Optical Mounts Research Articles

Sub-system mechanical design for an eLISA optical bench

We present the design and development status of the opto-mechanical sub-systems that will be used in an experimental demonstration of imaging systems for eLISA. An optical bench test bed design incorporates a Zerodur® baseplate with lenses, photodetectors, and other opto-mechanics that must be both adjustable - with an accuracy of a few micrometers - and stable over a 0 to 40°C temperature range. The alignment of a multi-lens imaging system and the characterisation of the system in multiple degrees of freedom is particularly challenging. We describe the mechanical design of the precision mechanisms, including thermally stable flexure-based optical mounts and complex multi-lens, multi-axis adjuster mechanisms, and update on the integration of the mechanisms on the optical bench.

Compact LCOS–SLM Based Polarization Pattern Beam Generator

In this paper, a compact optical system for generating arbitrary spatial light polarization patterns is demonstrated. The system uses a single high-resolution liquid crystal (LC) on silicon (LCOS) spatial light modulator. A specialized optical mount is designed and fabricated using a 3D printer, in order to build a compact dual optical architecture, where two different phase patterns are encoded on two adjacent halves of the LCOS screen, with a polarization transformation in between. The final polarization state is controlled via two rotations of the Poincare sphere. In addition, a relative phase term is added, which is calculated based on spherical trigonometry on the Poincare sphere. Experimental results are presented that show the effectiveness of the system to produce polarization patterns.

Vertical and Horizontal Seismic Isolation Performance of the Advanced Virgo External Injection Bench Seismic Attenuation System

During the combined commissioning and science run of Virgo in 2010, an extensive noise study revealed that vibrations of some of the injection/detection optics on the external injection bench (EIB) made a significant contribution to the interferometer's noise budget. Several resonances were identified between 10 and 100Hz of the EIB support structure and between 200 and 300Hz of the optics mounts. These resonances introduced a significant amount of beam jitter that would limit the sensitivity of Advanced Virgo. This beam jitter needed to be reduced for Advanced Virgo to reach its full potential. To eliminate this noise source we developed a seismic attenuation system to isolate the EIB from ground vibrations: EIB-SAS. It employs vertical and horizontal passive seismic filters based on negative stiffness technology to attenuate seismic noise by 40dB above 10Hz. The isolation capabilities of the system have been characterized up to 400Hz with the aid of a custom designed piezoelectric actuated shaking platform. The results of the vertical and horizontal transfer function measurements are presented.

SU‐F‐BRE‐12: Optical Resonator Water Calorimeter

Purpose:Water calorimetry based on resistance thermometry has matured as a primary standard. Developing an optical technique hold the promise to push the boundaries of what is currently achievable with dosimetry. We will present a feasibility study and the current progress of construction of a Fabry‐Perot resonator for dose to water measurement. Additionally, estimations of the theoretical limits resonator sensitivity and potential sources of noise for the system are described.Methods:A temperature change from the dose to water would be measured by the change in the index of refraction from the water in the cavity. Calculations are presented of the expected signal from the resonator for dose to water. The Fabry‐Perot resonator constructed from optical quality narrowband mirrors is described. A water cell will be inserted into the cavity gap to provide the medium swept cavity length technique is explored as a specific implementation of this technique.Results:Calculations indicate that a dose to water on the order of a Gray is measureable with a reasonably implementable system. A resonator is currently under construction and progress towards a proof of principle measurement will be presented. The primary sources of noise, in order of importance, are expected to be; optical absorption by the medium, mechanical perturbations of the cavity length and thermal expansion of the optical mounts. Estimations of these noise sources and mitigation techniques will be discussed.Conclusion:A Fabry‐Perot resonator is a promising technique for measuring the absorbed dose to water from a radiotherapy beam. This technique has the potential to serve as a check on the current primary standard for dose to water measurements. As well, i0074 may be the foundation for a new class of optical property based dosimetry measurement.

