Promoting spintronic terahertz radiation via Tamm plasmon coupling

Spectral fingerprint and terahertz(THz)field-induced carrier dynamics demands the exploration of broadband and intense THz signal sources.Spintronic THz emitters(STEs),with high stability,a low cost,and an ultrabroad bandwidth,have been a hot topic in the field of THz sources.One of the main barriers to their practical application is lack of an STE with strong radiation intensity.Here,through the combination of optical physics and ultrafast photonics,the Tamm plasmon coupling(TPC)facilitating THz radiation is realized between spin THz thin films and photonic crystal structures.Simulation results show that the spectral absorptance can be increased from 36.8%to 94.3%for spin THz thin films with TPC.This coupling with narrowband resonance not only improves the optical-to-spin conversion efficiency,but also guarantees THz transmission with a negligible loss(~4%)for the photonic crystal structure.According to the simulation,we prepared this structure successfully and experimentally realized a 264%THz radiation enhancement.Furthermore,the spin THz thin films with TPC exhibited invariant absorptivity under different polarization modes of the pump beam and weakening confinement on an obliquely incident pump laser.This approach is easy to implement and offers possibilities to overcome compatibility issues between the optical structure design and low energy consumption for ultrafast THz optospintronics and other similar devices.

Operando optical fiber monitoring of nanoscale and fast temperature changes during photo-electrocatalytic reactions

In situ and continuous monitoring of thermal effects is essential for understanding photo-induced catalytic processes at catalyst's surfaces.However,existing techniques are largely unable to capture the rapidly changing temperatures occurring in sub-μm layers at liquid-solid interfaces exposed to light.To address this,a sensing system based on a gold-coated conventional single-mode optical fiber with a tilted fiber Bragg grating inscribed in the fiber core is proposed and demonstrated.The spectral transmission from these devices is made up of a dense comb of narrowband resonances that can differentiate between localized temperatures rapid changes at the catalyst's surface and those of the environment.By using the gold coating of the fiber as an electrode in an electrochemical reactor and exposing it to light,thermal effects in photo-induced catalysis at the interface can be decoded with a temperature resolution of 0.1℃and a temporal resolution of 0.1 sec,without perturbing the catalytic operation that is measured simultaneously.As a demonstration,stable and reproducible correlations between the light-to-heat conversion and catalytic activities over time were measured for two different catalysis processes(linear and nonlinear).These kinds of sensing applications are ideally suited to the fundamental qualities of optical fiber sensors,such as their compact size,flexible shape,and remote measurement capability,thereby opening the way for various thermal monitoring in hard-to-reach spaces and rapid catalytic reaction processes.