Auto-Correlation Spectral Imaging System (ACSIS) is an IF, correlation, reduction, and display system for the submillimeter telescope James Clerk Maxwell Telescope (JCMT). It can produce calibrated spectral images in real time and enables rapid imaging of large areas of the sky over a wide spectral range or at high resolution from up to 16 receiver feeds. Now more than 20 years old, the original 8-10GHz synthesizers for the down conversion module are obsolete and no longer available. Due to the hardware changes in the new 4-10GHz model, an interface circuit is needed to shorten the rise time of the serial clock signal. Further upgrades can better support wide IF band 2-12GHz receiver applications, such as Atacama Large Millimeter Array (ALMA) band-6 receivers. This paper discusses the observatory’s development of a new correlator that utilizes several existing electronics to support current and future receivers.
The James Clerk Maxwell Telescope (JCMT) is the largest single dish telescope in the world focused on submillimeter astronomy - and it remains at the forefront of sub-millimeter discovery space. JCMT continues its push for higher efficiency and greater science impact with a switch to fully remote operation. This switch to remote operations occurred on November 1st 2019. The switch to remote operations should be recognized to be part of a decade long process involving incremental changes leading to Extended Observing - observing beyond the classical night shift - and eventually to full remote operations. The success of Remote Observing is indicated in the number of productive hours and continued low fault rate from before and after the switch.
Most telescope proposal science cases are governed by the need to achieve a given SNR (Signal-to-noise ratio). However, traditionally telescopes award applicants a certain number of hours rather than an SNR or noise. Noise calculators cannot solve this problem entirely, due to variations in weather, elevation and instrument performance when an observation is actually carried out. The JCMT is currently shifting towards awarding users (when appropriate) a given RMS towards their source/s instead of a time spent observing, initially for our new 230 GHz instrument Ū ū. The JCMT already had many necessary parts of this process in place (noise calculators, a robust ‘live’ pipeline, and an extremely flexible queue based system). This presentation describes our efforts to start implementing this process for our users, discusses the necessary systems and software required, and describes the lessons applicable for other observatories.
Namakanui is an instrument containing three inserts in an ALMA type Dewar. The three inserts are ‘Ala’ihi, ‘U’ū and ‘Āweoweo operating around 86, 230 and 345GHz. The receiver is being commissioned on the JCMT. It will be used for both Single dish and VLBI observations. We will present commissioning results and the system.
We have fabricated new superconductor-insulator-superconductor (SIS) mixers chips for the 16-element Heterodyne Array Receiver Program (HARP) instrument on the James Clerk Maxwell Telescope (JCMT). The original spare mixer chips were limited and not performed as well as the used ones in HARP. The ability to manufacture new mixer chips would therefore be important for the repair and upgrade of HARP. Our immediate goal is to replace the current nonfunctional mixers in HARP with new chips. We modified the designs of waveguide probe and the matching circuit of the SIS mixer chip. The newly designed chips were fabricated with a quality factor (Rsg/Rn) over 10. The double-sideband (DSB) receiver noise temperature (Trx) is lower than 80K at frequencies between 325 GHz and 375 GHz, which is comparable to the best of the original devices. Three of the sixteen mixers have been replaced and they work very well.
The Sub-millimeter Common-User Bolometer Array 2 (SCUBA-2) large format Transition Edge Sensor (TES) arrays are optimized to maximize mapping speed with two commissioned regular observing scan patterns. The ancillary instruments POLarimeter 2 (POL-2) and Fourier Transform Spectrometer 2 (FTS-2) impose different demands on the arrays compared to regular stand-alone SCUBA-2 observing. This includes a change in the background optical power loading on the arrays and a requirement for a larger dynamic range from the individual TES bolometers. In this paper, we discuss the process for optimizing the TES arrays specifically for POL-2 and FTS-2 operations and report the improvements that we have obtained.
SCUBA-2 is a world leading wide field submillimeter camera on the JCMT with two, large format background limited TES arrays, which are used to image simultaneously in the 450μm and 850um atmospheric windows. SCUBA-2 has been producing excellent science for over 6 years however, as we reported previously, excess in-band power loading of the arrays is a concern. One possibility that we considered was that the currently installed hot-pressed filters at the 4K stage were being warmed significantly above 4K by incoming infrared radiation. In an attempt to reduce the power loading we cryogenically tested a new 60K filter stack that incorporated a redesigned thermal blocking filter. A direct comparison was then made to the performance of the existing 60K filter stack installed in SCUBA-2. We saw a tremendous improvement in the infrared rejection with the new design and proceeded to install the new filter stack into SCUBA-2.
In this paper, we describe the testing and installation of the new and improved design of thermal blocking filter into the instrument and report the resulting performance change based on data from the first 12 months of science operation with the new filters. We also present the combined filter bandpass profiles as measured in-situ with FTS-2.
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.
Fourier transform spectroscopy (FTS) is a measurement technique widely used in characterizing the spectrum of light sources and the frequency response of detectors. Some “ghost” spectral lines, however, are often observed in measured Fourier transform spectra, such as high-frequency harmonics of the light source due to multiple reflections in the measurement system and unexpected high frequency lines owing to low-frequency interferences in the data acquisition. Here we study the effects of multiple reflections and low-frequency interferences on the THz spectra measured by a Fourier transform spectrometer for different THz sources and detectors. Experimental and simulation results will be presented.
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