Stationary Mirror Research Articles

Multi-axis modulated compact fiber-based Fabry-Perot interferometric probe.

This paper presents design and operation of a multi-axis optical probe for independently measuring the relative displacements of external surfaces. Displacement is measured by mechanically modulating the optical cavity formed by an internal surface and the external surfaces, each of which comprise a Fabry-Perot interferometer. Multiple sensing axes are created using a beam splitter, and these sensing axes are separated by modulating the measurement paths at different frequencies. Two probes have been fabricated and tested; the first uses a single laser source with axes monitored by shuttering; the second probe uses two source wavelengths with beam splitting achieved using dichroic mirrors. Experimental results are presented for mirrors moving independently over distances of 1 to 2 µm with displacement noise less than 10-nm rms that is higher than the noise floor of 2.8 nm for stationary mirrors. Currently, the bandwidth is limited to the modulation frequencies ranging between 200 Hz and 2.43 kHz.

Violation of equivalence in an accelerating atom-mirror system in the generalized uncertainty principle framework

We study the spontaneous excitation of a two-level atom in the presence of a perfectly reflecting mirror, when the atom, or the mirror, is uniformly accelerating in the framework of the generalised uncertainty principle (GUP). The quantized scalar field obeys a modified dispersion relation leading to a GUP deformed Klein-Gordon equation. The solutions of this equation with suitable boundary conditions are obtained to calculate the spontaneous excitation probability of the atom for the two separate cases. We show that in the case when the mirror is accelerating, the GUP modulates the spatial oscillation of the excitation probability of the atom, thus breaking the symmetry between the excitation of an atom accelerating relative to a stationary mirror, and a stationary atom excited by an accelerating mirror. An explicit violation of the equivalence principle seems to be thus manifested. We further obtain an upper bound on the GUP parameter using standard values of the system parameters.

Small Mirrors Do the Trick: A Simple, but Effective Method to Study Mirror Self-Recognition in Chimpanzees

Mirror self-recognition (MSR) is considered an indicator of self-awareness. Standardized mirror tests reveal compelling evidence for MSR in a few non-human species, including all great apes. However, substantial inter-individual variation of MSR within species resulted in an ongoing methodological controversy, questioning the appropriateness of standard MSR tests for cross-species comparisons. Lack of motivation, in particular, is discussed as one possible cause for false negative results. Here, we compare the spontaneous behavioral response of 47 zoo-housed chimpanzees (Pan troglodytes) to (i) standard body-sized, stationary mirrors and (ii) small, portable hand mirrors. We predicted that the monopolizability and maneuverability of small mirrors increase the chances of identifying MSR across a larger proportion of individuals. Chimpanzees both revealed a substantially higher frequency of general mirror-related behaviors and engaged in significantly more and longer behaviors specifically indicating MSR when provided with small mirrors compared to a large mirror. Handheld mirrors provide a more sensitive measure for MSR within and likely between primate species than the traditional large mirrors, and thereby are a potentially valuable tool for studying self-awareness across species.

Linear aplanatic Fresnel reflector for practical high-performance solar concentration

We propose the linear aplanatic Fresnel reflector (LAFR) as a novel optical design that is suitable for solar thermal power plants. It comprises a segmented primary reflector and a totally stationary secondary mirror and receiver. We show that it is capable of attaining the high intercept factors of conventional parabolic troughs at high concentration, while offering the practical and lower-cost benefits of linear Fresnel reflectors. The fact that dual-mirror Fresnel concentrators can be aplanatic had been overlooked, mainly due to the perception that Fresnel concentrators offer only one degree of design freedom (specifically, the shape of the secondary mirror). The problem is that the two leading orders of geometric aberration must be eliminated to achieve aplanatism, and hence two degrees of design freedom are necessary. After identifying the solar tracking strategy of the segmented primary reflector as the additional degree of design freedom, we derive analytic relations for its placement and curvature. The secondary mirror shape follows directly from the basic aplanatic formalism. We demonstrate that practical high-performance LAFR designs can achieve intercept factors as high as 0.84 at concentration values of ~26.

Shaking photons from the vacuum: acceleration radiation from vibrating atoms

Acceleration radiation—or Unruh radiation—the thermal radiation observed by an ever accelerating observer or detector, although having similarities to Hawking radiation, so far has proved extremely challenging to observe experimentally. One recent suggestion is that, in the presence of a mirror, constant acceleration of an atom in its ground state can excite the atom while at the same time cause it to emit a photon in an Unruh-type process. In this work we show that merely by shaking the atom, in simple harmonic motion for example, can have the same effect. We calculate the transition rate for this in first order perturbation theory and consider harmonic motion of the atom in the presence of a stationary mirror, or within a cavity or just in empty vacuum. For the latter we propose a circuit-QED potential implementation that yields transition rates of ∼10−4 Hz, which may be detectable experimentally.

