Quantum-optical signatures of stimulated emission

Emission-line stars such as eta Car are promising locations in searching for quantum-optical phenomena in radiation. Light carries more information than is contained in the classical quantities of intensity, spectrum or coherence. Temporal correlations between successively arriving photons (their degree of ordering) may contain information on how the photons were created in the source (through stimulated or spontaneous emission), and how they have been scattered since. Such properties are studied in the laboratory, and might become observable also in astronomical sources.