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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

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

slide2

TABLE OF CONTENTS

SCIENTIFIC BACKGROUND

IFTSUV DEFINITION

METROLOGY

FURTHER WORK

slide3

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)

slide4

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’’

slide5

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
slide6

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

slide7

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

slide8

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

slide9

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

slide10

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

slide11

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

further work
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

slide13

THANK YOU!

MERCI!

GRACIAS!