Polarization-asymmetric bidirectional random laser emission from a twisted nematic liquid crystal

Abstract

This paper reports on the observation and detailed investigation of the bidirectional random lasing emitted from an active twisted nematic liquid crystal, of which the polarization states are asymmetric (non-parallel to each other). In such a laser, the liquid crystal acts as a random distributed feedback cavity with an inherently built-in polarization rotator. While propagating in the anisotropic cavity, the polarization of the dye-emitted light rotates with the gently twisted optic axis. The output polarization states are, therefore, parallel to each of the surface alignment directions. The mode stability and electrical switchability of the laser were also examined. Moreover, correlations between the lasing threshold, alignment direction, dye concentration, and film thickness were established. The findings not only suggest an optimum concentration for low-threshold random lasing operation but also disclose the threshold inversion behavior of nematic random lasers.

Magnetically controllable random laser in ferromagnetic nematic liquid crystals

“…At the bulk layer in our sample, the random laser polarization is along the local nematic director whose direction is the same as the magnetic field and emitted without being rotated as shown in Fig. 7(b) because the local nematic director is not twisted as previously explained the random laser action in twisted nematic liquid crystals [15,21]. In this way, the random laser polarization for vDFNLC was parallel to the magnetic field direction.…”

“…Because the multiple scattering of light is driven by nematic director fluctuations [10,11], the random laser emission from NLCs is bidirectional [11] and polarized [10,12,13], unlike the omnidirectional behaviors in most of random laser resonators [14]. Because the laser action is correlated with the orientational direction of liquid crystals [15], it could respond to the molecular reorientation by a variety of external stimuli. In fact, the wavelength, intensity and polarization of the random laser in NLCs can be controlled by electrical [16][17][18][19], thermal [13,20] and magnetic [19] stimuli, and the alignment of LC cells [15,21].…”

“…Because the laser action is correlated with the orientational direction of liquid crystals [15], it could respond to the molecular reorientation by a variety of external stimuli. In fact, the wavelength, intensity and polarization of the random laser in NLCs can be controlled by electrical [16][17][18][19], thermal [13,20] and magnetic [19] stimuli, and the alignment of LC cells [15,21]. In particular, the optical switching owing to the molecular reorientation in a magnetic field [22] has some advantages in remote operability [8].…”

Liquid crystal random lasers

“…The experimental results showed that the output LCRL is linearly polarized light, and its polarization direction is related to the maximum scattering direction and the LC director direction. Chen et al 55 observed and studied in detail bidirectional LCRL emission from an active twisted nematic LC, where the polarization states were asymmetric (nonparallel to each other). In such a laser, the LC acts as a random distributed feedback cavity with an inherently built-in polarization rotator (Fig.…”

Controlling Disorder by Electric-Field-Directed Reconfiguration of Nanowires To Tune Random Lasing

“…Although anisotropic particles have been previously shown to impact lasing properties in random but fixed configurations, reconfigurable particle orientation has hitherto not been used as a tool to control the lasing emission characteristics. Tuning of random lasers has primarily been approached by techniques such as liquid-crystal alignment, which generates local differences in refractive index to introduce scattering − and spatial light modulation of pump beams, which are used to manipulate the spatial distribution of gain in the lasing medium. , In contrast, our approach is based on controlling the orientation of nanowires as anisotropic scatterers using an electric field and thus provides opportunities to dynamically control a variety of parameters including both the scattering and gain landscapes.…”