Other investigated constructions include microlasers in the form of whispering gallery mode (WGM) based systems (plasmonic and biological). The latter mentioned process is called random lasing, which was achieved in various LC-based media, like luminescent organic dye, semiconductor, or perovskite-doped nematics and polymer-dispersed LCs (PDLCs). Nonclassic laser action can be obtained either in systems with gain or refractive index (periodic) distribution pumped by a suitable light source, inducing population inversion or random light scattering in amplifying medium containing luminescent dye. Tunable resonators or lasers, including distributed feedback (DFB), distributed Bragg reflectors (DBRs), or in the form of vertical-cavity emitters can tune the resonance frequency through changes in size, shape, or temperature or the external electric field. Therefore, such materials are interesting for applications in designing new laser light sources. These materials can slow down and even trap light with frequencies in close vicinity of the photonic band-gap. Despite the passage of so many years, liquid crystalline systems still have attracted considerable attention because of their potential application in devices devoted to controlling light propagation. Various methods of emission tuning were also developed and presented, ,, ,. Mirrorless lasing was observed in one-dimensional helical cholesteric materials, three-dimensional photonic-bandgap materials, free-standing cholesteric liquid single crystal elastomers, or chiral ferroelectric smectic materials. Since then, multiple studies have addressed the utilization of LCs in light amplification phenomena. Goldberg, and Schnur put forward the original concept of lasing in liquid crystal laser in 1973, but the first experimental demonstration was done 25 years later by Kopp et al. A combination of fluidity and long-range orientational order enables easy tuning of their properties affected by optical, magnetic, and electric fields. Liquid crystals (LCs) belong to the soft matter class that merges the properties typical of crystals and liquids. Finally, the potential applications, perspectives, and conclusions will be discussed at the end of the article. We will also discuss how the LC phases can influence the design of laser devices. The article will be divided into separate sections concerning different approaches of LC lasers realization, including band edge, DFB, DBR, VECSEL, and random cavities utilization. We will describe the physical background necessary to understand the operation principles of LC lasers, including a description of radiative transition phenomena and LC matter. In this review, we summarize the most appealing progress in developing liquid crystalline (LC) micro and nano-lasers during the last decade, together with their applications and description of perspectives for the future. The search for new materials for light amplification is one of the fundamental subjects of modern photonics and nanotechnology. The lasers have significantly influenced the development of new approaches to spectroscopy, giving previously undreamed insights into physics, chemistry, and other scientific areas. The demonstration of the first ruby laser in 1960 led to a revolution in science and technology.
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