Development of automated angle-scanning, high-speed surface plasmon resonance imaging and SPRi visualization for the study of dropwise condensation

This paper describes the fabrication and testing of a novel angle-scanning surface plasmon resonance imaging (SPRi) instrument. The combination of two stationary mirrors and two angle-controlled mirrors provides high accuracy (up to 10−3°) and high-speed angular probing. This instrument minimizes the angle-dependent image artifact that arises due to beam walk, which is the biggest challenge for the use of SPRi with angular modulation (AM). In the work described in this paper, two linear stages were employed to minimize the image artifact by adjusting the location of the angle-controlled mirrors and the camera. The SPRi instrument was used to visualize coalescence during dropwise condensation. The results show that the effect of the environment’s temperature on reflectance was less than 1% when the incident angle was carefully chosen for SPRi with intensity modulation (IM). This means that condensation visualization can be carried out at ambient temperatures, without the need for a Peltier stage or a thermally controlled condensing surface. The concept of pixel neighboring was employed to assess the probability of noise and the standard error of thin film measurement. Experimental analyses during dropwise condensation show (1) the presence of a thin film with thickness of one monolayer, and (2) surface coverage of 0.71 m2/m2 by the thin film in the area between the droplets. In addition, analyses showed the existence of a dry area at the part of the substrate exposed by coalescence to ambient air. The results of this work undermine the validity of the film rupture theory as the dropwise condensation mechanism.Graphic abstract

A Possible Advantage of Telescopes with a Noncircular Pupil

Most telescope designs have a circular-shape aperture. We demonstrate that telescopes with an elongated pupil have better contrast, at lower separations, between a bright central star and a faint companion. We simulate images for an elongated-pupil telescope and for a circular-pupil telescope of equal aperture area and integration time, investigating specifically what is the maximal contrast for finding faint companions around bright stars as a function of angular separation. We show that this design gives better contrast at lower separation from a bright star. This is shown for diffraction-limited (for perfect and imperfect optics) and seeing-limited speckle images, assuming equal aperture area and observing time. We also show the results are robust to errors in measurement of the point spread function. To compensate for the wider point spread function of the short axis, images should be taken at different rotation angles, either by rotating the telescope around the optical axis or by allowing a stationary mirror array to scan different parallactic angles with time. Images taken at different rotation angles are added using the proper image coaddition algorithms developed by Zackay & Ofek. The final image has the same contrast in all angles, rather than in specific areas of diffraction nulls. We obtained speckle observations with a small, ground based elongated-aperture telescope and show the results are consistent with simulations.

The equivalence principle at work in radiation from unaccelerated atoms and mirrors

The equivalence principle is a perennial subject of controversy, especially in connection with radiation by a uniformly accelerated classical charge, or a freely falling charge observed by a supported detector. Recently, related issues have been raised in connection with the Unruh radiation associated with accelerated detectors (including two-level atoms and resonant cavities). A third type of system, very easy to analyze because of conformal invariance, is a two-dimensional scalar field interacting with perfectly reflecting boundaries (mirrors). After reviewing the issues for atoms and cavities, we investigate a stationary mirror from the point of view of an accelerated detector in ‘Rindler space’. In keeping with the conclusions of earlier authors about the electromagnetic problem, we find that a radiative effect is indeed observed; from an inertial point of view, the process arises from a collision of the negative vacuum energy of Rindler space with the mirror. There is a qualitative symmetry under interchange of accelerated and inertial subsystems (a vindication of the equivalence principle), but it hinges on the accelerated detector’s being initially in its own ‘Rindler vacuum’. This observation is consistent with the recent work on the Unruh problem.

Crossed Czerny-Turner Spectrometer with Extended Spectrum Using Movable Planar Mirrors.

This study reports a crossed Czerny-Turner spectrometer with multiple mirrors to extend the inspected spectrum. A design example with two movable mirrors and a stationary planar mirror is experimentally demonstrated to offer two additional spectral bands, thereby leading to thrice the spectral range of the original Czerny-Turner spectrometer. The results indicate that the configurations to measure the three bands have almost identical parameters. The moving direction of the planar mirror and the plane of incidence are orthogonal; thus, the influence of mirror movement on the repeatability of the spectrum is minimized. In addition to the merits of cost-effectiveness and rapid inspection, the reported mechanism of mirror movement is applied to general spectrometers to extend the spectral coverage without sacrificing the resolution.

The evolution of field distribution in a dynamic cavity

The results of calculations of the dynamics of a field in a cavity that consists of a stationary mirror and a periodically displacing mirror are presented. The initial distribution of the field corresponds to the equilibrium thermal (Planck) distribution. It is shown that, if conditions of a resonant excitation are implemented, pulses can be formed the degree of unipolarity of which increases from the initial zero degree to an almost maximum (unit) degree.

