1. Beam Measurement Characterization and Optics Tolerance Analysis of a 900 GHz HEB receiver for the ASTE telescope
Alvaro Gonzalez, K. Kaneko, Y. Uzawa
National Astronomical Observatory of Japan, NAOJ
T. Soma, T. Shiino, S. Yamamoto
University of Tokyo

2. Outline ASTE Telescope ASTE THz receiver by Univ. of Tokyo
Noise temperature
900-GHz optics
Beam pattern measurements at NAOJ
Tolerance analyses
Conclusions

3. ASTE (Atacama Submm Telescope Experiment)
ASTE is operated by NAOJ as part of the Chile Observatory together with ALMA

4. THz receiver for ASTE Dual band receiver (0.9 and 1.5 THz)
Trx=350 K
1.475 THz
Trx=490 K
NbTiN mixers
Dual band receiver
(0.9 and 1.5 THz)
based on NbTiN HEB mixers
with state-of-the-art
noise temperature performance

5. Sensitivity of a telescope
Sensitivity indicates the faintest signal flux detectable with a telescope.
Nsys: noise power introduced by antenna and receiver. Also specified as noise temperature. Nsys depends on the efficiency η. Usually, higher η means less Nsys.
η: radiation coupling efficiency from aperture to detector
A: total collecting aperture area
BW: observation bandwidth
τ: observation integration time
Detector
(+ Optics)
Antenna and Receiver Optics
Antenna size / Interferometry
Limited by receiver technology

6. Receiver RF optics
Efficiently bring the EM radiation from antenna secondary to the detectors
Good efficiency optics reduce observation times, improve sensitivity for a given time, introduce polarization discrimination
Mixers noise, atmosphere, antenna… usually limit the sensitivity. However, improvement of optics is necessary too!
Daily Telegraph
Maybe too much information. Just keep point 3 as a conclusion. Highlight that normally the attention in on the detector, antenna, atmosphere… in the case of ALMA optics become very important to improve sensitivity

7. ASTE THz receiver and ALMA band 10
ALMA type cartridge
RF frequencies of the lower freq band overlap ALMA band 10
IF frequencies and mixer technology are different from ALMA band 10
HEB vs SIS
IF ~1 GHz vs IF 4-12 GHz
ALMA band 10 test cryostat and beam measurement system modified for characterization of this receiver

8. Modification of LO injection
ASTE LO injection from side window in cryostat
ALMA band 10 test cryostat only has 1 top window
LO injection from top cryostat window was possible

9. Beam measurement system
Based on: A. Gonzalez et al, Infrared Phys&Tech (2011) 54:488

10. Experimental set-up

11. Physical Optics simulations

12. Measurement results
Far-fields were also calculated

13. Tolerance analysis Physical Optics (GRASP)
Based on A. Gonzalez, Y. Uzawa, IEEE Trans AP, Vol. 60, No. 7, July 2012
3. Beams received by optics and horns with errors
Mirrors/horns orientation angles/ offsets, mirror shapes, horn dimensions and radiating modes…
1. Random values for diagonal horn and optics analysis
Analysis software (MATLAB)
4. Gaussian beam
parameters calculated
Physical Optics (GRASP)
2. Accurate analysis at THz freq
This analysis is repeated thousands of times with different sets of random errors
and efficiency statistics are generated

14. Tolerance analysis
Design variables as Gaussian variables with average = design value and std dev = tolerance/3
First set of analysis
1. 20-um fabrication, assembly errors
+ 1mrad for pointing errors (usual tolerance values)
2. Double values for errors
3. Same as 1. but with diagonal horn feeding errors
Second set of analysis
Ideal optics but large errors in diagonal horn (non- diagonal shape + feeding errors)
Ideal optics but large errors in mirror (non-ellipsoidal shape)
All results showed radiation patterns without much distortion

15. Confirmation of fabrication error
By room-temp measurement of beam reflected in mirror
By 3D laser measurement

16. Observation with ASTE
In spite of the defective mirror, observations could be successfully performed in the ASTE telescope
Orion A 13CO J=8-7
P.W.V.~0.19 mm, Y factor ~ 0.9 dB
Orion A HDO
P.W.V.~0.23 mm, Y factor ~ 0.6 dB
Artificial

17. Conclusions
Optics of HEB receiver (~900 GHz) designed by Prof. Yamamoto’s group at University of Tokyo have been characterized
Results show distorted beams, which translates in reduced efficiencies and image distortion of astronomical sources
The proposed tolerance analysis show that measurement results can only be explained by fabrication defaults in ellipsoidal mirror
Measurement results confirm large defaults in the current mirror
The proposed tolerance analysis is useful not only to assess performance ranges of optics, but also to identify defective components
A. Gonzalez et al, J Infrared Milli Terahtz waves (2014) 35:743