Solid angle unit

FOM = number of photons/unit time/solid angle/unit wavelength/unit circulating current (3-1)... 

Since Equation 14 determines the power of light energy per unit area, a solid angle unit receives... 

As main idea, PL intensity model was developed for the theoretical approach concerning an emission process in nanoclusters. A transition between the electronic cluster states j) and I k) manifested by a dipolar radiation are characterized by a single spectral line at the frequency (Oji(. The intensity of spectral line, per unit source volume and per solid angle unit, reads as follows ... 

A unifonn monoenergetic beam of test or projectile particles A with nnmber density and velocity is incident on a single field or target particle B of velocity Vg. The direction of the relative velocity m = v -Vg is along the Z-axis of a Cartesian TTZ frame of reference. The incident current (or intensity) is then = A v, which is tire number of test particles crossing unit area nonnal to the beam in unit time. The differential cross section for scattering of the test particles into unit solid angle dO = d(cos vji) d( ) abont the direction ( )) of the final relative motion is... 

Number of lesl particles scattered by one field dfy(i i jf. particle into unit solid angle per unit time dS2 Current of incident beam... 

Brightness. This is defined as the power emitted per unit area of the output mirror per unit solid angle and is extremely high compared with that of a conventional source. The reason for this is that, although the power may be only modest, as in, for example, a 0.5 mW helium-neon gas laser, the solid angle over which it is distributed is very small. 

Radiant flux per unit solid angle in a given direction. 

The distribution of orientation of the structural units can be described by a function N(0, solid angle sin 0 d0 dtp d Jt. It is most appropriate to expand this distribution function in a series of generalised spherical harmonic functions. 

The quantity N(6, cp, i//) sin ddddcpdi// represents the fraction of structural units oriented in the generalized solid angle sinOdOdtfidij/, with the following... 

Consider a coordinate system in which the orientation of the paramagnetic species is defined by the orthogonal axes and H is a vector as described in Fig. 11. The sphere has unit area and every orientation or point on the sphere is equally probable. Now the number of radicals with a magnetic field orientation between 0 and 0 + A0 and between and + A is given by the solid angle Afi where... 

Consider continuous radiation with specific intensity I incident normally on a uniform slab with a source function 5 = Bv(Tex) unit volume per unit solid angle to the volume absorption coefficient Kp and is equal to the Planck function Bv of an excitation temperature Tcx obtained by force-fitting the ratio of upper to lower state atomic level populations to the Boltzmann formula, Eq. (3.4). For the interstellar medium at optical and UV wavelengths, effectively S = 0. 

Two other definitions are important the power P of radiation is the energy of the beam that reaches a given area per second. The intensity / is the power per unit solid angle in a particular direction. Both are related to the square of the amplitude, and are often used interchangeably, but they are not synonymous. 

Consider the vector that lies along the z-axis of the molecular frame. It has orientation QL = (uP) in the laboratory frame. The conditional probability per unit solid angle, g(i2/ ft00), that this vector with orientation 20 at time... 

A laser is spatially coherent as is a conventional source that is infinitely small. Referring to Figure 8, this may be achieved by moving the observation point P to infinity, at which point a, the angle subtended at P, approaches zero as does the area of emission. We should point out, however, that brightness for a finite source is defined as power per unit area per unit solid angle. Therefore, achieving coherency in this manner reduces the intensity to zero and would require infinite exposure time. Fortunately we do not need perfect coherency, a point that will be treated in more detail later. 

For comparison the output power of a high-pressure mercury lamp (Osram HBO 200) also is listed. The reader has to consider, however, that the mercury lamp radiates this power into the unit solid angle (= 60°) distributed over the spectral range from 2000 to 6000.A, whereas the laser intensity is concentrated at a single wavelength and collimated in a beam with a very small divergence between 10 and 10" sterad. 

The SI unit of luminous flux, abbreviated hn. One lumen is the amount of luminous flux emitted in a unit solid angle of one steradian by a uniform point source having a luminous intensity of one candela. 2. The interior space of a tubular structure such as an intestine or artery. 

If the beam is divergent from an elementary cone of the solid angle (dfi) containing the given direction (9), then L = d P/(dOd5 cos 9). In this instance, the radiance has units of watts per square meter per steradian. 

Luminance is the luminous flux emitted per unit solid angle or per unit projected area of a surface in a light source it is a measure of brightness. 

Jauncey has recently described a corpuscular quantum theory of the scattering of polarized X-rays, in which a formula for the intensity of the scattering in any direction is derived. From this formula an expression for the linear scattering coefl cient per unit solid angle in any direction 4> may be obtained. In particular this linear scattering coefficient for the case where plane polarized X-rays are scattered in the plane of the electric vector of the primary X-rays is given by... 

The photoelectric cross-section o is defined as the one-electron transition probability per unit-time, with a unit incident photon flux per area and time unit from the state to the state T en of Eq. (2). If the direction of electron emission relative to the direction of photon propagation and polarization are specified, then the differential cross-section do/dQ can be defined, given the emission probability within a solid angle element dQ into which the electron emission occurs. Emission is dependent on the angular properties of T in and Wfin therefore, in photoelectron spectrometers for which an experimental set-up exists by which the angular distribution of emission can be scanned (ARPES, see Fig. 2), important information may be collected on the angular properties of the two states. In this case, recorded emission spectra show intensities which are determined by the differential cross-section do/dQ. The total cross-section a (which is important when most of the emission in all direction is collected), is... 

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