Mirror Substrates Research Articles

Wide-Aperture Bimorph Deformable Mirror for Beam Focusing in 4.2 PW Ti:Sa Laser

The bimorph deformable mirror with a diameter of 320 mm, including 127 control electrodes, has been developed and tested. The flatness of the initial mirror surface of about 1 μm (P-V) was achieved by mechanically adjusting the mirror substrate fixed in the metal mount. To correct for the aberrations and improve the beam focusing in the petawatt Ti:Sa laser, the wide-aperture adaptive optical system with the deformable mirror and Shack–Hartmann wavefront sensor was developed. Correction of the wavefront aberrations in the 4.2 PW Ti:Sa laser using the adaptive system provided increases the intensity in the focusing plane to a value of 1.1 × 1023 W/cm2

Diamond-carbide-silicon composite "skeleton" as a promising material for X-ray optical substrates

The paper proposes the use of diamond-carbide-silicon composite "Skeleton"oledR coated with amorphous silicon as substrates for multilayer X-ray mirrors for powerful synchrotron radiation sources (3+ and 4th generation). The surfaces with the following parameters were obtained using standard deep polishing methods: flatness at the level of RMS90%=54.2 nm; effective roughness sigmaeff~1.0 nm; high-frequency roughness sigma2x2~0.1 nm. Keywords: x-ray optics, x-ray mirrors, substrates for x-ray mirrors, roughness.

Алмаз-карбид-кремниевый композит "скелетон" как перспективный материал для подложек рентгенооптических элементов

The paper proposes the use of diamond-carbide-silicon composite "Skeleton"® coated with amorphous silicon as substrates for multilayer X-ray mirrors for powerful synchrotron radiation sources (3rd+ and 4th generation). The surfaces with the following parameters were obtained using standard deep polishing methods: flatness at the level of RMS90%=54.2 nm; effective roughness sigmaeff~1.0 nm; high-frequency roughness sigma2х2~0.1 nm.

Dynamic wavefront distortion in resonant scanners.

Dynamic mirror deformation can substantially degrade the performance of optical instruments using resonant scanners. Here, we evaluate two scanners with resonant frequencies >12kHz with low dynamic distortion. First, we tested an existing galvanometric motor with a novel, to the best of our knowledge, mirror substrate material, silicon carbide, which resonates at 13.8 kHz. This material is stiffer than conventional optical glasses and has lower manufacturing toxicity than beryllium, the stiffest material currently used for this application. Then, we tested a biaxial microelectromechanical (MEMS) scanner with the resonant axis operating at 29.4 kHz. Dynamic deformation measurements show that wavefront aberrations in the galvanometric scanner are dominated by linear oblique astigmatism (90%), while wavefront aberrations in the MEMS scanner are dominated by horizontal coma (30%) and oblique trefoil (27%). In both scanners, distortion amplitude increases linearly with deflection angle, yielding diffraction-limited performance over half of the maximum possible deflection for wavelengths longer than 450 nm and over the full deflection range for wavelengths above 850 nm. Diffraction-limited performance for shorter wavelengths or over larger fractions of the deflection range can be achieved by reducing the beam diameter at the mirror surface. The small dynamic distortion of the MEMS scanner offers a promising alternative to galvanometric resonant scanners with desirable but currently unattainably high resonant frequencies.

Effects of metallic underlayer on SERS performance of a metal film over nanosphere metasurface

Metal film over nanosphere (MFON) metasurfaces have numerous applications, specifically as nanosensors for bio and chemical detection. Additionally, their interesting optical properties have also attracted the attention of many research groups. In this work, we study the influence of the metallic underlayer on the surface-enhanced Raman scattering (SERS) effect of the MFON structure. Two sets of MFON on silicon and mirror substrates were prepared for SERS measurement with rhodamine 6G. Experimental results show that the mirror layer boosts the SERS signal by two to five times. Finite difference time domain simulation was performed to gain insights into this improvement. Numerical results show that metallic underlayer helps to increase the concentration of the electric field at the hot spots. Moreover, it reflects the Raman signal via the extraordinary optical transmission channel of the MFON structure, improving the back-scattered Raman signal collection efficiency. Both of these effects can contribute to the increase of the SERS signal in agreement with the experimental results. More importantly, it provides an additional tool to tailor the optical properties of MFON metasurfaces.

