Circular Polarization Fraction Research Articles

Depolarization of light in turbid media: a scattering event resolved Monte Carlo study

Details of light depolarization in turbid media were investigated using polarization-sensitive Monte Carlo simulations. The surviving linear and circular polarization fractions of photons undergoing a particular number of scattering events were studied for different optical properties of the turbid media. It was found that the threshold number of photon scattering interactions that fully randomize the incident polarization (defined here as <1% surviving polarization fraction) is not a constant, but varies with the photon detection angle. Larger detection angles, close to backscattering direction, show lower full depolarization threshold number for a given set of sample's optical properties. The Monte Carlo simulations also confirm that depolarization is not only controlled by the number of scattering events and detection geometry, but is also strongly influenced by other factors such as anisotropy g, medium linear birefringence, and the polarization state of the incident light.

Measurement of optical rotation and phase retardance of optical samples with depolarization effects using linearly and circularly polarized probe lights

This paper presents an experimental technique for measuring the optical rotation, depolarization, and phase retardance of optical samples. In the proposed approach, the optical properties of the sample are derived using a Stokes–Mueller matrix formalism in conjunction with linearly and circularly polarized probe lights. For a compound sample comprising a half-wave plate positioned in front of glucose solutions with concentrations ranging from 0 to 1.2 g/dl, the average normalized error in the measured rotation angle is determined to be 3.11% when using a linearly polarized light. The average surviving linear and circular polarization fractions of the glucose solutions are determined to be 1.0252 and 0.9945. The average normalized error in the measured retardance of the half-wave plate is 3.45%. When measuring a compound sample comprising a half-wave plate positioned in front of the scattered glucose solutions with turbidities from 0% to 50% by the addition of milk, experimental results show that the induced rotation angle increased as the turbidity increased, whereas both surviving linear and circular polarization fractions decreased as the turbidity increased. The effect of the turbidity on rotation angle is more significant than that on both surviving linear and circular polarization fractions. The average normalized error in the measured retardance of the half-wave plate is 1.43%. Consequently, a simplified geometry of the polarimeter is proposed to independently estimate the rotation angle, surviving linear and circular polarization fractions, and retardance from the derived viable algorithm.

Experimental Observations of O-X-B Heating of Overdense Plasmas in CHS

Evident increases in the plasma stored energy by applying 54.5-GHz electron cyclotron (EC) waves have been observed in overdense plasmas sustained by neutral beam injection in the Compact Helical System. The heating effect was seen even for a high density of 8 × 1019 m-3, that is, more than twice the cutoff density of 3.8 × 1019 m-3 of the 54.5-GHz waves. The 54.5-GHz EC wave beams were obliquely injected into high-density plasmas. Dependences of the heating effect on the experimental conditions such as the polarization and the injection power of the EC waves, and the magnetic field were investigated. A higher left-hand circular polarization fraction and higher injection power resulted in a longer plasma duration time and a higher increment of the plasma stored energy. Variation of the electron temperature profile in the magnetic field scan experiment shows the power deposition in the plasma core region inside the plasma cutoff layer. These experimental results show that the main cause for this heating mechanism is electron Bernstein wave heating via an Ordinary-eXtraordinary-Bernstein (O-X-B) mode conversion process.

Magnetic-field-induced alignment-to-orientation conversion in sodium.

We report a detailed investigation of excited-state alignment-to-orientation conversion in the presence of an external magnetic field. This counterintuitive phenomenon occurs under intermediate-coupling conditions. A weak, linearly polarized, cw laser beam was used to excite and align the Na 3${\mathit{P}}_{3/2}$ state in an atomic beam along the z direction. The degree of circular polarization of the resulting fluorescence was detected along the z direction as a function of magnetic-field strength. The spectrally integrated transitions originating from individual F levels of the 3${\mathit{S}}_{1/2}$ state yield a maximum circular-polarization fraction of \ensuremath{\sim}40%; integrating the circular polarization over all the allowed 3${\mathit{S}}_{1/2}$-3${\mathit{P}}_{3/2}$ transitions gives rise to an \ensuremath{\sim}8% effect. The results are predicted by the Breit formula, which is in excellent agreement with our observations.

