We have recently commissioned a novel infrared (0:9-1:7 μm) integral field spectrograph (IFS) called the Wide Integral Field Infrared Spectrograph (WIFIS). WIFIS is a unique instrument that offers a very large field-of-view (5000 x 2000) on the 2.3-meter Bok telescope at Kitt Peak, USA for seeing-limited observations at moderate spectral resolving power. The measured spatial sampling scale is ~ 1 x 1" and its spectral resolving power is R ~ 2; 500 and 3; 000 in the <i>z</i>J (0:9 - 1:35 μm) and Hshort (1:5 - 1:7 μm) modes, respectively. WIFIS's corresponding etendue is larger than existing near-infrared (NIR) IFSes, which are mostly designed to work with adaptive optics systems and therefore have very narrow fields. For this reason, this instrument is specifically suited for studying very extended objects in the near-infrared such as supernovae remnants, galactic star forming regions, and nearby galaxies, which are not easily accessible by other NIR IFSes. This enables scientific programs that were not originally possible, such as detailed surveys of a large number of nearby galaxies or a full accounting of nucleosynthetic yields of Milky Way supernova remnants. WIFIS is also designed to be easily adaptable to be used with larger telescopes. In this paper, we report on the overall performance characteristics of the instrument, which were measured during our commissioning runs in the second half of 2017. We present measurements of spectral resolving power, image quality, instrumental background, and overall efficiency and sensitivity of WIFIS and compare them with our design expectations. Finally, we present a few example observations that demonstrate WIFIS's full capability to carry out infrared imaging spectroscopy of extended objects, which is enabled by our custom data reduction pipeline.
We present the optomechanical design and development of the Wide Integral Field Infrared Spectrograph (WIFIS). WIFIS will provide an unrivalled integral field size of 20”×50” for a near-infrared (0.9-1.7 μm) integral-field spectrograph at the 2.3-meter Steward Bok telescope. Its main optomechanical system consists of two assemblies: a room-temperature bench housing the majority of the optical components and a cryostat for a field-flattening lens, thermal blocking filter, and detector. Two additional optical subsystems will provide calibration functionality, telescope guiding, and off-axis optical imaging. WIFIS will be a highly competitive instrument for seeing-limited astronomical investigations of the dynamics and chemistry of extended objects in the near-infrared wavebands. WIFIS is expected to be commissioned during the end of 2016 with scientific operations beginning in 2017.
We present an overview of the design of IRIS, an infrared (0.84 - 2.4 micron) integral field spectrograph and imaging
camera for the Thirty Meter Telescope (TMT). With extremely low wavefront error (<30 nm) and on-board wavefront
sensors, IRIS will take advantage of the high angular resolution of the narrow field infrared adaptive optics system
(NFIRAOS) to dissect the sky at the diffraction limit of the 30-meter aperture. With a primary spectral resolution of
4000 and spatial sampling starting at 4 milliarcseconds, the instrument will create an unparalleled ability to explore high
redshift galaxies, the Galactic center, star forming regions and virtually any astrophysical object. This paper summarizes
the entire design and basic capabilities. Among the design innovations is the combination of lenslet and slicer integral
field units, new 4Kx4k detectors, extremely precise atmospheric dispersion correction, infrared wavefront sensors, and a
very large vacuum cryogenic system.
