The interaction of light and matter. The laser pointer is actually derived from the interaction of light and matter. The microscopic particles that make up the matter absorb or radiate photons. At the same time, they change their own movement. Microscopic particles have a specific set of energy levels (usually these energy levels are discrete). At any moment the particles can only be at a level corresponding to a certain energy level. In recent years, 593.5nm yellow-orange laser flashlights have also begun to appear. Divided by wavelength, it can be divided into red light 635-650nm, green light 532nm, orange light 593.5nm, blue-violet 405-445nm (445nm already belongs to near blue light), pure blue light 473nm and invisible infrared 808nm, 980nm, 1064nm. In the way of light output, it can be divided into LD direct light output, such as 650nm, 635nm, 445nm. The crystal pumps infrared light, typically 532nm green light. 593.5 yellow light. If you understand the source of the laser pointer, you will understand the power of the laser flashlight.
Laser state (or simply expressed as being at a certain energy level). When interacting with photons, particles transition from one energy level to another and absorb or radiate photons accordingly. The energy value of the photon is the energy difference △E of these two energy levels, and the frequency is ν=△E/h (h is Planck's constant). Excited absorption (abbreviated as absorption): When the particles at a lower energy level are excited by the outside world (that is, they interact with other particles with energy exchange, such as inelastic collisions with photons) when they absorb energy, they transition To a higher energy level corresponding to this energy. This transition is called stimulated absorption. Spontaneous emission: the excited state that a particle is excited to enter is not a stable state of the particle. If there is a lower energy level that can accept the particle, the particle has a certain probability even if there is no external action. The spontaneously excited state from the high energy level (E2 ) The transition to the low energy ground state (E1), while radiating photons with energy (E2-E1), photon frequency ν=(E2-E1)/h. This radiation process is called spontaneous radiation. The light emitted by many atoms by spontaneous radiation does not have the same phase, polarization state, and propagation direction. The laser pointer is physically called incoherent light.