2,318 research outputs found
Design of light concentrators for Cherenkov telescope observatories
The Cherenkov Telescope Array (CTA) will be the largest cosmic gamma ray
detector ever built in the world. It will be installed at two different sites
in the North and South hemispheres and should be operational for about 30
years. In order to cover the desired energy range, the CTA is composed of
typically 50-100 collecting telescopes of various sizes (from 6 to 24-m
diameters). Most of them are equipped with a focal plane camera consisting of
1500 to 2000 Photomultipliers (PM) equipped with light concentrating optics,
whose double function is to maximize the amount of Cherenkov light detected by
the photo-sensors, and to block any stray light originating from the
terrestrial environment. Two different optical solutions have been designed,
respectively based on a Compound Parabolic Concentrator (CPC), and on a purely
dioptric concentrating lens. In this communication are described the technical
specifications, optical designs and performance of the different solutions
envisioned for all these light concentrators. The current status of their
prototyping activities is also given
Optical concentrators for ÄŚerenkov light detector
RICH1 (Ring Imaging Cherenkov) detector is an important part of COMPASS particle physics experiment in CERN. Its central area photon detection part is being upgraded from wire chambers with CsI layers to very fast UV extended Hamamatsu MAPMTs (Multi Anode Photo Multiplier Tubes) array. MAPMTs have approx. 3 times smaller active area than the covered region, thus optical concentrators transforming image from old system focal plane to the new photocathode were needed. System was expected to be efficient from 200 to 600nm with best performance at 300nm and with angular acceptance including all interesting physics processes. Several design types (including i.e. a hollow waveguide) were investigated and the “telescopic” two lens aspherical design concept was selected for its proven functionality in HERA-B experiment. Chosen material was UV grade fused silica. System consists of a field lens placed in the focal plane of the RICH mirrors and a condenser lens downstream. Designing procedure started with a high optical quality fully aspherical system and continued by a gradual decrease in imaging performance to match the budget but still satisfy the physics requirements. Particle simulations showed a necessity of the system tilt but mounting constraints didn’t fully allow it, so the field lens was made prismatic with one flat side and the condenser lens off centered and tilted. Performance of the designs was tested by Monte Carlo method allowing a better optimization. Testing by rays from complex detector simulation implied a necessity of tilt in another plane. Design ready for production satisfies all performance, dimensional, mounting and cost expectations
ROBAST: Development of a ROOT-Based Ray-Tracing Library for Cosmic-Ray Telescopes and its Applications in the Cherenkov Telescope Array
We have developed a non-sequential ray-tracing simulation library, ROOT-based
simulator for ray tracing (ROBAST), which is aimed to be widely used in optical
simulations of cosmic-ray (CR) and gamma-ray telescopes. The library is written
in C++, and fully utilizes the geometry library of the ROOT framework. Despite
the importance of optics simulations in CR experiments, no open-source software
for ray-tracing simulations that can be widely used in the community has
existed. To reduce the dispensable effort needed to develop multiple
ray-tracing simulators by different research groups, we have successfully used
ROBAST for many years to perform optics simulations for the Cherenkov Telescope
Array (CTA). Among the six proposed telescope designs for CTA, ROBAST is
currently used for three telescopes: a Schwarzschild-Couder (SC) medium-sized
telescope, one of SC small-sized telescopes, and a large-sized telescope (LST).
ROBAST is also used for the simulation and development of hexagonal light
concentrators proposed for the LST focal plane. Making full use of the ROOT
geometry library with additional ROBAST classes, we are able to build the
complex optics geometries typically used in CR experiments and ground-based
gamma-ray telescopes. We introduce ROBAST and its features developed for CR
experiments, and show several successful applications for CTA.Comment: Accepted for publication in Astroparticle Physics. 11 pages, 10
figures, 4 table
Multiwavelength polarization insensitive lenses based on dielectric metasurfaces with meta-molecules
Metasurfaces are nano-structured devices composed of arrays of subwavelength
scatterers (or meta-atoms) that manipulate the wavefront, polarization, or
intensity of light. Like other diffractive optical devices, metasurfaces suffer
from significant chromatic aberrations that limit their bandwidth. Here, we
present a method for designing multiwavelength metasurfaces using unit cells
with multiple meta-atoms, or meta-molecules. Transmissive lenses with
efficiencies as high as 72% and numerical apertures as high as 0.46
simultaneously operating at 915 nm and 1550 nm are demonstrated. With proper
scaling, these devices can be used in applications where operation at distinct
known wavelengths is required, like various fluorescence microscopy techniques
Design of a compact objective for SWIR applications
Lately the short-wave infrared (SWIR) has become very important due to the recent appearance on the market of the small detectors with a large focal plane array. Military applications for SWIR cameras include handheld and airborne systems with long range detection requirements, but where volume and weight restrictions must be considered. In this paper we present three different designs of telephoto objectives that have been designed according to three different methods. Firstly the conventional method where the starting point of the design is an existing design. Secondly we will face design starting from the design of an aplanatic system. And finally the simultaneous multiple surfaces (SMS) method, where the starting point is the input wavefronts that we choose. The designs are compared in terms of optical performance, volume, weight and manufacturability. Because the objectives have been designed for the SWIR waveband, the color correction has important implications in the choice of glass that will be discussed in detai
Design of laser uniform illumination system based on aspheric lens and compound ellipsoidal cavity
In order to achieve uniform laser illumination with small aperture diameter
and large field Angle,study laser active illumination system.An aspheric mirror
combined with a composite ellipsoidal cavity is designed to achieve uniform
illumination in this paper.Through an aspheric mirror,the fundamental mode of
Gaussian beam is shaped into double Gaussian radiation and Flat-top
radiation.The double Gaussian radiation rays are reflected again by the complex
ellipsoidal cavity and decomposed into equal radiation flux,which is
superimposed with the through Flat-top radiation rays to form a uniform
distribution.The parameters of the complex ellipsoidal cavity are obtained by
mapping equalization algorithm.After the superposition of the aspherical
transmission Flat-top shaping and the composite ellipsoidal cavity secondary
reflection shaping,the aperture is 29.7mm,whose aperture angle is 84.0
degrees,and the uniformity is 92.7% with 2m distance and 3.6m diameter.The
optimization of uniformity is influenced by three factors:RMS,transmission and
reflection power density ratio MT/R and transmission and reflection overlap
degree.RMS and MT/R determine the design effect of the composite ellipsoidal
cavity, which depends on the maximum reflection Angle and transmission
Angle.MT/R is negatively correlated with the maximum reflection of Angle,and
RMS is positively correlated with the transmission Angle.When the maximum
reflection Angle is set to 32.0 degrees and the transmission Angle to 8.0
degrees,the minimum root-mean-square focusing radius is 108.6um,and the minimum
effective transmission reflection power density ratio is 1.07.The degree
overlap of transmission and reflection directly affects the uniformity of the
target plane.The degree of transmission and reflection is adjusted by setting
an adjustment factor.When the adjustment factor is 0.9,the uniformity of the
target plane reaches the maximum.Comment: 7 pages, 13 figure
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