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Register a new userOn Fabry-Perot Etalon-based Instruments. III. Instrument applications
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The spectral, imaging, and polarimetric behavior of Fabry-Perot etalons have an influence on imaging vector magnetograph instruments based on these devices. The impact depends, among others, on the optical configuration (collimated or telecentric), on the relative position of the etalon with respect to the polarimeter, on the type of etalon (air-gapped or crystalline), and even on the polarimetric technique to be used (single-beam or dual-beam). In this paper we evaluate the artificial line-of-sight velocities and magnetic field strengths that arise in etalon-based instruments attending to the mentioned factors. We differentiate between signals that are implicit to telecentric mounts due to the wavelength dependence of the point-spread function and those emerging in both collimated and telecentric setups from the polarimetric response of birefringent etalons. For the anisotropic case we consider two possible locations of the etalon, between the modulator and the analyzer or after it, and we include the effect on different channels when dual-beam polarimetry is employed. We also evaluate the impact of the loss of symmetry produced in telecentric mounts due to imperfections in the illumination and/or to a tilt of the etalon relative to the incident beam.
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We describe techniques concerning wavelength calibration and sky subtraction to maximise the scientific utility of data from tunable filter instruments. While we specifically address data from the Optical System for Imaging and low Resolution Integrated Spectroscopy instrument (OSIRIS) on the 10.4~m Gran Telescopio Canarias telescope, our discussion is generalisable to data from other tunable filter instruments. A key aspect of our methodology is a coordinate transformation to polar coordinates, which simplifies matters when the tunable filter data is circularly symmetric around the optical centre. First, we present a method for rectifying inaccuracies in the wavelength calibration using OH sky emission rings. Using this technique, we improve the absolute wavelength calibration from an accuracy of 5 Angstroms to 1 Angstrom, equivalent to ~7% of our instrumental resolution, for 95% of our data. Then, we discuss a new way to estimate the background sky emission by median filtering in polar coordinates. This method suppresses contributions to the sky background from the outer envelopes of distant galaxies, maximising the fluxes of sources measured in the corresponding sky-subtracted images. We demonstrate for data tuned to a central wavelength of 7615~$rmAA$ that galaxy fluxes in the new sky-subtracted image are ~37% higher, versus a sky-subtracted image from existing methods for OSIRIS tunable filter data.
We describe the recent modifications to the data reduction technique for observations acquired with the scanning Fabry-Perot interferometer (FPI) mounted on the 6-m telescope of the Special Astrophysical Observatory that allow the wavelength scale to be correctly computed in the case of large mutual offsets of studied objects in interferograms. Also the parameters of the scanning FPIs used in the SCORPIO-2 multimode focal reducer are considered.
In this work we present a new mechanism for designing phase-gradient metasurfaces (PGMs) to control an electromagnetic wavefront with high efficiency. Specifically, we design a transmission-type PGM formed by a periodic subwavelength metallic slit array filled with identical dielectrics of different heights. It is found that when Fabry-Perot (FP) resonances occur locally inside the dielectric regions, in addition to the common phenomenon of complete transmission, the transmitted phase differences between two adjacent slits are exactly the same, being a non-zero constant. These local FP resonances ensure total phase shift across a supercell that can fully cover the range of 0 to 2Pi, satisfying the design requirements of PGMs. More studies reveal that due to local FP resonances, there is a one-to-one correspondence between the phase difference and the permittivity of the filled dielectric. A similar approach can be extended to the reflection-type case and other wavefront transformation, creating new opportunities for wave manipulation.
The distributions of stars, gas, and dark matter in disk galaxies provide important constraints on galaxy formation models, particularly on small spatial scales (<1kpc). We have designed the RSS Imaging spectroscopy Nearby Galaxy Survey (RINGS) to target a sample of 19 nearby spiral galaxies. For each of these galaxies, we are obtaining and modeling Halpha and H1~21~cm spectroscopic data as well as multi-band photometric data. We intend to use these models to explore the underlying structure and evolution of these galaxies in a cosmological context, as well as whether the predictions of LCDM are consistent with the mass distributions of these galaxies. In this paper, we present spectroscopic imaging data for 14 of the RINGS galaxies observed with the medium spectral resolution Fabby-Perot etalon on the Southern African Large Telescope. From these observations, we derive high spatial resolution line of sight velocity fields of the Halpha line of excited hydrogen, as well as maps and azimuthally averaged profiles of the integrated Halpha and [NII] emission and oxygen abundances. We then model these kinematic maps with axisymmetric models, from which we extract rotation curves and projection geometries for these galaxies. We show that our derived rotation curves agree well with other determinations and the similarity of the projection angles with those derived from our photometric images argues against these galaxies having intrinsically oval disks.
Open Fabry-Perot microcavities represent a promising route for achieving a quantum electrodynamics (cavity-QED) platform with diamond-based emitters. In particular, they offer the opportunity to introduce high purity, minimally fabricated material into a tunable, high quality factor optical resonator. Here, we demonstrate a fiber-based microcavity incorporating a thick (> 10 {mu}m) diamond membrane with a finesse of 17,000, corresponding to a quality factor Q ~ $10^6$. Such minimally fabricated, thick samples can contain optically stable emitters similar to those found in bulk diamond. We observe modified microcavity spectra in the presence of the membrane, and develop analytic and numerical models to describe the effect of the membrane on cavity modes, including loss and coupling to higher-order transverse modes. We estimate that a Purcell enhancement of approximately 20 should be possible for emitters within the diamond in this device, and provide evidence that better diamond surface treatments and mirror coatings could increase this value to 200 in a realistic system.
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