Jean-François Cliche

SPT-3G: a next-generation cosmic microwave background polarization experiment on the South Pole telescope

We describe the design of a new polarization sensitive receiver, spt-3g, for the 10-meter South Pole Telescope (spt). The spt-3g receiver will deliver a factor of ~20 improvement in mapping speed over the current receiver, spt-pol. The sensitivity of the spt-3g receiver will enable the advance from statistical detection of B-mode polarization anisotropy power to high signal-to-noise measurements of the individual modes, i.e., maps. This will lead to precise (~0.06 eV) constraints on the sum of neutrino masses with the potential to directly address the neutrino mass hierarchy. It will allow a separation of the lensing and inflationary B-mode power spectra, improving constraints on the amplitude and shape of the primordial signal, either through spt-3g data alone or in combination with bicep2/keck, which is observing the same area of sky. The measurement of small-scale temperature anisotropy will provide new constraints on the epoch of reionization. Additional science from the spt-3g survey will be significantly enhanced by the synergy with the ongoing optical Dark Energy Survey (des), including: a 1% constraint on the bias of optical tracers of large-scale structure, a measurement of the differential Doppler signal from pairs of galaxy clusters that will test General Relativity on ~200Mpc scales, and improved cosmological constraints from the abundance of clusters of galaxies

Canadian Hydrogen Intensity Mapping Experiment (CHIME) pathfinder

A pathfinder version of CHIME (the Canadian Hydrogen Intensity Mapping Experiment) is currently being commissioned at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, BC. The instrument is a hybrid cylindrical interferometer designed to measure the large scale neutral hydrogen power spectrum across the redshift range 0.8 to 2.5. The power spectrum will be used to measure the baryon acoustic oscillation (BAO) scale across this poorly probed redshift range where dark energy becomes a significant contributor to the evolution of the Universe. The instrument revives the cylinder design in radio astronomy with a wide field survey as a primary goal. Modern low-noise amplifiers and digital processing remove the necessity for the analog beam forming that characterized previous designs. The Pathfinder consists of two cylinders 37m long by 20m wide oriented north-south for a total collecting area of 1,500 square meters. The cylinders are stationary with no moving parts, and form a transit instrument with an instantaneous field of view of ~100 degrees by 1-2 degrees. Each CHIME Pathfinder cylinder has a feedline with 64 dual polarization feeds placed every ~30 cm which Nyquist sample the north-south sky over much of the frequency band. The signals from each dual-polarization feed are independently amplified, filtered to 400-800 MHz, and directly sampled at 800 MSps using 8 bits. The correlator is an FX design, where the Fourier transform channelization is performed in FPGAs, which are interfaced to a set of GPUs that compute the correlation matrix. The CHIME Pathfinder is a 1/10th scale prototype version of CHIME and is designed to detect the BAO feature and constrain the distance-redshift relation. The lessons learned from its implementation will be used to inform and improve the final CHIME design.

A 100-GHz-tunable photonic millimeter wave synthesizer for the Atacama Large Millimeter Array radiotelescope

We propose a broadband photonic millimeter wave synthesizer based on the optical phase locking of telecom-grade DFB semiconductor lasers. A mathematical model of the OPLL shows that the frequency noise profile of these lasers is such that millimeter wave beat notes with residual phase noise levels of 2 x 10-5 rad2 can be achieved with loop path lengths as long as 60 cm. Experiments on a simplified proof-of-concept unit validate this model. The synthesizer is tunable over more than 100 GHz by changing the laser junction temperature. The photonic millimeter wave synthesizer will be used to generate and distribute the LO reference signal of the Atacama Large Millimeter Array radiotelescope.

A high-coherence high-stability laser for the photonic local oscillator distribution of the Atacama Large Millimeter Array

We present the architecture and the characterization results of a Master Laser prototype that can be used to distribute a phase-coherent millimeter wave reference within the Atacama Large Millimeter Array. This source is obtained by frequency-locking a 1556-nm narrow linewidth DFB fiber laser to a two-photon transition in rubidium 85 at 778 nm after second harmonic generation in a non-linear waveguide crystal. The prototype yielded an absolute wavelength of 1556.210 843 nm, a stability of 2x10-12 at tau = 1 s, a linewidth of 2 kHz over 1 ms, a coherence of 40% at 50 km over 1 ms, and a RIN below -145 dBc/Hz for f>10 MHz. Using this laser, the transmission of an 18.6 GHz reference over 10 km of fiber was achieved with a residual phase fluctuations lower than 0.22 degrees RMS (33 fs RMS) over 10 s.

