Figure 7
Spatial Fourier transform of an incident spherical wave as given by Saka et al. (1973 ). Crystal thickness and reflection parameters are the same as in Fig. 1 . The surface-reflected wave is given by s(q) = J0(2Aq)+J2(2Aq) and, neglecting absorption, the first back-reflected contribution by b(q) = J0[2A(q2-1)1/2] + 2[(q-1)/(q+1)] J2[2A(q2-1)1/2] + {[(q-1)/(q+1)]2 × J4[2A(q2-1)1/2]}. q is a normalized spatial coordinate, Jn are Bessel functions. In reality, with absorption the echo, of course, would be smaller than the direct pulse. Note the similarity to Fig. 1 , taking absorption into account, which mainly affects the echo. |