Smallest angle of incidence at which total internal reflection occurs.
Note:
If \(n_{2}\) and \(n_{1}\) are the refractive indices, and \(n_{2} > n_{1}\), at the boundary, \(\sin \theta_{\rm{c}} = n_1/n_2\).
Source:
PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 742 (https://doi.org/10.1515/pac-2019-0203)