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Light also has a polarization, which is the direction in which the electric or magnetic field oscillates. Unpolarized light is composed of incoherent light waves with random polarization angles. The electric field of the unpolarized light wanders in every direction and changes in phase over the coherence time of the two light waves.
Likewise if a coherent-state light beam is partially absorbed, then the remainder is a pure coherent state with a smaller amplitude, whereas partial absorption of non-coherent-state light produces a more complicated statistical mixed state. [11]
The light from stars (other than the Sun) arrives at Earth precisely collimated, because stars are so far away they present no detectable angular size.However, due to refraction and turbulence in the Earth's atmosphere, starlight arrives slightly uncollimated at the ground with an apparent angular diameter of about 0.4 arcseconds.
The second order coherence for thermal, stellar and coherent light as a function of time delay. τ 0 {\displaystyle \tau _{0}} is the coherence length of the light beam. Similar to the case of Young's double slit experiment, the classical and the quantum description lead to the same result, but that does not mean that two descriptions are ...
Nevertheless, the intuitive pure-frequency heterodyne concept still holds perfectly for the wideband case provided that the signal and LO are mutually coherent. Crucially, one can obtain narrow-band interference from coherent broadband sources: this is the basis for white light interferometry and optical coherence tomography.
A coherent state, as output by a laser far above threshold, has Poissonian statistics yielding random photon spacing; while a thermal light field has super-Poissonian statistics and yields bunched photon spacing. In the thermal (bunched) case, the number of fluctuations is larger than a coherent state; for an antibunched source they are smaller ...
In physics, coherence length is the propagation distance over which a coherent wave (e.g. an electromagnetic wave) maintains a specified degree of coherence. Wave interference is strong when the paths taken by all of the interfering waves differ by less than the coherence length. A wave with a longer coherence length is closer to a perfect ...
While coherent states belong to the semi-classical states, since they can be fully described by a semi-classical model, [8] squeezed states of light belong to the so-called nonclassical states, which also include number states (Fock states) and Schrödinger cat states.