cohere hamdusidan (#) Fr.: adhérer, être cohérent 1) To stick together; be united; hold fast, as parts of the same mass. From L. cohaerere "to cleave together," from → com- "together," + haerere "to stick." Hamdusidan, from ham- "together," → com-, + dusidan (Dehxodâ) "to stick, to adhere," → adhere. |
coherence hamdusi (#) Fr.: cohérence The property of two or more electromagnetic waves when they are in fixed phase relationship over time. If the crests and troughs of the waves meet at the same time and place they are said to be in phase. |
coherence area pahne-ye hamdusi Fr.: zone de cohérence Of an → electromagnetic wave, the area of a surface perpendicular to the direction of → propagation, over which the wave maintains a specified → degree of coherence. According to the van Cittert-Zernike theorem, the coherence area is given by: A_{c} = D^{2}λ^{2}/(πd^{2}), where d is the diameter of the light source and D is the distance away. The coherence area is an important parameter in photon correlation experiments. In the → Young's experiment the → interference pattern is only seen if slits are inside one coherence area. |
coherence length derâzâ-ye hamdusi Fr.: longueur de cohérence The distance over which an → electromagnetic wave train maintains a specified → degree of coherence. The coherence length is related to the → coherence time multiplied by vacuum → velocity of light. |
coherence time zamân hamdusi Fr.: temps de cohérence The time over which a propagating → electromagnetic wave may be considered → coherent. The coherence time of an interferometer is the interval during which the fringe phase remains stable. |
coherent hamdus (#) Fr.: cohérent Two or more wave sources are said to be coherent sources if the phase difference between a pair of points, one in each source, remains constant. Coherent, adj., → coherence. |
coherent light nur-e hamdus (#) Fr.: lumière cohérente Light waves that have the same wavelength and possess a fixed phase relationship, as in a laser. |
coherent optics nurik-e hamdus Fr.: optique cohérente A branch of optics that uses coherent radiation to produce holographic three-dimensional images of objects. |
coherent scattering parâkaneš-e hamdus Fr.: diffusion cohérente A scattering process in which the scattered radiation bears the same frequency and phase as the incident radiation. → coherent; → scattering. |
coherent source xan-e hamdus Fr.: source cohérente One of two light beams derived from the same source in → interference experiments. It is impossible to obtain interference from two separate sources because their → wavefronts do not have a constant → phase difference. In → Young's experiment, → Fresnel's biprism, → Fresnel's mirrors, and → Lloyd's mirror the two sources always have a point-to-point correspondence of phase, since they are both derived from the same source. |
degree of coherence dareje-ye hamdusi Fr.: degré de cohérence The extent of → coherence of an → electromagnetic wave, as indicated by a → dimensionless number. Since interference takes place when waves are → coherent, using a → Young's experiment, the degree of coherence is measured from the → fringe → visibility, V. It is defined as the ratio V = (I_{max} - I_{min}) / (I_{max} + I_{min}), where I_{max} is the intensity at a maximum of the → interference pattern, and I_{min} is the intensity at a minimum of the interference pattern. The electromagnetic wave is considered to be highly coherent when the degree of coherence is about 1, incoherent for nearly zero values, and partially coherent for values between 0 and 1. |
incoherent waves mowjhâ-ye nâhamdus (#) Fr.: ondes incohérentes The lack of a fixed phase relationship between two or more waves. → coherent. Incoherent, from negation prefix → in- + → coherent; → wave. |
non-coherent radiation tâbeš-e nâhamdus (#) Fr.: rayonnement incohrént Radiation having waves that are out of phase in space and/or time; radiation which is not → coherent. |
noncoherent scattering parâkaneš-e nâhamdus Fr.: diffusion incohérente The absorption of a photon and its re-emission at a different frequency (in the observer's frame of reference) by scattering atoms. → non-; → coherent scattering. |
spatial coherence hamdusi-ye fazâyi Fr.: cohérence spatiale In a wave train, a correlation between the phases of waves at points separated in space at a given time. |
temporal coherence hamdusi-ye zamâni Fr.: cohérence temporelle A measure of the correlation between the phases of an → electromagnetic wave at different points along the direction of propagation. Temporal coherence indicates to what extent a source is monochromatic. Imagine a source emitting waves with wavelength λ ± Δλ. Waves with wavelength λ and λ + Δλ, which at some point in space constructively interfere, will no longer constructively interfere after some path length l_{c} = λ^{2}/(2πΔλ); l_{c} is called the → coherence length. |