Oblique Incidence Geometry Research Articles

Excitionic light reflection and absorption in semiconductor microcavities at oblique incidence

Exact calculations of TE and TM polarized light reflection and absorption spectra have been performed for a semiconductor microcavity containing an embedded quantum well (QW) in the QW exciton resonance region. The approach is based on the transfer matrix method and theory of nonlocal dielectric response. Rabi splitting of polariton branches as function of the incidence angle has been calculated. For the first time, the triplet structure has been found in reflectivity and absorption spectra at the light hole exciton resonance in oblique incidence geometry and the dispersion of light hole exciton polaritons is calculated.

The application of ion optics in time-of-flight mass spectrometry

The ion time-of-flight (TOF) through accelerating, decelerating and reflecting fields is the key to determining ion optical properties and the resolution of most TOF mass spectrometers. The initial velocity- and position-induced energy spread aberrations, as well as the role of the time lag, are considered for linear drift TOF mass spectrometers. Peak shapes for stable and metastable ions are presented for these instruments. On a specific geometry the resolution is estimated for realistic assumptions. The post source focusing method ion-optical capabilities are discussed. The ion-optical properties of the single and double stage mirrors with first and second order energy focusing in time respectively are detailed for linear and packet oblique incidence geometries. Again, illustrative peak shapes for stable and metastable ions are given. The resolution of typical mirror TOF mass spectrometers was calculated and compared with those of linear drift instruments. The TOF ion optical properties of the parabolic potential with plane and axial symmetry are described for mirrors and accelerating systems. Matrix elements are given for cylindrical electrostatic mirrors, applicable to electrostatic particle guides. Means to focus transversally and to tune ion packets to the detector i.e. electrostatic lenses and plane deflectors are briefly mentioned. The TOF basic parameters of multisector electrostatic systems are exemplified on a three deflector geometry. The main TOF ion optical parameters of four magnetic-sector analyzers are also specified.

Two-beam coupling measurements of grating phase in a photorefractive polymer

We investigate in detail the grating properties of a recently discovered organic photorefractive polymer as a function of electric field by using two-beam coupling. Using an oblique-incidence geometry, we present measurements of index and absorption grating phase relative to the intensity interference pattern as well as measurements of the amplitude of both the absorption and index gratings. We find that in low electric fields a weak in-phase grating (possibly photochromic) and the low electro-optic coefficient prevent observation of a phase-shifted photorefractive grating. However, in moderate-to-high electric fields a much stronger photorefractive index grating with a phase shift approaching 90° dominates. The presence of an index grating with a 90° phase shift at high fields provides strong evidence that these polymers are indeed photorefractive.

Observation of longitudinal excitons in uniaxially-strained RbI and KI crystals

Polarized reflection spectra of uniaxially-strained RbI and KI crystals have been measured in oblique-incidence geometry at 11 K. A structure has been observed in the p-polarized spectrum on the high-energy side of the 1 s exciton peak. This structure is attributed to the longitudinal exciton, which is caused by a uniaxial-stress field.

Computer aided design and verification of megavoltage tissue compensators for oblique beams.

A computer based radiotherapy dose compensator system is presented. A plane of uniform dose (pud) is chosen which passes through the central axis at a reference depth in the patient. The pud is oriented at an arbitrary angle. Tissues thicknesses are the ray line distances from the patient surface to the pud. Relative dose estimates on the pud are derived from tissue-air ratio, tissue-maximum ratio, or tissue-phantom ratio tables interpolated for field size and tissue thickness. An inverse square law correction is also applied. Compensator thicknesses are calculated from measured effective attenuation coefficients to attenuate the beam by a factor proportional to the estimated dose on the pud. Water phantom measurements for 60Co for both oblique incidence and wedge geometries demonstrate dose uniformity to better than +/- 4%. Dose measurement with radiographic films sandwiched between the two halves of a wax phantom verify adequate compensation for neck irradiation by 60Co opposed lateral beams and 6-MV x-ray inferiorly angled lateral beams. Compensator factors used for absolute dose determination are accurate to better than +/- 3%. The dose modeling routine, QCBEAM, is found to be sufficiently accurate for routine compensator verification for these geometries.

Influence of entropy-fluctuation on the Rayleigh spectrum

We discuss the light scattering cross section due to entropy-fluctuation on the region of the central peak of the spectrum. A back-scattering oblique incidence geometry is used in our theoretical calculations which are based on the linear response function approach. Our results show that the power spectrum varies significantly with the incident angle and frequency and so does the light scattering cross section. The results are illustrated with numerical calculations for silicon.

On the entropy-fluctuation contribution to Rayleigh scattering of light

We discuss the power spectrum due to entropy fluctuations near the surface for quasielastic Rayleigh scattering in isotropic crystals. A back-scattering, oblique incidence geometry, is used in our theoretical calculations. Some interesting novel aspects are presented and their importance is discussed.

Absolute measurements of the elastic constants of nematic liquid crystals by light scattering

The absolute determination of the three Frank elastic constants of nematic liquid crystals (MBBA) has been performed by light scattering differential-cross-section measurements. The use of an optimized oblique-incidence geometry allows us to reduce several causes of error, like multiple scattering and spurious scattering due to crystal defects. All the three elastic constants have been obtained on the same specimen homeotropically aligned without changing the alignment of the director, thus reducing boundary distortion effects. It will be shown that the new technique has several advantages with respect to previously used ones. A full description of the experimental arrangement and a discussion of the obtained results is given in the text.