tailieunhanh - Coherence and Ultrashort Pulse Laser Emission Part 15

Tham khảo tài liệu 'coherence and ultrashort pulse laser emission part 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Heat Absorption Transport and Phase Transformation in Noble Metals Excited by Femtosecond Laser Pulses 551 Ag Mott 1936 Baber 1937 . The TTM result with the inclusion of this reduced electron conductivity is shown as crosses in Fig. 5. Although the new results agree much better with the experiments it still underestimates the melt-depth at larger film thicknesses. Increasing the constant C by another order of magnitude open-circle does not significantly change the result. An additional heat confinement mechanism is needed to explain the experimental data. We explore possible additional mechanisms that can create the heat confinement necessary to explain the experimental results using the TTM we do this by adding a thermal interface impedance. This is rationalized by recognition of the sharp interface that is created by the d-band excitations in the surface region. Since a large temperature gradient exists over a distance that is small compared to the electron mean free path X of Ag . X 50 nm at RT Kittle 2005 electron conductance on the cold side of the interface can be overestimated in the above TTM. In other words the excited d-band electrons should have influence on Kel in the un-excited region extending to a distance on the order of X. A similar argument for non-local heat transport has been employed previously in Mahan Claro 1988 to describe the reduction in phonon conductivity when the curvature in the temperature depth profile is large. We place the interface at a depth of 20 nm and assume its conductance varies inversely with the number of d-band holes. Since the number of d-band holes increases approximately linearly with electron temperature Te above some critical temperature 4000 K we take the interface conductance as 10000xG Ts-4000 where Ts is the surface temperature and G is a fitting constant with the unit of interface conductance. In the first 3-4 ps Ts falls from around 15 000 K to a temperature below 4 000 K. Therefore the interface is only .