Application
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Laser adjustment and laser stabilization The active media of very many lasers, e.g. laser diodes, titanium-sapphire or dye lasers can have rather broad gain bandwith. However, it is not always desirable for the laser to operate over the entire band width simultaneously. A dispersive element integrated into the resonator can be used to adjust the wavelength emitted by the laser. Alternatively, part of the decoupled radiation can be fed back into the resonator, selected by its wavelength.
Therefore, it is common to place a grating at the exit of a laser diode. Then, the zero order is used for the actual application, while the first order is used for wavelength selection via feed back. This can be done either by diffracting the first order directly (Littrow configuration) or via a mirror, and from there recoupling it into the resonator via the grating (Littmann configuration). The benefit of the more complex Littmann configuration is that the mirror and not the grating is adjusted and the direction of the application beam does not change when the laser is tuned. As a result, the wavelength of a wide-band laser can be selected or a laser stabilized in a mode of its discrete mode spectrum.to varying degrees. Highly-efficient gratings are therefore ideal for stretching pulses for amplification and then compressing them again. Further applications Gratings are also occasionally used for, e.g. beam splitting and as setting gauges. Beam splitting Splitting a light bundle into two or more usually interference-capable partial bundles is described as beam splitting. The most commonly used method of splitting light rays is the use of partly reflecting surfaces on an otherwise transparent substrate.
This splitting is then approximately wavelengthindependent and is described as division of amplitude. The required components are partially or semi-permeable mirrors, plate beam splitters or cubic beam splitters. However, division of ampliude can also be performed by gratings by using the different diffraction orders of an incident light beam as split beams. This beam splitting plays a key role in interferometers for the precise determination of lengths, wavelengths, refractive indices and the form of surfaces. The most important basic forms of such interferometers are the Michelson and the Mach-Zehnder interferometer, on which gratings are used as beam splitters.
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