🔎 MagNIFIES Design
🔎 MagNIFIES Design
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Our design philosophy is to keep the instrument simple and optimize for spectral grasp and sensitivity.Â
In a single exposure, MagNIFIES will observe the entire spectrum transmitted through the Earth's atmosphere from 1.08 - 5.4 μm while simultaneously providing very high wavelength sampling (resolution).Â
Enabling this are six custom fabricated silicon immersion gratings that provide its very high efficiency and compact size. The instrument is essentially six spectrographs in one, all sitting on a single cryogenic bench with a common entrance slit, with no moving cryogenic parts and a fixed spectral format to allow efficient data reduction.Â
The total size of the dewar is 1.7 m in diameter by 0.88 meter in depth. The total mass is 780 kg including the cryostat, benches, optics, and coolers.
Spectrograph Layout
Spectrograph Layout
All the spectrograph optics from the slit onward sit on a single cryogenic bench. A single 90 μm (0.35 arcsec) slit, which is lithographically formed in a gold-coated Si mirror, feeds all six spectrograph units. This slit width provides spectral resolution of 45,000 at 1.08 - 2.5 μm and 60,000 at 2.9 - 5.4 μm. The slit length is 5.3 arcsec. The reflected light will go to the slit-viewing camera, to form a ~1 arcmin diameter K-band image of the field.
Dichroics split the beams into individual spectrographs, each with a silicon immersion grating. The cross-dispersers are VPH gratings for JHK and silicon immersion grisms at LM.
By dividing the L-band, we can use 2K X 2K detectors (Teledyne H2RGs) for all bands, while preserving both the slit length and adequate spectral sampling. Because L-band spectra will be background-limited, the transition orders will be combined to recover the full sensitivity.
For more information, see: GMTNIRS optical system design  Lee, H. et al. 2022, SPIE, 12184, 121843I
Advanced Technology / Materials
Advanced Technology / Materials
The Silicon immersion gratings at the heart of MagNIFIES were fabricated at University of Texas at Austin after years of design-development to achieve high efficiency and very low ghosting or scattering. Our gratings are 90 mm R3 (for JHK) and 130 mm R4 (for LM) .
We are currently investigating / fabricating immersion grisms as our L and M-band cross-dispersers.
In an immersion grating, the light is incident on the grating surface from the inside, where the wavelength is shortened by a factor equal to the refractive index (3.4 for Si). This allows a grating of a given size to have 3.4 times the resolving power of a conventional front-surface device.
For more information, see GMTNIRS: progress toward the Giant Magellan Telescope near-infrared spectrograph. Jaffe, D. T. et al. Â 2016, SPIE, 9908, 990821, Manufacturing silicon immersion gratings on 150-mm material. Kidder, B. T., et al. 2018, SPIE, 10706, 1070624Â and Near infrared blaze metrology of silicon immersion gratings. Dix, C., et al. 2024, SPIE, 13100, 131005J
Spectrograph Cameras
Spectrograph Cameras
The cameras image every channel's echellograms onto a H2RG array. With the support of the Heising-Simons Foundation, we contracted New England Optical Systems (now part of FLIR and Teledyne Technologies Incorporated) to fabricate the cameras. The six cameras provide nearly diffraction-limited performance across the echellograms. Each camera was designed to operate at the instrument optical bench temperature of 70 ± 10 K. We have received the cameras at UT Austin, and they passed our survivability cold-testing and inspection.
Cryostat Design
Cryostat Design
In MagNIFIES, the upper bench is populated with foreoptics that adjust the focal ratio and the lower bench holds the spectrograph, which remains unchanged as GMTNIRS. In its GMT configuration, the upper bench holds the on-instrument wavefront sensor for the facility adaptive optics. In the MagNIFIES implementation, there is a different, untilted, warm window offset from the GMTNIRS position.
The spectrograph bench is thermally isolated from the dewar /Â passive shield and surrounded by a single-body active shield. The bench and immersion gratings will be cooled to 64 K and 70 K, respectively. The detectors will be cooled to 37 K.
The total size of the dewar is 1.7 m in diameter by 0.88 meter in depth. The total mass is 780 kg including the cryostat, benches, optics, and coolers.
The total cold mass is 268 kg and our thermal analysis shows a total cooling time of 3.5 - 5 days depending on our final choices of cold heads and pending tests in a Test Chamber currently operating at KASI.
For more information, see: GMTNIRS: mechanical design strategy for the MagNIFIES pathfinder on Magellan Telescope, Kim, Sanghyuk et al. 2026, SPIE Astronomical Telescopes + Instrumentation and GMTNIRS: Prototyping and Test, Oh et al. 2026, SPIE Astronomical Telescopes + Instrumentation
Magellan Mount
Magellan Mount
We will mount to the standard Magellan guider at a Nasmyth port. The instrument will rotate to position the slit to the parallactic angle or to a user specified slit position angle. The detector electronics (gray box) ride along on the fixture that holds the dewar. The cable wrap will carry the power, optical fibers for data transfer, and helium cooling hoses from connectors on the dewar to connectors on the Nasmyth platform.
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