Thin Mirror Research Articles

SU-8-meta-phenylenediamine-conjugated thin film for temperature sensing.

Polymers have distinctive optical properties and facile fabrication methods that have been well-established. Therefore, they have immense potential for nanophotonic devices. Here, we demonstrate the temperature-sensing potential of SU8-meta-phenylenediamine (SU8-mPD), produced by epoxy amination of the SU-8 polymer. Its properties were examined through a series of molecular structural techniques and optical methods. Thin layers have demonstrated optical emission and absorption in the visible range around 420 and 520 nm, respectively, alongside a strong thermal responsivity, characterized by the 18 ppm °C-1 expansion coefficient. A photonic chip, comprising a thin 5-10 μm SU8-mPD layer, encased between parallel silver and/or gold thin film mirrors, has been fabricated. When pumped by an external light source, this assembly generates a pronounced fluorescent signal that is superimposed with the Fabry-Pérot (FP) resonant response. The chip undergoes mechanical deformation in response to temperature changes, thereby shifting the FP resonance and encoding temperature information into the fluorescence output spectrum. The time response of the device was estimated to be below 1 s for heating and a few seconds for cooling, opening a new avenue for optical sensing using SU8-based polymers. Thermoresponsive resonant structures, encompassing strong tunable fluorescent properties, can further enrich the functionalities of nanophotonic polymer-based platforms. This article is part of the theme issue 'Celebrating the 15th anniversary of the Royal Society Newton International Fellowship'.

Electromagnetic Signatures of Mirror Stars

Mirror stars are a generic prediction of dissipative dark matter (DM) models, including minimal atomic DM and twin baryons in the mirror twin Higgs model. Mirror stars can capture regular matter from the interstellar medium through extremely suppressed kinetic mixing interactions between the regular and the dark photon. This accumulated “nugget” will draw heat from the mirror star core and emit highly characteristic X-ray and optical signals. In this work, we devise a general parameterization of mirror star nugget properties that is independent of the unknown details of mirror star stellar physics, and use the Cloudy spectral synthesis code to obtain realistic and comprehensive predictions for the thermal emissions from optically thin mirror star nuggets. We find that mirror star nuggets populate an extremely well-defined and narrow region of the Hertzsprung–Russell diagram that only partially overlaps with the white dwarf population. Our detailed spectral predictions, which we make publicly available, allow us to demonstrate that optically thin nuggets can be clearly distinguished from white dwarf stars by their continuum spectrum shape, and from planetary nebulae and other optically thin standard sources by their highly exotic emission-line ratios. Our work will enable realistic mirror star telescope searches, which may reveal the detailed nature of DM.

Bilayer and trilayer X-ray mirror coatings containing W, Pt, or Ir<?oxy_insert_start author="CKapler" timestamp="20231211T162235-0500"?>,<?oxy_insert_end?> in combination with C, C/Co, B4C, or B4C/Ni: X-ray reflectance, film stress, and temporal stability

X-ray reflectance and film stress were measured for 12 bilayer and trilayer reflective interference coatings and compared with a single-layer Ir coating. The interference coatings comprise a base layer of W, Pt, or Ir, top layers of either C or B4C, and, in the case of the trilayer coatings, middle layers of either Co or Ni. The coatings were deposited by magnetron sputtering. Film stress was measured using the wafer curvature technique, while X-ray reflectance was measured at grazing incidence over the ∼0.1−10keV energy band using synchrotron radiation. Re-measurements over a period of more than two years of both stress and X-ray reflectance were used to assess temporal stability. The X-ray reflectance of all 12 bilayer and trilayer coatings was found to be both stable over time and substantially higher than single-layer Ir over much of the energy range investigated, particularly below ∼4keV, except near the B and C K-edges, and the Co and Ni L-edges, where we observe sharp, narrow drops in reflectance due to photo-absorption in layers containing these materials. Film stress was found to be substantially smaller than single-layer Ir in all cases as well; however, film stress was also found to change over time for all coatings (including the single-layer Ir coating). The effective area of future X-ray telescopes will be substantially higher if these high reflectance bilayer and/or trilayer coatings are used in place of single-layer coatings. Additionally, the smaller film stresses found in the bilayer and trilayer coatings relative to single-layer Ir will reduce coating-stress-driven mirror deformations. Nevertheless, as all the interference films studied here have stresses that are far from zero (albeit smaller than that of single-layer Ir), methods to mitigate such deformations must be developed in order to construct high-angular-resolution telescopes using thin mirror segments. Furthermore, unless film stress can be sufficiently stabilized over time, perhaps through thermal annealing, any such mitigation methods must also account for the temporal instability of film stress that was found in all coatings investigated here.

