Lloyd S Mirror: Lloyd's Mirroris a Classicopticsexperiment and Was First Described in 1834

Lloyd’s Mirror: Lloyd's mirroris a classicopticsexperiment and was first described in 1834 and again in 1837 byHumphrey Lloydin the proceedings of theRoyal Irish Academy of Science. In the experiment, light from amonochromaticslit sourcereflectsfrom a glass surface at a small angle and appears to come from avirtual sourceas a result. The reflected light interferes with the direct light from the source, forminginterferencefringes.

Lloyd’s Mirror is used to produce two-source interference patterns that have important differences from the interference patterns seen inYoung's experiment.

In a modern implementation of Lloyd's mirror, a diverging laser beam strikes a front-surface mirror at agrazing angle, so that some of the light travels directly to the screen (blue lines in Fig.1), and some of the light reflects off the mirror to the screen (red lines). The reflected light forms a virtual second source that interferes with the direct light.

Difference:

In Young's experiment, the individual slits display a diffraction pattern on top of which is overlaid interference fringes from the two slits (Fig.2). In contrast, the Lloyd's mirror experiment does not use slits and displays two-source interference without the complications of an overlaid single-slit diffraction pattern.

In Young's experiment, the central fringe representing equal path length is bright because ofconstructive interference. In contrast, in Lloyd's mirror, the fringe nearest the mirror representing equal path length is dark rather than bright. This is because the light reflecting off the mirror undergoes a 180° phase shift, and so causesdestructive interferencewhen the path lengths are equal or when they differ by an integer number of wavelengths.

Resolving power and dispersive power of a diffraction grating:

The ability of an optical instrument expressed in numerical measure to resolve the image of two nearby points in terms as resolving power.

The dispersive power of a diffraction grating is defined as the rate change of the angle of diffraction with wavelengths of light.

Anti Reflection coating:Anantireflectiveoranti-reflection(AR)coatingis a type ofoptical coatingapplied to the surface oflensesand other optical devices to reducereflection. This improves the efficiency of the system since lesslightis lost. In complex systems such as atelescope, the reduction in reflections also improves thecontrastof the image by elimination ofstray light. This is especially important inplanetary astronomy. In other applications, the primary benefit is the elimination of the reflection itself, such as a coating oneyeglasslenses that makes the eyes of the wearer more visible to others, or a coating to reduce the glint from a covert viewer'sbinocularsortelescopic sight.