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Dynamic control of motion at the molecular level is a core issue in promoting the bottom-up programmable modulation of sophisticated self-organized superstructures. Self-assembled artificial nanoarchitectures through subtle noncovalent interactions are indispensable for diverse applications. Here, the active solar renewable energy is used to harness cholesteric liquid crystal (CLC) superstructure devices via delicate control of the dynamic equilibrium between the concentrations of molecular motor molecules with opposite handedness. Thus, the spectral position and handedness of a photonic superstructure can be tuned continuously, bidirectionally, and reversibly within the entire working spectrum (from near-ultraviolet to the thermal infrared region, over 2 μm). With these unique horizons, three advanced photoresponsive chiroptical devices, namely, a mirrorless laser, an optical vortex generator, and an encrypted contactless photorewritable board, are successfully demonstrated. The sunlight-fueled chirality inversion prompts facile switching of functionalities, such as free-space optical communication, stereoscopic display technology, and spin-to-orbital angular momentum conversion. Motor-based chiroptic devices with dynamic and versatility controllability, fast response, ecofriendly characteristics, stability, and high efficiency have potential to replace the traditional elements with static functions. The inexhaustible natural power provides a promising means for outdoor-use optics and nanophotonics.

This study presents the reliability of diamond-like carbon (DLC) ultrathin films fabricated by DC magnetron sputtering as the gate dielectric layer in metal–insulator–semiconductor (MIS) devices. Stress-induced leakage current (SILC) and time-dependent dielectric breakdown (TDDB) measurements were performed to determine the reliability of the devices. The MIS device with DLC film deposited at 1100-V bias exhibited little variation of SILC under different constant voltage stress times and had a long TDDB lifetime. The results indicate excellent reliability of DLC films used as gate dielectrics. Moreover, several soft breakdown events occurred during TDDB measuring. An extended percolation model was adopted for explanation of the current versus time characteristics.

This study investigates the all-optical directional control of emission in a cholesteric liquid crystal (CLC)-infiltrated photonic crystal fiber (PCF) laser. A laser dye-doped CLC (LD-CLC) and an azobenzene LC-doped CLC (ALC-CLC), which are selectively infiltrated into the hollow core and holey-matrix cladding of the PCF, function as an optically active cavity and an all-optical emission direction-controllable light valve, respectively, in the photonic LC fiber (PLCF) laser. Experimental results show that the PLCF has a low energy threshold (approximately 63 nJ/pulse) and a large circular polarization anisotropy (g ≅ 2) in lasing output. The lasing output from the LD-CLC-filled core of the PLCF can be all-optical controlled to emit omni- or semi-directionally or to off-emit by controlling the isothermal phase transition of the CLC between the scattering focal conic state and the transparent isotropic state by the all-optical-induced reversible photoisomerization of the doped ALCs in the cladding region. The emission direction-controllable PLCF laser has significant potential in various applications, such as bio-image, photo-therapy, wearable devices, displays, sensors, and lighting.

This study investigates and develops for the first time an electrically tunable liquid-crystal–polymer composite laser with a symmetric sandwich structure. This structure includes two identical pol...

Self-organized periodic micro/nanostructures caused by stimulus-responsive structural deformation often occur in anisotropic self-assembled supramolecular systems (e.g., liquid crystal systems). However, the long-range orderliness of these structures is often beyond control. In this article, we first demonstrate that a large-area disordered two-dimensional (2D) microgrid chiral structure appears in the cholesteric liquid crystal (CLC) reactive mixture because of the photopolymerization-induced Helfrich deformation effect under exposure to the single UV-laser beam. The result is attributed to the impact of an internal longitudinal strain, which is caused by the pitch contraction of the CLC-monomer region through the continuing compression of the thickening CLC polymer layer adhered on the illuminated substrate of the sample during photopolymerization. The experimental results further show that a one-dimensional (1D) UV-laser interference field can be used to effectively control the postformed 2D microgrid structure to arrange in an orderly manner throughout the large exposed area (an order of centimeter). The optimum ability for controlling the orderliness of the microgrid structure can be achieved if the spacing width of the interference field approximates the periodicity of the postformed 2D microgrids. Several factors, such as the pitch of the CLC mixture and the included angle and intensity of the two interfering laser beams, which influence the orderliness and properties of the 2D microgrid structure, are explored in this study. The result of this research opens a new page to improve the applicability of the Helfrich deformation phenomenon and further provides a reference platform for manipulating, modifying, and even tailoring periodic micro/nanostructures in self-organized supramolecular soft-matter systems for application in advanced optics/photonics.

