Fundamental Research Of Laser Induced Dynamics On Ultra-thin Mirrors

Light is unique for its wave-particle duality.It can behave like waves in the diffraction and interference phenomena,while the particle-nature can be presented through the photoelectric effect.There is one physical effect that can link both of them,namely,optical pressure.The optical pressure is generated by the momentum and energy exchange between the material and the light during the process of reflection or refraction when light propagates between different media.The optical pressure from common light source is usually on the order of nano-Newton.With the development of laser technology,high-power energy output can be achieved and thus increases the light pressure by orders of magnitude,and could even produce observable mechanical effects on the reflector,which is the so-called light induced dynamics(or optodynamics).This phenomenon can not only be used for characterization and measurement of optical pressure,but also has wide prospects in the fields of nondestructive measurement and light power measurement.In this thesis,the optical pressure and light induced dynamics are systematically studied.Mathematical framework of optical pressure is deduced based on Maxwell equations,and the formula of the optical pressure is presented,which is suitable for non-magnetic uniform metal material.The simulation results show that the optical pressure acts on the surface of the reflector,and this force is dependent on parametes including incidence angle,reflective index and so on.Due to the high laser power,the optical pressure induced by laser is always accompanied with thermal effect.In order to study the optical pressure,a suitable reflector should be designed.Ultra-thin reflector has unique mechanical and thermal properties,and is a suitable optical element to be used in the study of topical pressure for its large specific surface area,which is a significant object in simulation and experiment.In this thesis,finite-element-method is carried out to study its mechanical properties,and the relationship between the reflector’s parameters and its modal.The ultra-thin ultra-high-reflectivity reflector with thickness of 100 microns and diameter of 20 mm is fabricated using ultra-precision machining.The optical pressure is calculated indirectly by measuring the laser induced displacement of the mirror under irradiation,and fits good with the simulation model,providing a new option for measurement of optical pressure.In this thesis,the relationship between the reflector structure and the optical pressure is also analyzed,and the mathematical model of energy density as well as optical pressure distribution on spherical structure are discussed.Light induced dynamics on thin spherical mirror is studied by coupling of mechanical and thermal model,the simulation results show that optical pressure from nanosecond pulsed laser can generate mechanical vibration,while the heat absorption can generate thermal expansion,these two phenomena can be used for characterization of mechanical and thermal component in optical pressure effect.In the experiment,the mechanical vibration and linear thermal expansion of the ultra-thin reflector under pulsed light are also observed by processed high-frequency sampled signal.The optical pressure obtained on a plane reflector from single reflection is very small,so a special nano-structured surface is designed to enhance the optical pressure through surface plasmon resonance.The simulation shows that this nano-structured surface can be employed to obtain optical pressure several times larger than that of a plane reflector at vertical incidence.Also,the deformation of the microstructure under high power irradiation is studied by multi-physics coupling simulation of mechanical,electromagnetic and thermal model,and the results show that the this has good structural stability.This thesis concentrates on theoretical and experimental study of optical pressure and light induced dynamics,mechanical and thermal response of ultra-thin reflector under laser irradiation are studied by applying different physics model.And realized observation of light induced dynamics under high power laser by introducing new precision optical element and measuring method,which provides fundamental understnding for expanding applications of optical pressure in the fields of science and engineering,and provides theoretical basis as well as reference for the future work.