Silicon immersion gratings exploit the large index of refraction of silicon (nNIR ∼ 3.4) to compactly disperse light at high resolution for near-infrared spectrographs. These instruments are crucial for many astronomical studies, including measurements of stellar and exoplanet atmospheres. In this work, we characterize silicon immersion gratings fabricated by patterning the silicon with contact photolithography, followed by wet-etching in potassium hydroxide. In this process, we take advantage of the different etch rates between the (100) and (111) planes of silicon to form the blazed grooves. However, the designed blaze tends to differ slightly from the blaze of the grating once etched. While this difference can be corrected when mounting the gratings, it can come at the cost of reducing the instrument’s total throughput. Accurate measures of the fabricated blaze prior to machining the immersion grating entrance face can help reach the optimal instrument efficiency. We present here a procedure for determining the fabricated blaze of silicon immersion gratings through an optical method that measures the intensity of light reflected off each facet of our etched grating. Using a rotation stage, we align diffraction orders near the peak of the blaze function in the Littrow configuration and fit a theoretical blaze function to the resulting intensity profile. We perform this procedure on 17 of our in-house gratings including immersion gratings manufactured for the Giant Magellan Telescope Near-Infrared Spectrograph (GMTNIRS) and report the resulting blaze measurements with a precision of ∼ 0.06 degrees.
We introduce an optical system design of the calibration system for Giant Magellan Telescope Near-Infrared Spectrograph (GMTNIRS), capable of operating across a wavelength range of 1.08 - 5.4 μm. The calibration system fulfills several critical functions, including flat-fielding, wavelength calibration, dark current measurements, and focusing of the spectrograph. The system consists of flat lamp collimator, illuminator, relay optics, and three targets – the USAF 1951 resolution target, a pinhole, and a dark mirror. The focal ratio of the output beam in image space is designed to be 8, replicating the Giant Magellan Telescope. The flatness of the light from the calibration system is evaluated using a non-sequential ray tracing method, confirming over 99% flatness across the slit area.
IGRINS-2 is a high-resolution, near-infrared spectrograph developed by Korea Astronomy and Space Science Institute (KASI) for Gemini Observatory as a new facility instrument. It provides spectral resolving power of ~45,000 and a simultaneous wavelength coverage of 1.49-2.46 μm. IGRINS-2 is an improved version of IGRINS (Immersion GRating INfrared Spectrometer) with minor optical and mechanical design changes, new detector controllers, and operating software to be fully integrated into Gemini operating systems. Since the project began in early 2020, project key milestones including assembly and pre-delivery performance verification were completed, and delivered to Gemini North in early September, 2023. After the successful post-delivery verification and telescope integration, the first light spectra were acquired in October 2023. We present design changes and upgrades made to IGRINS-2 from the original IGRINS, assembly and alignment procedures, and verification of the instrument requirements. We also report the preliminary results of the system performance tests.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.