The three most common lidar transmitter-receiver configurations are illustrated, along with the basic transmitter components. The components are described sequentially, starting with the laser, with a table of the most important laser characteristics for lidar systems. Lidar beam expanders are described. Lasers are then discussed in terms of their basic requirements (an active medium, a population inversion, and optical feedback), and the properties of laser light (monochromaticity, directionality, and often polarization). Beam parameters and beam quality are then described starting with the Gaussian beam model. Measures of laser beam quality include the beam propagation ratio, spectral purity, and polarization purity. Methods for changing the wavelength are discussed, including stimulated Raman scattering, harmonic generators, and optical parametric oscillators. Laser safety, eye safety standards in terms of maximum permissible exposure, and laser classes are then covered, and the transmitter of an eye safe elastic backscatter lidar is described as an example, with an illustration and a table of its parameters.

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.