This study demonstrates a broadband-tunable photonic bandgap (PBG) and thermally convertible laser with an ultra-low lasing threshold based on a gradient-pitched cholesteric liquid crystal (CLC) polymer template. The lowest energy threshold of the laser is 16 nJ per pulse under a pumped diameter of ca. 250 μm (i.e., 0.33 μJ per pulse per mm2), a value that is superior to those of other band-edge lasers based on most dye/quantum-dot-doped CLC systems. Owing to its multiple advantages, such as high stability, ultra-low lasing threshold, wide-band and linear spatial PBG-tunability, and lasing-mode convertibility, the CLC template device can be potentially used for photonics and display applications.

ZnO nanowires (NWs) were directly grown on ductile zinc foil by thermal oxidation at 500 °C. The highly crystalline ZnO NWs exhibited bidirectional growth preferentially oriented in the [101] orientation. The ZnO NWs were highly resistant to hydroxyl groups and water compared with Zn foil that was oxidized naturally. The narrow excitonic photoluminescence (PL) peak combined with strongly suppressed visible emission demonstrated the high optical quality of the NWs. The binding energies of the donor bands and an acceptor band were obtained through temperature-dependent PL analysis. The NWs would be suitable for flexible planar UV device applications.

Dye-doped nematic liquid crystal refilled gradient-pitched enantiomorphic cholesteric liquid crystal polymer templates are demonstrated. The enantiomorphic device has high reflectivity and wide spectral tunability throughout the entire visible region. This device can also provide low threshold lasing emission with both right- and left-circular polarizations from the blue to the red region.

ZnO nanowires (NWs) were directly grown on zinc foils through a two-step process: (i) Zn foils fabrication and (ii) thermal oxidization at temperature 400 °C. The dense and orderly aligned ZnO NWs grown on Zn hexagonal-faceted surface presented preferential growth in the [101] orientation and showed bidirectional growth mode with an intersection angle of about 60°. The faceted and bidirectional growth mode of ZnO NWs would be applicable in the fabrication of planar nanodevices. The edge growth mechanism is proposed for the growth of NWs. In photoluminescence (PL) studies, we have observed exciton peak around 368 nm with a small PL full width at half maximum (~ 8 meV) and visible emission was strongly suppressed. These characteristics indicated that the ZnO NWs had high optical properties.

ZnO nanowires (NWs) were directly grown on ductile zinc foils through a two-step process: (a) large, thin, and ductile Zn foils were fabricated from a mixture of Zn and ZnO powders; and (b) ZnO NWs were produced by thermal oxidation at temperatures of 300–600 °C. The ZnO NWs presented preferential growth in the [101] orientation. The highly crystalline NWs synthesized at 500 °C exhibited a bidirectional mode with an angle of approximately 60° between their longitudinal axes. On foils oxidized at 600 °C, the NWs evolved into nanotowers. The photoluminescence (PL) spectra showed strong peaks at approximately 368 nm and weaker peaks at approximately 374 nm in the UV region; moreover, a broad deep-level-related green emission peak was recorded at approximately 520 nm in the visible region. The PL green emission line was strongly suppressed for the samples produced at higher oxidation temperatures, which indicated good optical qualities. These good optical qualities, combined with the bidirectional mode and the ductility of the foil, are expected to be useful for flexible planar device applications. The electrical properties of a single ZnO NW were investigated. I–V measurements revealed the Schottky characteristics of the NWs and the resistivity of the ZnO NWs was measured to be ∼93 Ω cm.

