This thesis details the development and characterization of the Near-Infrared Gatherer of Helium Transits (NIGHT), a high-resolution, near-infrared, narrow-band spectrograph. NIGHT is specifically designed to study atmospheric escape from exoplanets using transmission spectroscopy of the He I triplet (1083.3nm). Understanding this escape process is vital for illuminating the evolutionary pathways of close-in exoplanets, particularly concerning observed underdensities like the Neptunian Desert and Radius Valley.

A dedicated instrument like NIGHT significantly accelerates helium atmosphere detections, which are often time-consuming. NIGHT has a focused bandpass (1081-1085nm) and a resolving power of R~40,000 (with an upgrade planned to 75,000), allowing it to observe the helium triplet across all known exoplanetary velocities. Its design employs a unique double-pass volume-phase holographic grating, permitting optimized coatings and repurposed components, making it flexible and cost-efficient.

NIGHT is currently undergoing testing at the 152cm telescope at Observatoire de Haute-Provence, where initial results mostly meet performance requirements. Following this campaign and the telescope's decommissioning, the instrument will be relocated to a larger aperture facility to commence a large-scale survey. This survey will provide a statistically significant view of atmospheric escape, offering vital insight into the evolution of the close-in exoplanet population.