Fix ttm/mod The laser shines in that direction

Hi, I’m a little confused about whether the laser is shining in the positive x direction or the negative x direction. Can you answer it for me?

if (duration < width) {
if (ix >= t_surface_l) mult_factor = (intensity/(dxskin_layer_d))exp((-1.0)(ix_d - surface_d)/skin_layer_d)exp((-1.0)(iy_diy_d + iz_diz_d)/(r_0r_0));
}
From the source code I think the laser is going in the x positive direction, but my simulations think the laser is going in the x negative direction.