An infrared (IR) reflector that has ultra-wide reflection band and high reflectance was successfully fabricated based on an enantiomorphic chiral polymer composite template-made method involving UV-curing, washing-out, stacking, and refilling. In this study, an IR reflector reflecting >80% of incoming solar IR light from 800 nm to 1500 nm and retaining acceptable transmittance in the visible region is demonstrated. This undertaking is achieved by stacking two enantiomorphic double-polymerized chiral polymer templates with large longitudinal pitch gradients as a composite template cell designed for the near-IR region. Heat insulation test reveals that the temperature can be effectively lowered by 2 °C–3 °C by using the IR reflector, thereby indicating that a considerable amount of incident heat could be isolated and a significant amount of energy could be saved by cooling. The sample has potential in green and military applications, such as energy-saving green windows and anti-IR devices.

This study applies a low-cost solvothermal method to synthesize all-inorganic (lead-free cesium tin halide) perovskite quantum dots (AIPQDs) and to fabricate AIPQD-doped lasers with cholesteric liquid crystal (CLC) lasing cavities. The lasers present highly qualified lasing features of low threshold (150 nJ/pulse) and narrow line width (0.20 nm) that are attributed to the conjunction of the suppression of photoluminescence (PL) loss caused by the quantum confinement of AIPQDs and the amplification of PL caused by the band-edge effect of the CLC-distributed feedback resonator. In addition, the lasers possess highly flexible lasing-wavelength tuning features and a long-term stability under storage at room temperature and under high humidity given the protective role of CLC. These advantages are difficult to confer to typical light-emitting perovskite devices. Given these merits, the AIPQD-doped CLC laser device has considerable potential applications in optoelectronic and photonic devices, including lighting, displays, and lasers.

Diamond-like carbon (DLC) has been studied as a dielectric material for future metal–insulator–semiconductor (MIS) technology. In this paper, ultrathin DLC films were deposited on silicon substrates by using the dc magnetron sputtering technique at various deposition voltages. The current–voltage characteristics indicated that the leakage currents of the MIS devices decreased with an increase in deposition voltages, and that a low leakage current ([Formula: see text] A/cm2) was achieved at −2 V bias voltage. The deposition voltage effects on the structures of films were investigated through Raman spectroscopy, which indicated that the sp3 bonding fraction decreased with an increase in the deposition voltage. The ramp-voltage breakdown test revealed high effective breakdown electric field ([Formula: see text]85 MV/cm) for the MIS device with the DLC film deposited at 1100-V deposition. Stress-induced leakage current measurement indicated that the DLC film exhibited excellent reliability.

This work successfully develops a largely-gradient-pitched polymer-stabilized blue phase (PSBP) photonic bandgap (PBG) device with a wide-band spatial tunability in nearly entire visible region within a wide blue phase (BP) temperature range including room temperature. The device is fabricated based on the reverse diffusion of two injected BP-monomer mixtures with a low and a high chiral concentrations and afterwards through UV-curing. This gradient-pitched PSBP can show a rainbow-like reflection appearance in which the peak wavelength of the PBG can be spatially tuned from the blue to the red regions at room temperature. The total tuning spectral range for the cell is as broad as 165 nm and covers almost the entire visible region. Based on the gradient-pitched PSBP, a spatially tunable laser is also demonstrated in this work. The temperature sensitivity of the lasing wavelength for the laser is negatively linear and approximately −0.26 nm/°C. The two devices have a great potential for use in applications of photonic devices and displays because of their multiple advantages, such as wide-band tunability, wide operated temperature range, high stability and reliability, no issue of hysteresis, no need of external controlling sources and not slow tuning speed (mechanically).