Ultrafast optomechanical pulse picking

State-of-the-art optical switches for coupling pulses into and/or out of resonators are based on either the electro-optic or the acousto-optic effect in transmissive elements. In high-power applications, the damage threshold and other nonlinear and thermal effects in these elements impede further improvements in pulse energy, duration, and average power. We propose a new optomechanical switching concept which is based solely on reflective elements and is suitable for switching times down to the ten-nanosecond range. To this end, an isolated section of a beam path is moved in a system comprising mirrors rotating at a high angular velocity and stationary imaging mirrors, without affecting the propagation of the beam thereafter. We discuss three variants of the concept and exemplify practical parameters for its application in regenerative amplifiers and stack-and-dump enhancement cavities. We find that optomechanical pulse picking has the potential to achieve switching rates of up to a few tens of kilohertz while supporting pulse energies of up to several joules.

A path to renewable Mg reduction from MgO by a continuous-wave Cr:Nd:YAG ceramic solar laser

The first successful ablation of magnesium oxide through a home-made continuous-wave Cr:Nd:YAG ceramic solar laser is reported. A stationary heliostat-parabolic mirror solar energy collection and concentration system was used. A stable continuous-wave laser output power of 19.2W was attained with laser beam brightness figure of merit 7.6 times higher than that of the previous scheme, enabling therefore the direct ablation of pure magnesium by our solar-pumped laser with only 1.6m2 effective collection area. This could be an important step towards renewable magnesium production, offering multiple advantages, such as reducing agent avoidance, in relation to that of the previous Fresnel lens Cr:Nd:YAG continuous-wave solar laser system.

Stability of warpedAdS3black holes in topologically massive gravity under scalar perturbations

We demonstrate that the warped AdS3 black hole solutions of Topologically Massive Gravity are classically stable against massive scalar field perturbations by analysing the quasinormal and bound state modes of the scalar field. In particular, it is found that although classical superradiance is present it does not give rise to superradiant instabilities. The stability is shown to persist even when the black hole is enclosed by a stationary mirror with Dirichlet boundary conditions. This is a surprising result in view of the similarity between the causal structure of the warped AdS3 black hole and the Kerr spacetime in 3+1 dimensions. This work provides the foundations for the study of quantum field theory in this spacetime.

Side-pumped continuous-wave Cr:Nd:YAG ceramic solar laser

To clarify the advantages of Cr:Nd:YAG ceramics rods in solar-pumped lasers, a fused silica light guide with rectangular cross-section is coupled to a compound V-shaped cavity within which a 7 mm diameter 0.1 at.% Cr:1.0 at.% Nd:YAG ceramic rod is uniformly pumped. The highly concentrated solar radiation at the focal spot of a 2 m diameter stationary parabolic mirror is transformed into a uniform pump radiation by the light guide. Efficient pump light absorption is achieved by pumping uniformly the ceramic rod within the V-shaped cavity. Optimum pumping parameters and solar laser output powers are found through ZEMAX© non-sequential ray-tracing and LASCAD© laser cavity analysis codes. 33.6 W continuous-wave laser power is measured, corresponding to 1.32 times enhancement over our previous results with a 4 mm diameter Nd:YAG single-crystal rod. High slope efficiency of 2.6 % is also registered. The solar laser output performances of both the ceramic and the single-crystal rods are finally compared, revealing the relative advantage of the Cr:Nd:YAG rod in conversion efficiency. Low scattering coefficient of 0.0018 cm−1 is deduced for the ceramic rod. Heat load is considered as a key factor affecting the ceramic laser output performance.

Concentrating sunlight with an immobile primary mirror and immobile receiver: Ray-tracing results

Abstract Using a combination of custom computer code and commercially available ray-tracing software, we explore variations of concentrator geometries where sunlight is first incident onto a stationary primary mirror of circular cross section. The reflected radiation is incident onto a smaller, secondary moveable mirror, which focuses the radiation onto a stationary target. Simulations for this trough geometry show peak concentrations of 38 solar equivalents.

Constructing Generalized Synchronization Manifolds by Manifold Equation

Full understanding of synchronous behavior in coupled dynamical systems beyond the identical case requires an explicit construction of the generalized synchronization manifold, whether we wish to compare the systems, or to understand their stability. Nonetheless, while synchronization has become an extremely popular topic, the bulk of the research in this area has been focused on the identical case, specifically because its invariant manifold is simply the identity function, and there have yet to be any generally workable methods to compute the generalized synchronization manifolds for non-identical systems. Here, we derive time dependent PDEs whose stationary solution mirrors exactly the generalized synchronization manifold, respecting its stability. We introduce a novel method for dealing with subtle issues with boundary conditions in the numerical scheme to solve the PDE, and we develop first order expansions close to the identical case. We give several examples of increasing sophistication, including coupled non-identical Van der Pol oscillators. By using the manifold equation, we also discuss the design of coupling to achieve desired synchronization.

