Jenna Kloosterman

Hot electron bolometer heterodyne receiver with a 4.7-THz quantum cascade laser as a local oscillator

We report on a heterodyne receiver designed to observe the astrophysically important neutral atomic oxygen [OI] line at 4.7448 THz. The local oscillator is a third-order distributed feedback quantum cascade laser operating in continuous wave mode at 4.741 THz. A quasi-optical, superconducting NbN hot electron bolometer is used as the mixer. We recorded a double sideband receiver noise temperature (T-rec(DSB)) of 815 K, which is similar to 7 times the quantum noise limit (hv/2k(B)) and an Allan variance time of 15 s at an effective noise fluctuation bandwidth of 18 MHz. Heterodyne performance was confirmed by measuring a methanol line spectrum

The Stratospheric THz Observatory (STO)

The Stratospheric TeraHertz Observatory (STO) is a NASA funded, Long Duration Balloon (LDB) experiment designed to address a key problem in modern astrophysics: understanding the Life Cycle of the Interstellar Medium (ISM). STO will survey a section of the Galactic plane in the dominant interstellar cooling line [C II] (1.9 THz) and the important star formation tracer [N II] (1.46 THz) at ~1 arc minute angular resolution, sufficient to spatially resolve atomic, ionic and molecular clouds at 10 kpc. STO itself has three main components; 1) an 80 cm optical telescope, 2) a THz instrument package, and 3) a gondola [1]. Both the telescope and gondola have flown on previous experiments [2,3]. They have been reoptimized for the current mission. The science flight receiver package will contain four [CII] and four [NII] HEB mixers, coupled to a digital spectrometer. The first engineering test flight of STO was from Ft. Sumner, NM on October 15, 2009. The ~30 day science flight is scheduled for December 2011.

Test and integration results from SuperCam: a 64-pixel array receiver for the 350 GHz atmospheric window

We report on both laboratory and telescope integration results from SuperCam, a 64 pixel imaging spectrometer designed for operation in the astrophysically important 870 micron atmospheric window. SuperCam will be used to answer fundamental questions about the physics and chemistry of molecular clouds in the Galaxy and their direct relation to star and planet formation. The SuperCam key project is a fully sampled Galactic plane survey covering over 500 square degrees of the Galaxy in 12CO(3-2) and 13CO(3-2) with 0.3 km/s velocity resolution In the past, all heterodyne focal plane arrays have been constructed using discrete mixers, arrayed in the focal plane. SuperCam reduces cryogenic and mechanical complexity by integrating multiple mixers and amplifiers into a single array module with a single set of DC and IF connectors. These modules are housed in a closed-cycle cryostat with a 1.5W capacity 4K cooler. The SuperCam instrument is currently undergoing laboratory testing with four of the eight mixer array modules installed in the cryostat (32 pixels). Work is now underway to perform the necessary modifications at the 10m Heinrich Hertz Telescope to accept the SuperCam system. SuperCam will be installed in the cassegrain cabin of the HHT, including the optical system, IF processing, spectrometers and control electronics. SuperCam will be integrated with the HHT during the 2009-2010 observing season with 32 pixels installed. The system will be upgraded to 64 pixels during the summer of 2010 after assembly of the four additional mixer modules is completed.

SuperCam: a 64 pixel heterodyne imaging spectrometer

We report on the development of SuperCam, a 64 pixel imaging spectrometer designed for operation in the astrophysically important 870 micron atmospheric window. SuperCam will be used to answer fundamental questions about the physics and chemistry of molecular clouds in the Galaxy and their direct relation to star and planet formation. The Supercam key project is a fully sampled Galactic plane survey covering over 500 square degrees of the Galaxy in 12CO(3-2) and 13CO(3-2) with 0.3 km/s velocity resolution.

A 4.7THz heterodyne receiver for a balloon borne telescope

We report on the performance of a high sensitivity 4.7 THz heterodyne receiver based on a NbN hot electron bolometer mixer and a quantum cascade laser (QCL) as local oscillator. The receiver is developed to observe the astronomically important neutral atomic oxygen [OI] line at 4.7448 THz on a balloon based telescope. The single-line frequency control and improved beam pattern of QCL have taken advantage of a third-order distributed feedback structure. We measured a double sideband receiver noise temperature (Trec(DSB)) of 815 K, which is ~ 7 times the quantum noise limit (hν/2kB). An Allan time of 15 s at an effective noise fluctuation bandwidth of 18 MHz is demonstrated. Heterodyne performance was further supported by a measured methanol line spectrum around 4.7 THz.

