Appendix H: treats the interaction between a light beam and a linear optical medium. This first part considers the propagation of a light beam in a sample of two-level atoms using a semiclassical approach, calculates the index of refraction of the medium and its gain when there is population inversion, and losses when the ground state is populated. It then treats in a full quantum way linear attenuation or amplification, for which the "3dB penalty" on the signal-to-noise ratio is derived from basic quantum principles. Finally, it considers the input–output relation for the two input modes of a linear beamplitter, an important example of a symplectic map.

This chapter treats two important steps in electronic sensor design. The first is the passage from functional blocks to lumped model electronic circuits. In this approach noise will be no more associated with functional blocks, but with circuit topology and electronic device elements. The second step is to analyze the effects of the readout mode on noise, emphasizing the differences between continuous and discrete-time approaches. Finally, we discuss some tradeoffs related to bandwidth and resolution in acquisition chains.