SU-E-T-410: Fringe Stability and Phase Shift Measurements in a Michelson Interferometer for Optical Calorimetry

Purpose: To identify the variables limiting the resolution of a Michelson interferometer used to measure phase shifts (PS) in water as part of a radiometric calorimeter. Methods: We investigated the output stability of a He-Ne laser and a laser diode. The short and long term stability of the fringe pattern in a Michelson interferometer was tested with different types of lasers, thermal insulation arrangements, damping systems and optical mounts to optimize system performance. PS were induced by electrically heating water in a 1 cm quartz cuvette located in one of the interferometer arms. The PS was calculated from fringe intensity changes and compared to a calculated PS using thermocouple-measured temperature changes in the water. Results: The intensity of the laser diode is more stable, but the gas laser’s profile is more suitable for fringe analysis and has better temporal coherence. The laser requires a warm-up time of 4 hours before its output is stabilized (SNR>95). The fringe’s stability strongly depends on the thermal insulation. When the interferometer is exposed to ambient temperature swings of 0.7 K, it is not possible to stabilize the fringe pattern. Enclosing the system in a 2.5 cm-thick Styrofoam box improves the SNR, but further insulationmore » will be needed to increase the SNR above 50. High frequency noise is significantly reduced by damping the system.Inducing a temperature rise in water, starting at 299 K, the average temperature increase for a 2π PS is 0.29 ± 0.02 K and the proportionality constant is -21.1 ± 0.8 radians/K. This is 5.8% lower than the calculated value using the thermocouple. Conclusion: Interferometric PS measurements of temperature may provide an alternative to thermistors for water calorimetry. The resolution of the current prototype is limited by ambient temperature stability. Calculated and measured thermally-induced PS in water agreed to within 5.8%.« less

大口径望远镜结构热分析

In order to evaluate the temperature effect of telescopes, a precise thermal finite element model consists of telescope optical assembly systems, mount structure and electrical equipment was established. Temporal and spatial temperature distributions of the optical assembly and telescope structure were calculated under various thermal conditions including conductions, air convections, radiation and heat flux loading. Moreover, the thermo-elastic analysis was made to obtain thermal deformations of the telescope structure based on the resulting temperature distributions. The obtained results show that temperature variation has large effect on telescope mount and main optical system, and induced displacement between primary and second mirror has a magnitude of millimeter, so it must be controlled strictly. At last some thermal control ways were given in terms of protection dome, mount, primary mirror and so on.

Note: Pneumatically actuated and kinematically positioned optical mounts compatible with laser-cooling experiments

We present two complementary designs of pneumatically actuated and kinematically positioned optics mounts: one designed for vertical mounting and translation, the other designed for horizontal mounting and translation. The design and measured stability make these mounts well-suited to experiments with laser-cooled atoms.

Synthesizing Parallel Flexures That Mimic the Kinematics of Serial Flexures Using Freedom and Constraint Topologies

The principles of the freedom and constraint topologies (FACT) synthesis approach are adapted and applied to the design of parallel flexure systems that mimic degrees of freedom (DOFs) primarily achievable by serial flexure systems. FACT provides designers with a comprehensive library of geometric shapes. These shapes enable designers to visualize the regions wherein compliant flexure elements may be placed for achieving desired DOFs. By displacing these shapes far from the point of interest of the stage of a flexure system, designers can compare a multiplicity of concepts that utilizes the advantages of both parallel and serial systems. A complete list of which FACT shapes mimic which DOFs when displaced far from the point of interest of the flexure system's stage is provided as well as an intuitive approach for verifying the completeness of this list. The proposed work intends to cater to the design of precision motion stages, optical mounts, microscopy stages, and general purpose flexure bearings. Two case studies are provided to demonstrate the application of the developed procedure.

Stochastic method for determining the coherence length of a TEA CO2 laser

Abstract In this work the results of the measurement of the coherence length of a TEA CO 2 laser developed in DEILAP are presented. A Michelson interferometer of about 5 m of optical path length difference was built for this purpose. A motorized translation optical mount was placed in one arm in order to enable the variation of the optical path length in many wavelengths. The length of the other arm was varied manually in steps of several tens of centimeters. Spatial filtering forced the laser to oscillate in a single transverse mode, TEM 00 . An innovative stochastic technique for data analysis allowed determining the amount of longitudinal modes, the amplitude and the individual average coherence length of each mode as well as the global coherence length of the laser. This technique was later compared with a method based on the analysis of the Fourier transform of the time series obtained at the interferometer input.

