Flat Mirror Research Articles

Full-parallax spherical light field display using mirror array

We propose a new optical system of glasses-free spherical 3D display and validity of the system is confirmed in this paper. The proposal display is light field display; a capable method to show 3D images to multiple viewers at once and perform complicated optical effect like occlusion effect. The proposal system is also capable to perform motion parallax effect in multiple directions (full-parallax). The proposal system is based on time-division multiplexing. The optical system consists of a rotating specially designed sphere-shaped flat mirror array and a high-speed projector. The rotating mirror array reflects rays from the projector to various angles. By controlling the intensity of the rays with the projector properly, a 3D image can be seen in the mirror array. From the results of the optical computer simulations using ray tracing method, expected 3D image was observed and we confirmed availability of the system as the 3D display. A prototype was developed using 3D printing and feasibility of the system was also confirmed. Additionally, color display of the same method was developed using 3 high-speed projectors.

Development of Millimeter Wave Fabry-Pérot Resonator for Simultaneous Electron-Spin and Nuclear Magnetic Resonance Measurement

We report a Fabry-Perot resonator with spherical and flat mirrors to allow simultaneous electron-spin resonance (ESR) and nuclear magnetic resonance (NMR) measurements that could be used for double magnetic resonance (DoMR). In order to perform simultaneous ESR and NMR measurements, the flat mirror must reflect millimeter wavelength electromagnetic waves and the resonator must have a high Q value (Q > 3000) for ESR frequencies, while the mirror must simultaneously let NMR frequencies pass through. This requirement can be achieved by exploiting the difference of skin depth for the two frequencies, since skin depth is inversely proportional to the square root of the frequency. In consideration of the skin depth, the optimum conditions for conducting ESR and NMR using a gold thin film are explored by examining the relation between the Q value and the film thickness. A flat mirror with a gold thin film was fabricated by sputtering gold on an epoxy plate. We also installed a Helmholtz radio frequency coil for NMR and tested the system both at room and low temperatures with an optimally thick gold film. As a result, signals were obtained at 0.18 K for ESR and at 1.3 K for NMR. A flat-mirrored resonator with a thin gold film surface is an effective way to locate NMR coils closer to the sample being examined with DoMR.

Measurement of surface position by focusing an interference pattern of multiple apertures with a confocal system.

We propose a method to measure the position of a flat mirror based on the identification of the best focused interferogram on the mirror. The interferogram is generated using a wavefront-splitting interferometer in a confocal configuration. The wavefront is sampled with an array of identical circular apertures. We analyze experimentally and theoretically the diffraction pattern for one, two, and three apertures when they are focused on the mirror. For the theoretical analysis we solve numerically the Rayleigh-Sommerfeld integral, and for the experimental analysis we measure the axial irradiance and the square power of the interferogram as a function of the axial displacement of the mirror. The maximum of these measurements corresponds to the best focused interferogram. The experimental and theoretical results are in good agreement. We found that the uncertainty associated with the axial position of the mirror is reduced significantly (about 161 times) when we use the interferogram generated by three apertures in comparison with the diffraction pattern for one aperture.

Enhancing the performance of a linear Fresnel reflector using nanofluids and internal finned absorber

The objective of this paper is to investigate thermal efficiency enhancement methods in a linear Fresnel reflector (LFR) with evacuated tube receiver. The primary reflectors of the collector are flat mirrors of 27 m2 total net aperture, while the secondary reflector has a parabolic shape. The working fluid is Syltherm 800, and the analysis is performed for temperatures up to 650 K. The use of nanofluids and internal fins is the investigated thermal enhancement methods in the receiver of the LFR. The examined nanofluid is Syltherm/CuO for concentrations 2, 4 and 6%, while the examined internal fins are 8 longitudinal fins which are symmetrically located in the absorber. The LFR is examined using nanofluids and pure thermal oil in smooth or finned absorber. According to the final results, the maximum thermal efficiency enhancement is up to 1% and it is greater for higher operating temperature levels. The use of internal fins is better enhancement method compared to the use of nanofluids, while the combination of these two techniques leads to the highest possible performance. For the inlet temperature of 600 K with 200 L min−1 flow rate, the thermal efficiency enhancement with 4% nanofluid and finned absorber is found 0.82%, while it is found 0.61 and 0.28% with finned absorber with pure oil and 4% nanofluid with smooth absorber, respectively.

