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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.
Frequency shift of an optical cavity mode due to a single-atom motion
Published in Journal of Modern Optics, 2019
Mojtaba Moazzezi, Yuri V. Rostovtsev
The fact that the dispersion of light depends on the atomic motion has been known for over a century (30–33). In our approach, we consider the effect of mechanical motion of the quantum system on the phase of the radiation by taking advantage of ultra strong dispersion provided by quantum coherence. Quantum coherence effects, such as coherent population trapping (CPT) (34) and electromagnetically induced transparency (EIT) (35–38), have been the focus of a broad range of research activity for the past two decades since they drastically change the optical properties of the medium. In EIT, for example, absorption practically vanishes in both the CW and the pulsed regime (36–41). A medium with an excited quantum coherence, phaseonium (35), can be used to make an ultra-dispersive prism (42) which will have several orders of magnitude greater angular spectral dispersion compared to a conventional one. Also the bending of light has been demonstrated using a transverse dragging effect (43). The corresponding steep dispersion results in the ultraslow (or ultrafast) propagation of light pulses (44–53). This, in turn, will produce huge optical delays (52, 53) and, therefore, ultrahigh enhancement in absolute and relative rotation sensing can be achieved (54).