Laser Emission from a Polymer‐Stabilized Liquid‐Crystalline Blue Phase

Abstract

The possibility of controlling light emission and propagation by exploiting periodic structures of dielectric media has attracted interest in the last decade. These photonic-bandgap materials, so-called photonic crystals, have generated considerable interest due to their wide applicability in optoelectronic and microwave devices.[1] In particular, emission control and lasing action in optically active photonic crystals can offer new applications for low-threshold lasers from small-size devices. [2][3][4] Currently an intensive effort is underway in molecular crystallography to develop photonic-bandgap materials with lattice parameters comparable to the wavelengths from visible to infrared light. This approach involves using liquid-crystalline materials that naturally form helical structures with a helical pitch in the optical-wavelength range.[5] The relevant optical property of the cholesteric phases of liquid crystals is the selective reflection of light over a range of wavelengths, that is, the photonic stop band. Previous studies have readily demonstrated that the lasing action of cholesteric liquid crystals can be attributed to the band-edge effect of the photonic stop band. These studies further explore mechanically, electrically, and chemically tunable photonic-stop-band responses [6][7][8] and a defect mode for a low-laser-threshold application. [9][10][11] Cholesteric liquid crystals can be regarded as one-dimensional photonic crystals, whereas the liquid-crystalline blue phases are three-dimensional cubic structures with lattice periods of several hundred nanometers, which give rise to selective Bragg reflections.[12] Therefore, probing light confinement in the blue phases and using them as novel molecularly assembled photonic crystals is of great interest. Although selective light reflections in the blue phases have already been studied for quite some time, [12][13][14] such three-dimensional extensions in molecular self-assembly are normally much more difficult to produce. A practical limitation of blue phases is their narrow temperature occupation (∼ 1-2°C) at the transition between the isotropic and cholesteric phases. The potential photonic application of the blue phases has been recently demonstrated by measuring the laser emission in three dimensions.[15]However, lasing action was still limited to a very narrow temperature range. Therefore, improving the temperature stability has been required for practical application of blue phases. [16,17] In this study, we describe the preparation of polymer-stabilized blue phases and the demonstration of laser emission attributed to the photonic effect of the blue-phase photonic crystal. The polymer network that forms in the blue phase leads to restriction of the deformation of the photonic crystal in a wide temperature range. We confirm the thermal stability of the polymer-stabilized blue phase by measuring laser emission over a wide range of temperature above 35°C. Pulsed excitation gives rise to laser emission with the low threshold excitation energy of a...

Optically pumped mirrorless lasing. A Review. Part II. Lasing in photonic crystals and microcavities

“…[30]. Later on, the same has been reported for the phase of the type BPI [31,32]. The pumping intensity threshold is almost twice as lower than that for the ChLC samples with the same dye concentration and under the same pumping conditions.…”

Blue-phase liquid crystal droplets

“…In the bulk, however, BPs are only found in a narrow range of temperature, between the cholesteric and the isotropic phases (1-6, 10-18), thereby placing limits on their practical utility. Recent efforts have therefore focused on increasing their stability over wider ranges of temperature and chirality, for example through addition of nanoparticles (19, 20, 21-23), polymers (24-26), or by manipulating their flexoelectricity (14).Confined chiral liquid crystals are of interest for applications in optical devices (27)(28)(29)(30)(31). Simulations of chiral LCs in channels have shown that their defect structure can be manipulated through confinement, thereby raising intriguing prospects for technology (32)(33)(34)(35).…”

Self-assembled organic and polymer photonic crystals for laser applications

“…In previous studies, optically excited laser action are successfully demonstrated by using low molecular weight bluephase LCs, 41 as well as polymer stabilized blue-phase LCs. 42 The typical experimental results of optically excited laser action from the CLCs doped with a fluorescent dye are described below (Figure 4). 43 In order to prepare the CLC hosts with PBGs in a visible wavelength range, we use two kinds of compounds of RDP-60774 as an achiral nematic LC and R-1011 as a chiral dopant (Figure 4a).…”