This chapter provides an introductory overview of sensors. The analysis is limited to small-angle (paraxial) optics. The purpose is to equip the reader to do a first-order design in the system context of this book. Detailed sensor design is beyond the scope of this chapter and indeed not required for this text. Fundamental to the sensor concept is the geometry of solid angles and how these are effected in the sensor. The second important element is the conversion of optical energy into electrical energy, including the effect of noise.
The path by which a ray propagates through an optical system can be mathematically calculated. The sine, cosine, and tangent functions are used in this calculation. These functions can be written as infinite Taylor series, i.e., sin(x) = x − x3/3! + x5/5! − x7/7! +· · ·. The paraxial approximation only uses the first term in the sum sin(x) ≈ tan(x) ≈ x, cos(x) ≈ 1. The paraxial approximation is valid only for rays at small angles with and near the optical axis. The paraxial approximation can be effectively used for first-order design and system layout despite the small-angle limitations.
The coverage of detectors and noise in this chapter is, similarly, only a brief introduction: sufficient detail is given to support first-order design and modeling.
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