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Optical design and verification of the sub-millimeter limb sounder TELIS
P. Yagoubov1, G. de Lange1, A. Baryshev2, R. Hesper2, V. Koshelets3, G. Wagner4, M. Birk4, A. Murk5
1Na

tional Institute for Space Research, SRON, the Netherlands 2Kapteyn Astronomical Institute /SRON 3Institute of Radio Engineering and Electronics, IREE, Russia 4Institute for Remote Sensing Technology, DLR, Germany 5Institute of Applied Physics, University of Bern, Switzerland

Vertical scan, mm

Vertical scan, mm

TELIS (Terahertz and submm Limb Sounder) is a cooperation between European institutes, DLR, RAL and SRON, to build a three-channel balloon-borne heterodyne spectrometer for atmospheric research. The optical front-end of the instrument consists of a dual-offset Cassegrain pointing telescope (elliptical shape 28x14 cm), calibration blackbody and the relay optics (common for the three channels). Beam separation between the channels is performed quasioptically by a dichroic filter and a polarizer. After the splitting, the three beams enter the liquid helium cooled cryostat, where each receiver has dedicated cold optics and mixer elements. In this poster we present the optical design and verification of the quasioptical 500 - 650 GHz channel for TELIS. It is based on a phase-locked Superconducting Integrated Receiver (SIR). The SIR chip is placed on the flat back surface of the elliptical silicon lens forming an integrated lens-antenna. Further shaping and relaying of the beam is done by means of reflective optics. Design and validation of the optics, as well as estimation of optical components tolerances, have been performed using commercial software packages ZEMAX and GRASP. We present experimental results of the far field amplitude beam measurements of the integrated lensantenna, amplitude-phase measurements of the SIR cold optics and first results of the vertical beam profile of the complete instrument performed at 600 GHz.

Abstract

Cold optics design & amplitude-phase measurements
Integrated lens-antenna (L6) Magnetic shield Ellipse (L3) SSB Wire grid Window (L2)

Termination load Flat

Parabola (L1)

Cryostat
Parabola (L5) Hyperbola (L4)

Layout of the SIR cold channel. In the test flight the SIR will operate in double sideband mode; SSB filter is replaced by a set of two plane mirrors (not shown in the picture).

Optical (dotted line) and quasioptical (solid line) trajectories (1/e field level @625GHz) in the cold channel. The curved mirrors (L1), (L3), (L4) and L5), the window (L2) and the integrated lensantenna (L6) are given schematically as thin vertical lines, representing thin lenses.

-60.00

-180.0

30 20 10 0 -10 -20 -30 -30 -20 -10 0 10 20 30

-54.00 -48.00 -42.00 -36.00 -30.00 -24.00 -18.00 -12.00 -6.000 0

30 20 10 0 -10 -20 -30 -30 -20 -10 0 10 20 30

-150.0 -120.0 -90.00 -60.00 -30.00 0 30.00 60.00 90.00 120.0 150.0 180.0

SIR chip design & Integrated lens-antenna characterization

Horizontal scan, mm

Horizontal scan, mm

FFO

SIR cold channel amplitude distribution. Distance from the waist position ­ 110mm. Frequency 600GHz.

SIR cold channel phase distribution. Distance from the waist position ­ 110mm. Frequency 600GHz.

HM Antenna & SIS mixer

SIR channel optics design
On-chip integration of the mixer and LO ­ Superconducting Integrated Receiver Quasioptical coupling using integrated lensantenna configuration
Liquid helium cryostat 4.2 K Telescope primary Secondary Tertiary Integrated lens-antenna Calibration load Polarizer Warm optics Cold optics

Dichroic

Window

Far-field 2D scan of the integrated lensantenna beam pattern. The isolines are at -5 dB, -10 dB, -15 dB, -20 dB etc
5 0 -5 -10

Schematics of the 500-650 GHz channel optics. The telescope is rotated around the axis coinciding with the direction of the output beam. W ire grid polarizer and dichroic plate are used to separate this receiver from the two other frequency channels (not shown). The cold optics and mixer element are located inside the cryostat at the ambient temperature 4.2 K.

Calculated by GRASP far field 1-D vertical (elevation) cut and Azimuthally Collapsed Antenna Pattern (ACAP) at 625 GHz.

Co-polar, dBi

-15 -20 -25 -30 -35 -40 -45 -6 -4 -2 0 2 4 6

Integrated lens-antenna has been modeled using PILRAP. Far field amplitude beam measured at 600GHz is in a good agreement with simulations. The optics has been designed using 1-D MathCad tool and verified by GRASP. Amplitude-phase beam measurements of the cold optics are performed at 600GHz. The measured beam waist is 2.25mm (within1% of the designed value), Gaussisity of the measured beam is 92.4%. Compact range (copy of the TELIS telescope with horizontally oriented slit source at the focus) is setup for the vertical beam profile measurements. Preliminary tests indicate 0.4deg FW HM beam at 600GHz, in excellent agreement with the design. The corresponding beamsize at tangent point is 1.6km.
vertical scan horizontal scan PILRAP simulation

Summary

Scan angle, deg

Vertical (blue curve) and horizontal (red curve) far-field scans. The fit (black curve) is calculated by PILRAP.

The authors thank M. van der Vorst for supplying PILRAP (Program for Integrated Lens and Reflector Antenna Parameters) and Jan Barkhof for assistance in amplitude-phase beam measurements. For further information p.a.yagoubov@sron.rug.nl please contact:

Acknowledgments