We report measurements of the fluctuations in atmospheric emission (atmospheric noise) above Mauna Kea
recorded with Bolocam at 143 GHz. These data were collected in November and December of 2003 with Bolocam
mounted on the Caltech Submillimeter Observatory (CSO), and span approximately 40 nights. Below ≃ 0.5 Hz,
the data time-streams are dominated by the f-δ atmospheric noise in all observing conditions. We were able to
successfully model the atmospheric fluctuations using a Kolmogorov-Taylor turbulence model for a thin wind-driven
screen in approximately half of our data. Based on this modeling, we developed several algorithms to
remove the atmospheric noise, and the best results were achieved when we described the fluctuations using a
low-order polynomial in detector position over the 8 arcminute focal plane. However, even with these algorithms,
we were not able to reach photon-background-limited instrument photometer (BLIP) performance at frequencies
below ≃ 0.5 Hz in any observing conditions. Therefore, we conclude that BLIP performance is not possible from
the CSO below ≃ 0.5 Hz for broadband 150 GHz receivers with subtraction of a spatial atmospheric template
on scales of several arcminutes.
We have developed a completely lithographic antenna-coupled bolometer
for CMB polarimetry. The necessary components of a millimeter wave radiometer - a beam forming element, a band defining filter, and the TES detectors - are fabricated on a silicon chip with photolithography. The densely populated antennas allow a very efficient use of the focal plane area. We have fabricated and characterized a series of prototype devices. We find that their properties, including the frequency and angular responses, are in good agreement with the theoretical expectations. The devices are undergoing optimization for upcoming CMB experiments.
We describe a new concept for a detector for the submillimeter and far infrared that uses a distributed hot-electron transition edge sensor (TES) to collect the power from a focal-plane-filling slot antenna array. Because superconducting transmission lines are lossy at frequencies greater than about 1 Thz, the sensors must directly
tap the antenna, and therefore must match the antenna impedance (≫ 30 ohms). Each pixel contains many TESs that are all wired in parallel as a single distributed TES, which results in a low impedance that can
match to a multiplexed SQUID readout. These detectors are inherently polarization sensitive, with very low cross-polarization, but can also be easily configured to sum both polarizations for imaging applications. The single polarization version can have a very wide bandwidth of greater than 10:1 with a quantum e±ciency greater than 50%. The dual polarization version is narrow band, but can have a higher quantum e±ciency. The use of electron-phonon decoupling obviates the need for micro-machining, making the focal plane much easier to fabricate than with absorber-coupled, geometrically isolated pixels. An array of these detectors would be suitable for an imager for the Single Aperture Far Infrared (SAFIR) observatory. We consider two near-term applications of this technology, a 32 £ 32 element imaging polarimeter for SOFIA and a 3501m camera for the CSO.
Bolocam is a millimetre-wave (1.1 and 2.1 mm) camera with an array of 119 bolometers. It has been commissioned at the Caltech Submillimeter Observatory in Hawaii and is now in routine operation. Here we give an overview of the instrument and the data reduction pipeline. We discuss models of the sensitivity of Bolocam in different observing modes and under different atmospheric conditions. We briefly discuss observations of star-forming Galactic molecular clouds, a blank field survey for sub-millimeter galaxies, preliminary results of a blank-field CMB secondary anisotropy survey and discuss observations of galaxy clusters using the Sunyaev-Zel'dovich effect.
We report test results for a single pixel antenna-coupled bolometric detector. Our device consists of a dual slot microstrip antenna coupled to an Al/Ti/Au voltage-biased transition edge superconducting bolometer (TES). The coupling architecture involves propagating the signal along superconducting microstrip lines and terminating the lines at a normal metal resistor colocated with a TES on a thermally isolated island. The device, which is inherently polarization sensitive, is optimized for 140 GHz band measurements. In the thermal bandwidth of the TES, we measure a noise equivalent power of 2.0 × 10-17 W/√Hz in dark tests that agrees with calculated NEP including only contributions from thermal, Johnson and amplifier noise. We do not measure any excess noise at frequencies between 1 and 200 Hz. We measure a thermal conductance G ~5.5 × 10-11 W/K. We measure a thermal time constant as low as 437μs at 3μV bias when stimulating the TES directly using an LED.
We present a design for multipixel, multiband submillimeter instrument: SAMBA (Superconducting Antenna-coupled, Multi-frequency, Bolometric Array). SAMBA uses antenna coupled bolometers and microstrip filters. The concept allows for a much more compact, multiband imager compared to a comparable feedhorn-coupled bolometric system. SAMBA incorporates an array of slot antennas, superconducting transmission lines, a wide band multiplexer and superconducting transition edge bolometers. The transition-edge film measures the millimeter-wave power deposited in the resistor that terminates the transmission line.
We describe the design and performance of Bolocam, a 144-element, bolometric, millimeter-wave camera. Bolocam is currently in its commissioning stage at the Caltech Submillimeter Observatory. We compare the instrument performance measured at the telescope with a detailed sensitivity model, discuss the factors limiting the current sensitivity, and describe our plans for future improvements intended to increase the mapping speed.