Development of a Millimeter Wave Grating Spectrometer for Time
Chao-Te Li1*, C. M. Bradford2, A. T. Crites3, Tashun Wei1, Corwin Shiu3, Tzu-Ching Chang1
1Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan
2Jet Propulsion Laboratory, Pasadena, CA, USA
3California Institute of Technology, Pasadena, CA, USA
* presenting author:Chao-Te Li,
The Tomographic Ionized-carbon Mapping Experiment (TIME) was designed to measure the red-shifted 157.7-µm line of singly ionized carbon [CII] from the Epoch of Reionization (EoR), when the first stars and galaxies formed and ionized the intergalactic medium. For 3-D intensity mapping, TIME uses an imaging spectrometer to measure a spatial–spectral data cube, in which the intensity is mapped as a function of the sky position and frequency. The data cube is then analyzed to produce a 3-D power spectrum. Spectral measurements incorporate redshift information that is needed to distinguish faint EoR signals from bright low-red-shift galaxies along the line of sight. [CII] is an energetic emission line in galaxies and a bolometric marker for total star formation activity. [CII] is also well matched to the 1-mm atmospheric windows for z between 5 and 9. The instrument is housed in a closed-cycle 4K–1K–300mK cryostat. Thirty-two waveguide grating spectrometers are assembled into two stacks of 16, coupling the same 1-D linear field on the sky through an array of feedhorns illuminated through a polarizing grid. The dispersed light is detected with 2-D arrays of transition edge sensor (TES) bolometers. The spectrometers and detectors are cooled with a dual-stage 250/300-mK refrigerator.

Keywords: epoch of reionization, intensity mapping, grating spectrometer