Optics Design and Verification for the APEX Swedish Heterodyne Facility Instrument (SHeFI)

• We present the design and verification of the receiver optics for the Single-Pixel HeterodyneFacility Instrument (SHFI) of the APEX telescope [1]. The SHFI is designed to cover thefrequency band 211 – 1390 GHz in 6 receiver channels. Four of the receiver channels have beendesigned, installed and characterized: 211-275 GHz (Band 1); 275-370 GHz (Band 2); 385-500 GHz (Band 3); 1250-1390 GHz (Band T2). The first three bands employ 2SB SIS mixertechnology and Band T2 employs HEB mixers in a waveguide balanced mixer configuration.The entire optics design was driven by the receiver position in the telescope Nasmyth cabin“A” (Fig.1) and the aperture limit of Ø150 mm, introduced by the elevation encoder inside theNasmyth tube A. This layout and the telescope geometry (~ 6 m distance from the focal plane tothe Cabin A) lead us to choose a single-pixel configuration and required using intermediateoptics with long focal distances. The common optics path, coupling the receivers to theCassegrain sub-reflector, consists of the three offset ellipsoidal mirrors, M3, M6, M8s, and threeflat mirrors, F4, F5, and F7s. The combination M3 and M6 via flat F4, F5, creates a Gaussiantelescope, providing frequency-independent re-imaging of the antenna focal plane from theCassegrain cabin into the Nasmyth cabin A. Switching between channels is achieved by theprecision rotating of the active mirror M8s. The mirror M8s in combination with each channelactive mirror M10 provides re-imaging of the secondary onto the feed horn aperture of theselected channel. Such a configuration provides frequency independent illumination of thesecondary with the edge taper -12dB. The angular position of the flat mirrors F9 is adjustable andgives additional possibility of fine-tuning of the beam alignment from the common optics toevery receiver channels.Verification of the optical designthrough measurements is essential inorder to align the beams from thecryostat windows to the commonoptics to minimize loss in thequasioptical guiding system. In orderto verify the design of the cold optics(corrugated horn + M10) in terms ofGaussian beam parameters, a newwideband vector field measurementsystem was developed [2]. Vectorfield measurements were performedfor band 1, 2, and 3, and scalarmeasurements were employed for theTHz band.

Subject headings

TEKNIK OCH TEKNOLOGIER  -- Elektroteknik och elektronik -- Annan elektroteknik och elektronik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Electrical Engineering, Electronic Engineering, Information Engineering -- Other Electrical Engineering, Electronic Engineering, Information Engineering (hsv//eng)

Keyword

Millimeter and Submillimeter Optics

APEX Telescope

Publication and Content Type

kon (subject category)

ref (subject category)