LTD16, Grenoble, 2015

Prototype High Angular Resolution LEKIDs for NIKA2

1. Institut de RadioAstronomie Millimétrique (IRAM) 2. Université Grenoble Alpes 3. Institut Néel & CNRS

Focal Plane Design

Experiment Result

Shibo Shu1,2, Samuel Leclercq1, Alessandro Monfardini2,3 Martino Calvo2,3 and Eduard Driessen1

Experiment Setup

Reference & Acknowledgement

NIKA2 1 mm Array This work

Inductor size 1.5*1.6 mm2 1*1 mm2

Pixel size 2*2 mm2 1.4*1.4 mm2

Resonance frequency 1.9-2.4 GHz 2.1-2.6 GHz

Number of Pixels 1140 1312

Pixels per readout line (500 MHz) 120-162 140-192

Coupling Q 10-15 K 10-15 K

Inductor width 4 μm 2.5 μm

Inductor volume 1149 μm3 449 μm3

Array diameter 80 mm 60 mm

Field-of-view 6.5' 4.9'

Resolution [FWHM] 10.80" 9.77"

50 K blackbody "Sky"

300 K ⌀4 mm metal ball "Planet"

"transparent" Nylon line

Distance to window: 0.6 mx

y

Sky simulator setup

• New IRAM KID Arrays 2 (NIKA2)1 is a lumped element kinetic inductance detector (LEKID)2,3 based instrument

• It has been installed at the IRAM 30-m telescope at Pico Veleta, Spain, in Oct. 2015

• Two frequency bands: • one polarization-insensitive 150 GHz (2 mm) array • two polarization-sensitive 260 GHz (1 mm) arrays

Introduction: NIKA2• A microstrip readout design • Polarization-insensitive Hilbert pattern inductor design • Band coverage: 230 - 275 GHz • Current 1 mm array design with 1.6 mm inductor size achieved

10.9" resolution on sky

1mm Array• To further approach the diffraction limit of the telescope, a 1

mm inductor is designed to have 9.8" resolution • We push the focal plane layout to a compact 1.4*1.4 mm2

pixel size design • The resolution of two arrays with 1 and 1.6 mm size inductors

are measured and analyzed

This work

3λ/4 250 μm

PhotonsLEKIDs

Back shortillumination mechanism of microstrip line readout LEKID

Pixel Design• We followed the NIKA2 1mm design with 130 μm width microstrip

readout, Hilbert pattern4, 250 μm backshort and 20 nm thick Al • Inductor width is decreased from 4 to 2.5 μm to match the free

space impedance

NIKA2 1mm Array This work

• A Gaussian distribution is used to fit the calculated Airy pattern

• After considering the cold pupil, the effective aperture is decreased to 27.5 m

• Calculated resolution improvement ratio is 1.11

Dx

Design Configuration

2*Dy

1

4

250

Resonance frequency shift compared to single LEKID

Resonance frequency changed by tuning capacitor finger length

• Sensitivity of this design is ~2 times higher than the current array

• Mapping speed is 39% of current 1 mm array with fixed readout bandwidth

• With doubled bandwidth, we could fill in our whole focal plane and have the same mapping speed

1. Adam, R., Adane, A., Ade, P. A. R., André, P., Andrianasolo, A., Aussel, H., et al (2017). arXiv preprint arXiv:1707.00908.

2. Day, P. K., LeDuc, H. G., Mazin, B. A., Vayonakis, A., & Zmuidzinas, J. (2003). Nature, 425(6960), 817-821.

3. Doyle, S., Mauskopf, P., Naylon, J., Porch, A., & Duncombe, C. (2008). Journal of Low Temperature Physics, 151(1), 530-536.

polarization direction

• Both arrays are fabricated with same process and measured during the same cooldown.

• The smaller pixels show a lower Qi than 1mm array under radiation

• This is caused by the high sensitivity resulting from smaller inductor volume

• NIKA2 1mm Array is not centered and located 5 mm away from the focal plane.

• This map shows a factor of 4 in frequency response difference.

• A factor of 2 could be explained by the misalignment, another factor of 2 is due to the sensitivity (confirmed with hot--cold load measurement).

• The new pixel design shows a factor 1.3 improvement in FWHM and only approximately 10% could be explained by the misalignment

• More accurate measurement are underway, but iimprovement of resolution is already demonstrated

4. Roesch, M., Benoit, A., Bideaud, A., Boudou, N., Calvo, M., Cruciani, A., ... & Leclercq, S. (2012). arXiv preprint arXiv:1212.4585.

• This work has been partially funded by the LabEx FOCUS ANR--1-LABX-0013. The authors would like to thank NIKA2 group and Akira Endo for helpful discussion.

polarizer

cold pupil two arrayssky simulator and planet cryostat

Distance to window: 0.6 m

Optics of test cryostat

• Planet is held by a thin Nylon wire with a 50 K blackbody behind. The scan is done in y-axis with x-axis sampled every 2 mm

• Measurements are done at a base temperature of 70 mK and resonances are read out with the same NIKEL system that is used for NIKA2

• The final data acquisition rate is 23.84 Hz

• The optics and sky simulator are designed to optically behave the same as the real instrument at the 30-m telescope: the planet image on focal plane <-> point spread function on telescope

• This optics has a F#1.48 and a magnification factor of 0.38

• With the polariser, we could measure two arrays simultaneously and the polarization directions are in parallel with the capacitor fingers of each array

cut plane

Numbers: FWHM [mm]

NIKA2 1 mm Array This work

FWHM: 16.26 +/- 0.11 mmFWHM: 12.11 +/- 0.06 mm

Model: Gaussian + Linear

NIKA2 1 mm Array This work