Diameter Fresnel Lens Research Articles

Mini-EUSO on Board the International Space Station: Mission Status and Results

The telescope Mini-EUSO has been observing, since 2019, the Earth in the ultraviolet band (290–430 nm) through a nadir-facing UV-transparent window in the Russian Zvezda module of the International Space Station. The instrument has a square field of view of 44°, a spatial resolution on the Earth surface of 6.3 km and a temporal sampling rate of 2.5 microseconds. The optics is composed of two 25 cm diameter Fresnel lenses and a focal surface consisting of 36 multi-anode photomultiplier tubes, 64 pixels each, for a total of 2304 channels. In addition to the main camera, Mini-EUSO also contains two cameras in the near infrared and visible ranges, a series of silicon photomultiplier sensors and UV sensors to manage night-day transitions. Its triggering and on-board processing allow the telescope to detect UV emissions of cosmic, atmospheric and terrestrial origin on different time scales, from a few microseconds up to tens of milliseconds. This makes it possible to investigate a wide variety of events: the study of atmospheric phenomena (lightning, transient luminous events (TLEs) such as ELVES and sprites), meteors and meteoroids; the search for nuclearites and strange quark matter; and the observation of artificial satellites and space debris. Mini-EUSO is also potentially capable of observing extensive air showers generated by ultra-high-energy cosmic rays with an energy above 1021 eV and can detect artificial flashing events and showers generated with lasers from the ground. The instrument was integrated and qualified in 2019 in Rome, with additional tests in Moscow and final, pre-launch tests in Baikonur. Operations involve periodic installation in the Zvezda module of the station with observations during the crew night time, with periodic downlink of data samples, and the full dataset being sent to the ground via pouches containing the data disks. In this work, the mission status and the main scientific results obtained so far are presented, in light of future observations with similar instruments.

Solar Pumped Lasers: High-Efficiency Multi-Pass Side Pumping Scheme with Fresnel Lens

A multi-pass side-pumping scheme for solar pumped Nd:YAG laser on 1 m diameter Fresnel lens is numerically analyzed. Using of the Monte Carlo photon-tracing numerical method, three different pumping schemes were studied. The results showed that a large efficiency improvement in a multi-pass side-pumping scheme compared to the double-pass side-pumping scheme. The study demonstrated that the multi-pass side-pumping scheme can double the overall efficiency of solar double-pass side-pumped Nd:YAG laser.

A compact and light-weight refractive telescope for the observation of extensive air showers

A general purpose instrument for imaging of Cherenkov light or fluorescence light emitted by extensive air showers is presented. Its refractive optics allows for a compact and light-weight design with a wide field-of-view of 12°. The optical system features a 0.5 m diameter Fresnel lens and a camera with 61 pixels composed of Winston cones and large-sized 6x6 mm2 photo sensors. As photo sensors, semi conductor light sensors (SiPMs) are utilized. The camera provides a high photon detection efficiency together with robust operation. The enclosed optics permit operation in regions of harsh environmental conditions. The low price of the telescope allows the production of a large number of telescopes and the application of the instrument in various projects, such as FAMOUS for the Pierre Auger Observatory, HAWC's Eye for HAWC or IceAct for IceCube. In this paper the novel design of this telescope and first measurements are presented.

High-efficiency solar laser pumping by a modified ring-array concentrator

To considerably improve solar laser efficiency, a 5.5 mm diameter 20 mm length Nd:YAG single-crystal rod can be efficiently pumped by highly concentrated solar radiation through a modified ring-array concentrator. Composed of several coaxial parabolic reflective rings and a small diameter Fresnel lens, the 1.5 m diameter modified ring-array concentrator can focus tightly incoming solar radiation into a 5.0 mm full width at half maximum focal spot. An innovative aspherical fused silica concentrator allows further pump light concentration into the Nd:YAG rod at the focal zone. A simple water cooling scheme within the aspherical concentrator constitutes another highlight of this scheme. Strong dependency of solar laser power on the rim angle of the ring-array concentrator was found through ZEMAX™ and LASCAD© analyses. 67.8 W continuous-wave 1064 nm solar laser power at 38.4 W/m2 collection efficiency was numerically calculated, being 1.22 times more than the previous record. Besides, 1.29, 1.03 and 1.85 times improvements in conversion, slope efficiencies and brightness figure of merit, respectively, were numerically achieved. The tracking error influence on solar laser output power was numerically calculated.

