Greg Smith

Performance of AAOmega: the AAT multi-purpose fiber-fed spectrograph

AAOmega is the new spectrograph for the 2dF fibre-positioning system on the Anglo-Australian Telescope. It is a bench-mounted, double-beamed design, using volume phase holographic (VPH) gratings and articulating cameras. It is fed by 392 fibres from either of the two 2dF field plates, or by the 512 fibre SPIRAL integral field unit (IFU) at Cassegrain focus. Wavelength coverage is 370 to 950nm and spectral resolution 1,000-8,000 in multi-Object mode, or 1,500-10,000 in IFU mode. Multi-object mode was commissioned in January 2006 and the IFU system will be commissioned in June 2006. The spectrograph is located off the telescope in a thermally isolated room and the 2dF fibres have been replaced by new 38m broadband fibres. Despite the increased fibre length, we have achieved a large increase in throughput by use of VPH gratings, more efficient coatings and new detectors - amounting to a factor of at least 2 in the red. The number of spectral resolution elements and the maximum resolution are both more than doubled, and the stability is an order of magnitude better. The spectrograph comprises: an f/3.15 Schmidt collimator, incorporating a dichroic beam-splitter; interchangeable VPH gratings; and articulating red and blue f/1.3 Schmidt cameras. Pupil size is 190mm, determined by the competing demands of cost, obstruction losses, and maximum resolution. A full suite of VPH gratings has been provided to cover resolutions 1,000 to 7,500, and up to 10,000 at particular wavelengths.

Features Predicting Weight Loss in Overweight or Obese Participants in a Web-Based Intervention: Randomized Trial

Background Obesity remains a serious issue in many countries. Web-based programs offer good potential for delivery of weight loss programs. Yet, many Internet-delivered weight loss studies include support from medical or nutritional experts, and relatively little is known about purely web-based weight loss programs. Objective To determine whether supportive features and personalization in a 12-week web-based lifestyle intervention with no in-person professional contact affect retention and weight loss. Methods We assessed the effect of different features of a web-based weight loss intervention using a 12-week repeated-measures randomized parallel design. We developed 7 sites representing 3 functional groups. A national mass media promotion was used to attract overweight/obese Australian adults (based on body mass index [BMI] calculated from self-reported heights and weights). Eligible respondents (n = 8112) were randomly allocated to one of 3 functional groups: information-based (n = 183), supportive (n = 3994), or personalized-supportive (n = 3935). Both supportive sites included tools, such as a weight tracker, meal planner, and social networking platform. The personalized-supportive site included a meal planner that offered recommendations that were personalized using an algorithm based on a user’s preferences for certain foods. Dietary and activity information were constant across sites, based on an existing and tested 12-week weight loss program (the Total Wellbeing Diet). Before and/or after the intervention, participants completed demographic (including self-reported weight), behavioral, and evaluation questionnaires online. Usage of the website and features was objectively recorded. All screening and data collection procedures were performed online with no face-to-face contact. Results Across all 3 groups, attrition was high at around 40% in the first week and 20% of the remaining participants each week. Retention was higher for the supportive sites compared to the information-based site only at week 12 (P = .01). The average number of days that each site was used varied significantly (P = .02) and was higher for the supportive site at 5.96 (SD 11.36) and personalized-supportive site at 5.50 (SD 10.35), relative to the information-based site at 3.43 (SD 4.28). In total, 435 participants provided a valid final weight at the 12-week follow-up. Intention-to-treat analyses (using multiple imputations) revealed that there were no statistically significant differences in weight loss between sites (P = .42). On average, participants lost 2.76% (SE 0.32%) of their initial body weight, with 23.7% (SE 3.7%) losing 5% or more of their initial weight. Within supportive conditions, the level of use of the online weight tracker was predictive of weight loss (model estimate = 0.34, P < .001). Age (model estimate = 0.04, P < .001) and initial BMI (model estimate = -0.03, P < .002) were associated with frequency of use of the weight tracker. Conclusions Relative to a static control, inclusion of social networking features and personalized meal planning recommendations in a web-based weight loss program did not demonstrate additive effects for user weight loss or retention. These features did, however, increase the average number of days that a user engaged with the system. For users of the supportive websites, greater use of the weight tracker tool was associated with greater weight loss.

AAOmega: a scientific and optical overview

AAOmega is a new spectrograph for the existing 2dF and SPIRAL multifibre systems on the Ango-Australian Telescope. It is a bench-mounted, dual-beamed, articulating, all-Schmidt design, using volume phase holographic gratings. The wavelength range is 370-950nm, with spectral resolutions from 1400-10000. Throughput, spectral coverage, and maximum resolution are all more than doubled compared with the existing 2dF spectrographs, and stability is increased by orders of magnitude. These features allow entirely new classes of observation to be undertaken, as well as dramatically improving existing ones. AAOmega is scheduled for delivery and commissioning in Semester 2005B.

Continuous weak measurement and nonlinear dynamics in a cold spin ensemble

A weak continuous quantum measurement of an atomic spin ensemble can be implemented via Faraday rotation of an off-resonance probe beam, and may be used to create and probe nonclassical spin states and dynamics. We show that the probe light shift leads to nonlinearity in the spin dynamics and limits the useful Faraday measurement window. Removing the nonlinearity allows a nonperturbing measurement on the much longer time scale set by decoherence. The nonlinear spin Hamiltonian is of interest for studies of quantum chaos and real-time quantum state estimation.

