Receiver
Specifications
FINER is a dual-polarization, sideband-separating (2SB) SIS receiver system. The table below summarizes the configuration installed for first light and the design goals of the full system.
| General | |
|---|---|
| Number of bands | 2 (one band observed at a time at first light) |
| Number of beams per band | 1 |
| Number of polarizations per band | 2 |
| Number of sidebands per band | 2 (2SB) |
| Band 4 (first light) | Band 6+7 | Band 4+5 (planned upgrade) | |
|---|---|---|---|
| Radio frequency | ≈138–178 GHz | ≈210–351 GHz | 120–210 GHz |
| Intermediate frequency (per sideband, per polarization) | 4–8 GHz | 4–20 GHz | 4–20 GHz |
| Receiver noise temperature (SSB, design goal) | — | 75 K | 45 K |
Measured performance will be reported here after commissioning on the LMT.
System overview
At first light FINER has two front-end receivers in a single cryostat: a Band 4 MMIC receiver and a wideband Band 6+7 receiver, both developed at NAOJ. A wideband Band 4+5 receiver covering 120–210 GHz is planned as a later upgrade. IF switches select which band feeds the four IF chains, so one band is observed at a time; simultaneous dual-band observation is an option for a future optics upgrade.
Optics
The FINER warm optics picks off the beam after the LMT’s M4 mirror with a pair of motorized mirrors (the “periscope”), which can be set and stowed remotely. A chopper with a blackbody load is used for intensity calibration. A fast sky chopper for quick position switching is planned in a later phase. The spatial resolution (PSF size) is about 7 arcsec × (frequency / 200 GHz)−1.
Front-end receivers
The front-end receivers exploit the high critical current density SIS mixer technology developed for the ALMA Wideband Sensitivity Upgrade (WSU) (Kojima et al. 2017, 2020; Kang et al. 2026), which provides a wide instantaneous frequency coverage.
Back-end spectrometers
- Wideband spectrometers (DRS4, ELECS Inc.). Two DRS4 chassis digitize eight 10.24 GHz-wide basebands with 3-bit, 20.48 GSa/s analog-to-digital converters and provide spectra with 20 MHz resolution (Hagimoto et al. 2024). Sideband separation is also performed digitally.
- High-resolution spectrometers (XFFTS, RPG). The XFFTS spectrometers of the LMT 2-mm receiver B4R (2.5 GHz bandwidth, 88 kHz resolution) remain available for high-resolution spectroscopy.
Data and software
FINER is controlled from the LMT Telescope Control System. The data format and the reduction pipeline are being developed together with the LMT team.
Technical documents
| Document | Version | Download |
|---|---|---|
| FINER proposal to the LMT | Version A, 15 June 2023 | PDF (5 MB) |
The proposal describes the original design and plan; the configuration and schedule have since been updated as described on this page.
References
See Publications for the instrument papers.