First observations with SuperCam and future plans

Supercam is a 345 GHz, 64-pixel heterodyne imaging array for the Heinrich Hertz Submillimeter Telescope (HHSMT). By integrating SIS mixer devices with Low Noise Ampliers (LNAs) in 8 - 1x8 pixel modules, the size needed for the cryostat and the complexity of internal wiring is signicantly reduced. All subsystems including the optics, cryostat, bias system, IF boxes, and spectrometer have been integrated for all 64 pixels. In the spring of 2012, SuperCam was installed on the HHSMT for an engineering run where it underwent system level tests and performed rst light observations. In the fall of 2012 SuperCam will begin a 500 square degree survey of the Galactic Plane in 12CO J=3-2. This large-scale survey will help answer fundamental questions about the formation, physical conditions, and energetics of molecular clouds within the Milky Way. The data set will be available via the web to all interested researchers.

Large format heterodyne arrays for observing far-infrared lines with SOFIA

In the wavelength regime between 60 and 300 microns there are a number of atomic and molecular emission lines that are key diagnostic probes of the interstellar medium. These include transitions of [CII], [NII], [OI], HD, H2D+, OH, CO, and H2O, some of which are among the brightest global and local far-infrared lines in the Galaxy. In Giant Molecular Clouds (GMCs), evolved star envelopes, and planetary nebulae, these emission lines can be extended over many arc minutes and possess complicated, often self absorbed, line profiles. High spectral resolution (R> 105) observations of these lines at sub-arcminute angular resolution are crucial to understanding the complicated interplay between the interstellar medium and the stars that form from it. This feedback is central to all theories of galactic evolution. Large format heterodyne array receivers can provide the spectral resolution and spatial coverage to probe these lines over extended regions. The advent of large format (~100 pixel) spectroscopic imaging cameras in the far-infrared (FIR) will fundamentally change the way astronomy is performed in this important wavelength regime. While the possibility of such instruments has been discussed for more than two decades, only recently have advances in mixer and local oscillator technology, device fabrication, micromachining, and digital signal processing made the construction of such instruments tractable. These technologies can be implemented to construct a sensitive, flexible, heterodyne array facility instrument for SOFIA. The instrument concept for StratoSTAR: Stratospheric Submm/THz Array Receiver includes a common user mounting, control system, IF processor, spectrometer, and cryogenic system. The cryogenic system will be designed to accept a frontend insert. The frontend insert and associated local oscillator system/relay optics would be provided by individual user groups and reflect their scientific interests. Rapid technology development in this field makes SOFIA the ideal platform to operate such a modular, continuously evolving instrument.

Micromachined Integrated Waveguide Transformers in THz Pickett–Potter Feedhorn Blocks

We present the design, fabrication technique, and performance of a circular-to-rectangular waveguide transformer integrated into a 1.9 THz Pickett–Potter feedhorn detector block. This design is applicable for instruments where circularly symmetric feedhorns are required to mate with rectangular waveguide-fed receiver devices that house the detector chip. The transformer was fabricated by direct metal micromachining, which offers significant advantages in reducing the complexity, timescale, and cost of manufacturing over competing techniques, such as transformer segments machined into separate blocks or machined into split-block segments. We simulate the tradeoff between the fabrication technique and the cost of rounding the edges of the rear rectangular waveguide. Simulations of the transformer circuitry using multiple electromagnetic software packages were used to finalize the dimensions of the optimized transformer. A single pixel feedhorn-transf ormer module was manufactured on a three-axis milling machine to test the feasibility of the design and manufacturing technique. We tested the performance of the integrated feedhorn-transformer modules using waveguide-fed hot electron bolometer mixers designed and fabricated at the Jet Propulsion Laboratory. Radiation patterns of the Pickett–Potter modules were measured using a high-power 1.9 THz multiplication chain as the source. We find good agreement between the simulated and measured beam pattern.