MARVEL is a new facility at the Mercator Observatory (La Palma) which comprises an array of four 0.8 metre telescopes, each feeding via fibre link into a single high-resolution spectrograph. The facility will provide dedicated target vetting and follow-up capability to support large exoplanet surveys through radial velocity measurements with precision at the metre-per-second level. The observatory site, with four new domes and a standalone stabilised spectrograph building, will soon be complete and ready for hardware installation and commissioning. Here we present an overview of the facility and a status update on several component subsystems: the telescope hardware, control software, and scheduling software; the fibre injection units at each telescope; the optical and mechanical design and tolerances of the spectrograph and vacuum vessel; the calibration system hardware and calibration strategies; and the progress in development of the instrument's data reduction pipeline.
MARVEL is a new state-of-the-art facility at the Mercator Observatory (La Palma, Spain) targeting high precision radial velocity measurements. The facility consists of an array of four 80-cm telescopes feeding a single stabilized high-resolution echelle spectrograph. It will provide essential ground-based RV follow-up on transit measurements by previous and upcoming space missions with an RV precision of 1 m/s. This precision requires simultaneous wavelength calibration monitoring on a reliable wavelength reference calibration source. The MARVEL calibration system will be powered by a continuum white light source spanning the target wavelength range of 380-950 nm, and both a ThAr hollow-cathode lamp and a Fabry-P´erot etalon, whose light will be used as a wavelength reference. The light from the continuum source will be divided for use in spectral flat fielding, and for the illumination of the Fabry-P´erot etalon. The wavelength comb of transmission peaks produced by the etalon will be tracked against the hyperfine lines of rubidium, for continuous evaluation of residual etalon drift. Furthermore, the ThAr lamp will serve as an absolute reference for the etalon spectrum. Optical fiber switches will select one of the three calibration sources, as well as transport the light to its destination: the spectrograph, the science fibers at the focus of each telescope, or to a flux monitoring system. In this contribution, we describe the MARVEL wavelength calibration system and the strategy that will be deployed to maximize calibration precision and long-term stability.
Consumer-level digital single-lens reflex (DSLR) cameras are typically not used in professional astronomy because of the systematic errors present in the data as a result of the strong intra- and interpixel variations associated with each of the three different colors (RGB) of the Bayer color filter array. Nevertheless, because the cost of DSLRs compared with traditional astronomical CCDs is so much lower, they represent a potentially underexplored area of scientific quality astronomical imaging, especially in the area of wide-field transient surveys. We demonstrate an algorithm that can achieve ≈ 1 % level photometry in each of the RGB color channels from a stellar source and discuss the application of this algorithm to a ground-based transiting exoplanet survey. The algorithm primarily takes advantage of the large number of stellar sources available for statistical averaging within a single image, using a “lucky point-spread function” approach to identify sources in the image that exhibit systematic errors consistent with a chosen target from the same image. The selection of the appropriate“lucky” reference stars is accomplished through a comparison of the stellar image morphology as it appears on the Bayer array and the reference stars. These references are linearly combined to form a synthetic comparison star that can be used for differential photometry with the target. One key to the algorithm is that all data are retained at the individual pixel-level until the final differential comparison, which helps to alleviate systematic effects that might otherwise cancel each other out during the flux-summing process. We demonstrate the algorithm on HD 339461, a mV = 8.93 G0-type star on which we achieve single-percent level photometry that approaches the fundamental noise floor possible from a single camera.
KEYWORDS: Spectrographs, New and emerging technologies, Velocity measurements, Single mode fibers, Adaptive optics, Near infrared, Cameras, Sensors, Optical design, Relays
Small diameter single-mode fiber (SMF) allows for the design of compact spectrographs that operate at the diffraction limit. The small instrument scale, in turn, allows cost-effective configuration flexibility to use the instrument as a testbed for infrared SMF spectrograph technologies. The same base instrument could be coupled to different adaptive optics (AO) and non-AO SMF feeds. We present the build for such a spectrograph, Iranti, which works in the near-infrared (NIR) range and incorporates novel techniques. Our implementation of this instrument has sufficient cross dispersion to allow testing of a range of input fiber links, including multiple fibers or multi-core fibers (MCFs); the camera optics and detector can also be swapped out easily for different wavelength ranges. The base system uses a white pupil design that relays a slow beam between the collimator, an R6 echelle grating with 13.33 lines/mm and a volume phase holographic grating (VPH) as a cross disperser. In Iranti, we also address mechanical and thermal considerations to improve stability in the instrument. We configure the instrument for ranges in 800 to 1300 nm and characterize system efficiency and stability.
