PLASMONICS - Exercise

Hi I'm having difficulties with the plasmonica exercise, I sell some books and scientific publications I came across that there are two or more ways to get the result but I don't know what the correct sequence is.

Values: τ, γ and mainly ωp^(2).

ωp^(2)= in most of the literature = Design and Application of Plasmonic Devices - A Thesis and
PLASMONICS: FUNDAMENTALS AND APPLICATIONS - STEFAN A. MAIER

And research I found that gets confusing: https://www.osapublishing.org/ao/fulltext.cfm?uri=ao-22-7-1099&id=26571

Hi I'm having difficulties with the plasmonica exercise, I sell some books and scientific publications I came across that there are two or more ways to get the result but I don't know what the correct sequence is.

Values: τ, γ and mainly ωp^(2).

ωp^(2)= in most of the literature = Design and Application of Plasmonic Devices - A Thesis and
PLASMONICS: FUNDAMENTALS AND APPLICATIONS - STEFAN A. MAIER

And research I found that gets confusing: https://www.osapublishing.org/ao/fulltext.cfm?uri=ao-22-7-1099&id=26571

Here is the question of the exercise, resolution and research material.

Obtain an expression for the electrical permittivity of a metal ε(ω) in the low-frequency regime in the free electron model. Using this expression determine the electrical permittivity of Au, Ag and Cu for a frequency of 10 GHz (microwave region). Tip get the necessary parameters for calculations from reported literature.

Souce

https://core.ac.uk/download/pdf/190334041.pdf

https://www.springer.com/gp/book/9780387331508

EX1.pdf