Vladimir Vassiliev UCLA

Vladimir Vassiliev UCLA

Reduce cost of FP instrumentation (small plate scale) Improve imaging quality (angular resolution) Minimize isochronous distortion (energy threshold, +) Increase FoV (sky survey, transients, morphology, +)

Prime Focus Telescopes (Whipple-like designs) Super-fast Super-etendue (throughput) Low image resolution ( Light Bucket ) Large Plate Scale Spot Size [arcmin] FP/D ratio [1] 10 9 8 7 6 5 4 3 2 1 0 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 f=f/d - number >5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 f=f/d - number FoV=12 deg

Optical system layout Tangential rms A. Schliesser, R Mirzoyan Astropart.Phys. 24 (2005) 382-390

Optical system: Fast Consists of minimal number of optical surfaces Spherical and Coma aberrations free Tolerable Astigmatism and high order Coma Primary aberrations Spherical ~1/f 3 Coma (1 st order) ~θ/f 2 Astigmatism ~θ 2 /f 1 Field curvature ~θ 2 /f 1 Fast (small f-ratio) systems are severely affected by spherical aberrations and coma.

10 deg 2 FoV, < 0.5 image quality LSST: 8.4-meter primary mirror, 3.4-meter secondary mirror, 5.2- meter tertiary mirror. The light reflected by this tertiary mirror then passes through a 1.4-meter lens to the camera detector. 30m IACT adaptation

Schmidt-Cassegrain Spherical primary mirror corrected by the Schmidt corrector plate, convex hyperbolic secondary mirror and a focal plane located behind the primary Maksutov-Cassegrain Either a spherical or parabolic primary mirror in conjunction with a meniscus-shaped corrector plate at the entrance pupil. The meniscus-shaped corrector plate allows for the use of an easily fabricated spherical secondary mirror rather than the hyperbolic mirror required for the Schmidt telescope. 3 optical elements design Main disadvantage: does not scale up to large apertures (>2 m), since the corrector plate rapidly becomes prohibitively large, heavy, and expensive.

The basic Schmidt design Vignetting 5 box 1 scale

Cherenkov telescopes with large cameras and Gascoigne aspheric corrector plate could imagine 10 o to 15 o diameter Fresnel lens wide-angle instruments nontrivial Fresnel lens huge focal plane (10 5 + channels) would probably want several (stereo) instruments of 10 m class From talk by W. Hofmann, 2005

Modified Baker-Nunn optics Primary Mirror: 1.8m FoV: 50 deg Resolution: 1 arcmin Cost-performance balance

Collector light Fresnel lens Lens diameter 3 m Lens weight 30 kg Lens geometrical area 7.06 m2 Lens trasmittance 0.95 (300-600 nm) Lens rms 0.1 degrees Focal length 4.2 m f# 1.4 Focal plane MAPMT R7600-03-M64 PMT number 300 PMT operation mode counting Pixel number 19200 Focal plane pixel size 4 arcmin Total FoV 10.5 degrees Mount Alt-Alt GAW telescope camera Schematic view of GAW telescope

AGIS Early British-Irish, and Russian Observatories, 1960-1970 Recycled military hardware ~50K$ Whipple 10m, HEGRA 1980-2000 ~1-3M$ CTA HESS, MAGIC, VERITAS 2000 --, ~30M$ AGIS, CTA 2010 --, ~150-200 M$

Camera May be cost effective PMTs MAPMTs, SiPMs, HPDs, etc. II, CMOS incompatible with conventional prime focus telescope design Telescope May be cost effective incompatible with conventional operation at low energies $~D 2.6

Generalized Schwarzschild theorem: For any geometry with reasonable separations between the optical elements, it is possible to correct n primary aberrations with n powered elements. (1905)

Fp concave s F=Fp Fs / ( Fs - s + Fp) F/Dp > 1/2 FoV 4 D π 4 Fs concave 2 2 2 π FPS 90 2 Aplanatic Highly aspherical nonconic mirror surfaces Astigmatism and high order Coma can be contained within specs for FoV ~15 deg. Focal Plane Size, FPS, cannot be made arbitrary small

Karl Schwarzschild (1873-1916) Found exact solution for figures of two aspheric mirrors which correct spherical aberrations and coma Telescope has never been built! In 1926 Andre Couder optimized design (3 rd order) by introducing curved focal plane

2RMS < 3 over full 15 deg FoV can be achieved (V. Vassiliev, S. Fegan, astro-ph/0612718)

The lines show OSs with minimal astigmatism for a given value of α Preferred solution for use in ACT applications has α=0.7, q=0.606

Light Collecting Area Focal Plane Curvature

S-C D-C Reduction of plate scale by a factor of 3-4 is possible ~1/10 Camera Cost Camera Cost < 0.1M$ (potentially) dramatic reliability increase

Preferred solution for use in ACT applications has α=0.7, q=0.606 F=500cm Design is isochronous

(optical system is being developed at UCLA) (by V. Guarino, ANL) Required tolerance of optical system support and alignment is similar to radio telescopes in mm range, such as ALMA and LMT Replication technology (electroforming, glass slumping, etc. ) can be used to reduce costs of manufacturing of aspheric mirrors

(by V. Guarino, ANL)

Tolerances normals 0.1 mrad P 0.2 mrad S Design is isochronous positions ~1mm P ~.1 mm S Mirror requirements Surface ~ a few x 10 μm roughness ~30nm rms

Surface ~ 4 μm, ~50nm rms A 0.5 m diameter 5-layer corrugated mirror blank. This mirror is 50 mm thick and has an areal density of 8 kg/m2. This mirror blank was constructed in 5 days from flat sheet glass to the assembled mirror blank. The combination of corrugated mirror blanks and this glass replication technique is a process that will yield large volumes of lightweight finished mirrors at low cost. Once the non-recurring tooling has been built, finished 2 meter class mirror segments for IR telescopes could be built in a few weeks and segments for visible telescopes could be built in a couple of months.

High accuracy replication process From presentation by Oberto Citterio INAF-OAB

INAF Osservatorio Astronomico di Brera Italy From presentation by M. Ghigo

Prime focus design (D-C, Parabolic) provides robust moderate angular resolution, moderate FoV solution for a large array. Large plate scale of this design translates to costly FP detector composed of individual PMTs (reliability?) S-C design is adequate for small plate scale, high angular resolution, and large FoV telescopes. Increase of the cost per aspheric mirror (~100 mirrors) can be compensated by the decrease of the cost per channel in a small plate scale instrument (~10,000 ch). Potentially cost effective for mass production as well as reliable for multipixel integrated sensors

The 9m diameter original Schwarzschild IACT is an inexpensive, high-performance telescope that is easy-to-use, maintenancefree, and completely portable. Its wide field of view, beautiful images and ease of use make it an excellent telescope for beginner and expert optical and gamma-ray astronomer alike. just a dream