Design and Development of a Fiber-Optic Hybrid Day-Lighting System

The primary objective of this study was to develop a fiber-optic hybrid day-lighting system for mobile application such as military shelters in order to cut energy use and the use of fossil fuels. The scope included the design, development, and testing of a hybrid lighting system that is capable of producing about 16,000 lm output with design challenges including light-weight, compactness, and optics that can tolerate a high tracking misalignment. The designed system is comprised of two subsystems: the solar collector and the solar hybrid lighting fixture (SHLF). The solar collector, consists of a housing, a structural stand (tripod), a dual axis tracking system, Fresnel lenses, secondary optics, and fiber-optic cables. The collector is a telescoping aluminum box that holds eight 10-in diameter Fresnel lenses, which focus sunlight onto eight secondary optics and deliver uniform light to the fiber-optic cables. The secondary optics have filters to block UV/IR. The optics has been designed to have a high half-acceptance angle of 1.75 deg and can accommodate a tracking accuracy of 1.50 deg or better. This novel SHLF consists of two components: a solar fiber-optic system and a light emitting diode (LED) system. The fiber-optic cable is coupled to an acrylic light diffusing rod that delivers the sunlight into the room. During sunny periods, the solar fiber-optic lighting could provide full illumination level. In order to keep the same level of lighting during cloudy periods, the LED portion of the light fixture can supplement the output of the SHLF. A compact, light-weight prototype system was built and tested. The results showed that the system's output per lens for the 20 ft cable was about 1750±50 lm at a global solar illuminance of 115,000 lx. The total system was capable of delivering 14,000 lm of sunlight.

High Dynamic Range (Δn) Two-Stage Photopolymers via Enhanced Solubility of a High Refractive Index Acrylate Writing Monomer.

Holographic photopolymers capable of high refractive index modulation (Δn) on the order of 10-2 are integral for the fabrication of functional holographic optical elements that are useful in a myriad of optical applications. In particular, to address the deficiency of suitable high refractive index writing monomers for use in two-stage holographic formulations, here we report a novel high refractive index writing monomer, 1,3-bis(phenylthio)-2-propyl acrylate (BPTPA), simultaneously possessing enhanced solubility in a low refractive index (n = 1.47) urethane matrix. When examined in comparison to a widely used high refractive index monomer, 2,4,6-tribromophenyl acrylate, BPTPA exhibited superior solubility in a stage 1 urethane matrix of approximately 50% with a 20% higher refractive index increase per unit amount of the writing monomer for stage 2 polymerizations. Formulations with 60 wt % loading of BPTPA exhibit a peak-to-mean holographic Δn ≈ 0.029 without obvious deficiencies in transparency, color, or scatter. To the best of our knowledge, this value is the highest reported in the peer-reviewed literature for a transmission hologram. The capabilities and versatility of BPTPA-based formulations are demonstrated at varying length scales via demonstrative refractive index gradient structure examples including direct laser write, projection mask lithography of a 1″ diameter Fresnel lens, and ∼100% diffraction efficiency volume transmission holograms with a 1 μm fringe spacing in 11 μm thick samples.

