests from the
instrument. We present active optics results obtained during commissioning of the prime focus cameras and
during science observations.
Proc. SPIE. 3676, Emerging Lithographic Technologies III
KEYWORDS: Signal to noise ratio, Lithography, Electron beam lithography, CMOS sensors, Scanning electron microscopy, Photomasks, Optical alignment, Semiconducting wafers, Signal detection, Charged-particle lithography
A manufacturable process for fabricating alignment marks that are compatible the SCALPEL lithography system is described. The marks were fabricated in a SiO<SUB>2</SUB>/WSi<SUB>2</SUB> structure using SCALPEL lithography and plasma processing. The positions of the marks were detected through e-beam resist in the SCALPEL proof of lithography (SPOL) tool by scanning the image of the corresponding mask mark over the wafer mark and detecting the backscattered electron (BSE) signal. Scans of 1 micrometers line-space patterns yielded mark positions that were repeatable within 20 nm 3(sigma) with a dose of 4 (mu) C/cm<SUP>2</SUP> and signal-to-noise of 32 dB. An analysis shows that the measured repeatability is consistent with a random noise limited response combined with SPOL machine factors. By using a digitally sequenced mark pattern, the capture range of the mark detection was increased to 13 micrometers while maintaining 35 nm 3(sigma) precision. Further improvements in mark detection repeatability are expected when the SCALPEL electron optics is fully optimized.
We have designed, constructed, and are now performing experiments with a proof-of-concept projection electron-beam lithography system based upon the SCALPEL<SUP>R</SUP> (scattering with angular limitation projection electron-beam lithography) principle. This initial design has enabled us to demonstrate the feasibility of not only the electron optics, but also the scattering mask and resist platform. In this paper we report on some preliminary results which indicate the lithographic potential and benefits of this technology for the production of sub-0.18 micrometer features.
A process for high-resolution patterning of the membrane- type masks used in the SCALPEL (SCattering with Angular Limitation in Projection Electron-beam Lithography) lithography system is described. SCALPEL is a 4X projection electron beam lithography tool with the potential to extend commercial lithographic capability well into the deep sub-micron range: the recently-completed SCALPEL proof- of-concept (SPOC) system has printed 0.08 micrometers lines in thick resist on Si. The details of the patterning process we currently employ and metrology results from the first series of masks are presented here. The SPOC mask blank consists of a segmented W-coated SiN (Si-rich) membrane, fabricated on a 4' Si wafer. The blank is patterned with 45 different test chips using a vector-scanned e-beam lithography tool. Metrology is performed on completed masks, and results from measurements of line-edge roughness, CD linearity, and pattern uniformity are presented. We examine the need for proximity effect correction of the pattern data, and compare the effect of correction on pattern data file size for a variety of mask technologies.
We have studied two mark geometries for possible use in a projection e-beam lithography system using SCALPEL (scattering with angular limitation in projection electron lithography). These are V-grooves and vertically etched geometries, pedestals or trenches. We report results of measurements of backscattered electron (BSE) contrast form topographic marks of varying size and as a function of energy up to 100 kV. The marks were fabricated on silicon wafers. The measurements were taken both in a scanning electron microscope and in an experimental SCALPEL machine operating in focused probe mode. The V-grooves ranged from 1.0 to 30 micrometers wide. The vertical etched features ranged from 2 to 30 micrometers wide and 0.6 and 50 micrometers depth. The results depended not only on the feature width and depth, but also on whether the features were isolated or in line and space patterns. Using a BSE ratio of 1.05 as a criterion for acceptable contrast from an alignment mark, V-grooves and vertical etched features had acceptable contrast with exception of the smallest and shallowest features for both geometries.
We have proposed an approach to projection electron beam lithography, termed the SCALPEL system, which we believe offers solutions to previous problems associated with projection electron beam lithography.