The present study develops and investigates for the first time a unique spatial continuously tunable cone laser based on a dye-doped cholesteric liquid crystal (DDCLC) film with an LC-birefringence (Δn) gradient. A continuous Δn variation can be generated in a cell by diffusion and self-organization of CLC after four DDCLC mixtures with a discrete variation of Δn are successively injected into an empty cell. Not only the CLC photonic structure but also the lasing wavelength and the cone angle of the obtained conically symmetric emitted lasing ring can be tuned continuously by continuously changing the pumped position of the cell with an Δn gradient. The continuous tunabilities in the lasing wavelength and the corresponding emitted cone angle of the lasing ring are 605.8 → 568.1 nm and 29° → 50°, respectively, within a spatial interval of about 33 mm in the cell.

This work investigates, for the first time, an optoelectronically tunable distributed feedback laser that is based on a planar DDCLC cell with a coated photoconductive (PC) layer. Experimental results show that the CLC reflection band and the lasing wavelength of the DDCLC can both be tuned optoelectronically by varying the intensity of one irradiating CW green beam or the magnitude of the applied dc voltage. The tunability of the DDCLC laser depends on the controllability of the optoelectronic properties of the PC layer and, therefore, on the voltage dropping on the CLC layer. Therefore, the CLC pitch can be controlled by exploiting the optoelectronically induced electrohydrodynamic effect which causes the spatially periodic deformation of the CLC structure. In addition, the dependences for other critical lasing parameters, e.g., energy threshold, lasing efficiency, and lasing linewidth, on external controlling signals are also measured and discussed in the current study.

This study investigates the nonlinear optical properties of azo-dye-doped nematic and polymer-dispersed liquid crystal (ADDPDLC) films with nano-sized LC droplets using the Z-scan technique, which is a simple but powerful technique for measuring the optical Kerr constants of materials. The results indicate that the optical Kerr constant ( n 2 ) of the azo-dye-doped nematic LC (ADDLC) film is large because of the photoisomerization effect and the thermal effect. Therefore, the optical Kerr constant of this material can be modulated by varying the temperature of the sample and the direction of polarization of incident laser. The range of n 2 modulated is from −5.26 × 10 −3 to 1.62 × 10 −3 cm 2 /W. The optical Kerr constants of ADDPDLC films at various temperatures are also measured. The experimental results reveal that liquid crystals in the ADDPDLC film strengthen the nonlinearity. The n 2 of the ADDPDLC film is maximal at ∼35 °C, because of the decrease in the clearing temperature of the ADDPDLC films. The clearing temperatures of the liquid crystals (E7), and the ADDPDLC film used in this work were found to be 61 °C and 43 °C, respectively.

This work presents an electro- and photo-controllable spatial filter that is based on a liquid crystal (LC) film with a photoconductive layer. The controllable spatial filter can be formed because of the controllability of the photoelectro-induced screen effect of the space charge in the LC cell. An applied dc voltage or incident pumped intensity can be controlled to enable different spatial distributions of the diffraction pattern of the target object to be selected for filtering by the LC cell, such that various reconstructed images can be obtained. A simulation using Fourier analysis is developed, and its results agree closely with experimental results. Additionally, the LC spatial filter has the extra advantage of controllable low or high filtering functions: they are controlled by switching the configuration between normally black and normally white modes.

This investigation elucidates a Fresnel lens using a simple approach that is based on a homogeneously aligned liquid crystal (LC) film with a preformed polymer relief pattern. Experimental results demonstrate that the LC Fresnel lens has polarization-dependent and electrically switchable focusing features. The LC lens has the further advantages of a weak operated field (~1.3 V/µm), and high diffraction efficiency (~34%).