A novel Lap-MRF method for large aperture mirrors

A novel magnetorheological finishing (MRF) method, which is named Lap-MRF, is proposed in this paper. The magnetorheological fluid (MR fluid) in the polishing zones can be renewed continuously so that the determinacy is ensured. A lap, instead of a large polishing wheel, is used to expand the polishing area, which improves the material removal rate largely. Lap-MRF uses flexible MR fluid as polishing pad to match the surface well. Moreover, the polishing pad executes planetary motion so as to obtain smooth surface. In this paper, the principle of Lap-MRF and the theoretical model of material removal rate are presented. Using the finite element analysis method, the permanent magnet unit is simulated and a multi-parameter optimization is conducted to improve the performance of Lap-MRF. Finally, a series of polishing experiments and simulation process are carried out. For K9 sample, the volume removal rate is up to 0.76 mm3/min and its relative change rate is less than 5.5%. For silicon modification layer sample, the surface roughness is improved to 0.788 nm RMS (root mean square) from 1.610 nm RMS. There is no deep pit and the polishing ripple is not apparent on the surface. For Φ1000 mm flat mirror, the convergence efficiency of simulation process is up to 97.2%. These results verify the validity of the proposed method, which makes Lap-MRF to be a promising finishing technology for large aperture mirrors.

Optical and thermal analysis of a linear Fresnel reflector operating with thermal oil, molten salt and liquid sodium

Linear Fresnel collectors are promising technologies for the exploitation of solar irradiation in medium and high temperatures. In this study, a linear Fresnel collector with flat primary mirrors and a parabolic shape secondary reflector is investigated. The location of the secondary reflector is simply optimized and then the collector is investigated under different incident angles (transversal and longitudinal). The next step is the thermal analysis of the collector with three different working fluids: thermal oil, molten salt and liquid sodium. The analysis is performed for temperatures up to 900 K with liquid sodium in order to examine the collector up to its stagnation temperature. Both the optical and thermal analysis are conducted with SolidWorks Flow Simulation. According to the final results, the exergy performance of the collector is maximized at 700 K and it is 30.20% with liquid sodium and 30.05% with molten salt. Generally, liquid sodium was found to be the best candidate according to performance criteria, with molten salt and thermal oil to follow. The high heat transfer coefficient is the reason for the superior performance of the liquid sodium. Moreover, the pumping work is maximized for operation with molten salt.

Metasurface Approach to External Cloak and Designer Cavities

A metasurface, with only a single layer of artificial atoms for ease of fabrication, can become a practical surface-equivalent route to transformation optical (TO) applications. The previous design paradigm for a metasurface carpet cloak is based on straightforward phase compensation, hampering more general wave manipulations. Here, we propose a theoretical approach in designing a metasurface using the concept of complementary media as an intermediate step. The metasurface, effectively storing all the original information in TO media, enables specific TO applications that normally require complementary media. A passive external metasurface cloak is numerically demonstrated here, which can hide an object on top of a reflective metasurface, mimicking a flat mirror. Furthermore, our scheme enables metasurfaces to be used to construct arbitrary standing waves on-demand, which will be useful for constructing tailor-made cavity modes, optical trapping, and illusion-type TO applications, which can project hologr...

Optimization of Fabry-Perot ring resonator embedding a grating based mirror

We study a triangular arrangement of two flat mirrors and a grating mirror for coupling a \(-1{\mathrm{st}}\) diffracted order light beam into a traveling-wave intra-cavity light recirculation and out-of-cavity output, combining the \(0\,{\mathrm{th}}\) and the repeatedly diffracted secondary \(+1{\mathrm{st}}\) order beams. The thus designed and then optimized grating Fabry-Perot ring cavity demonstrates high output contrast and detection resolution for wavelength, cavity length and incidence angle.

Tunable colloidal quantum dot distributed feedback lasers integrated on a continuously chirped surface grating.