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.
In the new era of Extremely Large Telescopes (ELTs) currently under construction, challenging requirements drive spectrograph designs towards techniques that efficiently use a facility's light collection power. Operating in the single-mode (SM) regime, close to the diffraction limit, reduces the footprint of the instrument compared to a conventional high-resolving power spectrograph. The custom built injection fiber system with 3D-printed microlenses on top of it for the replicable high-resolution exoplanet and asteroseismology spectrograph (RHEA) at Subaru in combination with extreme adaptive optics of SCExAO, proved its high efficiency in a lab environment, manifesting up to ~77% of the theoretical predicted performance.
The Macquarie University campus observatory has recently undergone a significant upgrade, with a new fully- automated 0.6 m telescope and on-site facilities including an instrumentation laboratory. Here we report on the design, assembly, and first on-sky tests of a new high-resolution echelle spectrograph for the observatory. This spectrograph will be a key resource at our campus observatory, providing high fidelity measurements that will enable future research, in particular Master and PhD theses that require stellar spectroscopy or radial velocity measurements. The instrument will also form a cornerstone of the laboratory components of the undergraduate astronomy degree, and together with the new 0.6 m telescope, a key tool for project-based learning at the campus observatory. The instrument has been developed with radial velocity precision as the driving metric, and with future work on the environmental stabilisation it is expected to reach a radial velocity precision of 3 m s−1, enabling the observation of a wide range of exoplanets.
Fiber modal noise is a performance limiting factor in high-resolution spectroscopy, both with respect to achieving high signal-to-noise ratios or when targeting high-precision radial velocity measurements, with multi-mode fiber-fed high resolution spectrographs. Traditionally, modal noise is reduced by agitating or “shaking” the fiber. This way, the light propagating in the fiber is redistributed over many different modes. However, in case of fibers with only a limited number of modes, e.g. at near-infrared wavelengths or in adaptive-optics assisted systems, this method becomes very inefficient. The strong agitation that would be needed stresses the fiber and could lead to focal ratio degradation, or worse, to damaging the fiber. As an alternative approach, we propose to make use of a classic optical double scrambler, a device that is already implemented in many high-precision radial-velocity spectrographs, to mitigate the effect of modal noise by rotating the scrambler’s first fiber end during each exposure. Because of the rotating illumination pattern of the scrambler’s second fiber, the modes that are excited vary continuously. This leads to very efficient averaging of the modal pattern at the fiber exit and to a strong reduction of modal noise. In this contribution, we present a prototype design and preliminary laboratory results of the rotating double scrambler.
KEYWORDS: Sensors, Indium gallium arsenide, Exoplanets, Commercial off the shelf technology, Stars, Telescopes, Charge-coupled devices, System identification, Planets, Space operations
In the search for exoplanets, the TESS mission shifts much of the focus in transit detection towards observing nearby cool stars.1 Many of the M-dwarf systems identified can be followed up from the ground with meter class telescopes or smaller to confirm the presence of rocky planets.2, 3 However, while space-based missions can easily justify the expensive mercury cadmium telluride (HgCdTe) detectors that perform well at the emission peaks of M-dwarfs, ground based searches at small facilities with modest budget need an alternative.4 Deep depletion charged-coupled devices (CCDs) are commercially available, but do not have good sensitivity beyond 1000 nm. Commercial off the shelf (COTS) indium gallium arsenide (InGaAs) detectors offer an alternative, but work needs to be done to characterise them, and adapt them to astronomical use. Towards this effort, we code automation software in Python for a commercially available unit and test the performance for typical use in astronomical instruments. We also integrate a unit into a spectroscopy instrument and demonstrate it on sky at near-infrared (NIR) ranges.
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.
Fiber modal noise is a performance limiting factor in high-precision radial velocity measurements with multi-mode fiber fed high-resolution spectrographs. Traditionally, modal noise is mitigated by agitating the fiber, this way redistributing the light that propagates in the fiber over many different modes. However, in case of fibers with only a limited number of modes, e.g. at near-infrared wavelengths or in adaptive-optics assisted systems, this method becomes very inefficient. The strong agitation that would be needed stresses the fiber and can lead to focal ratio degradation. As an alternative approach, we propose to use a classic optical double scrambler and to rotate the scrambler’s first fiber end during each exposure. Because of the rotating illumination pattern of the scrambler’s second fiber, the modes that are excited vary continuously. This leads to very efficient averaging of the modal pattern at the fiber exit and to a strong reduction of modal noise. In this contribution, we present a prototype design and first laboratory results of the rotating double scrambler.