This work investigates the performance evolution of color cone lasing emissions (CCLEs) based on dye-doped cholesteric liquid crystal (DDCLC) cells at different fabrication conditions. Experimental results show that the energy threshold (E(th)) and relative slope efficiency (η(s)) of the lasing signal emitted at each cone angle (0°-35°) in the CCLE decreases and increases, respectively, when the waiting time in a homogenously rubbed aligned DDCLC cell is increased from 0 hr to 216 hr (9 days). This result occurs because defect lines gradually shrink with the anchoring of the surface alignment when the waiting time is increased. Hence, the scattering loss decreases, and the dwelling time of the fluorescence photons in the resonator increases, which in turn enhances the CCLE performance. With the aligned cell given the pretreatment of a rapid annealing processing (RAP), the waiting time for obtaining an optimum CCLE can markedly be reduced sixfold. The surface alignment of the DDCLC cell also plays a necessary role in generating the CCLE. This work provides an insight into the temporal evolution of the performance for the CCLE laser and offers a method (RAP) of significantly speeding up the formation of a CCLE laser with optimum performance.

A surface stabilized ferroelectric liquid crystal (SSFLC) film, doped with an azo dye, methyl red (MR), is fabricated. A holographic grating is written in this film, using two coherent Ar+ laser beams. Such a grating is formed by the re-orientation of the liquid crystal molecules caused by interaction with the photo-induced adsorption of the doped azo dyes. Experimental results show that the formed grating is permanent but electrically switchable, with a field of ~0.08 V/μm.

A polarization grating (PG) written in an azo-dye-doped film of polymer-balltype polymer dispersed liquid crystals (PBT-PDLCs) was investigated. The writing beams were two mutually orthogonal (s- and p-polarized) polarized beams. The PG resulted from the LC molecular reorientation due to their interaction with the dye molecules adsorbed on the surface of the polymer balls. Polarization properties of the diffracted beams and the grating pattern were studied under a polarizing optical microscope with a crossed analyzer. The results indicate that the PG diffracts the linearly polarized incident light into beams with different polarizations. Accordingly, the grating can be employed as an un-polarized or polarized beam splitter depending on the polarization of the incident light. The simulation based on the Jones matrix method is developed and the results correspond well with the experimental results.

Dynamic holography and polarimetric methods are used to study torques on liquid crystals exerted by photo excited dyes doped in planar nematic liquid crystal (NLC) films. The dye used is methyl red (MR). The dynamical reorientation of liquid crystal directors induced by photo-excited dyes is examined. The results indicate that the dynamics include the initial transient reorientation, followed by the transient three-dimensional rotation, and finally the stable LC alignment parallel to the optical field. A model is presented to explain these results. Quantitative analyses of the grating dynamics yield the dye-diffusion coefficients in the directions parallel and perpendicular to the LC director.

This study demonstrates for the first time a continuously tunable photonic bandgap (PBG) of wide spectral range based on a blue phase (BP) wedge cell. A continuously shifting PBG of the BP wedge cell occurs due to the thickness gradient of the wedge cell at a fixed temperature. The wedge cell provides a gradient of boundary force on the LCs and thus forms a distribution of BP crystal structure with a gradient lattice. Additionally, a spatially tunable lasing emission based on a dye-doped BP (DDBP) wedge cell is also demonstrated. The tunable band of the PBG and lasing emission is about 130 nm and 70 nm, respectively, which tuning spectral ranges are significantly wider than those of CLC and DDCLC wedge cells, respectively. Such a BP device has a significant potential in applications of tunable photonic devices and displays.

A surface stabilized ferroelectric liquid crystal (SSFLC) film, doped with an azo dye, methyl red (MR), is fabricated. A holographic grating is written in this film, using two coherent Ar+ laser beams. Such a grating is formed by the reorientation of the liquid crystal molecules caused by interaction with the photo-induced adsorption of the doped azo dyes. Experimental results show that the formed grating is permanent but electrically switchable, with a field of ~0.08 V/µm. The dye-doped SSFLC grating possesses the electrically bistable characteristics of an SSFLC sample.

This paper describes a recording of a holographic grating on a homeotropically aligned dye-doped liquid crystal (DDLC) cell. The photo-excited azo dyes, methyl red (MR), diffuse and adsorb onto the substrates, thereby forming a ripple structure. The adsorbed dye and the laser-induced ripple structure then reorientate the liquid crystal molecules, and induce a holographic grating.

