Characterization of high power laser beams with the aid of nonlinear optical processes

We have demonstrated both experimentally and theoretically that applying nonlinear optical processes can enable new devices to be realized which allow direct measurement of the power density of laser beams, determination of focal spot location and the beam waist size, as well as visualization and analysis of complex beams' profiles, determination of the beam quality factor and the Strehl ratio. Materials with non-absorptive nonlinearity allow in-line non-distorting measurements. Furthemore, the absence of absorption makes the devices applicable to high power laser beams, and in the focal plane. The resolution of the method is extremely high and is principally limited by the wavelength making possible parallel measurements for a large number of beams. Use of ''intrinsic interference'' allows one to obtain high accuracy with simple schemes. We have identified liquid crystals as a highly suitable medium for these purposes due to their giant, non-resonant and non-absorptive orientational optical nonlinearity.