“…The phenomenon can be properly described by the D'Alembert equation for the displacement u along z ‐direction, with the temperature as driving term:
where β = −3 Y α L /ρ is a constant, containing the Young modulus Y = 300 GPa (highest value in the temperature range considered in [
64]), the linear expansion coefficient α L = 8.3 × 10 −6 K −1 and the density ρ = 5.21 × 10 3 kg m −3 of TiN. [
65,66 ] By solving the above equation, the deformation η( z , t ) along the z ‐direction is retrieved at each temporal delay (see Section 7 for details), and then the skin layer thickness variation can be determined as
. This modulation is in turn responsible for a plasma frequency modulation in the skin layer, which can be computed as:
…”