New far infrared and millimetric telescopes for differential measurements with a large chopping angle in the sky

Marco De Petris; Massimo Gervasi; Fabrizio Liberati

doi:10.1364/AO.28.001785

Applied Optics
Vol. 28,
Issue 10,
pp. 1785-1792
(1989)
•https://doi.org/10.1364/AO.28.001785

New far infrared and millimetric telescopes for differential measurements with a large chopping angle in the sky

Marco De Petris, Massimo Gervasi, and Fabrizio Liberati

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Marco De Petris, Massimo Gervasi, and Fabrizio Liberati, "New far infrared and millimetric telescopes for differential measurements with a large chopping angle in the sky," Appl. Opt. 28, 1785-1792 (1989)

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Abstract

The optical design of two Cassegrain-type telescopes of 1200- and 2500-mm primary mirrors has been studied by wobbling subreflectors to obtain differential measurements in wavelengths ranging from 300 μm to 2 mm of the spectrum. Wide chopping angles in the sky have been reached in spite of the large apertures and high secondary magnifications. Diffraction-limited performances are maintained by tilting the secondary mirror around the primary focus. This work is included in the TIR (Telescopio InfraRosso) project.

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Telescope: 1200 mm
Minimum frequency for two fields of modulation	6.4 × 10⁻³ c/mm
Minimum frequency for three fields of modulation	9.9 × 10⁻³ c/mm
Maximum frequency for a 45-mm detector aperture	1.1 × 10⁻² c/mm
Telescope: 2500-mm flux collector
Minimum frequency for two fields of modulation	5.1 × 10⁻³ c/mm
Minimum frequency for three fields of modulation	8.3 × 10⁻³ c/mm
Maximum frequency for a 45-mm detector aperture	1.1 × 10⁻² c/mm
Telescope: 2500-mm array
Minimum frequency (maximum sky separation)	1.1 × 10⁻² c/mm
Maximum frequency for a 9-mm detector aperture	5.5 × 10⁻² c/mm
Maximum frequency for a 3-mm detector aperture	1.6 × 10⁻¹ c/mm

Primaries
Primary diameter	2500 mm
Primary curvature radius	2494.5 mm
Primary f/No.	0.5
Flux collector configuration
Effective primary diameter	2000 mm
Subreflector diameter	410 mm
Subreflector curvature radius	539.78 mm
Cassegrain f/No.	4.05
Effective focal length	8151 mm
Distance subreflector–primary mirror	1019 mm
Distance subreflector–Cassegrain focus	1480 mm
Distance subreflector vertex–pivot axis	228.6 mm
Magnification	8.1
Cone aperture diameter	45 mm
Half power beamwidth	19.2 min of arc
Maximum sky field separation	1.05°
Maximum subreflector chop angle	2.5°
Telescope throughput	0.77 cm² sr
Array configuration
Effective primary diameter	2400 mm
Subreflector diameter	360 mm
Subreflector curvature radius	434.01 mm
Cassegrain f/No.	3.97
Effective focal length	9273 mm
Distance subreflector–primary mirror	1059 mm
Distance subreflector–Cassegrain focus	1393 mm
Distance subreflector vertex–pivot axis	181.5 mm
Magnification	7.94
Cone aperture diameter A	3 mm
Cone aperture diameter B	9 mm
Half-power beamwidth A	1.15 min of arc
Half-power beamwidth B	3.45 min of arc
Maximum sky field separation	31.5 min of arc
Maximum subreflector chop angle	1.5°
Telescope throughput A	3.4 × 10⁻³ cm² sr
Telescope throughput B	3.1 × 10⁻² cm² sr

Primary diameter	1200 mm
Primary curvature radius	1002 mm
Primary f/No.	0.417
Effective primary diameter	900 mm
Subreflector diameter	250 mm
Subreflector curvature radius	296.1 mm
Cassegrain f/No.	3.0
Effective focal length	2645 mm
Distance subreflector–primary mirror	380.4 mm
Distance subreflector–Cassegrain focus	620.2 mm
Distance subreflector vertex–pivot axis	114.3 mm
Magnification	7.2
Cone aperture diameter	45 mm
Half power beamwidth	1.0°
Maximum sky field separation	2.36°
Maximum subreflector chop angle	4°
Telescope throughput	1.52 cm² sr
Photometer throughput	0.62 cm² sr

Telescope: 1200 mm
Minimum frequency for two fields of modulation	6.4 × 10⁻³ c/mm
Minimum frequency for three fields of modulation	9.9 × 10⁻³ c/mm
Maximum frequency for a 45-mm detector aperture	1.1 × 10⁻² c/mm
Telescope: 2500-mm flux collector
Minimum frequency for two fields of modulation	5.1 × 10⁻³ c/mm
Minimum frequency for three fields of modulation	8.3 × 10⁻³ c/mm
Maximum frequency for a 45-mm detector aperture	1.1 × 10⁻² c/mm
Telescope: 2500-mm array
Minimum frequency (maximum sky separation)	1.1 × 10⁻² c/mm
Maximum frequency for a 9-mm detector aperture	5.5 × 10⁻² c/mm
Maximum frequency for a 3-mm detector aperture	1.6 × 10⁻¹ c/mm

Primaries
Primary diameter	2500 mm
Primary curvature radius	2494.5 mm
Primary f/No.	0.5
Flux collector configuration
Effective primary diameter	2000 mm
Subreflector diameter	410 mm
Subreflector curvature radius	539.78 mm
Cassegrain f/No.	4.05
Effective focal length	8151 mm
Distance subreflector–primary mirror	1019 mm
Distance subreflector–Cassegrain focus	1480 mm
Distance subreflector vertex–pivot axis	228.6 mm
Magnification	8.1
Cone aperture diameter	45 mm
Half power beamwidth	19.2 min of arc
Maximum sky field separation	1.05°
Maximum subreflector chop angle	2.5°
Telescope throughput	0.77 cm² sr
Array configuration
Effective primary diameter	2400 mm
Subreflector diameter	360 mm
Subreflector curvature radius	434.01 mm
Cassegrain f/No.	3.97
Effective focal length	9273 mm
Distance subreflector–primary mirror	1059 mm
Distance subreflector–Cassegrain focus	1393 mm
Distance subreflector vertex–pivot axis	181.5 mm
Magnification	7.94
Cone aperture diameter A	3 mm
Cone aperture diameter B	9 mm
Half-power beamwidth A	1.15 min of arc
Half-power beamwidth B	3.45 min of arc
Maximum sky field separation	31.5 min of arc
Maximum subreflector chop angle	1.5°
Telescope throughput A	3.4 × 10⁻³ cm² sr
Telescope throughput B	3.1 × 10⁻² cm² sr

Abstract

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Figures (12)

Tables (3)

Equations (5)

Applied Optics