Fabrication of large dual-polarized multichroic TES bolometer arrays for CMB measurements with the SPT-3G camera

This work presents the procedures used at Argonne National Laboratory to fabricate large arrays of multichroic transition-edge sensor (TES) bolometers for cosmic microwave background (CMB) measurements. These detectors will be assembled into the focal plane for the SPT-3G camera, the third generation CMB camera to be installed in the South Pole Telescope. The complete SPT-3G camera will have approximately 2690 pixels, for a total of 16 140 TES bolometric detectors. Each pixel is comprised of a broad-band sinuous antenna coupled to a Nb microstrip line. In-line filters are used to define the different bands before the millimeter-wavelength signal is fed to the respective Ti/Au TES bolometers. There are six TES bolometer detectors per pixel, which allow for measurements of three band-passes (95, 150 and 220 GHz) and two polarizations. The steps involved in the monolithic fabrication of these detector arrays are presented here in detail. Patterns are defined using a combination of stepper and contact lithography. The misalignment between layers is kept below 200 nm. The overall fabrication involves a total of 16 processes, including reactive and magnetron sputtering, reactive ion etching, inductively coupled plasma etching and chemical etching.

Ultra-narrowband fiber Bragg gratings for laser linewidth reduction and RF filtering

We review the improved performances of a narrow linewidth laser using negative electrical feedback obtained through advances on narrowband FBG filters. Noteworthy, the tolerance of the laser to vibrations is significantly improved. As an extension of this work, these narrow filters are proposed for filtering optical signals in RF photonics systems.

Calibrating CHIME: a new radio interferometer to probe dark energy

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a transit interferometer currently being built at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, BC, Canada. We will use CHIME to map neutral hydrogen in the frequency range 400 { 800MHz over half of the sky, producing a measurement of baryon acoustic oscillations (BAO) at redshifts between 0.8 { 2.5 to probe dark energy. We have deployed a pathfinder version of CHIME that will yield constraints on the BAO power spectrum and provide a test-bed for our calibration scheme. I will discuss the CHIME calibration requirements and describe instrumentation we are developing to meet these requirements.

Laser synthesizer of the ALMA telescope: Design and performance

The Laser Synthesizer of the Atacama Large Millimiter Array telescope in Chile has been designed and built by TeraXion. We present the design and performance achieved with this instrument.

High-power and ultranarrow DFB laser: the effect of linewidth reduction systems on coherence length and interferometer noise

In many sensing systems, a highly coherent laser source is necessary to perform sensitive interferometric or coherent measurements. At TeraXion, we have built a compact laser system that provides a stable laser frequency with a very narrow linewidth using a 60 mW DFB semiconductor laser. The linewidth reduction system uses a frequency discriminator to measure the laser frequency noise and provides an electrical feedback to reduce this noise over a given bandwidth. Experimental work shows that the phase noise of the DFB semiconductor laser can be reduced by more than 4 orders of magnitude from 10 Hz to 100 kHz. We analyzed the effect of the particular frequency noise spectrum of such a laser on its degree of coherence, its linewidth and the resulting interferometric noise. The laser linewidth computed from the power spectral density of frequency noise of the laser is reduced from 570 kHz down to an equivalent of 1.8 kHz when the output signal is observed for 30 ms, and from 370 kHz to 18 Hz for 1 ms. Similarly, the coherence length is increased from 145 m up to 45 km for fringes observed over 30 ms. Each result is compared with those obtained with a fiber laser.

Integrated performance of a frequency domain multiplexing readout in the SPT-3G receiver

The third generation receiver for the South Pole Telescope, SPT-3G, will make extremely deep, arcminuteresolution maps of the temperature and polarization of the cosmic microwave background. The SPT-3G maps will enable studies of the B-mode polarization signature, constraining primordial gravitational waves as well as the effect of massive neutrinos on structure formation in the late universe. The SPT-3G receiver will achieve exceptional sensitivity through a focal plane of ~16,000 transition-edge sensor bolometers, an order of magnitude more than the current SPTpol receiver. SPT-3G uses a frequency domain multiplexing (fMux) scheme to read out the focal plane, combining the signals from 64 bolometers onto a single pair of wires. The fMux readout facilitates the large number of detectors in the SPT-3G focal plane by limiting the thermal load due to readout wiring on the 250 millikelvin cryogenic stage. A second advantage of the fMux system is that the operation of each bolometer can be optimized. In addition to these benefits, the fMux readout introduces new challenges into the design and operation of the receiver. The bolometers are operated at a range of frequencies up to 5 MHz, requiring control of stray reactances over a large bandwidth. Additionally, crosstalk between multiplexed detectors will inject large false signals into the data if not adequately mitigated. SPT-3G is scheduled to deploy to the South Pole Telescope in late 2016. Here, we present the pre-deployment performance of the fMux readout system with the SPT-3G focal plane.