| Description |
Photonic crystals (PhC) with pseudo band gap property have verities of applications in optics and optoelectronics. Three-dimensional (3-D) PhC is a periodic arrangement of dielectric material along three orthogonal directions and it can restrict the propagation of electromagnetic waves through it. The restricted wavelength range is known as the photonic stop band. The crystal which shows different stop bands at different directions is called pseudo band gap material. The main aim of this work was to demonstrate microcavity PhC lasers. For this purpose, 3-D dye doped polymeric PhC was used to study the laser induced emissions of Rhodamine-B dye embedded into it. The embedded dye molecules were excited with the second harmonic of a Q-switched nano-second Nd: YAG laser of repetition rate 10 Hz. An angle-dependent modification in the spontaneous emission spectrum of the dye was observed due to the non-uniform distribution of the density of states in the PhC. Directional spectral narrowing with sharp lasing threshold was observed at input pump power of 74 mW. In this system, the dye as gain medium got optical feedback from the Bragg planes of the PhC. Two dyed PhCs with nearly similar properties were kept together to increase the optical gain length in the system. Spectral narrowing was observed at relatively higher pump power because of the losses at the interface of the two PhCs. PhC heterostructures (HS) was fabricated by growing the dyed PhC in between two bare crystals in sandwich form. The reflectance of the HS was lesser as compare to individual PhCs. The spectral narrowing could be possible at nearly the same pump power as the previous case in the HS because the bare PhCs on both sides worked as external reflecting mirrors to the emission from the dyed crystal. The dye doped PhC was coated with thin layer of gold due to which the reflectance of the crystal has increased. The gold coated PhC shows lasing with sharp threshold at 60 mW which is lesser than the other crystals.
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