This lecture covers the basics of laser operation, including dispersion, absorption, and emission processes, as well as the concepts of shot noise, relative intensity noise, and signal-to-noise ratio in optical detectors. It also delves into the principles of photodetectors, photomultiplier tubes, and photodiodes, explaining their specifications and noise characteristics. The instructor provides examples illustrating the impact of shot noise in digital images and discusses the significance of signal-to-noise ratio for detecting signals in the presence of noise.