MN228 Glass: Optical Absorption Characterization
MN228 Glass: Optical Absorption Characterization
yonggang@aurora.tech Apr 2026
Theory: Internal Absorption Coefficient
According to SCHOTT Technical Information TIE-35, the total transmittance ($T$) of a glass plate is the result of surface reflection losses and internal absorption. It is defined as:
T = P · τiWhere P is the reflection factor (dependent on the refractive index $n$) and τi is the internal transmittance. The internal transmittance follows the Bouguer-Lambert Law of exponential decay:
τi = e-α·dSubstituting this yields: T = P · e-α·d. Taking the natural logarithm:
ln(T) = ln(P) - α · dComputation Method
By fitting the logarithm of measured transmittance against the sample thickness ($d$), the absorption coefficient (α) is determined as the negative slope of the line. This multi-sample approach is scientifically superior because it separates the material constant (α) from surface reflection factor (P), making it independent of the refractive index $n$.
1. Measured Raw Transmittance Curves (%)
Plotting the transmission values for 2mm, 4mm, and 5mm samples using a continuous linear wavelength scale.
2. Computed Internal Absorption Coefficient (α) [mm⁻¹]
The absorption coefficient α derived for each wavelength point via linear regression of $ln(T)$ vs $d$.