Enhanced sensitivity of time-resolved reflectivity measurements near Brewster´s angle

A method for enhancing the sensitivity of time-resolved reflectivity measurements in semiconductors is discussed. By appropriate choice of the angle of incidence near Brewster´s angle, the photoinduced reflectivity changes are easily increased by one order of magnitude. Two examples, the lifetime of a dense electron-hole plasma and the picosecond laser-induced melting transition in silicon, illustrate the method. Extension to the case of thin films is possible, as demonstrated by experiments performed on thin polycrystalline silicon films. Possible complications due to the use of very tightly focused beams and ultrashort pulses near a strong resonance are considered and, together with other considerations of a more experimental nature, lead to general guidelines for signal-enhancement and easy implementation and data analysis.