Birefringent. Lyot filter

Fabry-Perot interferometers, polarization interference, birefringence, Lyot filters... 

The operation of an LCTF may be understood by considering a simplified Lyot filter stack, in which (N +1) polarizers are separated by N layers of liquid crystals sandwiched between birefringent crystals. The optical retardation, Rnm, introduced by birefringent crystals is dependent on the thickness of the crystal, tfnm, and the difference between the refractive index of the ordinary ray, and the extraordinary ray, tie, at the wavelength of interest ... 

Some interferometers utilize the optical birefringence of specific crystals to produce two partial waves with mutually orthogonal polarization. The phase difference between the two waves is generated by the different refractive index for the two polarizations. An example of such a polarization interferometer is the Lyot filter [4.23] used in dye lasers to narrow the spectral linewidth (Sect. 4.2.9). 

The basic principle of the birefringent interferometer or Lyot filter [4.23,4.53] is founded on the interference of polarized light that has passed through a birefringent crystal. Assume that a linearly polarized plane wave... 

Fig. 4.59a,b. Lyot filter (a) schematic arrangement (b) index ellipsoid of the birefringent crystal... 

The elementary Lyot filter consists of a birefringent crystal placed between two linear polarizers (Fig. 4.59a). Assume that the two polarizers are both parallel to the electric vector (0) of the incoming wave. The second polarizer parallel to E(0) transmits only the projection... 

Fig. 4.60. (a) Transmitted intensity Ij X) of a Lyot filter composed of three birefringent crystals with lengths L, 2L, and 4L between polarizers, (b) Arrangement of the crystals and the state of polarization of the transmitted wave... 

Commercial cw dye laser systems (Sect. 5.5) generally use a different realization of single-mode operation (Fig. 5.41). The prisms are replaced by a birefringent filter, which is based on the combination of three Lyot filters (Sect. 4.2.9), and the thick etalon is substituted by a Fabry-Perot interferome-... 

Coarse wavelength tuning can be accomplished with a birefringent filter (Lyot filter, see Sect. 4.2.9) that consists of three birefringent plates with thicknesses d, q d, Q2d (where q, q2 are integers), placed under the Brewster angle inside the dye laser resonator (Fig. 5.93). Contrary to the Lyot filter discussed in Sect. 4.2.9, no polarizers are necessary here because the many Brewster faces inside the resonator already define the direction of the polarization vector, which lies in the plane of Fig. 5.93. 

The gain volume is at the focal point of a folded cavity, consisting of two spherical mirrors and a flat output coupler. Tuning is accomplished with a birefringent, so-called Lyot filter [8.71]. This consists of one or several crystalline quartz plates mounted at the Brewster angle. The dominant transmission maximum of this filter can be moved by turning the optical axis of the filter with respect to the plane of polarization of the light in the... 

Figure 8 Schematic of Lyot birefringence interference filter (A) transmittance of an individual Lyot stage as a function of wavelength (B) schematic of multiple Lyot stages cascaded end to end (C) and transmittance of multiple Lyot stages in series as a function of a wavelength (D).

Similar to the laser-pumped dye lasers, reduction of the linewidth and wavelength tuning can be accomplished by prisms, gratings, interference filters [5.153] Lyot filters [5.154], and interferometers [5.155]. A combination of a Lyot filter and FPI, composed of a birefringent crystal with mirror coatings on both end faces, inserted between two polarizers parallel to each other allows tuning with a higher finesse and therefore smaller linewidth [5.156]. 

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