On the photon energy conservation in stimulated emission. Experiment

Quantum electrodynamics predicts identity of incident and emitted photons in stimulated emission. This fundamental law is important to test experimentally. In this work stimulated emission in GaAs semiconductor amplifier was investigated and positive frequency shift of the amplified beam was detected. In relative units this frequency shift was found equal $\Delta\nu/\nu = (+1.7 \pm 0.2)\cdot10^{-18}$. This indicates violation of the photon energy conservation in stimulated emission.