Search

The Keck Planet Finder (KPF) is a fiber-fed, high-resolution, high-stability spectrometer in development at the UC Berkeley Space Sciences Laboratory for the W.M. Keck Observatory. KPF is designed to characterize exoplanets via Doppler spectroscopy with a goal of a single measurement precision of 0.3 m s-1 or better, however its resolution and stability will enable a wide variety of astrophysical pursuits. Here we provide post-preliminary design review design updates for several subsystems, including: the main spectrometer, the fabrication of the Zerodur optical bench; the data reduction pipeline; fiber agitator; fiber cable design; fiber scrambler; VPH testing results and the exposure meter.

We describe a dark matter axion detector designed, constructed, and operated both as an innovation platform for new cavity and amplifier technologies and as a data pathfinder in the 5–25 GHz range ( ∼ 20 – 100 μ eV ) . The platform is small but flexible to facilitate the development of new microwave cavity and amplifier concepts in an operational environment. The experiment has recently completed its first data production; it is the first microwave cavity axion search to deploy a Josephson parametric amplifier and a dilution refrigerator to achieve near-quantum limited performance.

Precise wavelength calibration is a critical issue for high-resolution spectroscopic observations. The ideal calibration source should be able to provide a very stable and dense grid of evenly distributed spectral lines of constant intensity. A new method which satisfies all mentioned conditions has been developed by our group. The approach is to actively measure the exact position of a single spectral line of a Fabry-Perot etalon with very high precision with a wavelength-tuneable laser and compare it to an extremely stable wavelength standard. The ideal choice of standard is the D2 absorption line of Rubidium, which has been used as an optical frequency standard for decades. With this technique, the problem of stable wavelength calibration of spectrographs becomes a problem of how reliably we can measure and anchor one etalon line to the Rb transition. In this work we present our self-built module for Rb saturated absorption spectroscopy and discuss its stability., SPIE ANZCOP conference, Melbourne 2019

We report on the results from a search for dark matter axions with the HAYSTAC experiment using a microwave cavity detector at frequencies between 5.6 and 5.8 GHz. We exclude axion models with two photon coupling gaγγ≳2×10−14 GeV−1, a factor of 2.7 above the benchmark KSVZ model over the mass range 23.15

We present a method of frequency stabilizing a broadband etalon that can serve as a high-precision wavelength calibrator for an echelle spectrograph. Using a laser to probe the Doppler-free saturated absorption of the rubidium D2 line, we stabilize one etalon transmission peak directly to the rubidium frequency. The rubidium transition is an established frequency standard and has been used to lock lasers to fractional stabilities of < 10-12, a level of accuracy far exceeding the demands of radial velocity (RV) searches for exoplanets. The stabilized bandwidth depends on the dispersion characteristics of the etalon. We describe a simple setup designed specifically for use at an observatory and demonstrate that we can stabilize the etalon peak to a relative precision of < 10-10; this is equivalent to 3 cm s-1 RV precision.

The Keck Planet Finder (KPF) is a fiber-fed, high-resolution, high-stability spectrometer in development for the W.M. Keck Observatory. The instrument recently passed its preliminary design review and is currently in the detailed design phase. KPF is designed to characterize exoplanets using Doppler spectroscopy with a single measurement precision of 0.5 m s^(−1) or better; however, its resolution and stability will enable a wide variety of other astrophysical pursuits. KPF will have a 200 mm collimated beam diameter and a resolving power greater than 80,000. The design includes a green channel (445 nm to 600 nm) and red channel (600 nm to 870 nm). A novel design aspect of KPF is the use of a Zerodur optical bench, and Zerodur optics with integral mounts, to provide stability against thermal expansion and contraction effects.

We report on the first results from a new microwave cavity search for dark matter axions with masses above 20 μeV. We exclude axion models with two-photon coupling g_{aγγ}≳2×10^{-14} GeV^{-1} over the range 23.55m_{a}24.0 μeV. These results represent two important achievements. First, we have reached cosmologically relevant sensitivity an order of magnitude higher in mass than any existing limits. Second, by incorporating a dilution refrigerator and Josephson parametric amplifier, we have demonstrated total noise approaching the standard quantum limit for the first time in an axion search.

