Brewster angle prism

Fig.13.8. Optical cavity with internal Brewster angle prism used to select one o several possible transitions for laser oscillation.

There are numerous polarizing optical components available. Their operation is based on birefringence, polarization at mirrors at the Brewster angle, optical dichroism, etc. Precision achieved with sheet polarizers is inadequate, thus devices like Glan-Thompson, Glan-Foucault or Rochon prisms have to be used. 

Fig. 3.8 Reflectivity in the vicinity of the resonance corresponding to a SP excitation. The experimental data are for a 45 nm thick Au film deposited onto a quartz prism. The increase in reflectivity at 41.3° corresponds to the Brewster angle.

To minimize fluctuations and drifts of the transmission maximum by air-pressure changes, the air space between the etalon plates should be as small as possible. An elegant solution is shown in Fig.6.33b where the etalon is formed by two Brewster prisms which are coated on a cathete surface and which also avoid reflection losses on the other surfaces due to the Brewster angle a. 

Brewster s law. Reflected light in general is more polarised than the incident light and according to Brewster s law, the polarisation is maximum when i + r = 90 where i and r are the angles of incidence and refraction. There are several methods described in the literature such as those based on the use of prisms and fluid immersion (in fluids of known refractive indices) and index matching. The so-called Becke line technique for index matching uses observations under microscope. 

In order to minimize the air gap between the reflecting surfaces of the FPI, the prism construction of Fig. 5.42b is often used, in which the small air gap is traversed by the laser beam at Brewster s angle to avoid reflection losses [5.57]. This design minimizes the influence of air pressure variations on the transmission peak wavelength Al. 

The reflectivity of the grating is very low at grazing incidence and the round-trip losses are therefore high. Using Brewster prisms for preexpansion of the laser beam (Fig. 5.87), the angle of incidence a at the grazing incidence... 

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