Note: Computer controlled rotation mount for large diameter optics

We describe the construction of a motorized optical rotation mount with a 40 mm clear aperture. The device is used to remotely control the power of large diameter laser beams for a magneto-optical trap. A piezo-electric ultrasonic motor on a printed circuit board provides rotation with a precision better than 0.03° and allows for a very compact design. The rotation unit is controlled from a computer via serial communication, making integration into most software control platforms straightforward.

大口径精密光学调整架的优化设计

大口径精密光学调整架的优化设计

Design of flexure-based precision transmission mechanisms using screw theory

This paper enables the synthesis of flexure-based transmission mechanisms that possess multiple decoupled inputs and outputs of any type (e.g., rotations, translations, and/or screw motions), which are linked by designer-specified transmission ratios. A comprehensive library of geometric shapes is utilized from which a multiplicity of feasible concepts that possess the desired transmission characteristics may be rapidly conceptualized and compared before an optimal concept is selected. These geometric shapes represent the mathematics of screw theory and uniquely link a body's desired motions to the flexible constraints that enable those motions. This paper is significant to the design of nano-positioners, motion stages, and optical mounts. It is also significant to the design of transmission-based microstructural architectures for creating new materials with extraordinary mechanical properties. The microstructural architecture for a material that achieves a negative Poisson's ratio as well as a hand-actuated two degree of freedom (DOF) microscopy stage are designed as case studies to demonstrate the utility of this theory.

Fabrication of sharp-needled conical polymer tip on the cross-section of optical fiber via two-photon polymerization for tuning-fork-based atomic force microscopy

Aiming at the use in tuning-fork-based atomic force microscopy (TF-based AFM), we propose and demonstrate fabrication methods of polymer tips on the cross-section of optical fibers by two-photon polymerization (TPP) using SCR500 resin. This method can be applied to any optical fibers or other bases regardless of the type. The specified polymer tips are fabricated with high reproducibility by this method. First, a conical polymer tip was fabricated via a continuous-scanning method and layer-by-layer accumulation of circular layers which reduce to a point along with the growth from the cross-section of optical fibers, by using a five-axis optical fiber mount combined with a two-photon nanofabrication system. A sharp-needled conical polymer tip of a 45nm radius of curvature was fabricated with attachment of four voxels. These voxels were fabricated by the gradually-decreasing-exposure-time method on the apex of the simple conical tip. We have also designed and fabricated a triple-tapered polymer tip to demonstrate the feasibility of fabricating various tip shapes by the TPP method for the TF-based AFM. Moreover, the photoluminous polymer tip was fabricated using ORMOCER mixed with quantum dots. The sharp-needled polymer tip was utilized for the TF-based AFM using an optical fiber probe to investigate the performance of the polymer tip fabricated by the TPP method, and we have obtained a topographic image of a pitted sample. Finally, the near-field image of the 30-nm-thick gold layer with holes of 250-nm-radius was successfully obtained by the aluminum-coated NSOM probe fabricated on the TPP conical polymer tip with a radius of curvature of 45nm in NSOM system.

IGRINS Mirror Mount Design for Three Off-Axis Collimators and One Slit-Viewer Fold Mirror

The Korea Astronomy and Space Science Institute and the Department of Astronomy at the University of Texas at Austin are developing a near infrared wide-band high resolution spectrograph, immersion grating infrared spectrometer (IGRINS). The compact white-pupil design of the instrument optics uses seven cryogenic mirrors, including three aspherical off-axis collimators and four flat fold mirrors. In this study, we introduce the optomechanical mount designs of three off-axis collimating mirrors and one flat slit-viewer fold mirror. Two of the off-axis collimators are serving as H and K-band pupil transfer mirrors, and are designed as system alignment compensators in combination with the H2RG focal plane array detectors in each channel. For this reason, the mount designs include tip-tilt and parallel translation adjustment mechanisms to properly perform the precision alignment function. This means that the off-axis mirrors` optomechanical mount designs are among the most sensitive tasks in all IGRINS system hardware. The other flat fold mirror is designed within its very limitedly allowed work space. This slit-viewer fold mirror is mounted with its own version of the six-point kinematic optics mount. The design work consists of a computer-aided 3D modeling and finite element analysis (FEA) technique to optimize the structural stability and the thermal behavior of the mount models. From the structural and thermal FEA studies, we conclude that the four IGRINS mirror mounts are well designed to meet all optical stability tolerances and system thermal requirements.