We present the design for a high resolution near-infrared spectrograph. It is fed by a single-mode fiber coupled to a high performance adaptive optics system, leading to an extremely stable instrument with high total efficiency. The optical design is a cross-dispersed Echelle spectrograph based on a white pupil layout. The instrument uses a R6 Echelle grating with 13.3 grooves per mm, enabling very high resolution with a small beam diameter. The optical design is diffraction limited to enable optimal performance; this leads to subtle differences compared to spectrographs with large input slits.

Accurate wavelength calibration is crucial for attaining superior Doppler precision with high resolution spectrographs. Upcoming facilities aim for 10 cm/s or better radial velocity precision to access the discovery space for Earth-like exoplanets. To achieve such precision over timescales of years, currently used wavelength cal- ibrators such as thorium-argon lamps and iodine cells will need to be replaced by more precise and stable sources. The ideal wavelength calibrator would produce an array of lines that are uniformly spaced, narrower than the spectrograph resolution, of equal brightness, cover the entire wavelength range of the spectrograph, and whose frequencies do not change with time. Laser frequency combs are an extremely accurate and stable, albeit technically challenging and costly, option that has received much attention recently. We present an alter- native method that uses a Fabry-Perot (FP) etalon illuminated by a white light source to produce a comb-like spectrum over a wide wavelength range. Previous work focused on the development of passively stabilized FP etalons for wavelength calibration. We improve on this method by locking the etalon to an atomic transition, the frequency of which is known to < 2 x 10-11.7 We use a diode laser to observe both the rubidium (Rb) D2 transition at 780 nm and the etalon transmission spectrum. Saturated absorption spectroscopy is used to resolve the Rb hyperfine lines and precisely determine their locations. Since the etalon spectrum is probed with the same laser, the etalon can be locked by ensuring that one of its transmission peaks coincides with a particular Rb hyperfine peak (via either temperature tuning or a piezoelectric transducer incorporated into the etalon). By measuring the frequency of one etalon peak directly via comparison with the Rb, we remove any drifts or aging effects of the etalon that could cause problems for passively stabilized etalon references. We demonstrate a locking precision that is equivalent to a Doppler precision of 3 cm/s RMS. Our setup is simple and robust, can be used with various etalons, and works in the infrared as well as the visible part of the spectrum. The combination of low cost, ease of use, and high precision make this calibration system an attractive option for new spectrographs and as a retrofit for existing facilities.

The axion is a light pseudoscalar particle which suppresses CP-violating effects in strong interactions and also happens to be an excellent dark matter candidate. Axions constituting the dark matter halo of our galaxy may be detected by their resonant conversion to photons in a microwave cavity permeated by a magnetic field. The current generation of the microwave cavity experiment has demonstrated sensitivity to plausible axion models, and upgrades in progress should achieve the sensitivity required for a definitive search, at least for low mass axions. However, a comprehensive strategy for scanning the entire mass range, from 1–1000 μeV, will require significant technological advances to maintain the needed sensitivity at higher frequencies. Such advances could include sub-quantum-limited amplifiers based on squeezed vacuum states, bolometers, and/or superconducting microwave cavities. The Axion Dark Matter eXperiment at High Frequencies (ADMX-HF) represents both a pathfinder for first data in the 20–100 μeV range (~5–25 GHz), and an innovation test-bed for these concepts.

