  An electromagnetic wave (EMW) interacting with the moving singularity of the
charged particle flux undergoes the reflection and absorption as well as
frequency change due to Doppler effect and nonlinearity. The singularity
corresponding to a caustic in plasma flow with inhomogeneous velocity can arise
during the breaking of the finite amplitude Langmuir waves due to nonlinear
effects. A systematic analysis of the wave-breaking regimes and caustics
formation is presented and the EMW reflection coefficients are calculated.
