In this study, we investigated some effective parameters related to the plasma and the laser characteristics on linear absorption mechanisms such as; plasma scale length, plasma density profile, laser intensity and laser pulse duration. We classify different approaches which lead to different solutions for the wave equation in plasma medium. We showed that, there are some restrictions with applying the linear theory in absorption. Finally we pointed out that there are some restrictions to apply linear theory in absorption. We will see in which regimes collisional or resonance absorption is dominant.