Enhanced Broadband Light Harvesting in Ultrathin Absorbers Enabled by Epitaxial Stabilization of Silver Thin Film Mirrors.

Silver thin film mirrors are attractive candidates for use as specular back reflectors to enhance broadband light absorption via strong optical interference in ultrathin film semiconductor photoabsorbers. However, deposition of metal-oxide absorbers often requires exposure to high temperature in an oxygen atmosphere, conditions that cause thermal etching and degrade the specular reflectance of silver films. Here, we overcome this challenge and demonstrate that epitaxial growth of silver mitigates thermal etching under the high-temperature oxygen-containing environments that cause polycrystalline films to degrade. The degree of thermal etching resistance is related to the epitaxial film structure, where high-quality films completely prevent thermal etching, allowing for direct deposition of metal-oxide thin film photoabsorbers at elevated temperatures without any degradation of the optical properties of the silver layer. As a proof of concept for device applications, a metal-oxide photoanode for photoelectrochemical water splitting is fabricated by directly growing epitaxial SnO2 and Ti-doped α-Fe2O3 (hematite) thin films onto stabilized silver reflectors by pulsed laser deposition. The photoanode displays enhanced broadband light absorption due to strong interference effects enabled by the highly reflective silver film and demonstrates stable operation in a photoelectrochemical cell under conditions of water photo-oxidation in alkaline electrolyte.

Optimized design and experimental study of a macroscopic mirror to achieve linear amplification of optical force-induced displacement.

A new thin plane mirror with an Archimedes spiral structure (Archimedes-structure thin plane mirror - ATPM) that implements an elastic support boundary is proposed in this study. An optimal structure of ATPM is developed to achieve a linear displacement response with respect to optical forces. The displacement response of the optimized ATPM is analyzed by considering the combined effects of optical force and gravity. The distribution of the optical force density is calculated based on a tilted Gaussian laser beam. Experimental results demonstrate that the optimized ATPM can produce a steady-state displacement of 24.18 nm on average in a normal-gravity environment when subjected to an average optical force of 132.17 nN. When the optical force exceeds 133 nN, the nonlinearity of the displacement response of the optimized ATPM is less than 6.28%. An amplification of the optical force-induced displacement is achieved by more than 15 times compared with that for an unstructured mirror of the same size. The results of this study can assist the development of a miniaturized macroscale optical force platform based on an ATPM for practical applications including the in-situ laser power measurement and nN level force source in the atomic and close-to-atomic scale manufacturing.

Active lateral support system for a thin 1-meter meniscus mirror with virtual fixed points

This publication presents an active lateral support system for the thin 1-m meniscus mirror of a Ritchey-Chrétien telescope system. The goal is to keep the mirror at its position under varying external influences, such as gravity and temperature, therefore maintaining the alignment and optical image quality. To achieve this, the lateral support consists of eight actuators, based on stepper motors with gearboxes, with local force measurement and three laser triangulation sensors to measure the mirror’s lateral position. A cascaded control structure with local force feedback in the inner loop and position feedback in the outer loop is proposed. In the outer loop, three single-input single-output PI-controllers are implemented to maintain mirror position in the three lateral degrees of freedom. The developed system is able to position the mirror with root mean square errors of 0.27 and 0.18 μm in translational directions and 5.1 μrad in the rotational direction over the operational altitude range with a slewing speed of 0.2 deg / s.

A subwavelength atomic array switched by a single Rydberg atom

Enhancing light–matter coupling at the level of single quanta is essential for numerous applications in quantum science. The cooperative optical response of subwavelength atomic arrays has been found to open new pathways for such strong light–matter couplings, while simultaneously offering access to multiple spatial modes of the light field. Efficient single-mode free-space coupling to such arrays has been reported, but spatial control over the modes of outgoing light fields has remained elusive. Here, we demonstrate such spatial control over the optical response of an atomically thin mirror formed by a subwavelength array of atoms in free space using a single controlled ancilla atom excited to a Rydberg state. The switching behaviour is controlled by the admixture of a small Rydberg fraction to the atomic mirror, and consequently strong dipolar Rydberg interactions with the ancilla. Driving Rabi oscillations on the ancilla atom, we demonstrate coherent control of the transmission and reflection of the array. These results represent a step towards the realization of quantum coherent metasurfaces, the demonstration of controlled atom–photon entanglement and deterministic engineering of quantum states of light.

