In Chapter 3, we move to a semiclassical treatment (quantum theory) of light absorption and scattering, specifically from atoms. We start with a description of how lidar measures Doppler shift, and the fundamental difference between the measurement when the laser is in resonance with an atomic transition (resonant) and when it is not (nonresonant). We follow with a treatment of quantum polarizability and the resulting absorption cross section, leading to the differential resonance scattering cross section and its contrast with the classical result. After quantum polarizability, we demonstrate the radiation pattern of coherently excited atoms. This takes us to an interpretation of the Hanle Effect. Following these descriptions of the phenomena that impact resonance lidar, we extend our understanding by closing the chapter with an overview of the rudimentary physics of sodium laser guide stars.

In Chapter 8, we give an overview of the optics that control beam transmission and signal reception. We open with a description of the use and benefits of a beam expander to control the output beam divergence. From there, we move to describing receiver optics, starting with the telescope and importance of size, field of view, and using high-quality optics. This includes using an optical fiber to transport the received photons to the downstream filtering and detection optics. Next, we discuss detector characteristics and the trade-offs one must consider when selecting an appropriate photon counting sensor. We follow with a short section on the value of computer modeling the receiver optics. We close the chapter with a concise discussion of atmospheric turbulence and of laser guide stars and adaptive optics for the mitigation of atmospheric turbulence effects on astronomical telescopes.