## 1 Introduction
[26] developed a finite element model to simulate the thermal history in LPBF. A constant metal powder absorptivity was employed in the simulation. [PERSON] et al. [27] also employed a finite element method to calculate the temperature profile of the part in additive manufacturing, considering temperature-dependent material properties. The molten pool dimensions and cross-sectional area were obtained through the FEM simulations. [PERSON] et al. [28] developed a transient model to compute the temperature distribution and molten pool behavior in additive manufacturing. The powder packing pattern was considered by a discrete element method. [PERSON] et al. [29] employed a multi-physics model to simulate the molten pool behavior and defect formation in additive manufacturing processes. [PERSON] et al. [30] proposed a finite element model for the prediction of temperature profiles and molten pool geometries in parts fabricated by the selective laser melting process. The Optical Penetration Depth of laser power was taken into consideration in the model. [PERSON] et al. [31] developed a new heat source model for the prediction of molten pool size through a finite element software. A relationship between laser absorptivity and molten pool depth was used in the simulations. Although iteration-based numerical methods can save the cost of experimental equipment, the computational cost of these methods is still too high to be widely used by academia and industry. To save computational resources, researchers proposed some efficient analytical modeling methods to study the LPBF process, based on some reasonable assumptions. [PERSON] et al. [32] developed an analytical method to study the residual stress in the selective laser melting process. [PERSON] et al. [33] predicted the grain size characteristics in metal additive manufacturing using an analytical strategy. [PERSON] et al. [34] proposed a complete analytical method to compute the part porosity in LPBF induced by lack-of-fusion, and the effect of powder packing density was considered. [PERSON] et al. [7] developed a simple analytical expression to estimate the surface roughness of parts built by selective laser melting, with the assumption of a circular molten pool cross-section above the substrate. [PERSON] et al. [35] proposed an analytical temperature prediction method based on the point-moving heat source model and a heat loss solution. The heat loss through part boundaries was considered in that model. [PERSON] et al. [36] and [PERSON] et al. [37] employed the Rosenthal equation to predict the temperature profiles and molten pool dimensions in LPBF, with absorptivity as constant values. [PERSON] et al. [38] also used the Rosenthal equation to obtain the molten pool size. The sensitivity analysis of predicted results to laser absorption was conducted in that paper. However, there is no reported model in the literature which takes into account the relationship between laser absorptivity and process conditions in the prediction of temperature distribution and molten pool shapes. The coefficient of laser absorption will significantly be affected by the process conditions in the laser powder bed fusion process [39; 40]. The consideration of process conditions-dependent laser absorptivity will simulate the melting behavior in LPBF better and thus increase the predictive accuracy of the computational models for temperature distribution and molten pool geometries. In this research, the molten pool dimensions of Ti6 Al4V in powder bed fusion additive manufacturing were predicted by an analytical thermal model, with the consideration of the difference in laser absorptivity under different process conditions. A scaling law-based empirical model for absorptivity was employed to compute the different laser absorptivity in LPBF. A point moving heat source model with a closed-form solution was used to compute the temperature profiles in single tracks. The absorptivity, thermal properties of the material, and process conditions were the inputs for the analytical thermal model.