This work demonstrates the feasibility of a novel photosensitive and all-optically fast-controllable photonic bandgap (PBG) device based on a dye-doped blue phase (DDBP), embedded with a low-concentration azobenzene liquid crystal (azo-LC). PBG of the DDBP can be reversibly fast-tuned off and on with the successive illumination of a weak UV and green beams. UV irradiation can transform the trans azo-LCs into bend cis isomers, which can easily disturb LCs at the boundary between the double twisting cylinders (DTCs) and the disclinations, and, then, quickly destabilize BPI to become a BPIII-like texture with randomly-oriented DTCs. Doing so may quickly destroy the BP PBG structure. However, with the successive illumination of a green beam, the BPI PBG device can be fast-turned on, owing to the fast disappearance of the disturbance of the azo-LCs on the boundary LCs via the green-beam-induced cis → trans back isomerization. The response time and irradiated energy density for turning off (on) the BP PBG device under the UV (green) beam irradiation are only 120 ms (120 ms) and 0.764 mJ/cm(2) (2.12 mJ/cm(2)), respectively, which are a thousand-fold reduction in photoswitching a traditional cholesteric LC (CLC) PBG device based on similar experimental conditions (i.e., materials used, azo-LC concentration (1 wt%), spectral position of PBG peak, sample thickness, and temperature difference for a working temperature lower than the clearing one). The BP PBG device can significantly contribute to efforts to develop a photosensitive and all-optically fast-controlling LC laser.

This study investigates high-resolution photoinduced biphotonic holographic gratings in azo-dye-doped liquid crystal films. A biphotonic grating (BG) is formed under the illumination of one linearly polarized green light with the simultaneous irradiation of an interference pattern created by two linearly polarized red lights. This study ascribes the formation of this grating to two mechanisms. One mechanism is the green-light-inducing strong dye absorption followed by adsorption through the trans–cis isomerization; the other mechanism is the inhibition effect of adsorption induced by the red light through the cis–trans inverse isomerization. These produce a twisted nematic structure-modulated pattern, which, in turn, causes the BG. Additional experiments demonstrate that the formed BGs are electrically switchable and thermally erasable.

This study demonstrates a tunable Fresnel lens in an azo-dye-doped liquid crystal (ADDLC) film using an interference technique. One Fresnel-patterned green beam using a Sagnac interferometer irradiated the UV-illuminated ADDLC cell, yielding a concentric zone plate distribution with homeotropic and isotropic structures in bright and dark regions of the green interference pattern. The proposed Fresnel lens is polarization independent, focus tunable, and the focusing efficiency of the device can be optically controlled.

This study elucidates for the first time an all-optically controllable random laser in a dye-doped polymer-dispersed liquid crystal (DDPDLC) with nano-sized LC droplets. Experimental results demonstrate that the lasing intensity of the random laser can be controlled to decrease by increasing irradiation time/intensity of one green beam, and increase by increasing the irradiation time of one red beam. The all-optical controllability of the random laser is attributed to the green (red)-beaminduced isothermal nematic--isotropic (isotropic--nematic) phase transition in LC droplets by trans--cis (cis--trans back) isomerization of azo dyes. This isomerization may decrease (increase) the difference between the refractive indices of the LC droplets and the polymer, thereby increasing (decreasing) the diffusion constant (or transport mean free path), subsequently decreasing the scattering strength and, thus, random lasing intensity.

