Photothermal Effect In Metallic Nano-structures And Its Application

Surface plasmon polariton (SPP) is characterized by enhanced optical near-field and subwavelength energy confinement, indicating applications in the field of optoelectronics circuits, biomedical, information storage and super-resolution imaging. The enhanced localized optical field will be excited on the surface when light shines on metallic micro- and nanostructures. The localized optical energy will be transferred into heat due to the intrinsic loss characteristics of metal, leading to the photothermal effect. Such locally enhanced photothermal effect in metallic nanostructures shows vast applications. This thesis mainly discusses the morphology change/transfer of the metallic nanostructures based on the photothermal effect, and the thermo-optic (TO) modulation devices.The theoretical basis for the photothermal phenomenon in metallic nanostructures, including light absorption, heat generation, and heat conduction, is briefly introduced. Based on these theories, numerically simulation based on finite-element method can be conducted to study the plasmonic heat generation in metallic nanostructures under pump light, which is helpful for structural design and theoretical explanations.Nanofabrication processes play an essential role in the field of nanophotonics, which bring the nanostructure designed through simulation methods into reality. The fabrication processes of metamaterial light absorbers and all-optical TO silicon switches are introduced, including electron-beam lithography, electron-beam evaporation and inductively coupled plasma etching, etc. The experimental systems for charactering the optical properties of the nanostructures are also introduced.Laser-induced forward transfer (LIFT) is the method to transfer/fabricate metallic nanostructures through the photothermal effect. Metamaterial light absorbers show nearly perfect absorption of incident light at specific wavelength and generate enhanced heat power in the structure. Based on this photothermal effect in the light absorber, the ns-pulse laser at low power (35 mJ/cm2) can achieve LIFT, resulting in over hundred nanoparticles transferred by one shot. The transfer nanoparticles show single-crystal structure and without chemical residues on the surface compared to those made through chemical systhesis methods.TO switch can be achieved based on the nonlinear TO effect in silicon. In this thesis, a Mach-Zehnder interferometer integrated with a metal-insulator-metal (MIM) light absorber is fabricated. The MIM structure is pumped by a continuous 1064 nm laser and heat the waveguide nearby through the photothermal effect thus changing the refractive index of the silicon waveguide. Therefore, the transmitted probe light is modulated by the pump light. Compared to the traditional TO switches, this MIM integrated switch achieve the non-contact all-optical switching, removing the electrical contact, leading to the minimized footprint (< 30 μm× 60 μm).In a word, the photothermal effect in metallic nanostructures is theoretically and experimentally studied in this thesis. Two kinds of applications based on such photothermal effect are discussed, which demonstrate the potential applications in the field of nanostructure fabrication and the field of optical interconnects.