Polarized light emission after grazing ion-surface scattering due to capture of spin-polarized electrons.

We have observed the capture of polarized electrons into excited terms of atoms after the interaction of fast ions with a magnetized Fe(110) surface at grazing incidence. The spin polarization of captured electrons results in a modified circular polarization fraction of fluorescence light. This experiment has considerable potential as a new analytical tool for investigating surface magnetism with extreme surface sensitivity, as a method for detailed studies of ion-surface interaction, and as a means to produce nuclear spin-polarized beams.

Magnetically induced circular polarization.

Helium atoms excited to an aligned (1s3d${)}^{3}$D state are produced by electron impact parallel to a magnetic field. The initial alignment of the atomic state evolves into an orientation with finite angular momentum along the magnetic field direction and thus gives rise to a circularly polarized component in the (1s3d${)}^{3}$D\ensuremath{\rightarrow}(1s2p${)}^{3}$P radiation propagating parallel to the magnetic field. Circular-polarization fractions of a few percent are observed, in general agreement with theory. The measured polarization fraction is found to be pressure dependent, indicating that secondary excitation and cascade processes must be included for a complete description.

Orientation of HE I n1D- and n3D-terms after ion beam tilted foil interaction

The circular polarization fraction S I of the emitted light of transitions from He I n 1D and n 3D(3 ⩽ n ⩽ 7 is measured after the interaction of fast He +-ions with a thin carbon foil which is tilted with respect to the beam axis. The dependence of the polarization on the irradiation dose of the foil, on the current density of the incoming ions, on the principal quantum number, and on the electronic spin is investigated. The results are compared with data obtained at the ion-surface interaction at grazing incidence.

Influence of the Stark-effect on the orientation of Rydberg-states in highly ionized nitrogen after ion beam surface interaction at grazing incidence

The orientation in the angular momentum distribution of highly ionized N-atoms after the interaction of N-ions with energies up to 15 MeV with a polycrystalline Cu-surface at grazing incidence is investigated by the circular polarization fraction S I in fluorescent light. In Rydberg-states of N V, N VI and N VII a dramatic variation of this orientation with respect to the ion-energy and the angle of incidence is observed. We interpret the data in terms of a modification of the collision induced orientation via the Stark-effect in the electric field in the vicinity of the surface caused by the image charge potential of the receding ion.

Ten-channel eikonal treatment of electron-metastable-helium collisions: Differential and integral cross sections for2P1,3andn=3excitations from He (2S1,3) and the (λ, χ, Π) parameters

We present a ten-channel eikonal treatment of the $2^{1,3}P$, $3^{1,3}S$, $3^{1,3}P$, and $3^{1,3}D$ excitations of atomic helium, initially in the $2^{1,3}S$ metastable states, by incident electrons with energy $E$ (eV) in the range $5\ensuremath{\le}E\ensuremath{\le}100$. Integral and differential inelastic cross sections are obtained. Also, the angular-correlation parameters $\ensuremath{\lambda}$ and $\ensuremath{\chi}$, which respectively provide the relative population and relative phase of the collisionally excited $P$ magnetic substates, and the circular polarization fraction $\ensuremath{\Pi}$ of radiation emitted from these $P$ states, are determined as functions of scattering angle $\ensuremath{\theta}$ and $E$. No measurements exist to date. The principle of detailed balance is explicitly demonstrated for the $2^{1}S\ensuremath{-}1^{1}S$ superelastic collision.

A ten-channel eikonal treatment of differential and integral cross sections and of the (λ,χ) parameters for the n=2 and 3 excitations of helium by electron impact

A ten-channel eikonal treatment of the n=2 and 3 collisional excitations of helium by incident electrons with energy E (eV) in the range 40<or=E<or=500 is performed. Differential and integral inelastic cross sections are obtained, together with theoretical predictions of the ( lambda , chi ) parameters which provide, as functions of scattering angle theta and E, the orientation and alignment vectors and the circular polarization fraction of the radiation emitted from the n1P levels. The results are in satisfactory agreement with recent measurements.