The preset study for the Geometrical Optics interface is the Ray Tracing study step. The Ray Tracing study step is similar to the Time Dependent study step but has a different default time step size, includes additional options for specifying a range of time steps, and includes built-in stop conditions for terminating a study when certain criteria are met.

By default, the Ray Tracing study step computes ray trajectories from t = 0 to t = 1 ns with a time step size of 0.01 ns. However, it is often useful to think of ray tracing in terms of the maximum distance of ray propagation instead of the maximum time. To express the duration of the study in terms of a maximum optical path length, change the Time step specification setting from the default, Specify time steps, to Specify maximum path length. Then select a Length unit (default m), enter a set of Lengths (default range(0,0.01,1)), and enter a Characteristic group velocity (default c_const), a built-in constant for the speed of light in a vacuum. With the default solver settings, the time-dependent solver must take at least one time step whenever the optical path length of a ray moving at the Characteristic group velocity would have reached one of the values in the list of Lengths.

Select a Stop condition — None (the default), No active rays remaining, or Active rays have intensity below threshold.

For None the study step does not create any stop conditions, although stop conditions can still be added to the solver sequence manually.

For No active rays remaining the study step ends if no rays are active. A ray is considered active if it has been released but has not reached a boundary with a Freeze, Stick, or Disappear wall condition.

For Active rays have intensity below threshold the study step ends if all remaining active rays have intensity less than the value entered in the Threshold ray intensity text field (default 1[W/m^2]). This option can only be selected if the ray intensity is computed; that is, the Intensity computation is set to Compute intensity or Compute intensity and power in the Ray Properties section of the physics interface node’s Settings window. This option can be used to prevent computational resources from being wasted by computing the trajectories of rays of negligibly small intensity.