Study On Dye-Dopd Liquid Crystal Random Laser With Different Liquid Crystal Phase

Compared with traditional laser, random laser does not need extra cavity, the multiple scattering provides the feedback needed. Random laser has the advantage of low production cost, small size and simple structure. So it has great application value. The liquid crystal random laser is one kind of random laser with liquid crystal as the scattering medium. Because of the influence of the outfield (temperature, electric field, magnetic field, etc.) on the liquid crystal molecules arrangement and phase transition, liquid crystal random laser has the controllability of temperature, electric field and so on. The liquid crystal can be divided into nematic phase, cholesteric phase and smectic phase. The choosing of different liquid crystal material can achieve different emission characteristics of liquid crystal random laser. In this paper, Dye Doped Nematic Liquid Crystal (DDNLC) random laser and Dye Doped Cholesteric Liquid Crystal (DDCLC) random laser are investigated based on the properties of nematic liquid crystal (NLC) and cholesteric liquid crystal (CLC).The order degree of NLC is lower than that of CLC. Therefore, the energy threshold of DDNLC random laser is higher than that of DDCLC laser. In this paper, the influence of structure parameters of DDNLC samples (orientation method, cell gap and external feedback) on the DDNLC random laser emission (the output spectrum, energy threshold) is studied. The study shows that by choosing the appropriate sample structure parameters, the pump energy threshold of DDNLC random laser will be reduced. Compared with the orientation methods of "two-side rubbing in same direction" (TSRS) and "two-side rubbing in reverse direction" (TSRR), the sample with the orientation method of "two-side rubbing in vertical direction" (TSRV) obtains higher energy threshold (for example, the 200um cells, the energy threshold increases from 2uJ/pulse to 3uJ/pulse). And when the cell gap ranges from 142 um to 245 um, the energy threshold of the DDNLC random laser is lowest (1.2uJ/pulse). The DDNLC random laser energy threshold can be decreased from 4.2uJ/pulse to 1.5uJ/pulse with the external feedback. At the same time, the influence of structure parameters on the voltage regulation characteristic of DDNLC random laser is also studied. This study provides an experimental basis for the practical application of low power DDNLC random laser.Mix the chiral agent S811 with NLC E7 and laser dye PM597 with two different ratios to make two different DDCLC samples. Random laser and band-edge laser are observed from the two samples, respectively. Heat the DDCLC sample with 15wt% chiral agent S811, the switch on and off of DDCLC random laser is realized. Heat the DDCLC sample with 26.6wt% chiral agent S811.With the temperature increasing from 27 ℃ to 29℃, the band-edge laser is emitted, and the center wavelength shifts blue. However, when the temperature increases to 32.1℃, the random laser is emitted, and the pump energy threshold is 8uJ/pulse. And the switch of band-edge laser and random laser is realized. Finally, add a layer of cholesteric liquid crystal reflector to the dye-doped nematic liquid crystal cell. With the temperature of CLC reflector increasing, the reflection band of the CLC shifts blue. With the optical rotation and selective reflection characteristic of cholesteric liquid crystal, the polarization direction and the polarization degree of the DDNLC random laser from the cell are changed. The transition of the polarization state in the same device broadens the application fields of liquid crystal random laser.