Frequency upshifting of electromagnetic radiation via oblique incidence onan ionization front

Frequency upshifting of electromagnetic radiation impinging on a relativist ically moving ionization front is theoretically investigated. Unlike previo us works in this field treating the case of normal incidence and qualitativ ely similar case of oblique incidence of a transverse electric polarized wa ve, oblique incidence of a transverse magnetic polarized wave on the front is considered. The peculiarities of the case under consideration are connec ted with the generation of Langmuir waves behind the front and Brewster's p henomenon. We present a complete analysis of the incident wave transformati on including analysis of the frequencies and amplitudes of the waves excite d ahead of and behind the front. Special emphasis is made on energy transfo rmation in the case when a wave packet is incident on the front. In particu lar, we show that even for negligible angles of incidence, energy losses vi a transformation into Langmuir waves may be very high (up to similar to 60% ). In general, generation of Langmuir waves may play a significant role in the plasma-based radiation sources with relativistic ionization fronts.