The invention of the laser is one of the major achievements of 20th century science and technology. It has finally given mankind the ability to control the luminescent processes of molecules and atoms, which are extremely small in scale, immense in quantity, and chaotic in motion, thus acquiring the ability to generate and amplify coherent infrared, visible light, and ultraviolet rays (even X-rays and γ-rays). The rise of laser science and technology has brought humanity to a brand new level in the understanding and utilization of light.