We report a colloidal quantum dot (CQD) distributed feedback (DFB) laser structure containing a chirped grating. The device exhibits single-mode DFB lasing, of which the wavelength is spatially dispersed in a single chip. A period-chirped surface grating is fabricated using a modified Lloyd-type laser interference lithography setup, where a flat Lloyd's mirror is replaced with a concave one. A dense red-emitting CdSe/CdS/ZnS CQD film is prepared on a temporary substrate by spin-coating, which is subsequently released and wet-transferred onto a period-chirped quartz surface grating. Upon optical excitation, the fabricated DFB laser device lases in a single mode at a laser threshold of ∼400 μJ cm-2, with its lasing wavelength shifted linearly (in proportion to the grating pitch) along the chirp direction from 613.4 nm to 623.2 nm over a distance of ∼5.6 mm.

Development and testing of glass substrate Wolter-1 X-ray focusing mirror

The wolter-1 X-ray focusing mirror can reflect grazing incidence X-ray to the focal plane, which plays an important role in the astronomical detection and other fields due to its good image detecting capability. A geometric model of the optical system is established for theoretically deriving the optical path equations which is useful in this glass based focusing mirror designing, all the design parameters of the focusing mirror can be obtained by solving these equations. In the manufacturing process, the D263T glass is chosen to be the structural material of the focusing mirror due to its light weight and super smooth surface, after a slumping process, the flat glass mirror will have the shape of Wolter-1 X-ray focusing mirror. This slumping process has been used successfully in the manufacturing process of an American mission named The Nuclear Spectroscopic Telescope Array, which was launched in 2012. According to X-ray reflecting theory, the reflectivity of the Wolter-1 mirror can be improved significantly by coating metal film on the surface of the mirror. In this work, an iridium film is coated on the surface of the glass mirror through a vacuum evaporating process. In order to learn the influence of the focal spot caused by the mirror shape tolerance, the morphology of the mirror is tested by using a 3-D laser scan instrument. The results show that 50% of the total test points are located in the tolerance range of-10-10 m, in which the tolerance represents the difference between the actual lens profile and the ideal lens profile. Then the focal spot test is carried out with the help of a visible light test system:a laser collimator is installed in front of focusing mirror as an incidence light source, and a charge coupled device (CCD) is placed in the focal plane to gather the image of the focal spot, by calculating the gray level distribution of the focal spot image taken by the CCD, the energy distribution characteristic of focal spot can be obtained. The experimental results show that the focal length of the focusing mirror is 1.6 m, and the half-power surrounding diameter of the focal spot is 0.33 mm, corresponding to the angular resolution of 0.7 arc min.

大口径平面镜局部采样瑞奇-康芒检验

大口径平面镜局部采样瑞奇-康芒检验

Stabilization of Astronomic Images Using a Controlled Flat Mirror

A prototype of a key element of adaptive-optics systems — a controlled flat mirror used to correct light beam tilts — was designed. An algorithm for correcting atmospheric distortions of low-intensity light waves and real-time software were developed. In laboratory experiments, a value of 100 Hz was achieved for the bandwidth of a closed-loop system. The efficiency of the developed software was confirmed by daytime observations of stars.

Optical design of compact linear fresnel reflector systems

Compact linear Fresnel reflector (CLFR) system employing multiple receivers is promising with better optical performance and cost effectiveness compared to linear Fresnel reflector (LFR) system, especially for applications with limited ground availabilities. Nevertheless, only few researches have been conducted to evaluate optical design and performance of the CLFR system. In this study, geometrical models for the CLFR system with flat mirrors and receivers are developed on the basis of polar orientation. A comparative study of concentration characteristics among the LFR, CLFR-complete and CLFR-hybrid systems is conducted based on numerical, ray tracing simulation and experimental results. In addition, optical design analyses of the CLFR-hybrid system are carried out from various design aspects. It is noteworthy that the mirror arrangement and focal length should be optimized for the CLFR-hybrid system with considerations of the associated geometrical characteristic and optical performance. For a small-scale CLFR-hybrid system with a solar field width of 2100mm and a focal length of 1500mm, the geometrical concentration ratio of 15.14 and ground utilization ratio of 0.95 are achieved respectively. The findings demonstrate the feasibility of the CLFR-hybrid system with flat mirrors and polar orientation, which provide progress to the concentrated solar power technology.