This investigation reports for the first time a novel phenomenon, called band-tunable color cone lasing emission (CCLE), based on a single-pitched one-dimensional photonic crystal-like dye-doped cholesteric liquid crystal (DDCLC) cell. The lasing wavelength in the CCLE pattern is distributed continuously at 676.7-595.6 nm as the oblique angle increases continuously from 0° to 50° relative to the helical axis. The variation of the lasing wavelength in the CCLE with the oblique angle is consistent with that of the wavelength at the long-wavelength edge (LWE) of the CLC reflection band (CLCRB) with the oblique angle. Simulation results obtained utilizing Berreman's 4×4 matrix method show that, at each oblique angle, the associated group velocity and density of photonic state (DOS) are near zero and large at the shortwavelength edge (SWE) and LWE of the CLCRB, respectively, and are in good agreement with experimental results. The particularly strong lasing ring emission at a cone angle of ~35° can be explained to be likely due to a special effect that, under the condition of overlap between the LWE of the CLCRB measured at 35° and the SWE of the CLCRB measured at 0°, the LWE and SWE fluorescence propagating along 35° and 0°, respectively, may indirectly enhance each other due to individual enhanced rate of spontaneous emission. Furthermore, the lasing band of the CCLE can be tuned from long-wavelength (deep red~orange) to short-wavelength (orange~green) regions by changing the concentration of the chiral or by the photo-irradiation on a DDCLC cell with a photoisoemerizable chiral dopant.

This work investigates the optical Kerr property of azo-dye doped nematic liquid crystal films using the biphotonic Z-scan technique. The results indicate that the nonlinear effect measured using the Z-scan technique with a red light can be modulated or switched with the simultaneous application of a green light, because of photoisomerization and thermal effects, as determined by dynamic measurements. The former dominates in the early stage when the green light is applied, while the latter dominates in the later stage.

This work first reports wide-band tunable photonic bandgap (PBG) devices based on nematic-refilling cholesteric liquid crystal polymer template samples. By changing the type of refilling nematic liquid crystal (NLC) and sample cell gap, the PBG features of the template sample can be crucially influenced. A physical model related with the NLC infiltration into the template nanopores based on capillary action is used to qualitatively explain the tunable PBG features of the refilling template samples. In addition, a nearly full white (480 nm − 720 nm) spatially tunable PBG device based on a NLC-refilling template wedge cell is demonstrated.

This study examines the surface-assisted photoalignment effect of dye-doped liquid-crystal films having a homogeneous alignment. Observations made using a polarizing optical microscope, a scanning electronic microscope, and an atomic force microscope confirm that the morphology of laser-induced surface-adsorbed dyes at the command surface strongly affects the orientation of liquid crystals (LC's) in a manner that depends significantly on the intensity and duration of the pumping. In weak-intensity regime, a homogeneous and fine layer of adsorbed dyes competes with a layer of ripple structure in reorienting LC's. These two effects dominantly cause LC's to reorient perpendicular and parallel to the polarization direction of the pump beam in the early and late stages, respectively. In the high-intensity regime, rough and inhomogeneous ribbonlike adsorbents produced by rapid and random aggregation and adsorption form on the top of the preformed microgrooves, reorienting LC's irregularly. This surface morphology does not enable photoalignment.

This paper presents an optically wavelength-tunable and intensity-switchable dye-doped cholesteric liquid crystal (DDCLC) spherical microlaser with an azo-chiral dopant. Experimental results present that two functions of optical control - tunability of lasing wavelength and switchability of lasing intensity - can be obtained for this spherical microlaser at low and high intensity regimes of non-polarized UV irradiation, respectively. If the DDCLC microdroplet is subjected to weak UV irradiation, azo-chiral molecules may transform to the bent cis state at a low concentration rate. The effect can slightly decrease the local order of LCs and thus the helical twisting power of the CLC in the microdroplet. As a result, the CLC pitch may become slightly elongated, which will cause the gradual red-shift of both omnidirectional PBG and lasing emission of the DDCLC spherical microdroplet. In contrast, when the microdroplet is subjected to strong UV irradiation, numerous azo-chiral molecules may simultaneously change to bent cis-isomers to seriously disarrange the helical texture of the CLC, which will quickly deform the PBG and deactivate the lasing emission of the microdroplet. Prolonged irradiation of a blue beam after strong UV irradiation may cause the cis azo-chiral molecules quickly convert back rod-like trans-isomers, which may then regenerate the CLC Bragg onion and PBG structures and reactivate the lasing emission of the microdroplet. Optical control of the DDCLC spherical microlaser is realized on a scale of seconds and minutes when UV irradiation is strong and weak, respectively. The 3D DDCLC spherical microlaser is a highly promising controllable 3D micro-light source or microlaser (e.g., all-optical 3D single photon microlaser) for applications of 3D all-optical integrated photonics, laser displays, and biomedical imaging and therapy, and as a 3D UV microdosagemeter or microsensor.

