Speckle is usually quantified by the speckle contrast. See adaptive optics, speckle imaging and optical interferometry. Two stars are only resolved by speckle interferometry. Thus, speckle and resonant Rayleigh-scattering are always superimposed to the incoherent emission. The speckle pattern which is seen when using a laser pointer is another diffraction phenomenon. In laser scattering this is known as speckle. Coherent beams are required in order to obtain 'far-field' diffraction patterns with speckle patterns. The methods used are either tissue Doppler or Speckle tracking echocardiography. Thus each vortex in the speckle pattern carries optical angular momentum. It also eases operation of adaptive optics and digital image reconstruction such as speckle imaging. Schematic of the experimental setup of multiple optical speckle illumination. However, vector Doppler is less computationally complex than speckle tracking. Speckle imaging excludes all possible stellar and brown dwarf companions. Other innovative imaging modalities consist of techniques such as speckle tracking. Typically vortices appear in speckle pattern in pairs.