Andrew T. Cenko

STELLAR ASTROPHYSICS WITH A DISPERSED FOURIER TRANSFORM SPECTROGRAPH. I. INSTRUMENT DESCRIPTION AND ORBITS OF SINGLE-LINED SPECTROSCOPIC BINARIES

We have designed and constructed a second-generation version of the dispersed Fourier transform spectrograph, or dFTS. This instrument combines a spectral interferometer with a dispersive spectrograph to provide high-accuracy, high-resolution optical spectra of stellar targets. The new version, dFTS2, is based upon the design of our prototype, with several modifications to improve the system throughput and performance. We deployed dFTS2 to the Steward Observatory 2.3 m Bok Telescope from 2007 June to 2008 June, and undertook an observing program on spectroscopic binary stars, with the goal of constraining the velocity amplitude K of the binary orbits with 0.1% accuracy, a significant improvement over most of the orbits reported in the literature. We present results for radial velocity reference stars and orbit solutions for single-lined spectroscopic binaries.

Initial Results from the USNO Dispersed Fourier Transform Spectrograph

We have designed and constructed a ‘‘dispersed Fourier transform spectrometer’’ (dFTS), consisting of a conventionalFTSfollowedbyagratingspectrometer.Bycombiningthesetwodevices,wenegateasubstantialfraction of the sensitivity disadvantage of a conventional FTS for high-resolution, broadband, optical spectroscopy, while preserving many of the advantages inherent to interferometric spectrometers. In addition, we have implemented a simple and inexpensive laser metrology system, which enables very precise calibration of the interferometer wavelength scale. The fusion of interferometric and dispersive technologies with a laser metrology system yields an instrument well suited to stellar spectroscopy, velocimetry,and extrasolar planet detection, which is competitive with existing high-resolution, high-accuracy stellar spectrometers. In this paper we describe the design of our prototype dFTS,explain the algorithmwe use to efficiently reconstruct a broadbandspectrum from a sequence of narrowband interferograms, and present initial observations and resulting velocimetry of stellar targets. Subject headingg binaries: spectroscopic — instrumentation: interferometers — instrumentation: spectrographs — planetary systems — techniques: interferometric

In-depth performance analysis of the HyperFlux spectrometer

Tornado Spectral Systems introduced the HyperFluxTM spectrometer to the market in early 2012. The Hyper- Flux is the world’s first HTVS (high-throughput virtual slit) enabled spectrometer and is able to achieve much greater system flux compared to slit-based spectrometers. Since the HyperFlux’s debut extensive studies into the manufacturability, stability, and detector electronic performance have been performed and are presented in this paper. A generalized quantitative approach to spectrometer comparison by using a clearly-defined Quality Factor is presented at the end of the paper.

High-performance hyperspectral imaging using virtual slit optics

Tornado Spectral Systems (TSS) has developed High Throughput Virtual Slit (HTVS) technology that improves the performance of spectrometers by factors of several while maintaining system size. In the simplest configuration, the HTVS allows optical designers to remove the lossy slit from a spectrometer, greatly increasing throughput without a loss of resolution. This is especially useful in many standoff applications, where every photon matters. TSS has tested multiple configurations of HTVS spectral sensing and spectral imaging technology, including standoff sensing, point scan imaging, long-slit pushbroom imaging and similar configurations. The HTVS throughput-resolution advantage allows us to increase scanning speed, decrease system size, decrease aperture, decrease source intensity requirements or some combination of all four. HTVS technology expands the realm of viable spectral imaging applications. We discuss the applicability of this technology to spectral imaging and standoff sensing and present experimental results from several prototype and production spectrometers.

Fundamental performance improvement to dispersive spectrograph based imaging technologies

Dispersive-based spectrometers may be qualified by their spectral resolving power and their throughput efficiency. A device known as a virtual slit is able to improve the resolving power by factors of several with a minimal loss in throughput, thereby fundamentally improving the quality of the spectrometer. A virtual slit was built and incorporated into a low performing spectrometer (R ~ 300) and was shown to increase the performance without a significant loss in signal. The operation and description of virtual slits is also given. High-performance, lowlight, and high-speed imaging instruments based on a dispersive-type spectrometer see the greatest impact from a virtual slit. The impact of a virtual slit on spectral domain optical coherence tomography (SD-OCT) is shown to improve the imaging quality substantially.