PANOPTES is a citizen-science based project to discover exoplanets with consumer cameras. It is open source and aims to be highly efficient at collecting photometric data by running a wide field survey using DSLR cameras and standard lenses. In the two years since the demonstration of the baseline design at SPIE 2016 the project has moved forward in getting the hardware design ready for citizen scientists and data analysis, benefiting from an influx of both professional and amateur support. At the same time the project has experienced a number of challenges related to the nature of a grassroots project with no specific institutional home. Here we present a status update to the project with a focus on the issues associated with creating, and maintaining, a successful “pro-am” astronomy project.
This talk will specifically focus on a couple of keys concepts related to the operation of PANOPTES as a distributed observatory built by a collection of professional and amateur astronomers. These concepts can largely be broken down as: software; hardware; and organizational. However, a central theme of the talk will also be the fact that PANOPTES operates without a centralized institution, which means that decisions related to software and hardware are necessarily tied into the organizational decisions. Likewise, since the project has no official operating budget but operates largely off the budgets of each individual team (in addition to a NASA/JPL grant, the attainment of which will also be discussed), the hardware decisions and the evolving landscape of commercial over-the-counter (COTC) hardware play a significant role in the operation and maintenance of the project as a whole, which in turn affects how the software is developed.
Through all of these areas PANOPTES has experienced successes and failures as well as simple deviations from original plans. As a project we have benefited enormously from the donation of time and storage on the Google Cloud Platform (GCP), allowing us to explore technologies and solutions that would otherwise be unfeasible, but as an unofficial project we have been unable to secure a permanent formal agreement with GCP, creating challenges related to the long-term viability of those software solutions.
Being a unique project that aims to be as scientifically productive as it is successful as an outreach tool, it is hoped that the talk will provide some valuable learned lessons for any future projects that hope to utilize the unique professional-amateur dynamic that exists within the field of astronomy and open-source software.
Microbends in multimode optical fibers are shown to lead to focal ratio degradation which compromises fiber fed spectrograph design and performance. By propagating specific vortex mode patterns through multimode fibers containing a single controlled microbend the mechanisms for FRD can be understood. For example, we see both experimentally and through ray tracing analysis that a microbend can produce spiral patterns in the far-field. These patterns are potentially useful tools for diagnosing termination problems in fiber assemblies. For example, by analyzing the spiral patterns produced by a single microbend it is possible to determine the location of a microbend hidden in the fiber termination.
Ever more precise radial velocity instruments are needed to observe potential earth-like exoplanet targets that are beyond the range of current generation high resolution echelle spectrographs. Meanwhile, extreme adaptive optics systems at 8 meter class facilities have made ground based observations possible at the diffraction limit. In the field of Doppler spectroscopy, one way to take advantage of these AO capabilities is by the development of ultra-stable single mode fiber fed spectrographs.1 Coupling the light efficiently into SMFs with an extreme adaptive optics system offers significant advantage in removing modal noise, reducing instrument size, enabling superior environmental control and curbing cost. We report the design and challenges in building an ultra-stable spectrograph for the near infrared range. The design wavelength range is 650 to 1500 nm.
RHEA is a compact high-resolution single-mode spectrograph that can easily be produced in larger quantities as budgets allow. The instrument will be housed in a temperature-stabilized vacuum chamber which is surrounded by several layers of thermal shielding. The optical design employs cost-effective commercially available compo- nents, a cooled CMOS detector, and a double-fiber input which permits simultaneous wavelength calibration.
Precise wavelength calibration is a persistent problem for highest precision Doppler spectroscopy. The ideal calibrator provides an extremely stable spectrum of equidistant, narrow lines over a wide bandwidth, is reliable over timescales of years, and is simple to operate. Unlike traditional hollow cathode lamps, etalons provide an engineered spectrum with adjustable line distance and width and can cover a very broad spectral bandwidth. We have shown that laser locked etalons provide the necessary stability with an ideal spectral format for calibrating precision Echelle spectrographs, in a cost-effective and robust package. Anchoring the etalon spectrum to a very precisely known hyperfine transition of rubidium delivers cm/s-level stability over timescales of years. We have engineered a fieldable system which is currently being constructed as calibrator for the MAROON-X, HERMES, KPF, FIES and iLocater spectrographs.
