when $x_d$ is 0.5055 and $x_m$ is 0.08638. We find that the GH shift at the reflectance dip is [*backward*]{} with negative values of $\delta_r$ when $W$ is larger than 40 $\mu$m in the present case. The maximum value of $\vert\delta_r\vert$ is about 140 when $W$ is 320 $\mu$m and about 30 when $W$ is 160 $\mu$m. Interestingly, for $W \leq 40$ $\mu$m, the value of $\delta_r$ at the reflectance dip becomes positive. The critical thicknesses in figure 4(a) for narrow beams with $W = 40$, 20 and 10 $\mu$m are $x_m = 0.08617$, 0.08530 and 0.08246 respectively. Thus in the calculation with $x_m = 0.08638$ presented here, narrow beams have positive GH shifts. In figure 6(b), we show the normalized half-width of the reflected beam $W_r / W$ as a function of the incident angle for each value of $W$. General characteristics are similar to the forward shift case shown in figure 5(b).

![\[fig7\] (a) Magnetic field intensity distribution associated with the reflected beam plotted versus $x$ for several different values of $W$, when $x_m=x_{m,f}$ and $\theta_i= 62.33^\circ$. The GH shift is positive in this case. (b) Magnetic field intensity distribution associated with the reflected beam plotted versus $x$ 