Boron carbide thin film surface characterization after graphitic carbon removal using low-pressure oxygen gas RF plasma.

B 4 C-coated thin film mirrors are used in high brilliance synchrotron and x-ray free electron laser beamlines due to their low absorption coefficient and high thermal stability. As in the case of gold, platinum, and other thin film mirrors, B 4 C-coated mirrors also are affected due to synchrotron radiation-induced carbon contaminations in beamlines. In the present study, a graphitic carbon (C) layer deposited on top of boron carbide (B x C) thin film surface is removed by five successive oxygen radio frequency (RF) plasma exposures (RF power, 10W; O 2 flow, 30sccm; exposure time, 10min each). Before and after the carbon layer removal, structural and compositional properties of the B x C/C bilayer are characterized by soft x-ray reflectivity, x-ray photoelectron spectroscopy, grazing angle x-ray diffraction, and Raman spectroscopy techniques. Characterization results reveal that in the first four exposures the carbon layer thickness decreases continuously without affecting the B x C layer properties; however, in the fifth exposure, the carbon layer is completely removed along with a partial etching of the B x C layer too.

High Frequency MEMS Capacitive Mirror for Space Applications.

Free space optics laser communication using modulating retroreflectors (MR) is a challenging application for an active mirror, due to the high frequencies (>100 kHz) required to enable sufficient data transfer. Micro Electromechanical (MEMS) mirrors are a promising option for high-frequency applications, given the very small moving mass typical of such devices. Capacitive MEMS mirrors are presented here for free space communications, based on a novel fabrication sequence that introduces a single-layer thin film aluminum mirror structure with an underlying silicon oxide sacrificial layer. The use of aluminum instead of gold as a mirror layer diminishes the heating generated by the absorption of the sun's radiation once the mirrors exit the earth's atmosphere. Thanks to the novel fabrication sequence, the presented mirror devices have a full range actuation voltage of less than 40 V, and a high operational frequency with an eigenfrequency above 2 MHz. The devices were manufactured and characterized, and their main parameters were obtained from experimental data combined with finite element analysis, thus enabling future design optimization of the reported MEMS technology. By optical characterization of the far field diffraction pattern, good mirror performance was demonstrated.

Verification of deformation of thin mirror by polishing pressure using additive manufacturing

In this study, magic and deformable mirrors were fabricated using an additive manufacturing (AM) process. This was to confirm the magic mirror effect caused by the grinding pressure of the mirrors produced by the AM-based manufacturing process. For verification, eight magic mirrors were fabricated under different conditions. The results showed that the magic mirror effect occurred on two mirrors with a diameter of 10 mm and wall thicknesses of 0.1 and 0.2 mm. AM is easy to machine thin-wall; therefore, a pneumatically deformable mirror was fabricated. The shape-control performance through air pressure fluctuations was confirmed. In this study, magic mirrors and deformable mirrors have been successfully fabricated using additive manufacturing technology. The method proposed in this study enabled the efficient production of lightweight and thin mirrors.

Verification of deformation of thin mirror by polishing pressure using Additive Manufacturing

Verification of deformation of thin mirror by polishing pressure using Additive Manufacturing

Study of the wind-pressure distribution of flat-roof parabolic condensers based on wind-tunnel tests

Abstract The structure of parabolic condensers makes them susceptible to wind load because of their thin and large windward mirrors. In this paper, the wind pressure on a model of a condenser mirror (1:35) on multistorey flat roofs is analysed via pressure measurement in a wind tunnel. The mean wind-pressure distribution law of flat-roof condenser mirrors (including the change law with working conditions and the maximum distribution characteristics) and the distribution law of fluctuating and extreme wind pressure are obtained. Furthermore, by comparison with the ground-based condenser distribution law, similarities and differences between the two are obtained. Research results show that the wind-pressure distribution law of flat-roof parabolic condenser mirrors is the same as those on the ground, but the mean wind-pressure coefficient (absolute value) is generally ~30% smaller. Furthermore, the maximum effect is generally located at the windward mirror edge and the mirror is more susceptible to wind pressure in wind directions of 30° and 135°–150°. The results of this study can provide a theoretical reference for wind-resistant structure design and multistorey flat-roof condenser-related research.

