YJH Spectrograph

The YJH Spectrograph (YS) is one of the four ANDES spectrographs covering the range from 950 nm out to 1800 nm.
The YJH Spectrograph will have two operational modes, seeing limited and Integral Field Unit (IFU). It will be installed in one of the Coudé rooms of the ELT.

The YJH Spectrograph receives input light from the Front-End via the Fibre Link subsystem. This provides the option of two input slits, one providing sky, object and calibration light for Seeing Limited mode and the other providing light from the Integral Field Unit (IFU) in the Front-End. Regardless of operational mode, the same optics within the YS are then used to disperse the light into a 2-dimensional spectrum through use of an echelle grating and cross disperser (per band). Each band, of the 3 present, has a dedicated camera which focuses the light onto an infrared detector.

One of the greatest challenges for the design and manufacture of the YJH spectrograph is maintaining a stable operational environment in order to enable the accuracy of measurements required for the science cases. Many factors contribute to the stability including vibration and pressure but by far the most impactful is the thermal stability. This must be held stable to around 1/1000 of a degree. Additionally, due to the wavelength range to be detected, the spectrograph must operate cryogenically and operate substantially below room temperature which also impacts design decisions.