AbstractNumerical computation of laser beam refraction may involve difficulties associated with ray paths through a caustic, where first‐order amplitude values become infinite. We choose the special test case of a stratified gas, and compare the results obtained by numerical integration of the ray differential equations with both asymptotic results and direct numerical solution of the exact wave equation. A final section evaluates the numerical solution of a parabolic approximation to the Helmholtz equation, with particular reference to the effect of the caustic. The final conclusion is that, with appropriate safeguards, any of these methods can effectively deal with the presence of a caustic surfac