Plasmon-assisted mode selection lasing in a lanthanide-based microcavity

Lanthanide-based microlasers have attracted considerable attention owing to their large anti-Stokes shifts,multiple emission bands,and narrow linewidths.Various applications of microlasers,such as optical communication,optical storage,and polarization imaging,require selecting the appropriate laser polarization mode and remote control of the laser properties.Here,we propose a unique plasmon-assisted method for the mode selection and remote control of microlasing using a lanthanide-based microcavity coupled with surface plasmon polaritons(SPPs)that propagate on a silver microplate.With this method,the transverse electrical(TE)mode of microlasers can be easily separated from the transverse magnetic(TM)mode.Because the SPPs excited on the silver microplate only support TM mode propagation,the reserved TE mode is resonance-enhanced in the microcavity and amplified by the local electromagnetic field.Meanwhile,lasingmode splitting can be observed under the near-field excitation of SPPs due to the coherent coupling between the microcavity and mirror microcavity modes.Benefiting from the long-distance propagation characteristics of tens of micrometers of SPPs on a silver microplate,remote excitation and control of upconversion microlasing can also be realized.These plasmon-assisted polarization mode-optional and remote-controllable upconversion microlasers have promising prospects in on-chip optoelectronic devices,encrypted optical information transmission,and high-precision sensors.

Direct molecular-level near-field plasmon and temperature assessment in a single plasmonic hotspot

Tip-enhanced Raman spectroscopy(TERS)is currently widely recognized as an essential but still emergent technique for exploring the nanoscale.However,our lack of comprehension of crucial parameters still limits its potential as a user-friendly analytical tool.The tip’s surface plasmon resonance,heating due to near-field temperature rise,and spatial resolution are undoubtedly three challenging experimental parameters to unravel.However,they are also the most fundamentally relevant parameters to explore,because they ultimately influence the state of the investigated molecule and consequently the probed signal.Here we propose a straightforward and purely experimental method to access quantitative information of the plasmon resonance and near-field temperature experienced exclusively by the molecules directly contributing to the TERS signal.The detailed near-field optical response,both at the molecular level and as a function of time,is evaluated using standard TERS experimental equipment by simultaneously probing the Stokes and anti-Stokes spectral intensities.Self-assembled 16-mercaptohexadodecanoic acid monolayers covalently bond to an ultra-flat gold surface were used as a demonstrator.Observation of blinking lines in the spectra also provides crucial information on the lateral resolution and indication of atomic-scale thermally induced morphological changes of the tip during the experiment.This study provides access to unprecedented molecular-level information on physical parameters that crucially affect experiments under TERS conditions.The study thereby improves the usability of TERS in day-to-day operation.The obtained information is of central importance for any experimental plasmonic investigation and for the application of TERS in the field of nanoscale thermometry.