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State-of-the-Art Active Materials for Organic Lasers
Published in Marco Anni, Sandro Lattante, Organic Lasers, 2018
In the last two decades, the field of organic laser materials has experienced an unprecedented development, pushing the limits of what was thought to be physically and chemically possible. Today, we are living an exciting era in organic photonics, in general, and in organic lasers, in particular, with many fundamental challenges being solved and an ever-growing number of fascinating new developments on materials, devices, and applications being demonstrated. In the near future, organic laser materials have several challenges to face. It would be a tremendous technological advancement to develop new dyes from the UV (< $ < $ 400 nm) to the IR (> $> $ 800 nm) that could be pumped at a single wavelength (e.g., 355 nm), with efficiencies reaching the quantum defect limit (each pump photon is converted into a laser photon) and record-breaking photostabilities. Some steps have been given in this direction by using coumarin-BODIPY cassettes (BODIPY 30, Fig. 3.4) [46]. In addition, efforts should be directed to enable the maturity of solid-state dye lasers. On the other hand, organic semiconductors, either molecular crystals and glasses or conjugated polymers, face common challenges of utmost importance to implement organic laser diodes: develop new materials with (a) much higher and well-balanced hole and electron mobilities (ambipolar transport), and (b) higher quantum yields to reduce the laser threshold, as it would not only reduce the needed injection current densities but would increase the final device operational lifetime. From the processing point of view, molecular crystals, in particular, should improve their mechanical performance and stability, as they are brittle materials difficult to post-process (cutting or polishing). Finally, and independently on the organic semiconductor, new cavity configurations with extremely reduced laser thresholds, even in the presence of electrodes, should be designed. In this regard, plasmonics is a path that could be explored [212,213].
Optical gain and photo-bleaching of organic dyes, quantum dots, perovskite nanoplatelets and nanodiamonds
Published in Liquid Crystals, 2023
Mahendran Vellaichamy, Miha Škarabot, Igor Muševič
While the organic laser dyes typically show single exponential decay mode of photobleaching, the nanoparticle optical gain materials are rather different. As shown in Figure 12, the intensity over number of excitation pulses show two exponential decay for silica nanobeads, QRs, QDs and perovskite CsPbBr3, while in the case of perovskites CsPbI3 and CsPb (Br/I)3 the ASE intensity is very weak and photostability can be described by one exponential decay. The most stable are QDs and QRs, where the fast decay is characterised by around 107 pulses and the slow decay lasts for around 109 pulses. Next are silica nanobeads, which have shorter half-life, around 106 pulses for faster and 108 pulses for slower decay. Among perovskites the most stable are CsPbI3 particles with half-life 8 × 108 pulses, but they exhibit smaller ASE intensity. The stability of CsPbBr3 particles was also described with two bleaching processes, which are characterised with relatively fast two decay processes with half-life 106 and 107 pulses, respectively, while the CsPb (Br/I)3 particles are the least stable with decay constant of around 107 pulses. The detailed data for all nanoparticles are collected in Table 4.
Circularly polarised lasing from all-solid organic semiconductor activated external distributed feedback based on polarisation grating
Published in Liquid Crystals, 2021
Yue Shi, Yingming Lai, Yong Li, Yan Jun Liu, Vladimir G. Chigrinov, Hoi-Sing Kwok, Dan Luo, Xiao Wei Sun
Organic microcavity lasers based on wavelength-scale periodic structure have attracted substantial attentions, which offers distributed feedback (DFB) for lasing generation [1,2]. In particular, the DFB lasers based on liquid crystals (LCs) are of great interest due to the compact volume, easy processing and excellent tunable properties [3]. On one hand, cholesteric, smectic and blue phase LCs have intrinsic periodic structures, providing DFB by themselves for laser emission [4–6]. On the other hand, holographic polymer dispersed liquid crystal (HPDLC) provides another versatile method for organic DFB laser fabrication [7]. When the prepolymer mixture of light-sensitive monomers and LCs are exposed to interference pattern with periodically varying intensity, the resultant phase separation of polymer and LC gives periodic refractive index (RI) contrast for DFB. Various photonic crystal and quasicrystal lasers based on HPDLC have been fabricated [8–12]. However, the PG structure from interference of two orthogonally circularly polarised beams is seldom applied for organic laser fabrication, because the interference results in a uniform intensity distribution and 1D modulated polarisation state which is not applicable to HPDLC [13,14].