Single-beam lifetime measurements via self-induced optical absorption.

We present self-induced absorption, a pump/probe-like modulation technique that uses a single monochromatic laser acting simultaneously as both a pump and a probe. The technique is applicable to any system where the phenomenon that us being excited simultaneously induces additional absorption in the beam through a secondary process, leading to a non-linear power component in the beam transmission. The technique is demonstrated on a silicon wafer, where the non-linear transmission is due to free-carrier absorption, and provides information about the recombination lifetime of the semiconductor. Reducing a two-beam technique to a single laser beam simplifies the alignment challenges of traditional dual-beam modulated pump/probe measurements, which require overlap of separate pump and probe lasers on the sample under study.