Fast and optimal broad-band Stokes/Mueller polarimeter design by the use of a genetic algorithm

A fast multichannel Stokes/Mueller polarimeter with no mechanically moving parts has been designed to have close to optimal performance from 430-2000 nm by applying a genetic algorithm. Stokes (Mueller) polarimeters are characterized by their ability to analyze the full Stokes (Mueller) vector (matrix) of the incident light. This ability is characterized by the condition number, $\kappa$, which directly influences the measurement noise in polarimetric measurements. Due to the spectral dependence of the retardance in birefringent materials, it is not trivial to design a polarimeter using dispersive components. We present here both a method to do this optimization using a genetic algorithm, as well as simulation results. Our results include fast, broad-band polarimeter designs for spectrographic use, based on 2 and 3 Ferroelectric Liquid Crystals, whose material properties are taken from measured values. The results promise to reduce the measurement noise significantly over previous designs, up to a factor of 4.5 for a Mueller polarimeter, in addition to extending the spectral range.Comment: 10 pages, 6 figures, submitted to Optics Expres

Influência da cobertura morta na produtividade de erva-mate.

A erva-mate é uma espécie arbórea, ombrófila, de crescimento lento ou moderado, típica de florestas maduras. Ocorre naturalmente em solos profundos, bem drenados, ácidos ou ligeiramente ácidos, não raro com altos teores de alumínio e de matéria orgânica, argilosos e muito imtemperizados. Buscando viabilizar os benefícios da cobertura morta na cultura da erva-mate e o reaproveitamento de resíduos gerados nas regiões produtoras, implantou-se um ensaio em condições de campo, para comparar o efeito de diversos tipos de cobertura morta na produtividade das erveiras. O estudo foi conduzido no município de São Mateus do Sul, no segundo planalto paranaense, altitude de 835 m e a 50o22‘58“ de longitude Oeste e 25o52‘28“ de latitude Sul. O clima da região, segundo a classificação de Koppen, é do tipo Cfb, subtropical úmido sem estação seca, precipitação média anual entre 1400 e 1500 mm, com a temperatura média do mês mais quente inferior a 22oC e a média do mês mais frio superior a 10 oC, com mais de cinco geadas por ano. O ensaio foi instalado num LATOSSOLO VERMELHO Distrófico típico com atributos A proeminente e textura muito argilosa. O delineamento experimental foi em blocos ao acaso com 10 tratamentos e quatro repetições em parcelas de linhas triplas, com 10 plantas úteis na fileira central, cujas plantas de erva-mate, com 2 anos e oito meses, eram espaçadas de 2,45 m x 1,73 m. A fim de comparar a influência de dois tipos de cobertura provenientes de resíduos típicos da região (serragem e “palitos da erva-mate”), com outro produzido através da roçagem de gramínea plantada como cultura intercalar, na presença e ausência de adubação, foram instalados os seguintes tratamentos: T1) Sem cobertura, sem adubo; T2) Sem cobertura, com adubo; T3) Palito (residual da erva-mate), sem adubo; T4) Palito (residual da erva-mate), com adubo; T5) Serragem, sem adubo; T6) Serragem, com adubo; T7) Gramínea (capim-elefante-anão), sem adubo; T8) Gramínea (capim-elefante-anão), com adubo. Concluiu-se que a adição de palitos, como cobertura morta, se constituiu no melhor tratamento para a produtividade das erveiras com até quatro anos e meio, consideradas as podas anuais, só sendo igualado pelos outros tratamentos pela aplicação de adubos

Ralph: A Visible/Infrared Imager for the New Horizons Pluto/Kuiper Belt Mission

The New Horizons instrument named Ralph is a visible/near infrared multi-spectral imager and a short wavelength infrared spectral imager. It is one of the core instruments on New Horizons, NASA's first mission to the Pluto/Charon system and the Kuiper Belt. Ralph combines panchromatic and color imaging capabilities with IR imaging spectroscopy. Its primary purpose is to map the surface geology and composition of these objects, but it will also be used for atmospheric studies and to map the surface temperature. It is a compact, low-mass (10.5 kg), power efficient (7.1 W peak), and robust instrument with good sensitivity and excellent imaging characteristics. Other than a door opened once in flight, it has no moving parts. These characteristics and its high degree of redundancy make Ralph ideally suited to this long-duration flyby reconnaissance mission.Comment: 18 pages, 15 figures, 4 tables; To appear in a special volume of Space Science Reviews on the New Horizons missio

