COSMO Large Coronagraph (COSMO LC) is a telescope dedicated to the measurement of the Sun magnetic field. This project is currently at a design phase funded by the National Science Foundation under the technical direction of the High Altitude Observatory.
COSMO LC is a refractive telescope whose objective lens has a clear aperture of 1.4m, it will be the largest refractive telescope in the world. This telescope can observe the Sun corona thanks to the internal occulter which is able to obscure the solar disk. This device needs to accomplish two main functions: 1) adapt its diameter to the Sun apparent size, 2) reject all the incoming heat to not start any air turbulence which leads to the degradation of image quality (seeing).
Diameter change is accomplished by means of a cam mechanism which actuates 14 petals arranged azimuthally while the occulter cooling is obtained through cold water running through internal channels and forced air convection.
This article describes the mathematical models employed to quantify the seeing effect on image resolution and the technical solutions adopted to implement the above-mentioned functions. In addition, the tests performed on this device are described along with the results.
WindCube is a NASA HFORT funded mission to study the coupling of thermospheric winds with the earth’s ionosphere. The optical system is based on a limb sensing Fabry-Perot etalon designed to measure the Doppler shift of the 630 nm oxygen airglow emission. The instrument payload is designed to fit within a 6U volume in a 12U CubeSat. The accuracy requirement for the wind speed retrieval is 5 m/s. This is the driving requirement for the opto-mechanical stability of the etalon system. Active temperature control of the etalon is employed to keep the mounted etalon within a +/- 0.1 C range. This paper discusses the design and analysis of the mounted etalon system to meet the accuracy requirement as well as surviving the rigors of vibration testing and the launch environment.
KEYWORDS: Signal processing, Signal detection, Sensors, Process control, Semiconductor lasers, Absorption, Calibration, Gases, Temperature metrology, Environmental monitoring
An ammonia monitor designed for in situ smoke stack or exhaust duct applications is discussed here. A probe composed of a diffusion cell with a protected multipass optical measurement cavity provides the optical interaction with the sample. Other components of the system include signal processing electronics and an embedded PC104 computer platform. This instrument is useful in a wide variety of ammonia monitoring and process control applications, particularly ammonia-based NOx control technologies, such as selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR). The in situ design eliminates sample handling problems, associated with extractive analysis of ammonia, such as sample line adsorption and heated sample trains and cells. The sensor technology exploited in this instrument is second harmonic spectroscopy using a near infrared diode laser. Data collected during field trials involving both SCR and SNCR applications demonstrate the feasibility and robust operation of this instrument in traditionally problematic operating environments. The instrument can measure other gases by changing the wavelength, either by changing the diode operational set point or by changing the diode. In addition, with straightforward modification the instrument can measure multiple species.
Tunable diode laser absorption spectroscopy (TDLAS) shows promise for a number of environmental monitoring applications. This technique is advantageous over more classical methods because of excellent dynamic range, signal to noise ratios, and narrow bandwidth detection. With the rapid advances in the communications industry, lasers and optical components necessary for sensor technology are becoming affordable as well. One serious obstacle towards this effort is the paucity of spectroscopic data for the most useful, albeit weak, transitions near fiber optic communications wavelengths, especially at elevated temperatures. This data is important not only for species of monitoring interest, but also for those of possible interferants. In the near infrared, these are typically overtone and combination bands and hence accurate prediction of location, linestrength, and broadening coefficients is non-trivial. This is especially true for transitions arising from a highly excited rotational lower energy state. These are lines which may not be observable at room temperature but can play an important role for in-situ monitoring of a hot duct or smokestack. We have developed a system comprised of an extended cavity tunable diode laser and high temperature oven to characterize absorption spectra as a function of temperature and pressure. The experimental apparatus is described and data presented for water near 1.55 microns form 100 to 300 degrees C and 30 Torr.
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