A laser is a device which emits a coherent beam of light through the process of optical amplification. The basic principle behind lasers is the stimulated emission of electromagnetic radiation. The word laser is an acronym for light amplification by stimulated emission of radiation. Laser beams possess spatial coherence, which makes it possible to focus them on a very tight spot. Some of the myriad devices which make use of laser technology are laser printers, fiber-optic communication, barcode scanners, optical disk drives and welding materials. There are various types of lasers, based on the materials which are used to make them. A few major types are gas lasers, chemical lasers, excimer lasers, solid-state lasers and fiber lasers. Laser technology is an upcoming field of science that has undergone rapid development over the past few decades. Some of the diverse topics covered in this book address the varied branches that fall under this category. As this field is emerging at a fast pace, this book will help the readers to better understand the concepts of this field.