Design and development of a faceted secondary concentrator for a fiber-optic hybrid solar lighting system

Fiber-optic solar hybrid lighting for mobile application such as military shelters in remote areas is appealing since high initial costs of such systems appear to be justified. This paper addresses the aspect of two-stage optics for a fiber-optic solar lighting system for the mobile application. More specifically, the focus of this paper is on the design and development of a second stage or secondary concentrator. Two-stage optics offers a distinct advantage of higher sun angle tolerance and hence a low-accuracy tracker can be used for the mobile application. The objective of this study was to design and develop a secondary concentrator that yielded a minimized peak illuminance on the fiber-optic inlet and achieved uniformity, to avoid localized heat damage to the fiber inlet. In addition, the overall goal was to increase the lumen output from the two-stage optics. Specifications for the design of the two-stage concentrator were: (1) the primary stage concentrator was a 10-in. diameter Fresnel lens; (2) solar tolerance angle or the half-angle of acceptance was ±1.75°; (3) the fiber half-acceptance angle was ±40°; and (4) the fiber optic cable diameter was 0.5-in. Raytracing was used to determine the optimum geometry for the secondary lens. Among various geometries simulated included a conical secondary, a Compound Parabolic Concentrator (CPC), and a combination of conical and Compound Elliptical Concentrator (CEC). The analysis showed that a combination design comprising conical/CEC geometry was better than the conical and CPC geometries in terms of greatest overall light output and most reduced peak illuminance on the fiber optic cable. Prototype secondary lenses based on the design were fabricated from acrylic and optical silicones. Testing of the prototype lenses revealed that acrylic secondary performed better than the silicone lenses in terms of the measured lumen output. Testing also showed that the fiber-optic cable temperature was within the maximum operating temperature of acrylic and didn’t suffer any high temperature damage during the five month long outdoor testing.

SU-F-T-583: Comparison of EBT3 Radiochromic Film Densitometry with Narrow Bandwidth LED Source in Point, Slot and Full Aperture Geometries

Purpose: Film densitometers optimized for radiochromic EBT3 film are not commercially available and flatbed document scanners are limited by broad spectral overlap of the red green and blue channels and polarization effects. Non-polarized, narrow bandwith, intensity stabilized light emitting diode (LED) light sources were constructed and transmission measurements compared for point, slot and full aperture geometries. Methods: LED's with 10 nm bandwidths were focused to 1 mm spots for point scanning. The LED's back-illuminated a 6 mm diameter diffuser near the focal point of a 25 cm diameter Fresnel lens for slot and full aperture transmission imaging. Films were located at the aperture plane, 15 cm from the lens and imaged with a 16 bit digital camera with 50 mm lens. Sheets, 10×8 cm, were irradiated to 25 Gy with a 4×4 cm 6 MV photon beam. Transmission measurements with a 633nm, linearly polarized laser were used as lowacceptance angle reference geometry. Results: LED intensity stabilized to spot(∼3%)> slot(∼5%)> full aperture(∼10%). The Fresnel lens introduced a 4-fold polarization symmetry that increased radially causing a 2% change in transmission at 10 cm from the optic axis for EBT3 film. Polarized spot densitometer and laser transmission were similar. Conclusion: Spectrally filtered LED sources were effective for transmission measurements of radiochromic films. Because of polarization sensitivity of EBT3 film, the scanning spot geometry is the most general for measuring unpolarised transmission of larger film sizes, ie > 15×15 cm. Due to EBT3 film scatter, spot scanning should provide the most accurate profiles of high dose gradients, for a given acceptance angle. The spot scanning densitometer provided useful transmission to ∼5, 25, >25 Gy with 635, 590 and 530 nm light respectively.

The JEM-EUSO instrument

In this paper we describe the main characteristics of the JEM-EUSO instrument. The Extreme Universe Space Observatory on the Japanese Experiment Module (JEM-EUSO) of the International Space Station (ISS) will observe Ultra High-Energy Cosmic Rays (UHECR) from space. It will detect UV-light of Extensive Air Showers (EAS) produced by UHECRs traversing the Earth’s atmosphere. For each event, the detector will determine the energy, arrival direction and the type of the primary particle. The advantage of a space-borne detector resides in the large field of view, using a target volume of about 1012 tons of atmosphere, far greater than what is achievable from ground. Another advantage is a nearly uniform sampling of the whole celestial sphere. The corresponding increase in statistics will help to clarify the origin and sources of UHECRs and characterize the environment traversed during their production and propagation. JEM-EUSO is a 1.1 ton refractor telescope using an optics of 2.5 m diameter Fresnel lenses to focus the UV-light from EAS on a focal surface composed of about 5,000 multi-anode photomultipliers, for a total of ≃3⋅105 channels. A multi-layer parallel architecture handles front-end acquisition, selecting and storing valid triggers. Each processing level filters the events with increasingly complex algorithms using FPGAs and DSPs to reject spurious events and reduce the data rate to a value compatible with downlink constraints.

