TITLE:
Using Narrow Line-Width Laser to Measure the Thickness and Refractive Index of the Film
AUTHORS:
Junjie Fang
KEYWORDS:
Particle Swamp Optimization, Narrow-Lined Laser, Thin-Film Thickness and Refractive Index
JOURNAL NAME:
Natural Science,
Vol.12 No.11,
November
24,
2020
ABSTRACT: We demonstrate applications of a novel setup which
is used for measuring the relative phase difference between S and P
polarization at an oblique incidence point in optically denser medium by
analyzing the relative frequency shift of adjacent axial modes of S and P
resonances of a monolithic folded Fabry-Perot cavity (MFC). The relative phase
difference at a reflection point A in an optically denser medium is inferred to
be around -167.4° for a confocal cavity and -201.1° for a parallel cavity. Given the n1, n3, φ1, φ3, λ, and Δ, the elliptic formula tan(ψ)exp(iΔ) = Rp/Rs is used to find a solution
for thickness d and refractive index n2 of the thin
film coated on point A, where Rs and Rp are total
refractive index of s and p component
of light related to two unknown values. Since it is hard to deduce an
analytical solution for thickness and refractive index of the film, we firstly
used exhaustion method to find the set of solution about thickness and
refractive index when assumed there is no light absorption by the film and then
Particle Swarm Optimization (PSO) to find a set of solution of thickness and
complex refractive index which accounts the light absorption by the film.