Fabrication Of Photonic Crystal Particles And Their Applications In Random Lasers

Random laser is a special source of stimulated emission in which the feedback is provided by multi-scattering in a gain medium.Particle distributed randomly in a gain medium provide coherent or incoherent feedback according to the Mie scattering or Rayleigh scattering theory.Random laser does not need the resonant cavity which is necessary for traditional laser.However the threshold of TiO2 nanoparticles random lasers are too high from the view of random laser practical application.To search new random laser systems and get better performance,such as lower threshold and narrower bandwidth,a lot of efforts have been made in this field.Photonic crystals(Ph Cs)are regularly ordered structures in which at least two materials with different dielectric constant are arranged periodically.Because of the effect of Bragg diffraction,this periodic dielectric structure lead to the so-called photonic band gap(PBG).The PBG represents the narrow range of specific wavelengths in which light propagation inside a Ph C is prohibited.In this letter,we demonstrate a new type of random laser based on spherical colloidal photonic crystals particles suspended in a dye solution.The research details are as follows:(1)Polystyrene opal spherical photonic crystal beads(PCBs)with different PBGs were prepared by extraction-assisted microemulsion method.The PS opal PCBs is spherical in the shape.PCBs has face-centered cubic structure.The reflection spectrum of PCBs has obvious reflection peaks.The peak shape is narrow and steep,which indicating PCBs has good crystallization quality.Photonic crystals with different PBGs were prepared by PS colloidal microspheres with different sizes.(2)Inverse opal TiO2 PCBs with different PBGs were prepared by liquid phase deposition(LPD)technique.The results show that the inverse opal TiO2 PCBs is spherical in the shape.In addition,inverse opal TiO2 PCBs has good crystallization quality.(3)Study on the optical output characteristics of dye solution doped PS Opal PCBs.It is found that the dye system doped PS Opal PCBs can emit random laser and the threshold of the random laser is related to the position of the PBG.When the central wavelength of the PBG of the PCBs is located near the wavelength of the pump light,the threshold of the random laser is the lowest.The mechanism of the random laser output of the dye system doped with photonic crystal particles is analyzed as follows:PCBs were act as scattering particles in this system,when the PBG is located near the wavelength of the pumped light,photons are reflected by the PCBs for multiple times to form optical feedback,and then realize light amplification.(4)Study on the optical output characteristics of dye solution doped TiO2 inverse Opal PCBs.It is found that the dye system doped TiO2 inverse Opal PCBs can emit random laser,and the threshold of random laser is related to the position of the PBG.Compared with PS opal photonic crystal particles,the threshold of the dye solution containing TiO2 inverse opal PCBs is lower.This is because the refractive index ratio of the two materials constituting the inverse opal PCBs is higher,and the inverse opal PCBs has a stronger reflectivity.