Magnetically Controllable Random Lasers

Abstract

characteristics. Thus, tuning elements can be coordinated with the resonator. On the other hand, these methods do not work for the random laser system due to the absence of a periodic cavity. The simplicity and randomness set a hurdle for controlling random lasers. However, several approaches have been proposed to break through the bottlenecks. Here, we classify related studies into four main categories: wavelength manipulation, mode control, directional confinement, and threshold abatement. Wavelength manipulation is one of the most crucial parts of random lasers. There are two kinds of tuning designs, which are known as preprocess and postprocess, respectively. The tuning strategies of preprocess include modifying the absorption condition, [21,22] the size of scatterers, [23] and the geometry of photonic crystals. [24] Besides, external parameters such as optics, [25] electricity, [26] temperature, [27][28][29] and deformation, [30] can realize wavelength tunability after the fabrication of disordered nanostructures, so called postprocess. Further, people drive persistent endeavors to control the random lasing modes. Mode-locking and single-mode random lasers, the longstanding scientific goals, have been demonstrated by the pumping scheme, [31] Raman gain, [32] intentional defect sites, [33] and bioinspired photonic structure. [34] Modetransition can also be accomplished by altering the pumping condition, [35] modulating the concentration of gain media or scatterers, [36,37] and the mechanically induced reformation. [38] Although inherent angle-free emissions of random lasers are useful for some specific applications, a directional output is also highly desired. Several directional confinements have been introduced into random lasing systems such as low-dimensional cavities, [29,39] optical waveguides, [40,41] and customized pump profiles. [42] The strategies for lowering the lasing threshold have been extensively studied, e.g., optimization of the mean free path and particle size [43,44] or fine-tuning the concentration or refractive index between scattering and gain media. [45,46] In addition, fluorescence resonance energy transfer and surface plasmon resonance have also been highly addressed. [47][48][49] Here, a simple and straightforward design of magnetically controllable random lasers (MCRLs) is presented. Stilbene 420 laser dye, titanium dioxide nanoparticles (TiO 2 NPs), and ferrous ferric oxide nanoparticles (Fe 3 O 4 NPs) are chosen to compose the MCRLs. Stilbene 420 laser dye is selected from various laser dyes as the gain media because of its exceptional Toward practical applications of random lasers, controllability is a key factor. Here, magnetically controllable random lasers (MCRLs) are designed, fabricated, and demonstrated. Under a prescribed magnetic field, the MCRLs composed of stilbene 420 laser dye, TiO 2 nanoparticles, and Fe 3 O 4 nanoparticles possess magnetic controllability and switchability with good responsivity and durability. The applied magnetic field can be used to manipulate t...

Inkjet‐Printed Random Lasers

“…This strong database provides numerous practical examples and universal solutions for following researchers to exploit random laser system with existing printing techniques and facilities. It is also worth mentioning that random lasers hold several amazing features, such as dexterity, transferability, tunability, flexibility, stretchability, self‐healability, recyclability, and transient capability, which are desirable for wearables, one‐off gadgets, and Internet of Things (IoTs), yet quite difficult to achieve in conventional lasers. Moreover, random laser with several exclusive superiorities, such as angle‐free emissions, lying somewhere between lasers and common illuminants, shows high application values in laser illumination, speckle‐free laser imaging, broad‐angular laser displays, and integrated photonic lab‐on‐a‐chip systems .…”

Substitution rules for icosahedral quasicrystals

“…The question is whether such structures may be also generated by the unique substitutional algorithm starting from the single triacontahedron? Suppose, we have properly placed the Mackay-, Bergman-, or Tsai-type clusters 11,37 within the initially empty triacontahedron. Its vertices are initially not occupied by any atoms, too.…”

“…We do not pretend to make a balanced review but rather refer the reader to more detailed descriptions of the modern viewpoints on the structure and properties of quasicrystals which may be found in literature. [8][9][10][11][12][13][14] In our study, we started with the idea of the fractal nature of Penrose tiling introduced by Bandt and Gummelt, 15 who proposed to replace the basic tiles in the kites-and-darts tiling by corresponding tiles with fractal boundaries obtained iteratively by multiple application of the deflation procedure. Recently, we have considered the rhombus Penrose tiling under the assumption that both inflation and deflation procedures were applied an infinite number of times.…”

Magnetically controllable random laser in ferromagnetic nematic liquid crystals

“…Since random lasers do not require any external optical resonators, they have raised attention as easy-to-make, low-cost and speckle-free lasers advantageous for applications in imaging [4], photonics [5] and biomedicine [6,7]. Meanwhile, in general, the light paths of random lasers are so chaotic that their mode control is difficult [8]. Therefore, several methods have been developed to solve the control problems of random lasers for future applications since the random laser action was first reported by Letokhov et al [9]; in particular, the random laser action in nematic liquid crystals (NLCs) has been vigorously investigated [10], whose anisotropic scattering behavior is different from the scattering behavior of colloidal suspensions as follows.…”

“…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]. However, to reorient the nematic director using a weak magnetic field, high magnetic anisotropy ∆ χ of the LC molecule is needed [23,24], which is defined as the subtraction of the molar magnetic susceptibility component ( χ ⊥ ) perpendicular to the molecular long axis from that ( χ ) parallel to the axis [25].…”