Optical coherence tomography holds promise for conserving art

Noninvasive examinations of human patients and art objects share more than the important modus operandi of ‘do no harm.’ Soon after medical x-rays were discovered, they were applied to inspect the underlying layers of paintings. More recently, that extended to the newer modality of x-ray tomography. Now, optical coherence tomography (OCT), which acquires and processes optical signals to produce high-quality 3D images, has entered the picture. Medical OCT was first described in 1991,1 and reports of its use to examine artwork2–4 emerged in 2004. OCT uses low-coherence interferometry, a tool to study lightwave properties, to determine the distance to the scattering center in an object that moderately absorbs light. The light source’s spectral width determines the localization precision: IR broadband light sources spanning 200nm allow for better than 2μm axial resolution. While this is still less than in phase interferometry, the result is free of the phase-ambiguity disadvantages that limit the height difference between two adjacent data points. The most popular interferometer configuration is Michelson’s type (see Figure 1), in which scattering-center positions are recovered from interference-fringe frequencies superimposed on the light sources’ spectra. In our conservation experiment, we used a home-grown instrument5 with 4μm axial resolution at a central wavelength of λ = 850nm, shown in Figure 1. The results were obtained with two CCD linear cameras: an Action Research 2048-pixel, 12-bit resolution model and a Dalsa Corp. 1024-pixel, 8-bit resolution, high-transfer camera. The former is used when high sensitivity and imaging depth are required, and the latter for fast, real-time imaging (two frames of 400 lines per second) for monitoring conservation treatments. An interesting example of a process requiring online monitoring is laser ablation to remove varnish.6 If varnish is dull or Figure 1. Experimental laser/interferometer artwork-conservation treatment setup. The optical isolator (OI) is inserted between the light source (LS) and the fiber coupler (FC) to protect the former from reflected light. Light passes through the coupler and then propagates in the interferometer’s reference and object arms. In the reference arm (top right), it passes through the polarization controller (PC), a neutraldensity filter (NDF), the dispersion compensator (DC), and is then back-reflected by the stationary reference mirror (RM). In the object arm, comprised of transversal scanners (X-Y) and a lens, the light beam is scanned across the object and then backscatters. The returning light from both arms is collected and then analyzed using a spectrometer consisting of the spectrograph lens (SL), diffraction grating (DG), CCD linear camera, and a personal computer (COMP).

Precise 3D Positioning of a Robotic Arm Using a Single Camera and a Flat Mirror

A novel visual servoing structure is presented for robot positioning under an eye-to-hand camera configuration using panoramic vision. The proposed algorithm is based upon Image-Based Visual Servoing (IBVS) and uses only one fixed camera in conjunction with a stationary flat mirror. A single landmark mounted on the robot's end-effector along with its mirror reflection provide enough information for 3D reasoning based on a 2D image when viewed by a camera. The equations describing the relationship between the velocity of the coordinate frame attached to the robot's end-effector and rate of change in image features called the image Jacobian are presented. A novel set of image features that yields a rank-efficient image Jacobian is introduced. The Visual servoing based on an online estimation of the image Jacobian using a Kalman Filter (KF) is also presented. Simulated and experimental results illustrate the robustness of the proposed visual servoing structure. Sensitivity tests and analysis conducted through numerous experimentations show promising results.

An Eye-To-Hand Panoramic Vision System for 3D Positioning of a Robotic Arm

A novel visual servoing structure is presented for robot positioning under an eye-to-hand camera configuration using panoramic vision. The proposed algorithm is based upon Image-Based Visual Servoing (IBVS) and uses only one fixed camera in conjunction with a stationary flat mirror. A single landmark mounted on the robot's end-effector along with its mirror reflection provide enough information for 3D reasoning based on a 2D image when viewed by a camera. The equations describing the relationship between the velocity of the coordinate frame attached to the robot's end-effector and rate of change in image features called the image Jacobian are presented. A novel set of image features that yield a full-rank image Jacobian is introduced. The Visual servoing based on an online estimation of the image Jacobian using a Kalman Filter (KF) is also presented. Simulated and experimental results illustrate the robustness of the proposed visual servoing structure. In addition, the accuracy of the proposed visual servoing structure is evaluated with an error analysis and sensitivity tests.

Transfer functions of fabry-perot interferometers with a time-variable base: Part II. Stationary mirror mode. “Superslow” mirror oscillation mode

A multibeam interferometer with oscillating mirrors is theoretically investigated. Transfer functions are presented and analyzed for two extreme cases, namely, for an interferometer with stationary mirrors and an interferometer operating in the mode of “superslow” mirror oscillations.