Study On Flexible Random Laser Based On Hydrogel

The random laser based on scattering gain medium was proposed by Letokhov for the first time in 1967.Due to the low spatial coherence,the random laser has been widely studied in disordered photonics.The random laser can be used for different areas by changing the shape and gain media because the generation of random laser does not need regular cavities.Hydrogel,as an object of extensive research in medical materials,will be more suitable for optical therapy when combining with laser.In view of the fact that random lasers need to add additional scatterers,emission wavelength is inconvenient to be tuned,and there are no biomedical applications and other related problems.In this thesis,the multiple scattering of random laser was developed by the three-dimensional network structure of hydrogel,and the random laser emission phenomenon were found in hydrogel without adding extra scattering particles.The emission wavelength of random laser can be controlled by temperature and hydrogel thickness,and the random laser based on hydrogel for phototherapy were explored.(1)Firstly,the emission characteristics of flexible random laser were studied.A Rh 6G doped flexible random laser was prepared by UV crosslinking polymerization of polyethylene glycol two acrylate(PEGDA)monomer,which has a lower threshold of 23.7 ?J,where,the porous network structure of hydrogel acts as a weak scattering medium.In this thesis,the emission characteristics of random lasers under different morphologies,laser dyes and concentrations,were studied.The mechanism of the random laser was explained further by some analytical methods,the three-dimensional network structure of hydrogel worked as a scattering medium provides multiple scattering for random laser.(2)Based on the PEGDA flexible random laser,control of the emission wavelength by temperature were investigated.The emission wavelength of the flexible random laser is red shifted by 3.2 nm in the range of 40 ?,and the red shift of the main peak wavelength has a good linearity with the change of temperature.In the experiment of temperature cycling,the flexible random laser can produce red or blue shift with the temperature increasing or decreasing.The results show that the random laser has good repeatability and stability.In this thesis,the internal mechanism of temperature changing random laser wavelength was analyzed theoretically,and its application in the field of phototherapy was explored.(3)The cholesteric liquid crystal doped random laser was studied.By using photosensitive polyvinyl alcohol styrene pyridinium salt(PVA-SBQ)hydrogel as flexible laser material,the luminescence properties of random laser under different liquid crystal types and liquid crystal concentrations were studied,it is found the emission wavelength shifts 8 nm when the thickness of hydrogel film increases by221 ?m,which can be explained by the loss of photon reabsorption.