Abstract: A new method of measuring small extention is put forward. The light intensity of single slit diffraction is converted to electric signal by CCD photo-electric measuring system and outputs curve of light intensity distribution after computer processing. Read the interval of diffraction marking from adjacent wave through and output results through simple operation of software. It implements date acquisition and operation results real-timely and semiautomaticly. It overcomes the difficulty of conventional measurement method and complex calculation of date-processing. The Young＇ s modulus of elasticity is measured by this method and the results agree with the nominal value very well.

Key words: single slit diffraction, Young＇ s modulus, CCD