This study investigates the influence of laser parameters on electromagnetic wave attenuation within a silicon waveguide over a wide frequency range of 67–220 GHz using 3-D full-wave simulations. A 10-layer cylindrical model mimicking the energy distribution of a Gaussian laser beam shape is utilized for the analysis. The conductivity of each layer is calculated, and the S-parameters are simulated via CST Studio Suite. Significantly different attenuation levels are observed for different laser wavelengths used in this study. A 980 nm laser resulted in a substantially higher attenuation comparison to a 405 nm laser which had a minimal impact. Furthermore, by increasing the laser intensity, an increase in attenuation is observed. Moreover, the low level of simulated return loss indicates that solid-state plasma absorption dominates the reflections.