Period of active material is a laser amplifier

This light passes through the working substance, the light energy will weaken not strengthen. To make stimulated emission dominate at high energy level E2 must be greater than the particles in the low-energy level E1 of the particles. This distribution coincides with the equilibrium distribution of particles when the opposite is called population inversion distribution, referred to as population inversion. How to technically achieve population inversion is a necessary condition for producing laser. Theoretical studies have shown that any work material, under appropriate excitation conditions, in particular the level of the particle system to achieve population inversion between energy levels. If microscopic particles such as atoms or molecules with high energy and low energy level E2 E1, E2 and E1 energy level populations on the number density of N2 and N1, in the two-level transition between the existence of spontaneous emission, stimulated emission and stimulated transitions absorption transition, three processes. Functions of laser pointer can determine the price of laser pointer .
Transitions generated by stimulated emission of light by stimulated emission, and the incident light has the same frequency, phase, propagation direction and polarization direction. Therefore, a large number of particles in the same excitation of coherent radiation field produced by the stimulated emission light is coherent. Stimulated emission transition probability and stimulated absorption transition probabilities are proportional to the incident monochromatic radiation field energy density. When the two-level statistical weights are equal, the probability of the two processes are equal. In the case of thermal equilibrium N2 <N1, so spontaneous transitions dominate the absorption of light through the material is usually due to shock absorption and attenuation. Excitation energy can damage the outside thermal equilibrium leaving the N2> N1, this state is called population inversion. In this case, the stimulated emission transition dominant. Light through a period of length l in the inversion state of the laser working substance (active substance), the light intensity increases eGl times. G is proportional to the (N2-N1) of the coefficient, called the gain factor, and its size is also working with the nature of the material and the laser light frequency. Period of active material is a laser amplifier. If, for some active substances on the two mirrors parallel to each other (at least one of which is part of the transmission's) constitute the optical resonator (Figure 1), at high energy particles will produce a variety of directions of the spontaneous emission.  laser pointer always has various parameters.