Simulated electric field distribution of an excited GNR on the surface of a 2.5-μm-diameter PMMA microfiber is presented in the inset of Fig. 2F) is reduced down to ~8.0 nm (corresponding to a quality factor of ~82) along with a 7.5-fold enhancement in the peak intensity, resulting from the strong mode coupling ( 24, 25). 2B), the linewidth of the dominant LSPR peak of the coupled GNR ( Fig. In contrast to the relatively broad linewidth of an uncoupled GNR ( Fig. S1), a clear red scattering spot can be observed at the position of the GNR due to the excitation of the nanorod-microfiber coupled system ( Fig. Under side illumination with a supercontinuum white light (fig. The long axis of the GNR is perpendicular to the length of the microfiber, forming a photon-plasmon hybrid cavity ( 24, 25, 28, 29). Figure 2C shows an optical microscope image of a suspended 2.5-μm-diameter PMMA microfiber with a GNR deposited on its surface, which can be visualized in the scanning electron microscope (SEM) image ( Fig.
By immersing a microfiber into a small droplet of diluted nanorod solution (1 pM) and drying it in air, individual GNRs can be deposited on the surface of the microfiber. PMMA microfibers were fabricated by using a direct solution drawing technique ( 27). The longitudinal LSPR peak of a GNR deposited on a glass slide is around 630 nm, with a typical linewidth of about 49 nm ( Fig. 2A, the sizes of GNRs are relatively uniform with average diameter and length of 38 and 84 nm, respectively. Experimentally, GNRs were synthesized using a seed-mediated method ( 26). The strong mode coupling between LSPR mode of a GNR and WGM of a pure PMMA microfiber (i.e., passive microfiber) was first studied. Strong mode coupling-enabled linewidth narrowing Therefore, together with the strong mode coupling-enabled linewidth narrowing, it is possible to break the current limitations to realize single plasmonic nanoparticle–based lasers with high performance. Compared with previously reported nanoparticle-based lasing systems relying on local gain media, which can only acquire gain within a limited volume surrounding the nanoparticle (i.e., optical near field of the nanoparticle), the gain accumulation provided by the WGM cavity of the hybrid photon-plasmon system can offer a much higher accessible gain for compensating plasmonic loss. When the pump intensity is strong enough (e.g., population inversion within the whole hybrid cavity), the PL increases while recirculating back to the LSPR mode of the GNR within the WGM cavity (inset of Fig.
When the dye-doped microfiber is excited by a pump laser, a certain fraction of the photoluminescence (PL i.e., dye emission) can be channeled into the hybrid mode as long as a good spectral overlap between the hybrid mode and the PL is satisfied.
The difficulty in the realization of single nanoparticle–based plasmonic lasers lies in the high parasitic Ohmic loss associated with highly localized surface plasmon resonance ( 20), which requires unrealistically high gain difficult to be provided by gain media located in the optical near field of the resonant nanoparticle, not to mention the thermal damage induced by the high-density pump ( 21, 22). However, up to date, almost all of the metal nanoparticle-based lasers are obtained in a cluster or an array of nanoparticles ( 14– 19), laser based on single metal nanoparticles has not yet been convincingly realized. Among them, metal nanoparticle-based lasers with the capability of extreme confinement of lasing modes, which is one of the ultimate goals of nanolasers ( 2), are of particular interest. Relying on various low-dimensional plasmonic nanostructures including metal films ( 10– 12), nanowires ( 13), and particles ( 14– 16), a number of plasmonic lasers have been successfully demonstrated by placing gain media in their optical near-field regions. Plasmonic lasers ( 1), using surface plasmons in metallic nanostructures to achieve optical confinement and feedback, are an emerging coherent light source that can achieve a lasing cavity mode with feature size far beyond the diffraction limit and ultrafast modulation speed up to terahertz ( 2– 9). With the rapid developments in areas such as superresolution imaging, biochemical sensing, optical data storage, and on-chip optical interconnects, the demands for coherent sources that can provide optical frequency radiation below the diffraction limit in one or more spatial dimensions are ever-increasing in recent years.
0 kommentar(er)