Analysis of stresses and shape changes in thin substrates with stressed film patterning using femtosecond laser micromachining

The accurate, high-throughput fabrication of light weight optical systems for applications like next-generation space telescopes and semiconductor wafers is both crucial and challenging. A potential solution is to first fabricate thin substrates with traditional methods, then apply surface stress to bend them into desired shapes to correct residual height errors. We have developed a stress-based figure correction method for thin silicon mirrors using a femtosecond laser micromachining technique to generate patterned stress fields, through the removal of selective stressed film regions and adjacent substrate regions. In this paper, we present an in-depth analysis for the laser-induced stresses and resulting shape changes of thin mirrors due to the periodic patterning of a stressed film (silicon oxide) on silicon substrates using femtosecond laser surface ablation. Experimental results are presented, and a 3D finite element model (FEM) is developed to study the substrate curvature in directions parallel and perpendicular to the patterned troughs in the substrates. We simulate the stress relief process in the thin-film/substrate system, and the numerical predictions compare reasonably well with curvature measurements for several different geometrical combinations of depth, width and spacing of the patterned troughs, achieving >82% quantitative agreement with the experiments. It is also shown in the simulations that certain geometries of patterned troughs induce more dramatic shape changes and counter-intuitive reversals of curvature in the direction perpendicular to the troughs, and a qualitative explanation involving the Poisson effect is presented. The 3D finite element methods and findings of this paper can be used to determine the optimal parameters of the stressed film patterns for figure correction of thin telescope mirrors and other types of thin substrates used in the semiconductor industry.

A novel and cost-effective optical detection of high magnitude current and magnetic pulses through a metallic cantilever

We report a novel optical technique to measure short duration high magnitude current and magnetic pulses based on deflection of a macroscopic ferromagnetic cantilever. Deflection of the cantilever as a transducer takes place due to the attraction by an electromagnet. The reflected laser beam from a small thin mirror at tip of the cantilever is scanned over two spatially distinct photodetectors. Different high magnitude magnetic pulses are produced by discharging a capacitor bank through an inductive coil with a ferrite core. The response of the sensor is observed at different charging limits of the capacitor bank and spatial intervals between cantilever and inductive coil. A repeatable and linear response is detected by the devised sensors in the range 158.53–380.47 A current and 0.19–0.48 T magnetic field with sensitivity of 39.15 A kV−1 and 50.98 mT kV−1 for current and magnetic field amplitudes respectively in response to 2.5–6.0 kV charging of the capacitor bank. The proposed technique is remote, nondestructive, cost-effective and has a large dynamic range.

Femtosecond laser micromachining for stress-based figure correction of thin mirrors

The fabrication of a large number of high-resolution thin-shell mirrors for future space telescopes remains challenging, especially for revolutionary mission concepts such as NASA’s Lynx X-ray Surveyor. It is generally harder to fabricate thin mirrors to the exact shape than thicker ones, and the coatings deposited onto mirror surfaces to increase the reflectivity typically have high intrinsic stress that deforms the mirrors further. Since the rapid development of femtosecond laser technologies over the last few decades has triggered wide applications in materials processing, we have developed a mirror figure correction and stress compensation method using a femtosecond laser micromachining technique for stress-based surface shaping of thin-shell x-ray optics. We employ a femtosecond laser to selectively remove regions of a stressed film that is grown onto the back surface of the mirror, to modify the stress states of the mirror. In this paper, we present experimental results to create both isotropic and anisotropic stress states on thin flat silicon mirrors with thermal oxide ( S i O 2 ) films using femtosecond lasers. We show that equibiaxial stress can be generated through uniformly micromachined holes, while non-equibiaxial stress arises from the ablation of equally spaced troughs. We also present results from strength tests to show how this process minimally affects the strength of mirrors. These developments are beneficial to the high-throughput correction of thin-shell mirrors for future space-based x-ray telescopes.

Finite element calculation for surface shape optimization of a polished synchrotron radiation thin mirror based on Bessel-point supporting

The X-ray optical mirror is one of the most important optical elements on the beam-line of a synchrotron radiation facility. The deformation of the working surface of the mirror greatly affects the quality of reflected beam, therefore it needs to be properly controlled. The deformation caused by gravity is one of the important sources of mirror shape error. In order to reduce the gravitational deformation and improve the surface accuracy, the mechanical responses of a Bessel-point supporting thin mirror (100 mm × 20 mm × 5 mm, length × width × height) with a downward working surface down is studied, via finite element analysis (FEA). In particular, to obtain the better surface accuracy, the top surface of the mirror is polished correspondingly to further reduce the deformation caused by gravity. Moreover, by comparing the results under a range of different polishing amounts, the recommended polishing amount is given according to the processing conditions and actual installation conditions. Finally, compared with the deformation results of the Bessel-point supporting theory, the obtained deformation (RMS) after polishing can be reduced by 30.86%, and the slope error (RMS) is reduced by 25.54%.