Multimetallic Nanoparticles on Mirrors for SERS Detection

Nanoparticle on mirror (NPoM) architectures are attractive for optical applications–particularly for sensing–due to their simplicity and reliability of their multicomponent plasmonic interactions. However, to date, work has predominantly focused on monometallic nanoparticles on different metallic films. While these studies have investigated the effect of geometry on the optical responses of NPoM structures, understanding the effect of nanoparticle composition is needed to gain a full understanding and complete control over these systems. To elucidate the role of composition on localized plasmonic resonances, a surface-based nanoparticle synthetic method, scanning block copolymer lithography (SPBCL), was used to synthesize and characterize single Au0.5Ag0.5 particles on a five-layer, thermally stable plasmonic mirror substrate. The use of SPBCL is important because it can easily be extended to almost a limitless number of polyelemental systems. We demonstrate the potential of the approach by using surface-enhanced Raman spectroscopy to detect benzene-1,4-dithiol adsorbed onto individual alloyed AuAg NPs in an NPoM geometry.

New DRIFT spectroscopic methodology for acquiring infrared spectra of fiberglass materials

We report a new approach for infrared spectroscopic analysis of fiberglass materials using a mirror substrate, which allowed the specular reflection from the sample surface to be minimized and detect the light passing through the sample. The application of this technique for platinum-containing fiberglass catalysts made it possible for the first time to identify sulfate compounds formed in glass fibers during the oxidation reaction of sulfur dioxide. The developed technique can be applied for a number of research samples that are difficult to analyze by conventional IR spectroscopic methods.

Removal of Mo/Si multilayer coatings on fused silica substrates by wet chemical etching

This work examined a novel etching procedure for the complete removal of Mo/Si multilayer coatings, as a means of reusing valuable mirror substrates employed in extreme ultraviolet imaging. A multilayer coating deposited on a fused silica substrate was etched with an alkaline solution containing potassium ferricyanide and sodium hydroxide, and the entire coating was removed within 60 min. The root mean square roughness and power spectrum density characteristics were subsequently assessed and the resulting values were equivalent to those before the deposition of the coating. These results demonstrate that such coatings can be removed while maintaining the original surface figure.

Crossed optical cavities with large mode diameters.

We report on a compact, ultrahigh-vacuum compatible optical assembly to create large-scale, two-dimensional optical lattices for use in experiments with ultracold atoms. The assembly consists of an octagon-shaped spacer made from ultra-low-expansion glass, to which we optically contact four fused silica cavity mirrors, making it highly mechanically and thermally stable. The mirror surfaces are nearly plane-parallel, which allows us to create two perpendicular cavity modes with diameters ∼1m m. Such large mode diameters are desirable to increase the optical lattice homogeneity, but lead to strong angular sensitivities of the coplanarity between the two cavity modes. We demonstrate a procedure to precisely position each mirror substrate that achieves a deviation from coplanarity of d=1(5)µm. Creating large optical lattices at arbitrary visible and near-infrared wavelengths requires significant power enhancements to overcome limitations in the available laser power. The cavity mirrors have a customized low-loss mirror coating that enhances the power at a set of relevant visible and near-infrared wavelengths by up to 3 orders of magnitude..

Temperature Control for an Intra-Mirror Etalon in Interferometric Gravitational Wave Detector Fabry–Perot Cavities

The sensitivity of interferometric gravitational wave detectors is optimized, in part, by balanced finesse in the long Fabry–Perot arm cavities. The input test mass mirrors of Advanced Virgo feature parallel faces, which creates an etalon within the substrate, adding variability in the total mirror reflectivity, in order to correct imbalanced finesse due to manufacturing tolerances. Temperature variations in mirror substrate change the optical path length primarily through varying the index of refraction and are tuned to correct for a finesse imbalance of up to 2.8% by a full etalon fringe of 0.257 K. A negative feedback control system was designed to control the mirror temperature by using an electrical resistive heating belt actuator for a heat transfer process modeled as a two-pole plant. A zero controller filter was designed which achieves temperature control within 2.3% of the etalon fringe and recovers to within 10% of the working point within 32 hours after a step input of one etalon fringe. A preliminary unlock condition control designed to compensate when the interferometer unlocks shows that the control remains stable even after a drastic change in the plant due to the absence of the laser heating. Further improvements to the control must also consider the full heat transfer mechanisms by using modern control state space models.

