Wavelength Tunable Random Laser Based On Polymer Stabilized Cholesteric Liquid Crystal

Random laser is a kind of unconventional laser whose feedback mechanism is based on disorder-induced light scattering,which does not require a precisely fabricated optical resonant cavity.Random laser has been widely studied in the fields of display,sensing,information and statistics,with characteristic of diverse morphology,low coherence,omnidirectional emission,low cost.The use of liquid crystals as scattering media helps to solve the drawback that random lasers are not easily modulated.Liquid crystals,as an optoelectronic anisotropic material,have a sensitive response to the stimulation of external fields(temperature,electric field,magnetic field,and light)and have the ability to switch among a variety of structural forms and exhibit different optical properties,making them ideal materials for the preparation of optoelectronic devices.In this paper,we studied the random laser in dye-doped polymer stabilized cholesteric liquid crystals,and modulated the wavelength of the random laser in this system using electric field to investigate its application characteristics in the field of imaging.Based on the potential of bandgap modulation in polymer-stabilized cholesteric liquid crystals,a dye-blending method was adopted to increase the fluorescence range for the goal that matching the bandgap broadening range,and it was found that non-ionic dyes with antioxidant ability under the action of strong light and electric field are required in the system of modulating polymer network-stabilized cholesteric liquid crystals using electric field.The dye-doped polymer stabilized cholesteric liquid crystals were infused into the nonoriented cell to form defective scattering structures.The use of high-frequency AC was adopted to induce the ordering of negative liquid crystal molecules before and during the polymerization process to achieve the purpose of erasing the texture defect.Therefore,the scattering structures caused by the process of self-assembling and polymer growth could be effectively contained.Multimode random lasers with different spectral widths caused by the diversity of degrees of scattering,which are closely related to their shape of bandgap edge.The enhancement of the multimode random laser by the band gap edge of cholesteric liquid crystals was demonstrated,and the band range of enhancement is related to the width of its bandgap edge,which has a mode selection effect on the multimode random laser.By applying DC to the dye-doped polymer stabilized cholesteric liquid crystal,the random laser that is enhanced at the bandgap edge blueshifted with the short wavelength edge of bandgap,and the purpose of modulating the random laser wavelength is achieved.Due to the use of a non-oriented cell,not only can the scattering structure be introduced within the cholesteric liquid crystal system,but also the absence of the orientation layer,this structure also greatly reduces the response voltage,that making the polymer network more sensitive to the electric field.While reducing the energy consumption,it also avoids the polarization of the liquid crystal film under strong electric fields and effectively increases the device stability.A wavelength tuning range of nearly 95 nm for the random laser was achieved using a lower drive voltage(saturation voltage of 3.8 V).The wavelength modulation process of this random laser is stable and the reversible performance is reliable,and shown a clear advantage in display testing.