Ultrafast optical switches and pulse lasers based on strong nonlinear optical response of plasmon nanostructures

Nonlinear optical (NLO) effects are ubiquitous in the interaction of light with different materials. However, the NLO responses of most materials are inherently weak due to the small NLO susceptibility and the limited interaction length with the incident light. In plasmonic nanostructures the optical field is confined near the surface of the structures, so that the electromagnetic field is greatly enhanced in a localized fashion by spectral resonance. This effect results in the enhancement of light-matter interaction and NLO response of the material. Ultrafast pulse lasers have been widely used in optical communication, precise measurement, biomedicine, military laser weapons and other important fields due to their excellent performances. Although commercial lasers become very matured, they can achieve ultra-high peak power and ultra-short pulse width and ultra-high repetition rate, but the ultra-fast pulses in the mid-to-far infrared band are seldom studied, so finding a saturable absorber material with excellent performance is of great significance for developing the pulsed lasers. In this paper, we review the recent research progress of the applications of exiton nanostructure in ultrafast optical switches and pulse lasers based on noble metal and non-noble metals. The metallic system mainly refers to gold and silver nanoparticles. For non-noble metals, we mainly introduce our researches of chalcogenide semiconductor, heavily doped oxide and titanium nitride. A variety of wide bandgap semiconductors can exhibit metal-like properties through doping. Since doping can form free carriers, when their size is reduced to a nanometer scale, they will show the characteristics of local surface plasmon resonance, thus realizing ultra-fast nonlinear optical response, and the concentration of doped carriers cannot reach the level of metal carriers, thus being able to effectively reduce the inter-band loss caused by excessively high carriers. Through pump probe detection and Z-scan testing, we found that these plasmonic nanostructures exhibit ultrafast NLO response in tunable resonance bandwidth, which has been utilized as a working material for developing the optical switch to generate the pulsed laser with duration down to a femtosecond range. These results take on their potential applications in ultrafast photonics. Finally, we make a comparison of the pros and cons among different plasmonic materials and present a perspective of the future development.