Amplified spontaneous emission in polymer–CdSe/ZnS-nanocrystal DFB structuresproduced by the holographic method

Abstract

Amplified spontaneous emission (ASE) is demonstrated in volume-distributedfeedback (DFB) structures, formed by colloidal CdSe/ZnS nanocrystals andZrO2 nanoparticles (NPs) in a polymer matrix. Periodic redistribution of the NPs in anorganic matrix was carried out by holographic photopolymerization in a speciallydeveloped light-sensitive nanocomposite. The composite consists of two acrylatemonomers and two types of inorganic NPs. The NPs provide for the formation oftwo co-phased gratings—a refractive index grating and an optical gain (losses)grating. The core–shell CdSe/ZnS nanocrystals are used as a gain medium, whileZrO2 NPs create the refractive index grating and enhance the distributed feedback. Theperiod of the volume structure provides the feedback for lasing at the wavelengthλlas of about 575 nm in the second diffraction order. In contrast to known laser systems based onvolume DFB cavities, in which the different components of the formulation provide optical gainand feedback, in our case the inorganic NPs serve as an emitting material and can providesimultaneously for feedback. By pumping of DFB structures by a titanium–sapphire laser (λpump = 400 nm, pulse duration of 120 fs) normal to the sample plane, the appearance of a sharpstimulated emission along the grating-vector direction is observed. Output intensity of ASEas a function of the pump energy shows a threshold behavior and full width athalf-maximum (FWHM) of the ASE spectral band decreases from 33 to 12 nm.