Study On Stimulated Emission From Polymer Film With DFB Structure

Conjugated polymers are attractive laser gain media materials due to their high phototuminescence quantum efficiencies,large stimulated emission cross section,chemically tunable emission wavelength and low fabrication cost.In this thesis, the work is concentrated on the study of the stimulated emission characteristics in MEH-PPV film which have an asymmetric waveguide DFB structure,some innovative research in the following aspects is also carried out.An asymmetric waveguide is fabricated by spin coating a thin film of MEH-PPV of xylene solution onto a DFB grating substrate and then works as gain medium. Stimulated emission in red wavelength region can be achieved under photo-pump.The spectra detected from the edge of the sample shows a gain narrowing and a clear threshold when increasing the pump intensity.The minimum threshold of MEH-PPV film with DFB structure is 0.47uJ/pulse.Compared to the MEH-PPV film with a planar waveguide structure whose threshold is about 2.2uJ/pulse,the MEH-PPV film with DFB structure has a notably low threshold.The phenomenon can be attributed to the grating structure and waveguide effects.When altering the grating constants,the spectral locations of the emission peak and the threshold have no significant change. With increasing the grating constants,the gain increases.That is because the grating constants are magnitude large than the optical wavelength.In addition,the influence of electric field treatment on stimulated emission is also investigated.When the electric field intensity increases,the gain of the MEH-PPV film increases rapidly.It may be the result of orientation of polymer molecules or the elimination of forming the nano-domine phase under the presence of an electric field.