Photothermal Signal Simulation Forlaser-irradiated Semi-transparent Media And Its Inverse Problems

Semi-transparent material has been widely used in various fields. Research on the optical and infrared properties of semi-transparent materials received a common concern by domestic and foreign scholars. Typical semi-transparent media are: water, ice, air, glass, resin, ceramic, biological tissue, porous media, dispersed particles, and so on. The effects of radiative heat transfer always need to be considered in the study of photothermal interaction between laser and semi-transparent media. From the direct and inverse problem of photothermal signal simulation for laser-irradiated semi-transparent media, the present dissertation focuses on steady radiative heat transfer, transient radiative transfer, frequency-domain radiative transfer, coupled radiative and conductive heat transfer, coupled radiative and phase-change heat transfer and inverse radiative heat transfer. The specific work of this thesis includes the following five aspects:1. The current development of Swarm Intelligence optimization algorithms was reviewed in this thesis, in which the common features of swarm intelligence optimization algorithm were also summarized. Moreover, the characteristics of several common algorithms were introduced, respectively. Particle Swarm Optimization (PSO) and Ant Colony Optimization (ACO) were discussed on the theory and realization. Meanwhile, the improvement of Quantum-behaved Particle Swarm Optimization (QPSO), Grid-based Ant Colony Optimization (GACO) and PDF-based Ant Colony Optimization (PACO) were given here. Through several standard test functions, the performances in accuracy, efficiency and stability of the improved algorithms were proved to have obvious enhancement.2. On the basis of the Finite Volume Method (FVM), combining with the idea of the Multi-Flux Method (MFM), arbitrary directional radiative intensity of multi-dimensional semi-transparent media were solved under diffused boundary condition. Moreover, the FVM was modified from two aspects using the idea of MFM, namely proposing a more precision associated format and putting forward an improved FVM which does not require angle interpolation to handle multi-layer media containing Fresnel interface.3. For the coupled radiative and conductive heat transfer problem, the effective thermal conductivity and radiative source term were used to decouple process. A new method for solving the effective thermal conductivity of porous media was proposed. Then the GACO was introduced to solve the inverse problem of coupled radiative and conductive heat transfer by measuring the temperatures and radiative heat flux on the boundaries. The scattering coefficient, absorption coefficient distribution and interface position were retrieved accurately. For the coupled radiative and phase-change heat transfer, the radiative transfer equation and enthalpy energy equation were both solved by FVM which was verified by results in reference. The control equations were nondimensionalized, and then the Stephen number and conduction to radiation parameter were retrieved successfully at last.4. For transient radiative transfer problem, the time-and frequency-domain transient radiative transfer equation were respectively solved by FVM. The simulated results were compared with those of Monte Carlo Method and Discontinuous Finite Element Method, respectively. The GACO and PACO were introduced to solve inverse problems of time-and frequency-domain transient radiative transfer. Then the physical properties of semi-transparent media such as optical thickness, scattering albedo, absorption coefficient, scattering coefficient and scattering asymmetry factor were retrieved by measuring the transmittance and reflectance on the boundaries.5. Based on Time-Correlated Single Photon Counting (TCSPC) technique, an experimental platform was built to measure the transmittance and reflectance of the semi-transparent media under pulsed laser irradiation. The equipment was calibrated and the experimental system was verified by standard solid imitations whose physical properties were known. Then the error sources and reliability of the measurement system were analyzed. Finally, the reflectance and transmittance of some biological tissues were measured in vitro and vivo. Then the absorption and reduced scattering coefficients were retrieved by utilizing the measured signals.