It is the sale situation of laser pointer in the market

It is the sale situation of laser pointer in the market.
In order to satisfy the phase matching conditions can be used in two basic ways: one point of view match, another temperature match. Angle matching the fundamental frequency in a particular angle and polarization state incident to the frequency-doubling crystal, Lee Figure 2-4 negative uniaxial crystal refractive index of spherical offset the effect of doubling crystal birefringence dispersion effect to the phase matching requirements. Angle matching is highly efficient second harmonic radiation is the most commonly used, the most important. Existence of normal dispersion effect due to the general media, the refractive index of the high-frequency light is greater than the refractive index of the low-frequency light, such as n2ω-nω about 102 orders of magnitude. k-≠ 0. For an isotropic crystal, due to birefringence, we can make use of the refractive index of the relationship between different polarized light, to find the phase matching conditions, to achieve k = 0. It shows clearly the market share of  laser pointer .
This method is commonly used in a negative uniaxial crystal, the following example of a negative uniaxial crystal. Figure 2-4 draw the relationship between the crystal light and second harmonic of the fundamental frequency of the two different polarization refractive index surface. The solid line sphere as the base frequency of the optical refractive index surface, dashed spherical z-axis for the fundamental frequency of the optical refractive index surface, spherical surface for the o-ray refractive index surface ellipsoid surface of the e-ray refractive index, optical axis. The definition of the refractive index of the surface: the leads from the center of the sphere a radius vector to reach the surface of a point the length of the crystal in order to vector the size of the diameter of the wave normal direction of the evanescent waves. Phase matching conditions, one is looking for a real face and virtual personal point location, in order to get through this intersection of the radius vector and optical axis angle. See in the picture, the fundamental frequency o light in the optical refractive index and the refractive index of the e ray in the second harmonic equal.
Later, the American physicist Charles Townes and the Soviet physicist of Masuo Fu, and the general Huoluo Fu has proposed the use of atoms and molecules stimulated radiation principle for generation and amplification of microwave design. 1954, mentioned earlier, American physicists Townes finally made the first ammonia molecular beam maser (Figure 1.1), successfully pioneered the use of molecular and atomic systems the coherent amplifier or oscillator as a microwave radiation precedent.