The Science Performance of JWST as Characterized in Commissioning

This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies

The James Webb Space Telescope Mission: Optical Telescope Element Design, Development, and Performance

The James Webb Space Telescope (JWST) is a large, infrared space telescope that has recently started its science program which will enable breakthroughs in astrophysics and planetary science. Notably, JWST will provide the very first observations of the earliest luminous objects in the Universe and start a new era of exoplanet atmospheric characterization. This transformative science is enabled by a 6.6 m telescope that is passively cooled with a 5-layer sunshield. The primary mirror is comprised of 18 controllable, low areal density hexagonal segments, that were aligned and phased relative to each other in orbit using innovative image-based wavefront sensing and control algorithms. This revolutionary telescope took more than two decades to develop with a widely distributed team across engineering disciplines. We present an overview of the telescope requirements, architecture, development, superb on-orbit performance, and lessons learned. JWST successfully demonstrates a segmented aperture space telescope and establishes a path to building even larger space telescopes.Comment: accepted by PASP for JWST Overview Special Issue; 34 pages, 25 figure

Fast spectrally encoded Mueller optical scanning microscopy

Mueller microscopes enable imaging of the optical anisotropic properties of biological or non-biological samples, in phase and amplitude, at sub-micrometre scale. However, the development of Mueller microscopes poses an instrumental challenge: the production of polarimetric parameters must be sufficiently quick to ensure fast imaging, so that the evolution of these parameters can be visualised in real-time, allowing the operator to adjust the microscope while constantly monitoring them. In this report, a full Mueller scanning microscope based on spectral encoding of polarization is presented. The spectrum, collected every 10 μs for each position of the optical beam on the specimen, incorporates all the information needed to produce the full Mueller matrix, which allows simultaneous display of all the polarimetric parameters, at the unequalled rate of 1.5 Hz (for an image of 256 × 256 pixels). The design of the optical blocks allows for the real-time display of linear birefringent images which serve as guidance for the operator. In addition, the instrument has the capability to easily switch its functionality from a Mueller to a Second Harmonic Generation (SHG) microscope, providing a pixel-to-pixel matching of the images produced by the two modalities. The device performance is illustrated by imaging various unstained biological specimens

Snapshot spectropolarimetry

Channeled spectropolarimetry is a novel method of measuring the spectral dependence of the polarization state of light. Amplitude modulation is employed to encode all four Stokes component spectra into a single optical power spectrum. The encoding is performed with a simple arrangement of two thick birefringent retarders and a linear analyzer. No moving parts are required, and the system is able to acquire its data in a single detector array integration time. We report the results of an in-depth study of channeled spectropolarimetry. The mathematics of the amplitude modulation analogy are explored, providing a basic design procedure. The system's spectral resolution is described in terms of the space bandwidth product. The technique is then analyzed in the general context of linear operator theory, using both analytic and computational approaches to the singular value decomposition and pseudoinversion of the system's operator. This analysis highlights the importance of the choice of object space in constraining linear reconstructions of data from under-determined systems, and provides the underpinnings of the calibration and reconstruction techniques for a hardware prototype. Calibration of the prototype is approached as experimental estimation of the system's operator. Our basic method of reconstruction involves pseudoinversion of the operator while constraining object space to a truncated Fourier basis. Apodization is helpful in reducing the ringing of reconstructions of spectra which extend beyond the edges of the system's spectral range. Experimental results are presented, including comparisons between measurements taken with the channeled spectropolarimeter and a reference rotating compensator, fixed analyzer instrument. We have used measurements of the effects of stress birefringence on light propagated through material subject to time-varying stress to demonstrate time-resolved snapshot spectropolarimetry. Continuing efforts include the combination of channeled spectropolarimetry with computed tomography imaging spectrometry to realize a snapshot imaging spectropolarimeter