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Laser linewidth is the spectral linewidth of a laser beam.. Two of the most distinctive characteristics of laser emission are spatial coherence and spectral coherence.While spatial coherence is related to the beam divergence of the laser, spectral coherence is evaluated by measuring the linewidth of laser radiation.
Spatial coherence of laser beams also manifests itself as speckle patterns and diffraction fringes seen at the edges of shadow. Holography requires temporally and spatially coherent light. Its inventor, Dennis Gabor , produced successful holograms more than ten years before lasers were invented.
Spatial coherence allows a laser to be focused to a tight spot, enabling applications such as optical communication, [6] laser cutting, and lithography. It also allows a laser beam to stay narrow over great distances ( collimation ), a feature used in applications such as laser pointers , lidar , and free-space optical communication .
Multimode helium–neon lasers have a typical coherence length on the order of centimeters, while the coherence length of longitudinally single-mode lasers can exceed 1 km. Semiconductor lasers can reach some 100 m, but small, inexpensive semiconductor lasers have shorter lengths, with one source [4] claiming 20 cm. Singlemode fiber lasers with linewidths of a few kHz can have coherence ...
A laser or synchrotron beam are also often used directly without additional collimation. The spatial coherence guarantees a uniform wavefront prior to beam splitting. Second, it is preferred to use a monochromatic or temporally coherent light source. This is readily achieved with a laser but broadband sources would require a filter.
Rotating diffusers—which destroys the spatial coherence of the laser light—can also be used to reduce the speckle. Moving/vibrating screens or fibers may also be solutions. [36] The Mitsubishi Laser TV appears to use such a screen which requires special care according to their product manual.
Mode locking is a technique in optics by which a laser can be made to produce pulses of light of extremely short duration, on the order of picoseconds (10 −12 s) or femtoseconds (10 −15 s). A laser operated in this way is sometimes referred to as a femtosecond laser, for example, in modern refractive surgery.
Laser surgery is a type of surgery that cuts tissue using a laser in contrast to using a scalpel. [ 1 ] Soft-tissue laser surgery is used in a variety of applications in humans ( general surgery , neurosurgery , ENT , dentistry , orthodontics , [ 2 ] and oral and maxillofacial surgery ) as well as veterinary [ 3 ] surgical fields.