Maximizing the grating efficiency is a key goal for the first light instrument IRIS (Infrared Imaging Spectrograph)
currently being designed to sample the diffraction limit of the TMT (Thirty Meter Telescope). Volume Phase
Holographic (VPH) gratings have been shown to offer extremely high efficiencies that approach 100% for high line
frequencies (i.e., 600 to 6000l/mm), which has been applicable for astronomical optical spectrographs. However, VPH
gratings have been less exploited in the near-infrared, particularly for gratings that have lower line frequencies. Given
their potential to offer high throughputs and low scattered light, VPH gratings are being explored for IRIS as a potential
dispersing element in the spectrograph. Our team has procured near-infrared gratings from two separate vendors. We
have two gratings with the specifications needed for IRIS current design: 1.51-1.82μm (H-band) to produce a spectral
resolution of 4000 and 1.19-1.37μm (J-band) to produce a spectral resolution of 8000. The center wavelengths for each
grating are 1.629μm and 1.27μm, and the groove densities are 177l/mm and 440l/mm for H-band R=4000 and J-band
R=8000, respectively. We directly measure the efficiencies in the lab and find that the peak efficiencies of these two
types of gratings are quite good with a peak efficiency of ~88% at the Bragg angle in both TM and TE modes at H-band,
and 90.23% in TM mode, 79.91% in TE mode at J-band for the best vendor. We determine the drop in efficiency off the
Bragg angle, with a 20-23% decrease in efficiency at H-band when 2.5° deviation from the Bragg angle, and 25%-28%
decrease at J-band when 5° deviation from the Bragg angle.
We present the efficiency of near-infrared reflective ruled diffraction gratings designed for the InfraRed Imaging
Spectrograph (IRIS). IRIS is a first light, integral field spectrograph and imager for the Thirty Meter Telescope
(TMT) and narrow field infrared adaptive optics system (NFIRAOS). IRIS will operate across the near-infrared
encompassing the ZYJHK bands (~0.84 - 2.4μm) with multiple spectral resolutions. We present our experimental
setup and analysis of the efficiency of selected reflective diffraction gratings. These measurements are used as a
comparison sample against selected candidate Volume Phase Holographic (VPH) gratings (see Chen et al., this
conference). We investigate the efficiencies of five ruled gratings designed for IRIS from two separate vendors.
Three of the gratings accept a bandpass of 1.19-1.37μm (J band) with ideal spectral resolutions of R=4000 and
R=8000, groove densities of 249 and 516 lines/mm, and blaze angles of 9.86° and 20.54° respectively. The other
two gratings accept a bandpass of 1.51-1.82μm (H Band) with an ideal spectral resolution of R=4000, groove
density of 141 lines/mm, and blaze angle of 9.86°. The fraction of flux in each diffraction mode was compared to
both a pure reflection mirror as well as the sum of the flux measured in all observable modes. We measure the
efficiencies off blaze angle for all gratings and the efficiencies between the polarization transverse magnetic (TM)
and transverse electric (TE) states. The peak reflective efficiencies are 98.90 ± 3.36% (TM) and 84.99 ± 2.74%
(TM) for the H-band R=4000 and J-band R=4000 respectively. The peak reflective efficiency for the J-band R=8000
grating is 78.78 ± 2.54% (TE). We find that these ruled gratings do not exhibit a wide dependency on incident angle
within ±3°. Our best-manufactured gratings were found to exhibit a dependency on the polarization state of the
incident beam with a ~10-20% deviation, consistent with the theoretical efficiency predictions. This work will
significantly contribute to the selection of the final grating type and vendor for the IRIS optical system, and are also
pertinent to current and future near-infrared astronomical spectrographs.
We are designing and constructing a new SETI (Search for Extraterrestrial Intelligence) instrument to search for direct
evidence of interstellar communications via pulsed laser signals at near-infrared wavelengths. The new instrument
design builds upon our past optical SETI experiences, and is the first step toward a new, more versatile and sophisticated
generation of very fast optical and near-infrared pulse search devices. We present our instrumental design by giving an
overview of the opto-mechanical design, detector selection and characterization, signal processing, and integration
procedure. This project makes use of near-infrared (950 - 1650 nm) discrete amplification Avalanche Photodiodes
(APD) that have > 1 GHz bandwidths with low noise characteristics and moderate gain (~104). We have investigated the
use of single versus multiple detectors in our instrument (see Maire et al., this conference), and have optimized the
system to have both high sensitivity and low false coincidence rates. Our design is optimized for use behind a 1m
telescope and includes an optical camera for acquisition and guiding. A goal is to make our instrument relatively
economical and easy to duplicate. We describe our observational setup and our initial search strategies for SETI targets,
and for potential interesting compact astrophysical objects.