Modeling scattering effects from time-varying sea surface based on acoustic reciprocity

In marine seismic processing, the sea surface is often considered a flat mirror; hence, the effects of different weather conditions during the acquisition are largely ignored. However, studies have shown that rough sea-surface ghosts can severely damage the 4D signal, if not handled properly in data processing. To account for realistic sea-surface effects in processing, the impact of time-varying rough sea surfaces needs to be studied. We derive a method for modeling source and receiver ghosts from the time-varying rough sea surface and their interaction with subsurface reflections. This method is based on acoustic reciprocity and leads to integral equations of nonstationary wavefields. These modeling equations can also serve as a basis for investigating source and receiver deghosting methods for time-varying rough sea surfaces. Our developed modeling algorithm is validated against a frequency-domain approach for a “frozen” rough sea surface. For a moving simple sea surface, the Doppler shift produced by our method is in very good agreement with the analytical solution. Using a Pierson-Moskowitz spectrum, we derive a time-varying rough sea surface and model the receiver ghost, the source ghost, and the source-receiver ghost for the subsurface primary reflections of a heterogeneous geologic model. The results highlight that the source and receiver ghost interactions with a time-varying sea surface differently affect the subsurface reflections, and these effects can significantly impact the seismic repeatability of 4D studies.

TERAHERTZ KLYNOTRON WITH AN AZIMUTHAL COMB

According to theoretical and experimental research of orotrons, which are diffraction radiation oscillators with spatially developed electromagnetic systems, usually being excited by non-relativistic spatially developed electron beams, this class of devices can be successfully used in the practical applications for THz frequency range. One of the major problems to be solved when the efficiency of such sources increases with the shortening of their operation wavelength is how to ensure a high utilization factor of all partial layers of a highly perveance spatially developed electron beam in the electron-wave interaction zone. This can be achieved by increasing the microwave field strength in the energy exchange zone between electrons and electromagnetic waves. The klynotronic effect has been proven to be an efficient way of increasing the utilization factor of all partial cross-sectional layers of a spatially developed electron beam. In this study, we will discuss the mathematically simulated energy characteristics of electron-wave interaction in a radial electron flow orotron with an underlying azimuthal comb serving as a diffraction grating mounted on the useful surface of a flat mirror in a two-mirror open cavity. The results of mathematical simulation and optimization of the energy characteristics of electron-wave interaction in the klynoorotron of the terahertz range made us believe that, due to the klynotronic effect, the electronic efficiency can be increased up to 20% in oscillators of this design.

Optimization of V-Trough photovoltaic concentrators through genetic algorithms with heuristics based on Weibull distributions

Photovoltaic V-Troughs use simple and low-cost non-imaging optics, namely flat mirrors, to increase the solar harvesting area by concentrating the sunlight towards regular solar cells. The geometrical dispositions of the V-Trough’s elements, and the way in which they are dynamically adjusted to track the sun, condition the optical performance. In order to improve their harvesting capacity, their geometrical set-up can be tailored to specific conditions and performance priorities. Given the large number of possible configurations and the interdependence of the multiple parameters involved, this work studies genetic algorithms as a heuristic approach for navigating the space of possible solutions. Among the algorithms studied, a new genetic algorithm named “GA-WA” (Genetic Algorithm-Weibull Arias) is proposed. GA-WA uses new heuristic processes based on Weibull distributions. Several V-Trough performance indicators are proposed as objective functions that can be optimized with genetic algorithms: (i) Ce‾ (average effective concentration); (ii) Cost (cost of materials) and (iii) Tsp (space required). Moreover, from the integration of these indicators, three multi-objective indices are proposed: (a) ICOE (Ce‾ versus Cost); (b) MICOE (Ce‾ versus Cost and Ce‾ versus Tsp combined) and (c) MDICOE (similar to MICOE but with discretization considerations). The heuristic parameters of the studied genetic algorithms are optimized and their capacities are explored in a case study. The results are compared against reported V-Trough set-ups designed with the interactive software VTDesign for the same case study. It was found that genetic algorithms, such as the ones developed in this work, are effective in the performance indicators improvement, as well as efficient and flexible tools in the problem of defining the set-up of solar V-Troughs in personalized scenarios. The intuition and the more holistic exploration of a trained engineer with an interactive software can be complemented with the broader and less biased evolutionary optimization of a tool like GA-WA.

