Full-process simulation of XPCS speckle dynamics based on the Monte Carlo method and analysis of key parameter dependencies

X-ray Photon Correlation Spectroscopy (XPCS) is vital for probing mesoscale material dynamics using synchrotron radiation, yet the complex influence of parameters such as light source properties, beam propagation, detector response on speckle dynamics is hard to directly observe. This study develops a Monte Carlo-based full optical path numerical model to systematically analyze these effects, aiding experimental optimization.A simulation framework integrating Brownian dynamics, beam coherence, and detector response was constructed to replicate the entire photon emission-to-detection process. A Fraunhofer diffraction-based speckle generation algorithm reproduced speckle fluctuations via atomic position evolution and phase modulation. Feasibility was validated via Siegert relation fitting (β, γ), Γ - q2 linearity (R2=0.99904), and consistency with the Einstein-Stokes law.Key parameter sensitivity analysis revealed:(1) Optimal aperture matching (r/σ=1) balances coherence and photon flux; (2) Mechanical vibrations with Δx/s=1500 induce periodic oscillations in g2(q, τ), masking intrinsic relaxation, as validated by a 24.658 Hz pump experiment; (3) Poisson noise and intensity fluctuations degrade low-light SNR, with Poisson noise causing discrete errors and classical noise inducing baseline shifts.This framework clarifies how source properties, optical parameters, and noise affect results, providing guidance for XPCS optimization and a foundation for extending its applications to high-precision coherent scattering scenarios.