Application of induced mechanical stresses in formation of spherical surfaces of interference mirror substrates

Application of induced mechanical stresses in formation of spherical surfaces of interference mirror substrates

Materials and technologies of powder metallurgy in components of aviation and space engineering

Examples of the implementation of powder metallurgy methods and their individual elements in the processes of producing materials with special properties and products thereof are considered. The possibility is shown and the results of producing radar-absorbing and radar-transparent materials in the form of solid bodies and coatings are evaluated. The addition of technological transitions, traditional for powder metallurgy, providing in general the production of radar-transparent materials, with the processes of mechanically activated synthesis and mechanically activated self-propagating high-temperature synthesis at the stages of preparing powders for molding, makes it possible to make the transition to the production of radar-absorbing materials. The high efficiency of both has been confirmed experimentally. The transition from a single-component composition of the initial charge mixture through the formation of the phase composition of the material due to the inclusion of powder components into the mixed charge, the composition and crystal structure of which remain unchanged at all stages of its preparation, to the synthesis of the required phase composition due to the interaction of powder components at one of the stages of technological conversion makes it possible to synthesize, for example, silicon carbide ceramics directly in practically useful products, particularly, substrates of optical mirrors for remote sensing of the Earth. The technological operations developed in powder metallurgy have become a background for the production of energy-saturated heterogeneous composite materials. Actively developing additive technologies, as a relatively new branch of powder metallurgy, expands its capabilities practically boundless.

Off-axis parabolas super polished under stress: the case of the Roman Space Telescope coronagraphic instrument mirrors.

Direct imaging of exoplanets requires high contrast imaging techniques that demand tight tolerances on the optical surface error. The Nancy Grace Roman Space Telescope (RST) (previously named WFIRST) aims to perform direct imaging of SuperEarth-like exoplanets through its active coronographic instrument (CGI). Eight off-axis parabola (OAP) mirrors are utilised within the CGI to create a compact instrument and to ensure access to the pupil and focal planes. The surface form error and surface roughness of these relay optics directly impact the quality of the dark hole, and therfore the observable location for exoplanets. A new fabrication process for OAP manufacture via stressed mirror polishing (SMP) is presented in this paper. First, the design of the mirror substrate is investigated to create an innovative thickness distribution capable of producing the OAP geometry with a simple warping harness composed by two micrometer screws. Second, the novel design is implemented on a 60 mm diameter OAP prototype in Zerodur; a description of the fabrication process chain and the characterisation of the optical surface over all spatial frequencies are presented. Results from this first prototype demonstrated that the surface form error deviates from < 1 nm root means square (RMS) from the simulations and with a surface roughness of 2.1 Å Ra.

Dynamics and stability of an optically levitated mirror

We analyse the dynamics of a one-dimensional vertical Fabry-P\'erot cavity, where the upper mirror levitates due to intra-cavity radiation pressure force. A perturbative approach is used based around separation of timescales, which allows us to calculate the physical quantities of interest. Due to the dynamics of the cavity field, we find that the upper mirror's motion will always be unstable for levitation performed using only a single laser. Stability can be achieved for two lasers, where one provides the trapping potential and the other a damping effect, and we locate and characterise all parameter regimes where this can occur. Finally we analyse photothermal effects due to heating of the mirror substrate. We show that this can stabilise the system, even with only a single input laser, if it acts to increase the optical path length of the cavity. This work serves as a foundation for understanding how levitated optical cavity schemes can be used as stable metrological platforms.

Advanced ultraviolet, optical, and infrared mirror technology development for very large space telescopes

The Advanced Mirror Technology Development (AMTD) project was a 6-year effort to mature technologies required to enable 4-m-or-larger monolithic or segmented ultraviolet/optical/infrared space-telescope primary-mirror assemblies for general astrophysics and exoplanet missions. AMTD used a science-driven systems-engineering approach. Starting with science requirements, engineering specifications were derived for the primary mirror aperture diameter, areal density, surface error, and stability. The most impactful specification may be 10 pm per 10-min wavefront stability. Advances were made to six key technologies: (1) fabricating large-aperture low-areal-density high-stiffness mirror substrates; (2) designing support systems; (3) correcting mid/high-spatial frequency figure error; (4) mitigating segment edge diffraction; (5) phasing segment-to-segment gaps; and (6) validating integrated models. AMTD successfully demonstrated a process to make substrates as large as 1.5 m and as thick as 40 cm by stacking multiple core elements and low-temperature fusing them together. To help predict on-orbit performance and assist in architecture trade studies, integrated models were created for two mirror assemblies (1.5-m Ultra-Low-Expansion (ULE®) mirror fabricated by AMTD partner Harris Corp. and 1.2-m Zerodur® mirror owned by Schott North American). X-ray-computed tomography was used to construct the 1.5-m ULE® mirror’s “as-built” model. These models were validated by testing full- and subscale components in relevant thermovacuum environments.

