Q3Engineering Physics
Question
Answer
Spatial coherence strictly defines the physical phase correlation strictly between different points in space on a single transverse wavefront, whereas temporal coherence mathematically defines the absolute phase correlation of a wave at a single fixed point over continuous time.
- Spatial Coherence (Transverse Coherence): This mathematically describes how well the physical phase of the light wave is strictly correlated across the entire physical width of the beam. It fundamentally dictates the extreme directionality and low angular divergence of a laser beam. Highly spatially coherent light can be perfectly focused down to a microscopic diffraction-limited spot.
- Temporal Coherence (Longitudinal Coherence): This mathematically describes how predictably the phase of a light wave behaves at one absolute fixed point in space as time progresses. It is fundamentally directly related to the extreme monochromaticity (spectral purity) of the laser source. High temporal coherence means a very long coherence length () and a very narrow spectral linewidth ().