Development of superconductive imaging submillimeter-wave camera with nine detector elements (SISCAM-9)

Abstract

We have developed the superconductive imaging submillimeter-wave camera with nine detector elements (SISCAM-9) for Atacama Submillimeter Telescope Experiment (ASTE). SISCAM-9 has nine SIS photon detectors as focal plane array detector at 680 GHz. To obtain background noise limited sensitivity, we need to operate detectors under the condition that noise is dominated by shot noise of background photo current. To realize this condition, we fabricated low noise readout circuits using Si-JFETs. In laboratory, we evaluated performance of nine SIS photon detectors. This is the first demonstration of 2D array of SIS photon detector for SISCAM-9. Measuring I-V characteristics, detector gap voltages were 4.9 mV and photo currents were 3 nA. Measuring spectral responses, they had almost same center frequency of 679 GHz and bandwidths of 77 GHz. They almost matched to 675 GHz atmospheric window from ASTE site. Detector noise under 300 K radiation were only a few times as large as the shot noise of photo current. Detector NEP was 1.7x10 -15 W/Hz 1/2 ,with the detector quantum efficiencies of 12%. For the first time, SIS photon detectors worked under shot noise limited condition under 300 K background radiation. We have developed observation system, SISCAM-9, to realize the first astronomical observations. Detectors were mounted in a cryostat that can be remotely operated to cool the detectors to 0.46 K. We installed SISCAM-9 in the ASTE telescope and measured system performance such as photo current and noise characteristics. For the first time, SIS photon detectors operated under the observing condition. We succeeded in making the first astronomical observation of the moon.