Random Laser Research Based On PDMS Waveguide Structure

There are many significant differences between random laser and traditional laser in the generation mechanism and luminescence properties,and random lasing does not require a resonant cavity,and optical feedback mainly depends on the multiple scattering of random medium in random medium.The multiple scattering get the photons travel a longer path in the media,and result in a narrower spectra and stronger emission intensity when the system is in low disorder degree,in which case the incoherent random laser occurs.And the coherent random may take place with distinguished sharp laser spikes on the spectra when the system is in high disorder degree,in which case the photons have a certain probability to return to the original location after multiple scattering,forming a resonant cavity of conventional laser,in which the light field get feedback.In this paper,the emission characteristics of polydimethylsiloxane(PDMS)liquid waveguide structure and solid state waveguide structure random laser has been investigated.In the liquid waveguide structure,the threshold,single direction,peak shift,stability and other characteristics of random laser has been studied;and in the solid waveguide structure,we studied the characteristics of random laser in pure dye doped thin films and silica(SiO2)nanoparticles doped thin films,including spectral,threshold,and peak shift etc.,and the reason of the formation of PM597 dye micro-nano crystals was studied.In the experiment of liquid waveguide structure random laser,the optical feedback of the coherent random laser is provided by both strong waveguide confinement and SiO2 NPs multiple scattering.The threshold of random laser is decreased by 1/12,which is 700uJ/cm2.The lowest threshold was obtained when the concentration of SiO2 nanoparticles is 1.3mg/mL,due to the transition from a weak-scattering regime to a strong-scattering regime.The energy of random laser is confined in an angle range of-6°?+5°,which has higher unidirectional.When we changed the types of solvent,the peak-shifted of random laser is observed in the quartz cuvette and liquid waveguide structure,and the results of experiment show that the random laser spectral red-shift and the space of two adjacent peak wavelength of emission laser in the liquid waveguide structure is larger than that in the quartz cuvette.Finally,the stability of the random laser in the liquid waveguide structure is studied.It can be observed that the emission intensity drops only by 18.8%after 40000 pump pulses for configurations contains SiO2 NPs.The results of experiment show that the liquid waveguide structure play an important role in reducing the energy loss,improving the directionality and stability of random laser,which provides a valuable reference for optofluidic random laser application in bio-chemical sensors and nano optoelectronics.In the solid waveguide structure random laser experiment,the optical feedback of our setup is provided by both multiple scattering and leaky-waveguide confinement mechanisms.Firstly in the pure dye film,the coherent random laser was obtained due to the PM597 dye molecules aggregate forming micro-nano crystals,and the threshold of random laser is 1.5mJ/cm2.The threshold is reduced to 0.75mJ/cm2 after NPs were doped.The threshold is increased when the film is peeled off from the glass,which shows that the leaky-waveguide structure plays an important role in reducing the random laser threshold.By changing the length of the pump stripe and the thickness of the film,the peak wavelength of the random laser red-shift 6.7nm,5.93nm,respectively.The minimum threshold of the random laser was 1.125mJ/cm2 when the film thickness was 9.6um.Finally,we systematically studied the causes of the formation of PDMS micro-nano crystals.Due to the the change of PM597 dye molecules solubility,the micro-nano crystals were formed in the process of solvent volatilization or during the period of time when the PDMS cures.The loss induced by the self absorption of low concentration dye film is smaller,which can greatly reduce the power consumption of random laser.The dye random laser of solid film has potential application in integrated optics,micro-nano optoelectronics,and display imaging.