STELLAR ASTROPHYSICS WITH A DISPERSED FOURIER TRANSFORM SPECTROGRAPH. II. ORBITS OF DOUBLE-LINED SPECTROSCOPIC BINARIES

We present orbital parameters for six double-lined spectroscopic binaries (ι Pegasi, ω Draconis, 12 Bootis, V1143 Cygni, β Aurigae, and Mizar A) and two double-lined triple star systems (κ Pegasi and η Virginis). The orbital fits are based upon high-precision radial velocity (RV) observations made with a dispersed Fourier Transform Spectrograph, or dFTS, a new instrument that combines interferometric and dispersive elements. For some of the double-lined binaries with known inclination angles, the quality of our RV data permits us to determine the masses M 1 and M 2 of the stellar components with relative errors as small as 0.2%.

Laser interference fringe tomography: a novel 3D imaging technique for pathology

Laser interference fringe tomography (LIFT) is within the class of optical imaging devices designed for in vivo and ex vivo medical imaging applications. LIFT is a very simple and cost-effective three-dimensional imaging device with performance rivaling some of the leading three-dimensional imaging devices used for histology. Like optical coherence tomography (OCT), it measures the reflectivity as a function of depth within a sample and is capable of producing three-dimensional images from optically scattering media. LIFT has the potential capability to produce high spectral resolution, full-color images. The optical design of LIFT along with the planned iterations for improvements and miniaturization are presented and discussed in addition to the theoretical concepts and preliminary imaging results of the device.

Robust reflective pupil slicing technology

Tornado Spectral Systems (TSS) has developed the High Throughput Virtual Slit (HTVSTM), robust all-reflective pupil slicing technology capable of replacing the slit in research-, commercial- and MIL-SPEC-grade spectrometer systems. In the simplest configuration, the HTVS allows optical designers to remove the lossy slit from pointsource spectrometers and widen the input slit of long-slit spectrometers, greatly increasing throughput without loss of spectral resolution or cross-dispersion information. The HTVS works by transferring etendue between image plane axes but operating in the pupil domain rather than at a focal plane. While useful for other technologies, this is especially relevant for spectroscopic applications by performing the same spectral narrowing as a slit without throwing away light on the slit aperture. HTVS can be implemented in all-reflective designs and only requires a small number of reflections for significant spectral resolution enhancement–HTVS systems can be efficiently implemented in most wavelength regions. The etendueshifting operation also provides smooth scaling with input spot/image size without requiring reconfiguration for different targets (such as different seeing disk diameters or different fiber core sizes). Like most slicing technologies, HTVS provides throughput increases of several times without resolution loss over equivalent slitbased designs. HTVS technology enables robust slit replacement in point-source spectrometer systems. By virtue of pupilspace operation this technology has several advantages over comparable image-space slicer technology, including the ability to adapt gracefully and linearly to changing source size and better vertical packing of the flux distribution. Additionally, this technology can be implemented with large slicing factors in both fast and slow beams and can easily scale from large, room-sized spectrometers through to small, telescope-mounted devices. Finally, this same technology is directly applicable to multi-fiber spectrometers to achieve similar enhancement. HTVS also provides the ability to anamorphically “stretch” the slit image in long-slit spectrometers, allowing the instrument designer to optimize the plate scale in the dispersion axis and cross-dispersion axes independently without sacrificing spatial information. This allows users to widen the input slit, with the associated gain of throughput and loss of spatial selectivity, while maintaining the spectral resolution of the spectrometer system. This “stretching” places increased requirements on detector focal plane height, as with image slicing techniques, but provides additional degrees of freedom to instrument designers to build the best possible spectrometer systems. We discuss the details of this technology for an astronomical context, covering the applicability from small telescope mounted spectrometers through long-slit imagers and radial-velocity engines. This powerful tool provides additional degrees of freedom when designing a spectrometer, enabling instrument designers to further optimize systems for the required scientific goals.

High-Performance Spectroscopy using Virtual Slit Optics

The High Throughput Virtual Slit (HTVS(TM)) is a novel spectroscopic technology which simultaneously maximizes spectral resolution and throughput. We describe the advantages of HTVS spectrometers for Raman measurements and hyperspectral imaging.

Telescope site survey at the US Naval Observatory, Flagstaff Station

We present the status of site testing being done at and near the US Naval Observatorys Flagstaff Station (NOFS). Differential image motion monitors (DIMM) will be used to measure r0, the Fried seeing parameter, at each candidate site. DIMM results will be correlated with image quality as measured by the NOFS 1.55-m telescope. In addition, sky darkness measurements will be made and analysis of water column measurements made nearby by NOAA will be discussed. Site history, measurement methodology, and preliminary results will be presented.