Machining Mechanism of Fresnel Lens Mold

This paper analyzed the large diameter Fresnel lens mold machining mechanism based on modal test methods .The design and mold machining principle of Fresnel lens were introduced . Explored the cutting speed and feed on chip formation process. The results show that: the material strength and plastic brittle have significant impact on chip morphology in the H62 brass mold processing, an improvement of material strength with the increase of strain rate and the evolution process of the chip can be divided into: ribbon cuttings, serrated chips, cell chips.

Novel Embossing System for Replicating Micro-Structures on Curved Surfaces

Abstract Hot embossing is widely used to replicate micro-structures on polymer plate surfaces. The polymer parts of curved surfaces with micro-structures have important functions in various optoelectronic components. However, due to the high precision needed for embossing machines and mold manufacturing, achieving uniform pressure on curved surfaces during the embossing process is difficult. This study modified conventional hot embossing processes to develop an elastic bag embossing system (EBES) for replicating micro-structures on curved surfaces. The pressure equalizing properties of the elastic bag enabled uniform application of pressure on curved surfaces embossed with a general hot compression machine. For the EBES-assisted hot embossing process, a nickel stamper was attached to the elastic bag to compress and replicate micro-structures on the PC film covering the mold surface with single direction curve. This study also developed an EBES-assisted UV exposure process that used a PDMS soft-mold attached to the elastic bag surface to compress the UV curable photoresist covering the surface of the convex lens. Micro-structures were then formed by exposing the photoresist. Experimental results showed that the EBES with Ni stamper could successfully replicated micro-structures onto a 200 mm × 200 mm curved PC film and that the EBES-assisted UV exposure could successfully produced a 50 mm diameter fresnel lens on a convex profile with material of UV photoresist. Experimental tests of pressure-sensitive film showed that EBES enables uniform application of pressure on curved surfaces during the embossing process on standard hot compression machines. The experimental results confirm that the EBES developed in this study is an efficient and economical method for replicating micro-structures on curved surface.

Research on Chip Formation Mechanism in Mold Processing of Large Diameter Fresnel Lens

This paper describes the analysis of the chip formation mechanism in mold machining process of large diameter Fresnel lens based on the ABAQUS finite element simulation software and modal test methods. Combined with the material constitutive relation and material failure criteria etc, a two-dimensional orthogonal cutting model was established and the chip derived from the simulation was compared with the chip from modal test, with a consequent verification of the feasibility of simulation chip model. The simulation contributes to an investigation into the effects of the cutting speed on chip formation process. The results show that: the material strength and plastic brittle have significant impact on chip morphology in the H62 brass mold processing, and material strength will improve with the increase of strain rate, the evolution process of the chip of material plastic reduction can be divided into: ribbon cuttings, serrated chips, cell chips.

Modal Analysis of the Bed Structure of Large Diameter Fresnel Lens Mold Machine Tool

Modeling of the large diameter Fresnel lens mold machine tool bed using 3D software solid works, and then import the ANSYS Workbench, natural frequencies and modal shapes are obtained by the study of the modal analysis and analysis of the structure characteristics of the machine bed, for the next step on the bed structure optimized to provide a reliable theoretical basis. Keywords: the bed; ANSYS Workbench; modal analysis; natural frequencies

The Simulation Experimental Research on Large Diameter Fresnel Lens Mold Machining

Reasonable selection and optimization of cutting parameters is an important part of the study on large diameter Fresnel lens mold process, which has a direct impact on the dynamic stability of processing state and processing quality of the large diameter Fresnel lens mold. Through a large number of experiments, we analyzed and summarized the influence law of spindle speed, feed and cutting speed on the dynamic stability of large diameter Fresnel lens mold processing state; The experiments show that when the cutting speed is more than 120m/min and the feed is about 1μm/r ~1.5μm/r , the continuous chip forms , breaks easily, the relative vibration amplitude between workpiece and tool is low, the cutting process is continuous and stable, and the machined surface quality is fine. The experiment results provide an important basis for the actual production of large diameter Fresnel lens mold.

