Critical angle total internal reflection

Figure 3.8 Ray diagram illustrating the phenomena of transmission, reflection, and refraction at the interface between two media of differing refractive index. In this example rays pass from a high (glass) to low (water) refractive index medium.At angles of incidence (0,) below the critical angle (0j transmitted (refracted) and reflected rays are produced (grey). Above the critical angle total internal reflection occurs (black) and no...

Attenuated total reflection (ATR), also called internal reflection, is based on the phenomenon of total internal reflection. In ATR the infrared beam is directed into an infrared-transmitting crystal so that it strikes the crystal surface at less than the critical angle and undergoes total internal reflection. 

Fig. 9.1. Principle of total internal reflection. Light propagation and refraction in a system with different refractive indices separated with a smooth surface is shown. Left The incident light is entering from the high refractive index medium under an angle 61 which is less than the critical angle 0C. Right total internal reflection because the incident light angle 61 is larger than 6C.

For total internal reflection to take place at the sample surface, 0 must be greater than the critical angle 0C, given by... 

The maximum input acceptance angle for a fiber-optic cable is determined by the critical angle for total internal reflection, which is given by Snell s law ... 

The luminous nonpolarized wings are due to part of the emission built up in the middle of the crystal. They can be understood when taking total internal reflection into account. Refraction of the emission from the object O at the zeolite L-air interface observed at an angle 2 is explained in Fig. 16a. The emission can appear between 0° and the critical angle for total reflection which is... 

For the air/water interface at 25°C, the critical angle c is 43.75°. For values of 0i > 0c, all the light is reflected to the optically dense phase. This condition is called total internal reflection. It is the key condition of optical wave guiding and thus the most fundamental condition of optical sensing. 

The internal angle of incidence is generally chosen to be 20° so that it is close to the critical angle of total internal reflection. The infrared absorption of each of the monolayers is measured both with and without the metal layers. The ATR technique is used only over the frequency range for which the substrate is transparent. For silicon substrates, this limits the applicable frequency ranges to between 4000 and 1700 cm 1 and below 420 cm 1. 

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