3.1 Introduction

Modern astronomical telescope systems are integrated opto- and electromechanical systems optimized to give excellent low-noise digital image quality over a required field of view (FOV) at the output of the instrument. It is the interaction of radiation with optical materials that enables telescopes and instruments to collect, concentrate, image, and detect radiation. In this chapter, we briefly introduce those aspects of the interaction of light and matter that are the foundation for geometrical optics. First-order optics uses geometrical optics to determine image location and size, geometric image quality, image brightness, and radiometry.

3.2 Interaction of Light and Matter

3.2.1 Index of refraction

A complete description of the way in which waves propagate requires that we consider two velocities. One is the group velocity V_G, and the other is phase velocity V_P. A ray of light bends when passing at an angle from one transparent dielectric medium into the next dielectric medium having a different refractive index. Index of refraction n is defined as

where c = 2.997924 × 10⁸ m/sec.

Wavelength λ and frequency v are related by

(3.2)

In a vacuum, where velocity is the speed of light,

(3.3)