Fourier Transform Spectrograph Development Project NARIT Research Colloquium / Research Project Evaluation 2018 August 2 nd, Flora Creek Hotel, Chiangmai C. Buisset 1, P. Artsang 2, P. Meemon 2, 1 National Astronomical Research institute of Thailand (Chiang Mai) 2 School of Physics, Suranaree University of Technology (Khorat)
NARIT Optical Technology Development Project 1. Introduction 2. Design and performance 3. Conclusions and next steps
Introduction Fourier Transfrom Spectroscopy: scientific tool widely used to measure the spectrum of objects with a high resolution in the visible, near and thermal IR FTS Applications: Chemistry, pharmacy, medicine, agriculture, defense. Project objective: Development of 1 imaging Fourier Transform Spectrometer (FTS) and test on astronomical target Acquisition of technological know-how and skills to develop our own imaging FTS
Introduction Science case: measurement of Jupiter spectrum on selected spectral bands over [800 nm, 1200 nm] to assess the spectrograph performance and to measure the planet pulsations. Specifications: Parameter Science spectral band Setup Architecture Specification [800 nm, 1200 nm] 1 Science channel + 1 metrology channel FOV extension 2 Metrology source Maximum Optical Path Difference Dynamic mirror tip-tilt control frequency Dynamic mirror Translating stage Detector He-Ne laser, λ M = 633 nm OPD Max 20 mm f > 1 khz Piezo-electric stage, 12 mm displacement range Si and InGaAs Detectors
Optical design: Michelson interferometer; plane mirrors, cube beam splitter. Metrology: 1 He-Ne laser co-propagating with science beam; combined and separated by using dichroic plates Required for accurate monitoring of dynamic mirror displacement. Control system: dynamic mirror displacement, science and metrology signal acquisition performed under labview software Laser source Fiber Dichroic plates Beam Splitter
Science channel and Metrology channel interferograms measured simultaneously during displacement of the dynamic mirror. Translating mirror displacement amplitude :1 mm, Displacement speed equal to 0.1 mm. Science Interferogram resampled by using the metrology channel signal peak detection. Results: Super continuum source + single mode fiber spectrum In line with specifications
Science channel and Metrology channel interferograms measured simultaneously during displacement of the dynamic mirror. Translating mirror displacement amplitude :1 mm, Displacement speed equal to 0.1 mm. Science Interferogram resampled by using the metrology channel signal peak detection. Results: Super continuum source + single mode fiber spectrum In line with specifications
Signal (ADU) 2017-2018 fiscal year activities: Focused on the measurement of polychromatic source spectrum with multi-mode fibers. Critical point identified: lost of contrast due to multi-mode fiber. Proposed solutions: procurement of balanced detectors or installation of the imaging FTS at the telescope image plane 2018-2019 fiscal year activities Super continuum source fringes in spectral domain Wavelength (nm)
Signal (ADU) 2017-2018 fiscal year activities: Focused on the measurement of polychromatic source spectrum with multi-mode fibers. Critical point identified: contrast lost due to multi-mode fiber and/or spectral enlargement. Proposed solutions: procurement of balanced detectors or installation of the imaging FTS at the telescope image plane 2018-2019 fiscal year activities Tungsten source + [700 nm, 900 nm] spectral band filter fringes in spectral domain Wavelength (nm)
Interferometer installed on the TNT beam simulator (NARIT Astropark) Objective: in-laboratory measurement of spectrum on extended sources. Status: First fringes obtained using metrology and alignment laser (He-Ne, λ 633 nm). Next step: measurement of spectrum on a white screen representing a source of angular extension equal to a few arcminutes.
Conclusion Achieved activities: We have developed 1 imaging FTS that comprises: 1 science channel. metrology channel and the processing algorithm Spectrum of supercontinuum source has been successfully measured, result in line with source specifications. Tungsten source fringes measured in spectral domain but low contrast Setup improvement required to measure wideband source spectrum Setup has been installed on the TNT beam simulator. Fringes from metrology laser already obtained on-axis object + SM fiber spectrum expected for September 2018. Next steps toward on-sky observations (2019 and 2020 fiscal year activities) : Setup upgrade: BS replacement, high frequency tip-tilt mirror installation. Science channel camera installation + synchronization with dynamic mirror movement Test on TNT beam simulator with extended sources. Mechanical design, manufacturing, installation on NARIT Astropark 0.7 m telescope