Large Millimeter Telescope

Instrumentation

The current suite of LMT instrumentation provides a combination of broad-band bolometer cameras and heterodyne array receivers, single-pixel instruments and a versatile digital autocorrelation spectrometer.

Some of these instruments (SEQUOIA, RSR, and AzTEC) have already been completed and successfully commissioned on other (sub)millimeter telescopes (FCRAO 14-m, JCMT, and ASTE). In addition to the first-light instruments, summarized below, a program of instrument development continues to take advantage of technological advances in the on-going effort to provide the next-generation of LMT instruments which will be installed a few years after the start of scientific operations. Additional information on the LMT instrumentation can be found at the web pages of the FCRAO Millimeter Wave Instrument Lab and Continuum Detector Laboratory.

Heterodyne instruments

SEQUOIA

SEQUOIA is a cryogenic focal-plane array of 32 pixels, arranged in dual-polarized 4x4 arrays, that operates in the range 85 - 116 GHz. The arrays which are feed by square horns separated by 2F\lambda are cooled to 18K and use low-noise Indium Phosphide (InP) monolithic microwave integrated circuit (MMIC) preamplifiers designed at UMASS to provide a characteristic receiver noise of 55K in the range 85-107 GHz, increasing to 90K at 116GHz. SEQUOIA has been the workhorse facility instrument for the FCRAO 14-m telescope for many years, and it will remain the largest heterodyne spectral line camera operating 3 mm when it operates on the LMT.

Redshift Search Receiver (RSR) System

A novel MMIC-based receiver has been designed to maximize the instantaneous receiver bandwidth to cover the 90 GHz atmospheric window (75-111 GHz) in a single tuning. The receiver has four pixels arranged in a dual-beam, dual polarized configuration. Orthogonal polarizations are combined in waveguide-based orthomode transducers. Beam-switching on the sky is achieved with a fast Faraday rotation polarization switch and a wire-grid to interchange the reflected and transmitted beams to each receiver. This ultra-wideband receiver typically achieves noise temperatures < 50K between 75-111 GHz. Because of the fast beam-switch involving no moving mechanical parts, the Redshift Search Receiver will have exceptional baseline stability, well-suited to the detection of redshifted transitions of the CO ladder from star-forming galaxies at cosmological distances. A innovative wideband analog autocorrelator system which covers the full 36 GHz with 31 MHz (100 km/s at 90 GHz) resolution serves as the backend spectrometer. The RSR has been commissioned on the FCRAO 14-m telescope in 2006 and several papers reporting early science results have already been published.

1mm SIS receiver

A single-pixel dual-polarization SIS (superconductor-insulator-superconductor) receiver is under development to provide high-sensitivity in the 210-275 GHz atmospheric window. This receiver is to be used for initial commissioning and scientific use of the 1mm window. Using a sideband separation scheme to provide 8 GHz of instantaneous bandwidth in each sideband, this instrument will have a single-sideband system temperature of < 100K.

Continuum instruments

AzTEC

AzTEC is a 144-pixel millimeter-wavelength camera that will operate at 1.1mm. Radiation is coupled to Si-Ni "spider-web" bolometers, arranged in a close-packed hexagonal pattern, with an array of conical feedhorns separated by 1.4 F&lambda. Scanning of the telescope or movements of the secondary mirror provide fully-sampled images.

The detector array is cooled to ~250 mK via a three-stage, closed-cycle³He refrigerator. The field-of-view of AzTEC on the LMT is 2.4 sq. arcmin and, with a per pixel sensitivity of ~3 mJy Hz^-1/2 and FWHM beam-size of 6 arcsecs at 1.1mm, AzTEC will have an extremely fast mapping-speed of ~0.36 deg²/hr/mJy².

AzTEC was successfully installed and commissioned at the JCMT in June 2005, and undertook an extensive program of guest observations on the JCMT in November & December 2005. AzTEC has also operated as a guest instrument on the Atacama Submillimeter Telescope Experiment (ASTE) at the ALMA site in northern Chile for two winters (2007-2008). The AzTEC camera has been developed at UMASS Amherst in collaboration with the BOLOCAM instrument team. More information about the instrument is available at the AzTEC website.