RHEA is a single-mode ´echelle spectrograph designed to be a replicable and cost effective method of undertaking precision radial velocity measurements. The instrument has a novel fiber feed with an integral field unit injecting into a grid of single-mode fibers reformatted to form a pseudo-slit, increasing throughput and enabling highspatial resolution observations when operating behind Subaru and the SCExAO adaptive optics system. The past 18 months have seen a replacement cable constructed for the instrument to address modal noise caused by closely packed fibers with similar path lengths. Here we detail the cable fabrication procedure, design improvements, increased precision in meeting the required sub-micron optical tolerances, throughput gains, and known remaining issues.
High precision Doppler observations of bright stars can be made efficiently with small aperture telescopes. We are constructing a high resolution echelle spectrograph for the new 0.6 m telescope at Central Washington University. The spectrograph is fed by a multimode fiber and operates in the visible wavelength range of 380-670 nm. The spectrograph uses a white pupil design with 100 mm beam diameter and a monolithic R4 echelle grating.
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.
The RHEA Spectrograph is a single-mode echelle spectrograph designed to be a replicable and cost effective method of undertaking precision radial velocity measurements. Two versions of RHEA currently exist, one located at the Australian National University in Canberra, Australia (450 - 600nm wavelength range), and another located at the Subaru Telescope in Hawaii, USA (600 - 800 nm wavelength range). Both instruments have a novel fibre feed consisting of an integral field unit injecting light into a 2D grid of single mode fibres. This grid of fibres is then reformatted into a 1D array at the input of the spectrograph (consisting of the science fibres and a reference fibre capable of receiving a white-light or xenon reference source for simultaneous calibration). The use of single mode fibres frees RHEA from the issue of modal noise and significantly reduces the size of the optics used. In addition to increasing the overall light throughput of the system, the integral field unit allows for cutting edge science goals to be achieved when operating behind the 8.2m Subaru Telescope and the SCExAO adaptive optics system. These include, but are not limited to: resolved stellar photospheres; resolved protoplanetary disk structures; resolved Mira shocks, dust and winds; and sub-arcsecond companions. We present details and results of early tests of RHEA@Subaru and progress towards the stated science goals.
The Replicable High-resolution Exoplanet and Asteroseismology (RHEA) spectrograph is being developed to serve as a basis for multiple copies across a network of small robotic telescopes. The spectrograph operates at the diffraction-limit by using a single-mode fiber input, resulting in a compact and modal-noise-free unit. The optical design is mainly based on off-the-shelf available components and comprises a near-Littrow configuration with prism cross-disperser. The échelle format covers a wavelength range of 430-650 nm at R=75,000 resolving power. In this paper we briefly summarize the current status of the instrument and present preliminary results from the first on-sky demonstration of the prototype using a fully automated 16" telescope, where we observe stable and semi-variable stars up to V=3.5 magnitude. Future steps to enhance the efficiency and passive stability of RHEA are discussed in detail. For example, we show the concept of using a multi-fiber injection unit, akin to a photonic lantern, which not only enables increased throughput but also offers simultaneous wavelength calibration.
SCExAO is the premier high-contrast imaging platform for the Subaru Telescope. It offers high Strehl ratios at near-IR wavelengths (y-K band) with stable pointing and coronagraphs with extremely small inner working angles, optimized for imaging faint companions very close to the host. In the visible, it has several interferometric imagers which offer polarimetric and spectroscopic capabilities. A recent addition is the RHEA spectrograph enabling spatially resolved high resolution spectroscopy of the surfaces of giant stars, for example. New capabilities on the horizon include post-coronagraphic spectroscopy, spectral differential imaging, nulling interferometry as well as an integral field spectrograph and an MKID array. Here we present the new modules of SCExAO, give an overview of the current commissioning status of each of the modules and present preliminary results.
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.
KEYWORDS: Surface plasmons, Near field scanning optical microscopy, Plasmonics, Near field optics, Gold, Microscopy, Scanning electron microscopy, Free space optics, Numerical simulations, Glasses
Surface plasmons have been launched from free space optical beams (at an excitation wavelength of 700 nm) and
focused in the plane using concentric curved gratings (or plasmonic lenses) etched into 30 nm-thick gold films. The
performance of these devices was studied with numerical simulation and verified by near-field scanning optical
microscopy experiments. These plasmonic lenses have been demonstrated to focus the launched surface plasmons
effectively to a high intensity focal spot.
