High‐Quality Hexagonal Nonlayered CdS Nanoplatelets for Low‐Threshold Whispering‐Gallery‐Mode Lasing

Abstract

threshold lasers, including 1) the gain media with high quantum efficiency and 2) a high-quality microresonator with high efficient optical feedback. As an important II-VI semiconductor with extraordinary optical gain properties, CdS has been qualified to be an excellent gain material for small-sized lasers in highly integrated photonic applications. [5][6][7][8] However, previous CdS nanowire (NW) lasers have suffered from high lasing threshold, due to the low end-face reflection [9] and high self-absorption induced energy loss [6,10] in NW cavity. Compared with Fabry-Pérot (F-P) mode cavity in NW lasers, whispering-gallery-mode (WGM) cavities have been demonstrated to hold stronger confinement of the optical fields due to the total internal reflection inside the cavity, leading to higher optical feedback. [11,12] Therefore, introducing WGM cavity into CdS laser would be an effective solution to reduce the lasing threshold. In this respect, polygonal CdS nanoplatelets (NPLs) are promising candidates for the development of low-threshold lasers. Considerable efforts have been made to realize the anisotropic growth on nonlayered crystals (such as PbS, [13] TiO 2 , [14] CdS, [15,16] and CdSe [17] ) but with limited success. However, direct synthesis of the 2D nonlayered CdS crystals is still challenging, since spitting the intrinsic isotropic chemical bond Low threshold micro/nanolasers have attracted extensive attention for wide applications in high-density storage and optical communication. However, constrained by quantum efficiency and crystalline quality, conventional semiconductor small-sized lasers are still subjected to a high lasing threshold. In this work, a low-threshold planar laser based on high-quality singlecrystalline hexagonal CdS nanoplatelets (NPLs) using a self-limited epitaxial growth method is demonstrated. The as-grown CdS NPLs show multiplewhispering-gallery-mode lasing at room temperature with a threshold of ≈0.6 µJ cm −2 , which is the lowest value among reported CdS-based lasers. Through power-dependent lasing studies at 77 K, the lasing action is demonstrated to originate from a exciton-exciton scattering process. Furthermore, the edge length-and thickness-dependent lasing threshold studies reveal that the threshold is inversely proportional to the second power of lateral edge length while partially affected by vertical thickness, and the lasing modes can be sustained in NPLs as thin as 60 nm. The lowest threshold emerges with the thickness of ≈110 nm due to stronger energy confinement in the vertical Fabry-Pérot cavity. The results not only open up a new avenue to fabricate nonlayered material-based coherent light sources, but also advocate the promise of nonlayered semiconductor materials for the development of novel optoelectronic devices.

3D Laser Displays Based on Circularly Polarized Lasing from Cholesteric Liquid Crystal Arrays

“…The clear knee behavior characteristics shown in the plots of the PL peak intensity versus pump fluence verify the lasing actions from the RGB CLC microunits (Figure S15, Supporting Information). [ 39–43 ] As the refractive index is periodically modulated in CLC superstructures, [ 44,45 ] strong single‐mode lasing with a narrow emission bandwidth (≈0.8 nm) was achieved in as‐fabricated RGB microunits, featuring high cavity quality of the CLC superstructures. Since their wavelengths locate near the border of the chromaticity diagram, such RGB single‐mode microlasers would define the most extensive possible color gamut.…”

A Universal In Situ Cross‐Linking Strategy Enables Orthogonal Processing of Full‐Color Organic Microlaser Arrays

“…The plot of λ 2 /∆λ versus D demonstrates a clear linear relationship, which indicates that the optical modulation is indeed originated from the photon confinement of WGM resonators. [ 52 ] The increasing mode spacing with decreasing the diameter of the microdisk provides an opportunity to acquire single‐mode lasers, which are favorable for high saturation for laser displays. Besides, we investigated the lasing performances of the directly prepared microdisk and the microdisk after two subsequent processing steps (Figure S19, Supporting Information).…”

Microstructure and domain engineering of lithium niobate crystal films for integrated photonic applications

“…Microring cavities for frequency conversion WGM microresonators as optical microcavities have been exploited for many different applications, including lasing on a chip, electro-modulation, nonlinear frequency conversion, and frequency comb generation [83][84][85] . Wang et al 86 demonstrated an on-chip integrated nonlinear frequency conversion process using microdisk resonators on an LNOI platform.…”