Emi Tamura | Search arXiv

arXiv2026

Laboratory Characterization of a Ge-CCD Prototype for Future Near-Infrared Astronomical Instrumentation

Germanium charge-coupled devices (Ge-CCDs) extend CCD imaging beyond the silicon cutoff and are candidate detectors for the near-infrared channel of future astronomical instruments, in particular the spectrographs of next-generation wide-field surveys. We report the laboratory characterization at Brookhaven National Laboratory (BNL) of a prototype fabricated at MIT Lincoln Laboratory. We describe the cryogenic test system and readout, and present measurements of the output waveform, dark current, readout noise, and X-ray response. The dark current at 94.69 K is $26.12 \pm 0.08$ e$^-$ pixel$^{-1}$ s$^{-1}$. Under $^{55}$Fe irradiation without on-chip binning, the charge generated by an X-ray is confined within $2\times2$ pixels, and the Mn K$α$ line has a full width at half maximum (FWHM) of $8.5 \pm 0.1$% for single-pixel events. Since the charge generated by X-rays above about 30 keV spreads over $3\times3$ or more pixels, the CCD was operated with $2\times2$ on-chip binning at higher energies. This yielded FWHMs of $8.4\pm0.4$% at 30.9 keV ($^{133}$Ba, ASCA grades 0, 2, 3, 4, and 6) and $7.45\pm0.04$% at 59.5 keV ($^{241}$Am, all grades). These results establish a baseline for the device and for the BNL test system. Measurements of the temperature dependence, optical response, and charge-transfer performance will connect this baseline to the requirements of near-infrared astronomical instruments.

hep-ex↗

arXiv2026

An RFSoC-Based 100 GbE Spectrometer/Correlator for the Baryon Mapping Experiment: Digital Backend Design and On-Sky Validation

We describe the implementation and on-sky commissioning of a two-input spectrometer/correlator built on a Xilinx ZCU208 Radio Frequency System-on-Chip (RFSoC) and deployed on the Baryon Mapping eXperiment (BMX) interferometric array at Brookhaven National Laboratory. The system combines direct RF sampling, FPGA-based correlation, and 100 Gigabit Ethernet (GbE) visibility transport. Two inputs are digitized directly at 1050 MHz without analog downconversion and channelized into 2048 frequency channels. The correlator forms two autocorrelations and the real and imaginary parts of the cross-correlation, accumulates them in on-chip memory, and transmits the spectra as UDP packets at a fixed firmware-controlled rate. Two independent campaigns using 500 ms and 100 ms accumulation times produced 958,918 consecutive accumulations with no lost, duplicated, or malformed packets. A Cauchy-Schwarz bound is satisfied across all 1.96e9 channel-samples, confirming correct field identification and scaling. On-sky validation includes compact-source transits in six GNSS bands with the expected fringes, coherent detection of the Cygnus A zenith transit at the predicted time, and a Galactic HI plane crossing detected independently in autocorrelation on both dishes. The correlator is parameterizable in input count, with arithmetic scaling quadratically. For extension to BMX's full eight-input dual-polarization system, an occupancy model validated against the deployed firmware indicates that visibility buffering fits when moved to UltraRAM, while multi-tile synchronization, logic utilization, and timing closure remain to be demonstrated in an eight-input implementation.

astro-ph.IM↗