Laser linewidth measurement based on image processing and non-air gap F-P etalon

Laser linewidth measurement has been realized in the paper through image processing and on non-air gap F-P. Firstly, The expression of linewidth measurement founded on non-air gap F-P has been obtained from the interference theory of multi-beam of light. Secondly, The practical linewidth of pulse Nd:YAG laser has been measured with the method above. An interference pattern produced by CCD was used for digital image processing. In the course of processing, Canny operator was applied for the sake of picking-up the edge of interference circle, then the inner and external radius of the interference circle can be acquired in the form of pixels. The actual physical size can be calculated through relative transformation according to the radius of the interference circle. At last, Nd: YAG laser with 28ns pulsed-width was used as the emission source, The experimental results based on the method above is 36.8 MHz. This data is in agreement with 34.2 MHz through Discrete Fourier Transform(DFT), As we all know, the frequency resolving power of DFT is depend on the effective acquisition points, So the cubic spline interpolation was introduced after the course of DFT, and the better result has been achieved.