Table 3. The optical constants of 2D MoS₂, MoSe₂, WS₂, and WSe₂ with different excitation wavelengths from 600 nm to 1024 nm.

TMDC	TMX2 (nm)	λ = 600 nm	λ = 633 nm	λ = 660 nm	λ = 785 nm	λ = 1024 nm
MoS2	0.65	ɛ′ = 17.7967,	ɛ′ = 24.4368,	ɛ′ = 23.4129,	ɛ′ = 21.4675,	ɛ′ = 20.8372,
		ɛ″ = 10.7801	ɛ″ = 11.9121	ɛ″ = 12.5610	ɛ″ = 1.0781	ɛ″ = 0.9662
MoSe2	0.70	ɛ′ = 21.3204,	ɛ′ = 20.3560,	ɛ′ = 19.3366,	ɛ′ = 17.7994,	ɛ′ = 14.9028,
		ɛ″ = 10.9486	ɛ″ = 9.3039	ɛ″ = 8.4366	ɛ″ = 7.0709	ɛ″ = 2.7611,
WS2	0.80	ɛ′ = 12.0258,	ɛ′ = 23.8511,	ɛ′ = 19.9701,	ɛ′ = 16.0968,	ɛ′ = 25.0445,
		ɛ″ =  4.2578	ɛ″ = 3.0578	ɛ″ = 1.8420	ɛ″ = 0.3203	ɛ″ = 2.5676,
WSe2	0.70	ɛ′ = 19.4125,	ɛ′ = 20.5156,	ɛ′ = 18.7344,	ɛ′ = 19.0563,	ɛ′ = 23.6474,
		ɛ″ = 8.4135	ɛ″ = 3.9423	ɛ″ = 2.1955	ɛ″ = 0.3205	ɛ″ = 2.3801

The dielectric constant is described by ε = ε′ + ε″i, where the real part ε′ relates to the stored energy within the medium and the imaginary part ε″ relates to the dissipation of energy within the medium. (The complex refractive index is defined as, where the real part n indicates the phase velocity, while the imaginary part κ known as the extinction coefficient refers to the mass attenuation coefficient).