ECHELLE SPECTROGRAPH BASICS

This section describes how the spectral format, or echellogram, of the IRCS echelle section is disposed on a detector. We assume an echellogram imaged by a perfect optical system. Although a real optical system has aberrations, distortions, and miss-alignment of the optical axis (e.g. shift, rotation, tilt, etc.), a perfect optical system provides sufficiently meaningful reference and basis for us to understand the characteristics of the echellogram and to compare it with a real one.