Lihua Ye

Thermally tunable random laser in dye-doped liquid crystals

A thermally tunable random laser in dye-doped liquid crystals (DDLCs) is reported. The gain medium of PM597 dye-doped E7 nematic LC is injected into a glass cell. The experimental results show that the random lasing is still obtained when the cell temperature becomes higher, even above the nematic–isotropic transition, and that its polarization changes at the same time. Temperature has little effect on the full width at half maxiumum of the random lasing. The center wavelength of the random lasing shifts from 575.69 nm to 593.43 nm when the temperature increases from 25.5°C to 148°C. Meanwhile, a random laser based on a solution of laser dye is first reported in this article. The reasons are possibly that nanoparticles consisting of dye molecules provide a new scattering mechanism in both solution and isotropic phase.

The electrically and magnetically controllable random laser from dye-doped liquid crystals

The electrically and magnetically controllable random laser from dye-doped liquid crystals (LCs) was studied. The rubbing-alignment of the polyimide in the LC cell influenced the threshold voltage and the response time of the electrically controllable random laser. When the applied electric field was increased, the response time of the random laser decreased. The magnetically controllable random laser was studied in the hollow fiber structure, of which the response time was less than 1 s.

Study on the Polarization of Random Lasers from Dye-Doped Nematic Liquid Crystals

Random lasers from dye-doped nematic liquid crystal (DDNLC) cells with different rubbing methods were observed due to different random ring cavities that were formed. Through constructing cells with different rubbing methods on the forward and backward surfaces of light-emitting sides, we can get two random laser beams with different polarization directions from one DDNLC cell at the same time, and the polarization direction is along the rubbing direction of the light-emitting sides. Additionally, the influence of external electric field on the polarization degree of random lasers was also studied.

The influence of Ag nanoparticles on random laser from dye-doped nematic liquid crystals

The threshold energy and electric field response characteristic of random laser have been investigated in dye-doped nematic liquid crystal (DDNLC) with the addition of different concentrations of Ag nanoparticles (NPs). Due to the localized surface plasmon resonance (LSPR) induced by Ag NPs, random laser from DDNLC with Ag NP doping had a lower threshold energy. From another point of view, nematic liquid crystals (LCs) in a DDNLC cell with the addition of Ag NPs could be more easily influenced by the electric field, which allowed the random laser to be controlled at a lower applied voltage. The turn-off time and turn-on time of random laser also decreased in the DDNLC cells with increasing the concentration of Ag NPs. This is due to the enhancement of the electro-optical characteristic of LC and the restoring force imparted by the locally ordered LCs induced by the Ag NPs, respectively.

Enhancement of random lasing assisted by Ag nanoparticle doped dye medium in solidified fiber

We have studied the random laser action from a Ag nanoparticle (NP) doped Rhodamine-B dye medium in different structures: cuvette, liquid crystal cell, fiber. For Ag NPs at a concentration of 50 μg ml−1, a much lower threshold of 0.15 mJ cm−2 was observed from the Ag NP doped Rhodamine-B dye medium in optical fiber. The experimental results indicate that the reduction of the threshold energy is due to the combination of localized surface plasmon resonance (LSPR) enhancement effects from the Ag NPs and the confinement effect of the fiber structure. Meanwhile, the solidification of the dye solution makes the lasing mode stable and the emission intensity higher.

Study of low-threshold and high-intensity random lasing in dye doped liquid crystals

Random lasers in dye-doped nematic liquid crystal (DDNLC) cells with different structures are studied. By choosing the cell gap and the cells rubbing methods, the DDNLC random laser obtains lower energy threshold. The DDNLC random laser energy threshold can also be decreased with an Al mirror as the external feedback from 4.2 μJ/pulse to 1.5 μJ/pulse. It is worth mentioning that the random laser shifts red and intensity increases with the Al mirror. The study of the DDNLC random laser with cell structure is aimed to obtain a low power consumption laser at a lower cost.

The controllable intensity and polarization degree of random laser from sheared dye-doped polymer-dispersed liquid crystal

Abstract The random laser from sheared dye-doped polymer-dispersed liquid crystal (DDPDLC) is investigated. As the emission intensity weakens, the threshold of random laser from DDPDLC increases from 2.0 mJ/pulse to 4.0 mJ/pulse, and the degree of polarization (DOP) increases from 0.1 to 0.78, obviously when the shear distance increases from 0 mm to 4 mm. As the liquid crystal droplets are gradually oriented in the shear direction caused by alignment direction of polymer chain and anisotropy of droplet shape, the scattering intensity perpendicular to the shear direction gradually decreases and that parallel to the shear direction gradually increases. The anisotropic absorption of the laser dye also plays a certain role as the shear distance is 0 mm. The controllable intensity and polarization degree of random laser have a huge potential for sensing applications.

Effect of alignment layer on polymer-dispersed liquid crystal random laser

Abstract The surface orienting effect of rubbed polyimide alignment layer on the random lasing (RL) properties of dye-doped polymer-dispersed liquid crystal (DDPDLC) was studied experimentally. Two groups of experiment were done and nematic liquid crystal E7 was used. In the first group, the samples were 25 μm non-oriented DDPDLC sample (N-DDPDLC) and 25 μm one-side oriented DDPDLC sample (P-DDPDLC). In the second, the samples were 10 μm N-DDPDLC and 10 μm P-DDPDLC sample. The results showed that compared to the N-DDPDLC, P-DDPDLC has a lower threshold, and the 10 μm P-DDPDLC has a lower threshold compared to the 25 μm P-DDPDLC. Apparently, the P-DDPDLC cell has stronger RL spike. The oriented layer changed the phase separation structure of DDPDLC which formed hierarchical structure so as to enhance the scattering intensity of system. It is a good way to reach high efficient random laser emission by tailoring the size and morphology of PDLC through surface orientation and Polymerization-induced phase separation process.

Coherent Random Lasing from Dye Aggregates in Polydimethylsiloxane Thin Films

The coherent random laser (CRL) from dye-doped polydimethylsiloxane (PDMS) has been investigated in both nanoparticle-doped (NP-doped) thin films and pure dye thin films. Compared with the literature, the pump threshold is only 1.5 mJ/cm2 in the pure dye thin film with a low dye concentration. The spontaneously formed micro-/nanocrystals of Pyrromethene 597 (PM597) dye support both gain and random feedback in the bulk of the PDMS during the sample preparation. When the SiO2 NPs were doped, the pump threshold was reduced to 0.75 mJ/cm2. The threshold increased after the film was peeled off from glass, which indicates that the photon localization effect of the leaky-waveguide structure plays an important role in the reduction of the CRL threshold. By a change in the pump stripe length or the thickness of the film, the peak wavelength red-shifts 6.7 or 5.93 nm, respectively. The PM597 dye molecule solubility changes, and they spontaneously aggregate in the process of toluene volatilization; the PDMS cures, which is the reason for the formation of PM597 micro-/nanocrystals. This thin film random laser with a low dye concentration can be used in integrated optoelectronics and display imaging.