swisscheesex an idea to obtain over-diffraction limited imaging with a seeing limited, extremely...

SwissCheesEx An idea to obtain over- diffraction limited imaging with a seeing limited, extremely large telescope over a wide range of wavelengths A. Richichi - Garching Science Day 2006

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$Page 1: SwissCheesEx An idea to obtain over-diffraction limited imaging with a seeing limited, extremely large telescope over a wide range of wavelengths A. Richichi$

SwissCheesEx

An idea to obtain over-diffraction limited imaging with a seeing

limited, extremely large telescope over a wide range of

wavelengths

A. Richichi - Garching Science Day 2006

$Page 2: SwissCheesEx An idea to obtain over-diffraction limited imaging with a seeing limited, extremely large telescope over a wide range of wavelengths A. Richichi$

The Moon’s limb acts as a straight diffracting edge.

The diffraction phenomenon occurs in “vacuum”, no turbulence effects.

High-angular information is embedded in the diffraction fringes.

The “resolution” is independent from telescope diameter (but depends on signal-to-noise ratio).

Temporal scales (depending on wavelength and apparent limb velocity ) are ~0.1s.

High temporal rates are needed, typically ~1 ms in the near-IR.

Diffraction patterns of two or more components add linearly.

Lunar Occultations

$Page 3: SwissCheesEx An idea to obtain over-diffraction limited imaging with a seeing limited, extremely large telescope over a wide range of wavelengths A. Richichi$

Why Lunar Occultations are good• Simple, economical (also in time)• High angular resolution (0.5-1 mas)• Sensitive (on a large telescope)

Why the are not good enough• Cannot choose the source• About 10% of sky covered by the Moon (in 18.5 years)• One-dimensional scan only

$Page 4: SwissCheesEx An idea to obtain over-diffraction limited imaging with a seeing limited, extremely large telescope over a wide range of wavelengths A. Richichi$

Artificial Occultations using Giant Sails

• Choose your own targets / time

• Repeat observations

• High sensitivity (no background)

• Tomographic Imaging (Swiss Cheese)

$Page 5: SwissCheesEx An idea to obtain over-diffraction limited imaging with a seeing limited, extremely large telescope over a wide range of wavelengths A. Richichi$

Why an ELT?Sails should be as large as possible, but won’t be as

large as the Moon

They have to be very close to Earth to have a decent angular coverage

They will have a high angular speed to remain in a stable orbit

Integration times will have to be correspondingly short

Short wavelenths (not hitherto possible) will also require short integration times

Telescope area is critical to set the limiting Telescope area is critical to set the limiting magnitude (not its optical quality)magnitude (not its optical quality)

$Page 6: SwissCheesEx An idea to obtain over-diffraction limited imaging with a seeing limited, extremely large telescope over a wide range of wavelengths A. Richichi$