Estimating the absorptivity in laser processing by inverse methodology

In the present study, a conjugate gradient method is applied to estimate the unknown time-dependent laser absorptivity during a laser processing, based on available temperature measurements. It is assumed that no prior information is available for the functional form of the unknown absorptivity. But depending on the temperature history at a measuring position, the unknown time-dependent absorptivity can be estimated by an inverse analysis. The accuracy of the current method is examined by using the simulated exact and inexact temperature measurements. Results show that excellent agreement on the absorptivity can be obtained for all the test cases considered in this study. Subsequently, accurate melting depth and temperature distributions can also be returned. The methodology presented here can also be applied to other various applications, such as calculating the cutting forces in nanomachining by atomic force microscopy (AFM), and estimating the heat sources in a X-ray lithographic process.