IRIS2: a working infrared multi-object spectrograph and camera

IRIS2 is a near-infrared imager and spectrograph based on a HAWAII1 HgCdTe detector. It provides wide-field (7.7’×7.7’) imaging capabilities at 0.4486”/pixel sampling, long-slit spectroscopy at λ/Δλ≈2400 in each of the J, H and K passbands, and the ability to do multi-object spectroscopy in up to three masks. These multi-slit masks are laser cut, and have been manufactured for both traditional multiple slit work (≈20-40 objects in a 3’×7.4’ field-of-view), multiple slit work in narrow-band filters (≈100 objects in a 5’×7.4’ field-of-view), and micro-hole spectroscopy in narrow-band filters allowing the observation of ≈200 objects in a 5’×7.4’ field.

Efficient Quantum-State Estimation by Continuous Weak Measurement and Dynamical Control

We demonstrate a fast, robust, and nondestructive protocol for quantum-state estimation based on continuous weak measurement in the presence of a controlled dynamical evolution. Our experiment uses optically probed atomic spins as a test bed and successfully reconstructs a range of trial states with fidelities of approximately 90%. The procedure holds promise as a practical diagnostic tool for the study of complex quantum dynamics, the testing of quantum hardware, and as a starting point for new types of quantum feedback control.

AAOmega: a multipurpose fiber-fed spectrograph for the AAT

The AAOmega project replaces the two 2dF spectrographs, which are mounted on the top end of the Anglo Australian Telescope, with a bench mounted double beam spectrograph covering 370 to 950nm. The 2dF positioner, field plate tumbler mechanism, and fiber retractors will be retained. The new spectrograph will be fed by 392 fibers from either of the two 2dF field plates, or by the 512 fiber Spiral integral field unit, located at the Cassegrain focus. New instrument control electronics has also been designed to drive the spectrograph. Stability will be improved by locating the spectrograph off the telescope, but the 2df fibers must be extended to thirty-eight metres length. Despite this, using fibers with improved characteristics, increased pupil diameter, volume phase holographic (VPH) gratings with articulated cameras, and more efficient coatings on optics we achieve a minimum twofold increase in throughput. We will also fit larger (4k x 2k pixel) detectors. The spectrograph comprises: a F/3.15 Schmidt collimator, incorporating a dichroic beamsplitter; interchangeable VPH gratings; and articulating red and blue F/1.3 Schmidt cameras. The beamsplitter may be exchanged with others which cut off at different wavelengths. A full suite of VPH gratings are provided to cover resolution to 8000.

Faraday spectroscopy in an optical lattice: A continuous probe of atom dynamics

The linear Faraday effect is used to implement a continuous measurement of the spin of a sample of laser-cooled atoms trapped in an optical lattice. One of the optical lattice beams serves also as a probe beam, thereby allowing one to monitor the atomic dynamics in real time and with minimal perturbation. A simple theory is developed to predict the measurement sensitivity and associated cost in terms of decoherence caused by the scattering of probe photons. Calculated signal-to-noise ratios in measurements of Larmor precession are found to agree with experimental data for a wide range of lattice intensity and detuning. Finally, quantum back-action is estimated by comparing the measurement sensitivity to spin projection noise, and shown to be insignificant in the current experiment. A continuous quantum measurement based on Faraday spectroscopy in optical lattices may open up new possibilities for the study of quantum feedback and classically chaotic quantum systems.

Echidna: the engineering challenges

The Anglo-Australian Observatorys (AAOs) FMOS-Echidna project is for the Fiber Multi-Object Spectroscopy system for the Subaru Telescope. It includes three parts: the 400-fiber positioning system, the focal plane imager (FPI) and the prime focus corrector. The Echidna positioner concept and the role of the AAO in the FMOS project have been described in previous SPIE proceedings. The many components for the system are now being manufactured, after prototype tests have demonstrated that the required performance will be achieved. In this paper, the techniques developed to overcome key mechanical and electronic engineering challenges for the positioner and the FPI are described. The major performance requirement is that all 400 science fiber cores and up to 14 guide fiber bundles are to be re-positioned to an accuracy of 10μm within 10 minutes. With the fast prime focus focal ratio, a close tolerance on the axial position of the fiber tips must also be held so efficiency does not suffer from de-focus. Positioning accuracy is controlled with the help of the FPI, which measures the positions of the fiber tips to an accuracy of a few μm and allows iterative positioning. Maintaining fiber tips sufficiently co-planar requires accurate control in the assembly of the several components that contribute to such errors. Assembly jigs have been developed and proven adequate for this purpose. Attaining high reliability in an assembly with many small components of disparate materials bonded together, including piezo ceramics, carbon fiber reinforced plastic, hardened steel, and electrical circuit boards, has entailed careful selection and application of cements and tightly controlled soldering for electrical connections.

Continuous Nondemolition Measurement of the Cs Clock Transition Pseudospin

We demonstrate a weak continuous measurement of the pseudospin associated with the clock transition in a sample of Cs atoms. Our scheme uses an optical probe tuned near the D1 transition to measure the sample birefringence, which depends on the component of the collective pseudospin. At certain probe frequencies the differential light shift of the clock states vanishes, and the measurement is nonperturbing. In dense samples the measurement can be used to squeeze the collective clock pseudospin and has the potential to improve the performance of atomic clocks and interferometers.