LASER ACTION IN STRONGLY SCATTERING MEDIA

THE radiative properties of an atomic or molecular system may be alter ed significantly in the presence of coherent optical scattering1,2. In the course of investigating the radiative properties of a laser dye d ispersed in a strongly scattering medium (a colloidal suspension of ti tanium dioxide particles), we have found that the emissions from such systems can exhibit spectral and temporal properties characteristic of a multimode laser oscillator, even though the systems contain no exte rnal cavity. The threshold excitation energy for laser action is surpr isingly low. We suggest that these composite systems might find applic ations in laser instrumentation and photonics.