This investigation elucidates for the first time electrically controllable random lasers below the threshold voltage in dye-doped liquid crystal (DDLC) cells with and without adding an azo-dye. Experimental results show that the lasing intensities and the energy thresholds of the random lasers can be decreased and increased, respectively, by increasing the applied voltage below the Fréedericksz transition threshold. The below-threshold-electric-controllability of the random lasers is attributable to the effective decrease of the spatial fluctuation of the orientational order and thus of the dielectric tensor of LCs by increasing the electric-field-aligned order of LCs below the threshold, thereby increasing the diffusion constant and decreasing the scattering strength of the fluorescence photons in their recurrent multiple scattering. This can result in the decrease in the lasing intensity of the random lasers and the increase in their energy thresholds. Furthermore, the addition of an azo-dye in DDLC cell can induce the range of the working voltage below the threshold for the control of the random laser to reduce.

This study investigates, for the first time, an all-optically controllable random laser based on a dye-doped liquid crystal (DDLC) cell added with a photoisomerizable dye. Experimental results indicate that the lasing intensity of this random laser can be all-optically controlled to decrease and increase sequentially with a two-step exposure of one UV and then one green beam. All-optically reversible controllability of the random lasing emission is attributed to the isothermal nematic(N)--isotropic(I) and I--N phase transitions for LCs due to the UV-beam-induced trans--cis and green-beam-induced cis--trans back isomerizations of the photoisomerizable dye, respectively. The former and the latter can decrease and increase the spatial fluctuations of the order and thus of the dielectric tensor of LCs, respectively, subsequently increasing and decreasing the diffusion constant (or transport mean free path), respectively, and thus decaying and rising the scattering strength for the fluorescence photons in their recurrent multi-scattering process, respectively. The consequent decrease and increase of the lasing intensity for the random laser and thus the rise and descent of its energy threshold are generated, respectively.

This study investigates, for the first time, a photoerasable and photorewritable spatially-tunable laser using a dye-doped cholesteric liquid crystal (DDCLC) with a photoisomerizable chiral dopant (AzoM). UV illumination via a photomask with a transmittance-gradient can create a pitch gradient in the cell such that the lasing wavelength can be spatially tuned over a wide band of 134nm. The pitch gradient is generated by the UV-irradiation-induced gradient of the cis-AzoM concentration and therefore the induced gradient of the cell HTP value, resulting in the spatial tunability of the laser. Furthermore, the laser has advantages of photoerasability and photorewritability. The spatial tunability of the laser can undergo more than 100 cycles of photoerasing and photorewriting processes without decay or damage.

This work investigates a novel color cone lasing emission (CCLE) based on a one-dimensional photonic crystal-like dye-doped cholesteric liquid crystal (DDCLC) film with a single pitch. The lasing wavelength in the CCLE is distributed continuously at 676.7-595.6 nm, as measured at a continuously increasing oblique angle relative to the helical axis of 0-50 degrees . This work demonstrates that lasing wavelength coincides exactly with the wavelength at the long wavelength edge of the CLC reflection band at oblique angles of 0-50 degrees . Simulation results of dispersion relations at different oblique angles using Berreman's 4X4 matrix method agrees closely with experimental results. Some unique and important features of the CCLE are identified and discussed.

This study developed an optically controllable transflective spatial filter in a dye-doped cholesteric liquid crystal (DDCLC) film. The mechanism to induce the spatial filter is attributable to the photoisomerization-induced controllability of the redshift of the reflection band in the DDCLC cell. At various pumped intensities, different spatial distributions of the diffraction pattern of the object can be selected to be filtered, such that high- and low-pass or notch- and band-pass transmitted and reflected images can be simultaneously obtained, respectively.