Rotational levels of molecular free radicals can be tuned to degeneracy using laboratory-scale magnetic fields. Because of their intrinsically narrow width, these level crossings of opposite-parity states have been proposed for use in the study of parity-violating interactions and other applications. We experimentally study a typical manifestation of this system using $^{138}$BaF. Using a Stark-mixing method for detection, we demonstrate level-crossing signals with spectral width as small as 6 kHz. We use our data to verify the predicted lineshapes, transition dipole moments, and Stark shifts, and to precisely determine molecular magnetic g-factors. Our results constitute an initial proof-of-concept for use of this system to study nuclear spin-dependent parity violating effects., This version is updated in response to referee's comments, and includes a more substantive conclusion than the original version

Heavy diatomic molecules have been identified as good candidates for use in electron electric dipole moment (eEDM) searches. Suitable molecular species can be produced in pulsed beams, but with a total flux and/or temporal evolution that varies significantly from pulse to pulse. These variations can degrade the experimental sensitivity to changes in spin precession phase of an electri- cally polarized state, which is the observable of interest for an eEDM measurement. We present two methods for measurement of the phase that provide immunity to beam temporal variations, and make it possible to reach shot-noise-limited sensitivity. Each method employs rapid projection of the spin state onto both components of an orthonormal basis. We demonstrate both methods using the eEDM-sensitive H state of thorium monoxide (ThO), and use one of them to measure the magnetic moment of this state with increased accuracy relative to previous determinations., Comment: 12 pages, 6 figures

We report detailed spectroscopic measurements of the X(0)[{sup 1}{sigma}{sup +}](v=0){yields}B(1)[{sup 3}{pi}](v=5) transition in PbO. Using a Stark-modulated laser absorption technique, we have measured the hyperfine constant of {sup 207}PbO in the B(1) state, as well as the B(1)(v=5) rotational constant, X-B isotope shifts, etc. The hyperfine constant of the B(1) state is of interest as a benchmark for calculations of PbO electronic structure related to experiments to search for the electric dipole moment of the electron.

Arrestins quench the signaling of a wide variety of G protein-coupled receptors by virtue of high-affinity binding to phosphorylated activated receptors. The high selectivity of arrestins for this particular functional form of receptor ensures their timely binding and dissociation. In a continuing effort to elucidate the molecular mechanisms responsible for arrestin's selectivity, we used the visual arrestin model to probe the functions of its N-terminal beta-strand I comprising the highly conserved hydrophobic element Val-Ile-Phe (residues 11-13) and the adjacent positively charged Lys(14) and Lys(15). Charge elimination and reversal in positions 14 and 15 dramatically reduce arrestin binding to phosphorylated light-activated rhodopsin (P-Rh*). The same mutations in the context of various constitutively active arrestin mutants (which bind to P-Rh*, dark phosphorylated rhodopsin (P-Rh), and unphosphorylated light-activated rhodopsin (Rh*)) have minimum impact on P-Rh* and Rh* binding and virtually eliminate P-Rh binding. These results suggest that the two lysines "guide" receptor-attached phosphates toward the phosphorylation-sensitive trigger Arg(175) and participate in phosphate binding in the active state of arrestin. The elimination of the hydrophobic side chains of residues 11-13 (triple mutation V11A, I12A, and F13A) moderately enhances arrestin binding to P-Rh and Rh*. The effects of triple mutation V11A, I12A, and F13A in the context of phosphorylation-independent mutants suggest that residues 11-13 play a dual role. They stabilize arrestin's basal conformation via interaction with hydrophobic elements in arrestin's C-tail and alpha-helix I as well as its active state by interactions with alternative partners. In the context of the recently solved crystal structure of arrestin's basal state, these findings allow us to propose a model of initial phosphate-driven structural rearrangements in arrestin that ultimately result in its transition into the active receptor-binding state.

We have developed an optical design for a high resolution spectrograph in response to NASA’s call for an extreme precision Doppler spectrometer (EPDS) for the WIYN telescope. Our instrument covers a wavelength range of 380 to 930 nm using a single detector and with a resolution of 100,000. To deliver the most stable spectrum, we avoid the use of an image slicer, in favor of a large (195 mm diameter) beam footprint on a 1x2 mosaic R4 Echelle grating. The optical design is based on a classic white pupil layout, with a single parabolic mirror that is used as the main and transfer collimator. Cross dispersion is provided by a single large PBM2Y glass prism. The refractive camera consists of only four rotationally symmetric lenses made from i-Line glasses, yet delivers very high image quality over the full spectral bandpass. We present the optical design of the main spectrograph bench and discuss the design trade-offs and expected performance.