Zhen-Hui Lin

Development of Superconducting Spectroscopic Array Receiver: A Multibeam 2SB SIS Receiver for Millimeter-Wave Radio Astronomy

We have developed a 3×3 multibeam sideband separation superconducting receiver-Superconducting Spectroscopic Array Receiver (SSAR)-for the 85-115 GHz frequency band. The receiver employs 2SB superconductor-insulator-superconductor (SIS) mixers with a typical single sideband (SSB) noise temperature of 60 K and image rejection ratio above 10 dB over the frequency band. Digital techniques are extensively applied in this receiver system for excellent operational stability and efficiency. They include fast Fourier spectrometers, digital LO and digital bias supplies. In our knowledge this is the first 2SB multibeam millimeter wavelength receiver in the world. This receiver has been successfully put into observation and its considerable enhancement of mapping speed has been demonstrated.

Upgrade procedure for the Delingha 13.7-m telescope

The 13.7-m millimeter-wave radio telescope of Purple Mountain Observatory operates at 3200-m above the sea level near Delingha, Qinghai Province, China. Equipped with a superconducting SIS receiver, the telescope is used in the millimeter-wave band ranging from 85 to 115 GHz. An upgrade procedure is reported here which includes a superconducting SIS receiver, a new phase-locked local oscillator, a dedicated multi-line backend system, and a new control system based on industrial computer with PCI bus. With the dedicated multi-line backend system, the CO and isotopic lines around 110 GHz are obtained simultaneously. In recent years, scientific activities with this telescope have been focused on studies of Galactic molecular clouds and star formation regions, including surveys of molecular lines from IRAS sources and large-scale map of molecular clouds. Other programs include studies of the circumstellar envelope of late-type stars and interaction of Galactic supernova remnants with dense molecular gas.

Development of a compact 500-GHz SIS receiver

We have constructed a 30-cm Portable Submillimeter Telescope (POST) which is dedicated mainly to explore the large-scale distribution of neutral atomic carbon along the galactic plane. The POST telescope is located at Delingha of Qinghai province (at an altitude of /spl sim/3200m) at present for the testing observation, and will be deployed to other sites of better atmospheric transparency at submillimeter wavelengths in the future. This telescope can be used for the site evaluation of the atmospheric environment as well. In this paper, we focus on the introduction of a compact 500-GHz superconductor-insulator-superconductor (SIS) receiver developed for the POST telescope.

The Superconducting Spectroscopic Array Receiver (SSAR) for Millimeter-wave Radio Astronomy

The studies on formation and evolution of interstellar molecular clouds and star formation give rise to high demands on imaging capability of millimeter-wave spectroscopic receiver. The Superconducting Spectroscopic Array Receiver (SSAR) of 3times3 pixels has been designed to work over 85-116 GHz. A number of new technological approaches are applied in the development of SSAR including of 4-K cooled superconducting SIS mixers using sideband separating scheme, automatically tuned digital bias, cooled SiGe HBT amplifiers, and digital FFT spectrometers. Development of the receiver system is undergoing. Upon completion, this instrument will enhance significantly the mapping capability in millimeter-wave line observations with high spectroscopic resolution. This paper introduces the main technological features applied in design and development of the receiver system.

Characterization of the Performance of a Quasi-Optical NbN Superconducting HEB Mixer

In this paper we focus mainly on the investigation of the performance of a quasi-optical (planar log-spiral antenna) phonon-cooled NbN superconducting hot electron bolometer (HEB) mixer, which is cryogenically cooled by a close-cycled 4-K cryocooler, at 500 and 850 GHz frequency bands. The mixers noise performance, stability of IF output power, and local oscillator (LO) power requirement are characterized for three NbN superconducting HEB devices of different sizes. The transmission characteristics of Mylar and Zitex films with incidence waves of an elliptical polarization are also examined by measuring the mixers noise temperature. The lowest receiver noise temperatures (with no corrections) of 750 and 1100 K are measured at 500 and 850 GHz, respectively. Experimental results also demonstrate that the bigger the HEB device is, the higher the stability of IF output power becomes.

Heterodyne Mixing and Direct Detection Performance of a Superconducting NbN Hot-Electron Bolometer

The heterodyne mixing and direct detection performance of a superconducting NbN hot-electron bolometer (HEB) integrated with a log-spiral antenna have been thoroughly characterized. The corrected receiver noise temperature and IF gain bandwidth are approximately 800 K at 0.5 THz, 750 K at 0.85 THz and 3 GHz at its optimum bias point. In addition, both the receiver noise temperature and IF gain bandwidth were found insensitive to the bath temperature, while the bias point was fixed, in good agreement with those simulated with the hot-spot model taking account of the HEBs current-dependent resistive transition. Furthermore, the HEBs frequency response was measured by a Fourier transform spectrometer at different bias points and bath temperatures. The estimated noise equivalent power (NEP) was close to 10-13 W/Hz0.5 around the HEBs transition temperature.

A 500-GHz Superconducting SIS Receiver for The Portable Submillimeter Telescope

We have developed a 500-GHz superconducting SIS (superconductor-insulator-superconductor) receiver for the Portable Submillimeter Telescope (POST), which, with an aperture of 30 cm, is a submillimeter-wave telescope dedicated mainly to explore the large-scale distribution of neutral interstellar gas along the galactic plane. The 500-GHz SIS receiver is developed on the basis of the parallel-connected twin junction tuning circuitry and is designed to be compact and of low power consumption to fulfill the requirement of portability. Performance of the superconducting receiver system and results from astronomical observation was presented.

THz Vector Field Measurement Comparison Between On-the-Fly and Step Scan Method

A fast terahertz vector field measurement system based on the on-the-fly (OTF) scan method is investigated. Compared with the step scan method, which samples at certain step, the OTF scan obtains the data with the scanner moving continuously, thus improving the measurement efficiency to some extent. The phase stability of the system is fully studied. Demonstration at approximately 500 GHz is compared with the result by the step scan method, showing that the OTF method can improve the measurement speed by a factor of 7 while the data accuracy is almost the same. Measurements at different scanning speeds and with different probes are also compared to understand their effects.

An 8×8 CPW MKIDs developed for terahertz superconducting imaging array

China is planning to construct a 5-meter THz telescope named DATE5 at Dome A, Antarctica. This paper reports on the development of an 8×8 CPW microwave kinetic detectors (MKIDs) for the terahertz superconducting imaging array (TeSIA), which is an instrument proposed for the DATE5. The 8×8 CPW MKIDs, operating at 0.35THz, make use of TiN superconducting film of Tc approximately equal to 4.3K. The resonance frequencies of the MKIDs span the 4-5.575GHz band with an interval of 25MHz. The design, fabrication and characterization of the 8×8 CPW MKIDs are presented.

Frequency spectrum of a THz QCL in pulse mode measured by an FTS system

In this paper, we report on the spectrum measurement of a terahertz (THz) pulse signal using a Fourier transform spectroscopy (FTS) system. The THz pulse signal is a quantum cascade laser (QCL) at 3.7THz with changeable repeating frequency and duty cycle. With a fixed duty cycle, the repeating frequency is changed to investigate the maximum value that can be measured with an FTS system. The relationship between the spectrum intensity and the pulse width is investigated through the variance of the duty cycle with a given repeating frequency. Detailed experimental results will be presented.