We conducted the first cooling‑cycle test of the optical unit. A cooling‑cycle test is performed at an early stage of instrument development to verify that optical components used at cryogenic temperatures—such as lenses, prisms, gratings, and mirrors—do not crack or suffer coating damage when cooled to the same temperature conditions as during actual observations.
In this test, six optical‑unit assemblies were installed inside the NINJA cryostat and cooled to the operational temperature of 75 K (−198°C). After the optical elements were warmed back up to room temperature, inspections confirmed that no issues were found in any of them.