Transmitted wavefront error of a volume phase holographic grating at cryogenic temperature

This paper describes the results of transmitted wavefront error (WFE) measurements on a volume phase holographic (VPH) grating operating at a temperature of 120 K. The VPH grating was mounted in a cryogenically compatible optical mount and tested in situ in a cryostat. The nominal root mean square (RMS) wavefront error at room temperature was 19 nm measured over a 50 mm diameter test aperture. The WFE remained at 18 nm RMS when the grating was cooled. This important result demonstrates that excellent WFE performance can be obtained with cooled VPH gratings, as required for use in future cryogenic infrared astronomical spectrometers planned for the European Extremely Large Telescope.

Spartan Infrared Camera, a High-Resolution Imager for the SOAR Telescope: Design, Tests, and On-Telescope Performance

ABSTRACTThe Spartan Infrared Camera provides tip-tilt corrected imaging for the SOAR Telescope in the 900–2500 nm spectral range with four 2048 × 2048 HAWAII-2 detectors. The camera has two plate scales: high-resolution () for future diffraction-limited sampling in the H and K bands and wide-field () to cover a 5′ × 5′ field, over which tip-tilt correction is substantial. The design is described in detail. Except for CaF2 field-flattening lenses, the optics are aluminum mirrors to thermally match the aluminum cryogenic-optical box in which the optics mount. The design minimizes the tilt of the optics as the instrument rotates on the Nasmyth port of the telescope. Two components of the gravitational torque on an optic are eliminated by symmetry, and the third component is minimized by balancing the optic. The optics (including the off-axis aspherical mirrors) were aligned with precise metrology. For the detector assembly, Henein pivots are used to provide frictionless, thermally compliant, lubricant-free, and thermally conducting rotation of the detectors. The heat load is 14 W for an ambient temperature of 10°C. Cooling down takes 40 hr. An activated-charcoal getter controls permeation through the large Viton O-ring for at least nine months. We present maps of the image distortion, which amount to tens of pixels at the greatest. The wavelength of the narrowband filters shift with position in the sky. The measured Strehl ratio of the camera itself is 0.81–0.84 at λ1650 nm. The width of the best K-band image was 260 mas in unexceptional seeing measured after tuning the telescope and before moving the telescope. Since images are normally taken after pointing the telescope to a different field, this supports the idea that the image quality could be improved by better control of the focus and the shape of the primary mirror. The instrument has proved to be capable of producing images that can be stitched together to measure faint, extended features and to produce photometry that agree internally to better than 0.01 mag and are well calibrated to 2MASS stars in the range of 12 < K < 16.

Picometre and nanoradian heterodyne interferometry and its application in dilatometry and surface metrology

A high-sensitivity heterodyne interferometer implementing differential wavefront sensing for tilt measurement was developed over the last few years. With this setup, using an aluminium breadboard and compact optical mounts with a beam height of 2 cm, noise levels less than 5 pm Hz−1/2 in translation and less than 10 nrad Hz−1/2 in tilt measurement, both for frequencies above 10−2 Hz, have been demonstrated. Here, a new, compact and ruggedized interferometer setup utilizing a baseplate made of Zerodur, a thermally and mechanically highly stable glass ceramic with a coefficient of thermal expansion (CTE) of 2 × 10−8 K−1, is presented. The optical components are fixed to the baseplate using a specifically developed, easy-to-handle, assembly-integration technology based on a space-qualified two-component epoxy. While developed as a prototype for future applications aboard satellite space missions (such as Laser Interferometer Space Antenna), the interferometer is used in laboratory experiments for dilatometry and surface metrology. A first dilatometer setup with a demonstrated accuracy of 10−7 K−1 in CTE measurement was realized. As it was seen that the accuracy is limited by the dimensional stability of the sample tube support, a new setup was developed utilizing Zerodur as structural material for the sample tube support. In another activity, the interferometer is used for characterization of high-quality mirror surfaces at the picometre level and for high-accuracy two-dimensional surface characterization in a prototype for industrial applications. In this paper, the corresponding designs, their realizations and first measurements of both applications in dilatometry and surface metrology are presented.

