1 Conceptual Design of a Compact Fizeau Interferometer Neng-hong Zhu, Xin-yang Chen Shanghai Astronomical Observatory

2 Background & Goal Dream: Optical long baseline interferometer based in space Reality: Optical interferometry of China is just in inital stage + limited money Option: Compact Fizeau Space Interferometer  short baseline  direct instantaneous imaging  small scale Step 1:  gound prototype with diameter equivalent to 1m  Step 2:  Fizeau space Interferometer with diameter equivalent to 2~4m  future:  longer baseline & more elements...

3 Array configuration Geometric Array Modulation Transfer Function: MTF=|FT(PSF)| α=0° α=10° α=20°α=30°

4 Beam combining errors (1/2) PSF vs. piston error piston=-0.2λpiston=-0.4λpiston=0.2λpiston=0.4λ MTF vs. pistonStrehl Ratio vs. piston SR≥ > piston P-V≤0.1λ [Cao Fang, et al, 2008]

5 Beam combining errors (2/2) PSF vs. tip/tilt error X tip=0 （ a ） Y Tilt Error=0 （ b ） Y Tilt Error=0.1λ (c ） Y Tilt Error=0.2λ (d) Y Tilt Error=0.3λ X tip=0.2 λ X tip=0.1 λ X tip=0.3 λ Y tilt=0 Y tilt=0.2 λ Y tilt=0.1 λ Y tilt=0.3 λ MTF vs. tip/tiltStrel Ratio vs. tip/tilt SR≥ > tip/tilt P-V≤0.055λ≈0.3 " [Cao Fang, et al, 2008]

6 Spec. of the ground prototype Y-4 array -----> (1) high stability due to symmetric structure (2) optimal MTF (3) tubes modulization common mounting -----> without optical delay line for compensating outer OPD C-shape board & triangle flatform -----> high stiffness & resonance freq. wide FOV ~ ±2 ' Direct Drive -----> no backlash, high tracking accuracy ~ RMS:0.01"(Dec=45°)

7 FEA of structure

8 Optics design sub-telescope optics folding & combiner opticsconfusion circle Φ≤ 0.7" Primary mirror Outer diameter(mm) 420Inner diameter(mm) 80 Thickness(mm)60Weight (Kg)20 f/D ratio2Eccentricity Secondary mirror Outer diameter(mm) 80Curvature radii336 Thickness(mm)15Weight (Kg)0.15 Eccentricity

9 Challenge How to measure and eliminate co-phasing errors between sub-telescopes?  pyramid wavefront sensor  fringe tracking  How to improve image quality?  interferometric image restoration method -> better MTF