tâbeš-e rizmowj (#)
Fr.: rayonnement micro-onde
Electromagnetic radiation carried by → microwaves.
mowj-e milimetri (#)
Fr.: onde millimétrique
Microwaves with wavelengths between 1 and 10 millimeter, corresponding to frequencies between 300 GHz to 30 GHz. → millimeter-wave astronomy.
axtaršenâsi-ye mowjhâ-ye milimetri (#)
Fr.: astronomie millimétrique
That part of radio astronomy which uses electromagnetic waves in the range 1-10 millimeter to study various components of the Universe, in particular the chemistry of interstellar matter.
mowj-e degarâhangidé (#)
Fr.: onde modulée
A combination of two or more waves resulting in the production of
frequencies not present in the original waves, the new frequencies being
usually the sums and differences of integral multiples of the frequencies
in the original waves.
Fr.: onde de Moreton
A large-scale → shock wave observed in Hα on the Sun's → chromosphere that is generated by the impact of a → solar flare. Moreton waves expand outward at about 1,000 km/s, and may travel for several hundred thousand kilometers. They are accompanied by meter-wave radio bursts.
Named after the American astronomer Gail E. Moreton (1960, A.J. 65, 494); → wave.
Fr.: onde neutre
Same as → neutral mode.
Fr.: onde P
Fr.: longueur d'onde pic
The wavelength at which the radiant intensity of a source is maximum.
Fr.: onde périodique
An oscillatory motion in which each point is repeatedly displaced at equal time intervals.
mowj-e taxt (#)
Fr.: onde plane
A wave whose wavefronts of constant phase are infinite parallel planes normal to the direction of propagation.
Fr.: lame quart d'onde
A plate of doubly refracting material cut parallel to the optic axis of the crystal and of such a thickness that a phase difference of 90° is introduced between the ordinary and extraordinary rays for light of a particular wavelength. → half-wave plate.
mowj-e râdioyi (#)
Fr.: ondes radio
The → electromagnetic radiation with the longest → wavelengths (and lowest energies), ranging from 0.3 mm to several km. Radio waves form a very broad category, which includes the → submillimeter waves (with a wavelength of 0.3-1 mm) and → microwave regions (1 mm to several cm).
Fr.: longueur d'onde radio
Fr.: onde de raréfaction
A pressure wave in a fluid generated by rarefaction. It travels in the opposite direction to that of a shock wave in the medium.
Fr.: onde retardée
An ordinary electromagnetic wave that goes forward with time. → Maxwell's equations are indifferent to the distinction between past and future. It is therefore permissible for the electromagnetic waves to go backward in time. Forward-in-time waves are called retarded, as they arrive after they are sent by the transmitter. Backward-in-time waves are called → advanced wave.
Fr.: onde de Rossby
A wave on a uniform current in a two-dimensional non-divergent fluid system, rotating with varying angular speed about the local vertical.
Fr.: onde S
→ shear wave.
Fr.: onde scalaire
mowj-e laez-yi (#)
Fr.: onde sismique
An → elastic wave generated in the → Earth by an → impulse such as an → earthquake or an → explosion. Seismic waves may travel either along or near the Earth's surface or through the Earth's interior.
Shack-Hartmann wavefront sensor
hessgar-e pišân-e mowj-e Shack-Hartmann
Fr.: analyseur de front d'onde
An optical device, a modern version of the → Hartmann test, used for analyzing the wavefront of light. Theses sensors can be used to characterize the performance of optical systems. Moreover, they are increasingly used in real-time applications, such as → adaptive optics to remove the wavefront distortion before creating an image. It consists of a microlens array placed in front of a CCD array. A planar wavefront that is transmitted through a microlens array and imaged on the CCD array will form a regular pattern of bright spots. If, however, the wavefront is distorted, the light imaged on the CCD will consist of some regularly spaced spots mixed with displaced spots and missing spots. This information is used to calculate the shape of the wavefront that was incident on the microlens array.
Named after the German astronomer Johannes Hartmann (1865-1936), who first developed the method, and R. V. Shack, who in the late 1960s replaced the screen by a microlens array; → wavefront; → sensor.