FIR polarimetry diagnostic for the C-Mod tokamak

A three-chord polarimeter on Alcator C-Mod will make measurements of the poloidal magnetic field and plasma fluctuations. The beams from two frequency-offset, 200 mW, FIR lasers operating at 117.73 μm are combined to produce collinear, counter-rotating, circularly polarized beams. The beams are divided into three chords which are directed into the plasma at one toroidal location. Corner cube retro-reflectors mounted on the inside wall return the beam for a double pass. The mixing product of the two beams is detected both before (reference) and after (signal) the plasma using polarization sensitive detectors that produce a beat signal at ∼ 4 MHz. During the plasma discharge, the phase delay of the signal mixer, which depends on the Faraday effect, is evaluated with respect to the reference and produces line-integrated information on the poloidal magnetic field. Measurements on C-Mod require the phase error to be at the 0.1 degree level, and great care in the design of optical mounts, polarizers, beam-splitters, focusing optics, and acoustic and magnetic shielding was required. Development of new planar diode Schottky detectors was necessary to provide high sensitivity for a diagnostic that will eventually have at least six chords. Absorption of the FIR laser light by water vapor requires that the entire beam path be purged with dry air. Six retro-reflectors on the inner wall arranged in an ITER-like configuration provide poloidally viewing chords from near the mid-plane to well into the plasma scrape off layer. A pneumatically controlled shutter protects the in-vessel optics during boronizations and during limited discharges that might accelerate damage to the retro-reflector surfaces. Tests indicate there is no measurable signal contamination from the toroidal magnetic field due to the Cotton-Mouton effect. Polarization sensitivity of the wire mesh beamsplitters necessitated system calibration. Good agreement to EFIT reconstructions has been observed along with plasma fluctuations up to 400 kHz.

Nieinwazyjne badania in situ wybranych obrazów z kolekcji malarstwa i pasteli autorstwa Meli Muter za pomocą tomografii optycznej OCT

Optical Coherence Tomography is a non-contact and non-invasive technique of depth-resolved structural imaging within media scattering and/or absorbing nearinfrared light moderately. It utilizes a concept of low-coherence interferometry and thus light sources must be characterized by low temporal (to ensure high axial resolution) and high spatial (to ensure high sensitivity) coherence. The instrument used in this study has 4 μm axial resolution and over 100 dB sensitivity. The modular construction based on fiber optics makes it fairly easy transportable and not requiring optical table mounting. The system’s portability together with fast and straightforward data acquisition, makes OCT especially well suited for quick in situ evaluation of large museum collections of paintings.A vast collection of seventy-one oil paintings and over one hundred drawings, watercolours, and graphics by Mela Muter (Maria Melania Mutermilch, 1876, Warsaw – 1967, Paris), gathered by Bolesław and Lina Nawrocki, is now on deposit to the Nicolaus Copernicus University Museum in Toruń. Artistically active in the first half of the twentieth century within the École de Paris, Mela Muter became recognized mostly for the portraits depicting socialites of the time, as well as images of motherhood, children and old people.The collection brings specific conservation problems. Since the works were mostly acquired from Muter herself, the attribution is not in question. Nevertheless, the majority of paintings bear signs of extent conservation treatment and/ or alterations performed by the artist in her late years, possibly including adding signatures.The aim of the survey of the group of nine Mela Muter’s paintings and two pastels was to define the conservation issues as well as to indicate the objects and areas for further examination with various analytical techniques. In result, the evaluation of secondary layers (varnishes and putties) was performed for seven paintings. The structure of the paint layer in the area of the signature was analyzed in three paintings. Finally, in case of two pastel paintings, the safety of pigment layer (its distance to the glass) was assessed.

FOUNDATION REQUIREMENTS FOR A LUNAR LASER RANGER FACILITY AT MATJIESFONTEIN, SOUTH AFRICA

This paper addresses foundation requirements to construct a new Geodetic/Geophysical Observatory at approximately five kilometers south of Matjiesfontein, in the southwestern Karoo. The observatory will host a Lunar Laser Ranger, Satellite Laser Ranger, and other collocated geophysical instruments, such as seismic and gravimeter stations, to be located in a specially designed vault. Field and laboratory tests and surveys show that the site is stable and capable of supporting the 5 ton weight of the Lunar Laser Ranger (LLR) structure that includes a one meter diameter optical telescope and mount to conduct laser-ranging experiments. The foundation requirements for auxiliary buildings and calibrating beacons required for the instrument and the envisaged experiments were also included in this study.