We present the opto-mechanical design and the characterization of the Replicable High-resolution Exoplanet and Asteroseismology (RHEA) spectrograph. RHEA is an ultra-compact fiber-fed echelle spectrograph designed to be used at 0.2-0.4 m class robotic telescopes where long term dedicated projects are possible. The instrument will be primarily used for radial velocity (RV) studies of low to intermediate-mass giant stars for the purpose of searching for hot Jupiters and using asteroseismology to simultaneously measure the host star parameters and de-correlate stellar pulsations. The optical design comprises a double-pass (i.e. near Littrow) configuration with
prism cross-disperser and single-mode fiber (SMF) input. The spectrograph has a resolving power of R>70,000 and operates at 430–670 nm with minimum order separation of ~180 μm. This separation allows a 1x6 photonic
lantern integration at a later stage which is currently under development. The current design is built with the aim of creating an inexpensive and replicable unit. The spectrograph is optimised for long-baseline RV observations through careful temperature stabilisation and simultaneous wavelength calibration. As a further improvement the echelle grating is housed in a vacuum chamber to maintain pressure stability. The performance of the current prototype is currently being tested on a 0.4 m telescope at the Macquarie University Observatory.
We present the results of an investigation of the spectroscopic properties of Ce3+:BaY2F8 (BYF), which is a potential laser
material with an emission wavelength range from 320 nm to 360 nm. We have employed a time-resolved pump-probe
technique to investigate the polarization-dependent absorption and emission properties, and the dynamic color centre
formation process. We observe strong absorption from colour centres with millisecond and second lifetimes that will
certainly prevent laser action with the crystals used here. Evidence suggests that there may be potential gain in this crystal
if long-lived colour centres can be reduced.
Ultraviolet (UV) miniature cerium fluoride lasers have been demonstrated using a low cost, frequency-quadrupled microchip Nd:YVO4 pump laser. The concept of miniature configuration of the cavities was shown to improve the laser performance in the low pump power region. Using a 10 μJ, 266nm pump pulse, we have obtained output energies of 3.5μJ at 287nm and 0.65 μJ at 311nm. The slope efficiencies were 45% and 35%, and the pump thresholds 2 μJ and 0.8 μJ respectively. Tunable operation of these lasers provides a simple compact wavelength converter from 266 nm to 282-333 nm.
We report the experimentally measured polarized small signal gain for Ce:LiLuF at 309 nm and 327 nm. The gain was found to be anisotropic and temperature dependent. Using a rate equation based model we have simulated the affect of excited state absorption (ESA) on the small signal gain in Ce:LiLuF. As a result we report the polarized emission and ESA cross-sections for Ce:LiLuF at 309 nm and 327 nm. We show the ESA to be temperature dependent and consequently demonstrate that ESA is the cause of the change in small signal gain with temperature in Ce:LiLuF. Further, we experimentally show the decrease, with temperature, of the ESA cross-sections at 309 nm causes a 70% increase in the laser output at 309 nm. We demonstrate how the introduction of a σ-biased loss into the cavity suppresses σ-polarized lasing at 327 nm. This counteracts the decrease in laser output below ~10°C caused by the anisotopic nature and temperature dependence of the ESA in Ce:LiLuF at 327 nm.
The performance of a small-scale KE-CVL operating at a pulse repetition rate of 50kHz has been investigated by comparing modelling results and experimental data to understand the underlying plasma kinetics issues for pulse repetition rate scaling. Comparison between initial modelling predictions and experimental results relating to the laser output power and the population densities of the metastable lower laser levels (Cu* 4s2 2D3/2,5/2 ) suggests that there is an additional de-excitation mechanism for the metastables in the KE-CVL. The most likely de-excitation mechanism involves vibrationally-excited H2(v) molecules Cu*2D+H2(v) => CuH+H. A rate-coefficient of 2x10-16m3s1 is obtained by comparing modelling results with experimental data relating to the laser output power and the time-evolution of the axial 2D3/2 metastable population density.
The copper vapor laser (CVL) is an efficient, high average power, high pulse rate visible laser, emitting in the green and the yellow. Previous applications of CVLs have been limited to those requiring a high power visible laser source but with no specific need for high output beam quality. Recently we have made substantial progress in understanding the factors that influence CVL beam quality. As a result we are now able to achieve efficient non-linear frequency conversion to produce a number of ultraviolet wavelengths with near- diffraction limited beam quality. The high repetition rate and low divergence uv output of the frequency-doubled CVL makes it an attractive alternative to the excimer laser for a number of applications, including high-speed precision hole-drilling, cutting and scoring in polymers and for deep-uv photolithography. We report here recent developments that have led to efficient generation of uv wavelengths from copper vapor lasers and we demonstrate its potential as a laser source for high-speed precision ultraviolet micromachining.
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