Calculation of the laser diffraction intensity of striated muscle by numerical methods.

The diffraction of a laser beam by striated muscle was treated as Fraunhofer diffraction of a homogeneous system. Assuming that the striated muscle was a three-dimensional array of cylindrical sarcomeres, a set of diffraction equations in cylindrical reciprocal coordinates for calculating the diffraction intensity as a function of the polar and azimuthal angles was derived. After the positions and dimensions of the sarcomeres were specified, numerical calculations according to the diffraction equations yielded the intensity pattern on both the meridional and equatorial planes. As a sample calculation for the diffraction intensity, the sarcomere positions and dimensions derived from light microscopy and light diffractometry on living muscle fibers were used. The calculated diffraction intensity pattern of a skeletal muscle fiber correlated well with experimental measurements.