Characterization of laser thermal loading on microelectromechanical systems-based fast steering mirror in vacuum

Microelectromechanical systems (MEMS) have produced high-quality, high-bandwidth, small form factor, and inexpensive fast steering mirror (FSM) devices potentially suitable for a large variety of applications, such as image stabilization and beam pointing in satellite-based and ground-based, free-space optical communication systems. However, one outstanding question for this application is power handling. The absorption of the mirror substrate is low, but non-negligible, so the question remains of whether thermal loading from laser radiation on a MEMS mirror will deform its surface and, if so, to what extent. We show experimental results of optical performance changes due to thermal loading for MEMS two-axis FSM devices from Mirrorcle Technologies, Inc. Results and reproducible behavior are reported and compared in ambient versus vacuum conditions, where the benefits of convective cooling are absent. Finite element analyses corroborate the experimental results and show that the mirror substrate can deform due to thermal expansion imbalances. The deformation changes the focusing characteristics of the mirror, with a peak to valley defocus (second-order Zernike mode) of up to 50 nm when the mirrors are tested in ambient and up to approximately 450 nm when under vacuum. Such defocusing negatively impacts the link budget for laser-based satellite communications.

Single CdSe/CdS colloidal nanocrystals embedded in an Ultra-Pure SiO2 matrix deposited by ion beam sputtering

We report the encapsulation of high-quantum-yield CdSe/CdS colloidal nanocrystals in a smooth and ultra-pure layer of SiO2 deposited by ion beam sputtering. The optical quality of the thin silica film is comparable to the mirror substrates used in gravitational-wave detection, with a density of impurities as low as a few ppm. We show that at least 30% of the nanocrystals survive the encapsulation process under full conservation of their favorable optical properties at the single-quantum-dot level, namely a high and stable emission rate combined with a short recombination lifetime. The emission rate of the embedded nanocrystals is increased by 100% due to the higher refractive index of the SiO2 film, in accordance with an effective-medium interpretation. Our device prototype thus provides a perspective for designing large-scale, high-quality and thickness-controlled light-emitting diodes based on semiconductor nanocrystals as active components in a durable inorganic matrix.

Reducing edge error based on further analyzing the stability of edge TIF and correcting the post-edge algorithm in MRF process

A precise and efficient edge-controlled method is of importance to ensure the final performance of the optical system. The authors put forward a novel method to reduce the edge effect in the magnetorheological finishing (MRF) process through further analyzing the stability of the MRF edge tool influence function (TIF) and correcting the post-edge algorithm of dwell time. To demonstrate the feasibility and advantage of this edge-controlled theory, two mirror substrates are taken as the experimental samples. The Φ 200 mm, R-200 mm concave sphere mirror (fused silica) is removed about 3 μm uniformly and the experimental results indicate that the edge error region can be effectively suppressed below 1.5 mm. Another Φ 610 mm, R-2100, K-1 lightweighting parabolic mirror is verified about the actual practicability. The residual error reaches RMS 6.5 nm from original RMS 182 nm after two run iterations; meanwhile, the edge effect is well controlled to a large extent. The simulations of edge error coincide well with the corresponding experimental results, which strongly verify the feasibility of the edge-suppressing theory presented in this paper.

Development of imaging x-ray telescopes at Tongji University

The imaging x-ray telescope (IXT) was first developed at the Institute of Precision Optical Engineering of Tongji University in 2007. Since then, we have made great progress on the development of mirror fabrication, coatings, and optic assembly. In this paper, we intend to provide an overview of the progress. Currently, we can routinely produce cylindrical mirror substrates with angular resolution of 30″ to 60″. To improve the effective area, coatings using C, Ni, and Pt layers were designed and achieved a high reflectivity at 0.5 to 10 keV. During the optic assembly, an in-situ measurement system and a three-dimensional ray-tracing program have been developed, thus guiding the assembly process in real time. Several prototypes have been fabricated, and one of them with 21 mirror layers was calibrated at the MPE PANTER x-ray test facility in Germany. The IXT prototype, with a focal length of 2052.5 mm, is characterized by a measured half-power diameter of 111″ and effective area of 39 cm2 at 1.49 keV.

Flattop output extra-wide tuning range tunable laser design technique

The laser oscillator design principle, which provides extended tunability together with a flattop output in the wide spectral range, is proposed and demonstrated on the examples of the dye laser. It is realized by using an high-reflecting (HR) moving intracavity mirror (scraper) with the sharp edge partially overlapping the laser radiation in the high-Q cavity and extracting it out. The technique provides the output laser beam with M2 < 1.2 and can be applied to any type of lasers operating from the far-IR to the VUV spectral ranges. Besides, wide-band HR cavity mirrors are only used, and there are no special demands to the material of the mirror substrate.