Totalreflektion

Totalreflektion, or total internal reflection, is an optical phenomenon that occurs when a light ray travels within a medium of higher refractive index and strikes the boundary with a medium of lower refractive index at an angle greater than a specific threshold. Under these conditions all of the light is reflected back into the original medium rather than refracted into the second medium.

The occurrence of total internal reflection follows Snell's law, n1 sin(theta1) = n2 sin(theta2). If light goes from a denser medium (n1) to a rarer one (n2) and the incident angle theta1 exceeds the critical angle theta_c, where sin(theta_c) = n2/n1, refraction in the second medium would require an angle greater than 90 degrees. Since that is not possible for propagating waves, no transmitted ray exists and the light is completely reflected. At angles above theta_c, the reflectivity approaches 100% and the reflection can be independent of polarization.

Even though no refracted beam propagates, an evanescent wave penetrates a short distance into the second medium. If another medium is placed close to the boundary, energy can couple into it, a phenomenon known as frustrated total internal reflection.

Applications of total internal reflection include confinement of light in optical fibers for communications, endoscopes, and various optical sensors. It also underpins techniques such as attenuated total reflectance spectroscopy, which uses the evanescent field generated by TIR to probe surfaces. Total internal reflection is a fundamental principle in designing devices that guide and control light with minimal loss.