Hossein Mahmoodzadeh

This paper presents the innovative field selector system (FSS) developed for VESPER, the multi-Integral field unit of the SHARP near-infrared spectrograph. The proposed system employs an array of movable light-collection probes (field selectors) that travel along parallel, vertically offset planes to avoid mechanical interference and vignetting. The true novelty, to our best knowledge, lies in its optomechanical synchronization: as each probe translates by Δy to select a target, a set of folding mirrors shifts by Δy/2. This maintains a constant optical path length, allowing multiple independently moving probes to share a single focal plane and form a continuous image on it, which is easy to slice by the slicer. A dedicated optical test setup was developed to characterize the positioning stability and repeatability of the probe motion. The measured mechanical errors were converted into equivalent optical tilts and incorporated into the SHARP optical model to assess their impact on instrument performance. The experimental results identified the dominant sources of positioning error and provided valuable insight into the relationship between mechanical tolerances and optical performance. The study also highlights several design improvements capable of significantly reducing probe tilting and enhancing system stability. The results demonstrate the viability of the proposed concept and indicate that, with the identified improvements, the system represents an excellent field-selection solution for SHARP and other multi-integral-field-unit (mIFU) spectrographs.

The design and verification of cryogenic near-infrared spectrographs require rigorous multidisciplinary analyses to ensure optical performance under realistic operational conditions. In this work, we present a structural–thermal–optical performance (STOP) analysis of the SHARP instrument, a multi-mode spectrograph designed for use with upcoming multi-conjugate adaptive optics (MCAO) systems on extremely large telescopes (ELTs). Transient and steady-state thermal simulations were performed using Ansys to model the cooldown process and temperature distribution within the opto-mechanical structure. The resulting temperature fields were mapped to structural models through linear interpolation, enabling the evaluation of thermal stresses and deformations of optical elements. Optical sensitivity and tolerance analyses were carried out using Ansys Zemax OpticStudio, with Monte Carlo simulations applied to assess robustness against decenter, tilt, and despace errors. Results indicate that SHARP maintains RMS spot radius values within the acceptance threshold and that the inclusion of compensators significantly enhances compliance with the ensquared energy (EE) requirement across all channels. The analysis confirms that SHARP can achieve its optical performance goals while remaining within mechanical and thermal constraints, providing a validated framework for the development of next-generation cryogenic astronomical instrumentation.

The next generation of Extremely Large Telescopes (ELTs), with their wide apertures and advanced multi-conjugate adaptive optics (MCAO) systems, will provide unprecedented sharp and deep observations, even surpassing the capabilities of the James Webb Space Telescope. SHARP, a near-infrared (0.95 to 2.45 μm) spectrograph, is designed to optimally exploit the collecting area and angular resolution of these forthcoming ELTs and specifically optimized for the MCAO unit MORFEO at the ELT. SHARP includes two main units: NEXUS, a multi-object spectrograph, and VESPER, a multi-integral field unit. We outline the opto-mechanical design of SHARP based on the scientific requirements of the project. The optical design is engineered to meet project specifications, featuring a compact mechanical structure that minimizes the required cryogenic power while ensuring ease of access for maintenance and straightforward assembly procedures.