Motion induced excitation and electromagnetic radiation from an atom facing a thin mirror

We evaluate the probability of (de-)excitation and photon emission from a neutral, moving, non-relativistic atom, coupled to the quantum electromagnetic field and in the presence of a thin, perfectly conducting plane ("mirror"). These results extend, to a more realistic model, the ones we had presented for a scalar model, where the would-be electron was described by a scalar variable, coupled to an (also scalar) vacuum field. The latter was subjected to either Dirichlet or Neumann conditions on a plane. In our evaluation of the spontaneous emission rate produced when the accelerated atom is initially in an excited state, we pay attention to its comparison with the somewhat opposite situation, namely, an atom at rest facing a moving mirror.

Ultrafast laser stress figuring for accurate deformation of thin mirrors.

Fabricating freeform mirrors relies on accurate optical figuring processes capable of arbitrarily modifying low-spatial frequency height without creating higher-spatial frequency errors. We present a scalable process to accurately figure thin mirrors using stress generated by a focused ultrafast laser. We applied ultrafast laser stress figuring (ULSF) to four thin fused silica mirrors to correct them to 10-20 nm RMS over 28 Zernike terms, in 2-3 iterations, without significantly affecting higher-frequency errors. We measured the mirrors over a month and found that dielectric-coated mirrors were stable but stability of aluminum-coated mirrors was inconclusive. The accuracy and throughput for ULSF is on par with existing deterministic figuring processes, yet ULSF doesn't significantly affect mid-spatial frequency errors, can be applied after mirror coating, and can scale to higher throughput using mature laser processing technologies. ULSF offers new potential to rapidly and accurately shape freeform mirrors.

Stability of Al and Ag metallic thin film mirrors in a space environment under the implantation of low energy helium ions

The stability of aluminum (Al) and silver (Ag) metallic thin films (MTFs) under helium ion bombardment has been investigated in the laboratory to replicate the effect of alpha particle bombardment on spacecrafts and satellites in a space environment. The implanted helium ions have varying fluence and energies ranging from 0.5 - 3 keV. The helium ion fluence in the present study has been chosen according to 4 and 6 years journey of a solar orbiter. The reflectivity of Al and Ag MTFs is investigated over a wide range of electromagnetic radiation covering ultraviolet to near infrared (200 - 2500 nm), prior and post helium ion implantation. It is observed that the degradation in the reflectivity of the above-mentioned MTFs is reasonably low for helium ion implantation and no significant impact is observed on reflectivity of both (Al and Ag) MTFs in the investigation. This opens a channel of utilization of these MTFs to provide better protection for the optical components used in spacecrafts. Surface characterization such as surface roughness is carried out to investigate the surface morphology of MTFs prior and post implantation using atomic force microscopy (AFM). It is observed that the effect of implantation on surface morphology is in accordance with the experimental results of reflectivity. SRIM/TRIM simulations help to obtain the distribution profile and penetration depth of helium ions inside the Al and Ag MTFs.

Nonclassical light from finite-range interactions in a two-dimensional quantum mirror

Excitons in a semiconductor monolayer form a collective resonance that can reflect resonant light with extraordinarily high efficiency. Here, we investigate the nonlinear optical properties of such atomistically thin mirrors and show that finite-range interactions between excitons can lead to the generation of highly non-classical light. We describe two scenarios, in which optical nonlinearities arise either from direct photon coupling to excitons in excited Rydberg states or from resonant two-photon excitation of Rydberg excitons with finite-range interactions. The latter case yields conditions of electromagnetically induced transparency and thereby provides an efficient mechanism for single-photon switching between high transmission and reflectance of the monolayer, with a tunable dynamical timescale of the emerging photon-photon interactions. Remarkably, it turns out that the resulting high degree of photon correlations remains virtually unaffected by Rydberg-state decoherence, in excess of non-radiative decoherence observed for ground-state excitons in two-dimensional semiconductors. This robustness to imperfections suggests a promising new approach to quantum photonics at the level of individual photons.