The laser pointer companies compete in the price of laser pointer

The laser pointer companies compete in the price of laser pointer .
1917 Einstein proposed stimulated emission, the laser has come out in 1960, separated by 43 years, why? The main reason is, ordinary light is produced by stimulated emission of particles in a very small probability. When the frequency of light launched into the work of certain substances, stimulated emission and stimulated absorption of two processes exist, the number of photons by stimulated emission of radiation to increase the number of stimulated photon absorption while filling decreases. Substances in thermal equilibrium, the particle distribution on each level, follow the equilibrium statistical distribution of particles under the law. By statistical distribution of the lower energy level E1 in the number of particles at the higher level must be greater than the number of particles of E2. 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. The price war will make the price of laser pointer reduce. 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. 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. The price advantage of laser pointer is really important.