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Design and performances of an Imager Fourier Transform Spectrometer in the UV (IFTSUV)

Design and performances of an Imager Fourier Transform Spectrometer in the UV (IFTSUV). Claudia Ruiz de Galarreta. Thèse dirigée par: Philippon,J.-C. Vial & T. Appourchaux. TABLE OF CONTENTS. SCIENTIFIC BACKGROUND IFTSUV DEFINITION METROLOGY FURTHER WORK. SCIENTIFIC BACKGROUND.

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Design and performances of an Imager Fourier Transform Spectrometer in the UV (IFTSUV)

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  1. Design and performances of an Imager Fourier TransformSpectrometer in the UV (IFTSUV) Claudia Ruiz de Galarreta Thèse dirigée par: Philippon,J.-C. Vial & T. Appourchaux

  2. TABLE OF CONTENTS SCIENTIFIC BACKGROUND IFTSUV DEFINITION METROLOGY FURTHER WORK

  3. SCIENTIFIC BACKGROUND UNDERSTAND THE PHYSICS OF THE OUTER SOLAR ATMOSPHERE UNSOLVED CORONA HEATING PROBLEM Requires the study in the UV linesformed in the Chromosphere, the Transition Region and the Corona T ~ 4500 – 1 000 000K SPECTRAL DOMAIN (VUV) ~80–140nm SoHO, EIT (May 1998)

  4. LymanαObservations Lymanα, λ = 121.567 nm is the STRONGEST emission line in the VUV SPECTROSCOPY Set of Lα profiles obtainedatdifferent positions in a Prominence, each profile isseparatedbyonearcsecond (SUMER, SoHO). • Thermodynamics • (Temperature, density, …) • Movement of matteralong the line of sight  FOV is not defined! IMAGING LαProminence and Filament observed by VAULT. • Structure morphology Lαradiance and profile provide important information on the structure of the outer Solar atmosphere • Not enough spectral resolution! • No spectral diagnostics! 250’’x250’’

  5. Science specifications  The study of the outerSolaratmosphererequirescombiningimaging and spectroscopy • Observe moderately large Field of View (FOV), within a sufficient spectral window • Collect data with spectral, Spatial and Temporal Resolution sufficient to reveal a range of physical processes  The study of the outerSolaratmosphererequires UV adapted instruments • Beam-splitter Limit ( < 140nm) implies an all-reflection design • Minimize the number of optical surface to have more signal • Compactness

  6. Imaging Fourier TransformSpectrometer (IFTS) Each pixel records the interferogramproduced by th controlled Optical PathDifference(OPD) betweenarms The spectrumisrecovered by taking the Fourier Transform (FT) of the interferogram A face of the cube is an OPD image. A line in the z-direction corresponds to the interferogram • Consistent with an all reflection system Michelsoninterferometer • Instantaneous 2D FOV • Throughput • Spectral Bandpassonlylimited by filter • Flexible spectral resolution  Equations Interferogram: POTENTIAL ADVANTAGES: • ResolvingPower • Compact • Resolution Spectrum: • Sampling and free spectralrange (Shannon) OPD: Paramètres: δ = opticalpathdifference(OPD), σ = wavenumber, 2L = max. OPD, dx =samplingstep, N = number of samplingsteps

  7. IFTSUV optical configuration - Two identical gratings (R1,R2) for splitting and then recombining the beam - Four mirrors, one of them moves to scan the OPD - The interfering beam is focused on the 2D detector by an off-axis parabola

  8. INSTRUMENTAL SPECIFICATIONS * TBD = tobedefined Solar dynamicsaimsforfastscanand asymmetricalacquisition ,S(s) = measuredsignal Fringecontrast Noise Signal to Noise Ratio (SNR) Budget Ms = Modulationfunction Zs = noisecontributions Signal maybeimproved by the aperture optics of the system

  9. SIGNAL TO NOISE BUDGET IMAGE CHAIN: Source Interfetometer and optics Detector Electronics - Photonnoise - Fluctuations • MotionStraightness • Samplingaccuracy • Wavefronterrors • Gratingefficiency • Velocityerrors • Environment • Shotnoise • Thermalnoise • Amplifiernoise • Digitnoise • Electricalnoise • Noise sources contribution • Samplingaccuracy • Motion straighness METROLOGY SYSTEM Dynamicservo-control

  10. METROLOGY SYSTEM AUTO-COLLIMATOR HOMODYNE MICHELSON INTERFEROMETER SERVO CONTROL  Interferometer DC output  Alignmenttip/tiltdeviationmeasuredbyQuadrantPhotodector (QPD)  ‘Symmetric’ with IFTSUV  Every fringe corresponds to a path difference of half a wavelength CLOSED LOOP PIEZO ACTUATORS OPD CLOCK MULTIPLE REFLECTIONS CONFIGURATION  l = 632.8 nm OpticalIsolator

  11. MULTIPLE REFLECTION CONFIGURATION 1. OPTICAL FRINGE SUBDIVISION (OFS) Resonancecondition: Phase Amplification: α = angle of incidence of theray(+M) Θ = anglebetween +M and M N = number of reflections in +M beforefolding back  FringeCounting M Zerocrossing: 2. ANGLE DEVIATION AMPLIFICATION +M Exampleα=30° θ=10°N=4 Gainlimits: 1.Mirrors: Travel + Diameter + Surfacequality 2. Laser: beamdiameter + Power + Stability

  12. FURTHER WORK MODELISATION METROLOGY 1. Mock-up Environmentparameters (pressure, temperature, humidity) have to bepreciselycontrolled and mechanical parts have to bevery stable in order to achievenanopositioning of the system 1.SNR Budget 1. OPTICAL ALIGNMENT • Noise budget 2. AUTO-COLLIMATOR • Optical surface quality QPD CALIBRATION  PZT CLOSED LOOP CONTROL 3. HOMODYNE MICHELSON INTERFEROMETER 2.Image quality System Aperture 2 PHASE QUADRATURE DETECTION • Spatial resolution • Vignetting  ELLIPTICAL CORRECTION ALGORITHM • Gratingefficacity • Aberrations 2.Test & Results

  13. THANK YOU! MERCI! GRACIAS!

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