Nonlinear crystal under the action of strong laser second nonlinear effect of the frequency to omega after laser through the crystal into a frequency of 2 frequency doubling light of omega, known as the frequency doubling technique, or second harmonic oscillation.Such as the 1064 nm laser through the frequency doubling crystal, into a 532 - nm green light.The CNI provides the frequency doubling crystal using frequency multiplication technology expanded laser wavelengths, can obtain more short wavelength laser.