Note: Simple 100 Hz N2 laser with longitudinal discharge tube and high-voltage power supply using neon sign transformer.

We developed a longitudinally excited N2 laser with a simple driver circuit and a simple power supply. The N2 laser consisted of a 20 cm-long glass tube with an inner diameter of 2.5 mm, a normal stable resonator formed by flat mirrors, a variable transformer, a neon sign transformer, a spark gap, and a 200 pF capacitance. The N2 laser produced a laser pulse with an energy of 379 nJ and a pulse width of 7.5 ns at a repetition rate of 100 Hz. The laser beam was circular and had a Gaussian profile with a correlation factor of 0.992 93.

Substantiation of the effectiveness of using a flat mirror concentrator in the solar dryer

We propose a procedure for calculating geometrical parameters of a flat mirror concentrator of solar energy. The procedure describes construction of the path of rays between the mirror and the collector in the form of a system of degree coordinates α . We obtained analytical dependences for the course of illumination of air collector by the sum of direct and reflected flows Е β ( τ ) and a flow gain coefficient k. This makes it possible to estimate efficiency of a flat mirror concentrator for different azimuthal angles of orientation of parameters of the horizontal receiving surface of air collector S and the system of degree coordinates α . The rational values for a dihedral angle (focline) α between the mirror and the collector are established, which are 90...120 o. It was found that a gain coefficient of the flow of solar energy k is implemented with the least expenditures from 1.8 to 1.2. We report results of experimental research into energy characteristics of work of the mirror concentrator in a combination with an air collector. It was established the application of a mirror concentrator in the solar dryer makes it possible, in the morning and in the evening, to improve annual average capacity of incoming solar radiation on the receiving surface of air collector by an order of 3.41 kW/m 2 during daylight. This enables receiving, amplifying, and directing to the absorber of AC from 1.5 to 2.3 kW·h of energy per day from 1 m 2 of FMC. The results obtained could be used for design and improvement of technical means of drying, in order to enhance technological and energy efficiency of the process.

Mode matching of a laser-beam to a compact high finesse bow-tie optical cavity for quartz enhanced photoacoustic gas sensing

We report on the optical characterization of a compact bow-tie cavity composed of two flat mirrors and two concave mirrors, all having a reflectance >99.99% in the spectral range between 4.8μm and 5.3μm, mounted in a stainless-steel enclosure. The cavity was designed for the implementation of an intracavity-quartz enhanced photoacoustic sensor system. The propagation parameters of the intra-cavity beam were determined using the ABCD-matrix method, allowing the analytical formulation of the size of two beam waists occurring inside the cavity. A collimated mid-infrared laser beam was optically coupled and mode matched into the bow-tie cavity via a focusing lens. A cavity finesse of∼2000 was measured at a pressure of 90Torr inside the cavity, corresponding to an optical power enhancement factor of∼320.

A surface shape test method for a thin flat mirror

An optical test method of the surface shape for very thin flat mirrors is presented and discussed. The effect of gravity on the mirror shape is greatly reduced by floating the mirror on water while the surface is measured using a Zygo interferometer. The floating mirror is supported by the buoyant force and surface tension. Mechanical analysis and error analysis show that the tested flat mirror can be considered as a rim supported mirror with a reduced gravity. The surface error caused by the rim constraint can be rather small because of the reduced effective gravity. The surface error of a flat mirror which is Ф102mm, 0.6mm thick was tested using this method. The results were compared to the method successfully used for the Hinode project. The Hinode method supports the mirror at three points and measures the surface for both the mirror facing up and facing down. The average of the face up and face down measurements yields the zero gravity shape. The test results including the surface error and the fringe of the surface shape by these two methods were in good agreement. Compared to the Hinode method, the method can be carried on before the mirror’s coating and can to be employed during the polishing process.