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Laser Beam Control
Published in Chunlei Guo, Subhash Chandra Singh, Handbook of Laser Technology and Applications, 2021
Three tuning mechanisms are in general use: Littrow prisms, diffraction gratings and birefringent filters. Littrow prisms (see Figure 8.15) and their close relative, the full-dispersing prism, are used extensively with gas lasers that operate at discrete wavelengths. In its simplest form, the Littrow prism is a 30°–60°–90° prism with the surface opposite the 60° coated with a broadband high-reflecting coating. The prism, which replaces the end mirror in the laser, is oriented so that the desired wavelength is reflected back along the optical axis and the other wavelengths are dispersed off axis. By rotating the prism, individual lines can be chosen. To improve performance, the prism’s angles can be modified so that the beam enters the prism exactly at Brewster’s angle, thereby reducing intra-cavity losses. For higher power lasers that require greater dispersion to separate closely spaced lines, the Littrow prism can be replaced by a full-dispersing prism coupled with a high reflecting mirror.
Optical Components
Published in Rajpal S. Sirohi, Mahendra P. Kothiyal, Optical Components, Systems, and Measurement Techniques, 2017
Rajpal S. Sirohi, Mahendra P. Kothiyal
Dispersion prisms disperse the beam into its spectral components. Incidence at the entrance face where the dispersion takes place is nonnormal. Common examples are 60° prisms, constant deviation prisms, Littrow prisms, etc. and are shown in Figure 2.6. These prisms can also be used in tandem. The Littrow prism is used both as a mirror and as a dispersive element in some laser cavities to provide wavelength selection. The angular disperson dθ/dλ of a prism is given by dθdλ=dθdndndλ
Lightguide type Maxwellian near-eye display with enlarged horizontal field of view by optical reconfiguration of input image
Published in Journal of Information Display, 2022
Woongseob Han, Jae-Min Jeon, Myeong-Ho Choi, Jae-Hyeung Park
Figure 3(b) shows the recording setup of the first out-coupler HOE, which is designed to diffract the lower part of the input image to a single focal spot in the eye pupil plane. Attached to the Littrow prism, the HOE is recorded by a collimated reference beam and a converging signal beam. A convex lens with a focal length of 35 mm is used to converge the signal beam. The signal beam axis is also horizontally slanted by about 9.80° to form the focal spot at the middle of two out-couplers with an eye-relief of 27 mm as shown in Figure 2.