Solar-Pumped TEM_00 Mode Nd:YAG laser

Here we show a significant advance in solar-pumped laser beam brightness by utilizing a 1.0 m diameter Fresnel lens and a 3 mm diameter Nd:YAG single-crystal rod. The incoming solar radiation is firstly focused by the Fresnel lens on a solar tracker. A large aspheric lens and a 2D-CPC concentrator are then combined to further compress the concentrated solar radiation along the thin laser rod within a V-shaped pumping cavity. 2.3 W cw TEM₀₀ (M² ≤ 1.1) solar laser power is finally produced, attaining 1.9 W laser beam brightness figure of merit, which is 6.6 times higher than the previous record. For multimode operation, 8.1 W cw laser power is produced, corresponding to 143% enhancement in collection efficiency.

Highly efficient solar-pumped Nd:YAG laser

The recent progress in solar-pumped laser with Fresnel lens and Cr:Nd:YAG ceramic medium has revitalized solar laser researches, revealing a promising future for renewable reduction of magnesium from magnesium oxide. Here we show a big advance in solar laser collection efficiency by utilizing an economical Fresnel lens and a most widely used Nd:YAG single-crystal rod. The incoming solar radiation from the sun is focused by a 0.9 m diameter Fresnel lens. A dielectric totally internally reflecting secondary concentrator is employed to couple the concentrated solar radiation from the focal zone to a 4 mm diameter Nd:YAG rod within a conical pumping cavity. 12.3 W cw laser power is produced, corresponding to 19.3 W/m(2) collection efficiency, which is 2.9 times larger than the previous results with Nd:YAG single-crystal medium. Record-high slope efficiency of 3.9% is also registered. Laser beam quality is considerably improved by pumping a 3 mm diameter Nd:YAG rod.

Fundamental study of a loop-tube-type thermoacoustic cooling system using heat energy from condensed sunlight

The feasibility of implementation of a sunlight-based loop-tube-type thermoacoustic cooling system is investigated. Sunlight is condensed using a 0.60 m diameter Fresnel lens and irradiated to the high-temperature heat exchanger. Then, the temperature of heat exchanger is risen. This heat energy from condensed sunlight is applied to the driving hear energy of the loop-tube-type thermoacoustic cooling system. The total length of the loop tube is 3300 mm, and a gaseous mixture of He and Ar (50% / 50%) is used as the working fluid. A 50-mm-long ceramic honeycomb is used for the stack. The channel radius of the prime mover stack is 0.45 mm; that of the heat pump is 0.35 mm. The cooling point temperature falls from 29°C to -4.3°C before sunlight is irradiated to the high-temperature heat exchanger. Consequently, a temperature drop of 33.3°C is achieved using sunlight. Result obtained in this experiment underscores the feasibility of implementation of a sunlight-based loop-tube-type thermoacoustic cooling system.

Design and construction of a solar-powered, thermoacoustically driven, thermoacoustic refrigerator

A thermoacoustically driven thermoacoustic refrigerator powered by solar thermal energy has been successfully built and tested. A 0.457 m diameter Fresnel lens focuses sunlight onto the hot end of a 0.0254 m diameter reticulated vitreous carbon prime mover stack, heating it to 475 °C, thereby eliminating the need for the most troublesome component in a heat driven prime mover, the hot heat exchanger. The high intensity sound waves produced by the prime mover drive a thermoacoustic refrigerator to produce 2.5 watts of cooling power at a cold temperature of 5 °C and a temperature span of 18 °C.