Advocating a statistical definition for the BRDF

The definition of BRDF as a ratio of radiance to irradiance assumes that the geometrical optics framework applies, implicitly meaning that spatial coherence and diffraction of light have no significant effect in the reflection process. However, recent applications of BRDF push at increasing the angular resolution and thus at reducing the solid angles for illumination and collection. Therefore speckle, an optical effect inherent to the stochastic nature of scattering objects, becomes apparent. We suggest that BRDF should be redefined as the statistical average over that effect.

Comment on ‘Do electromagnetic waves always propagate along null geodesics?’

We study the propagation of Maxwellian electromagnetic waves in curved spacetimes in terms of the appropriate geometrical optics limit, notions of signal speed, and minimal coupling prescription from Maxwellian theory in flat spacetime. In the course of this, we counter a recent major claim by Asenjo and Hojman (2017) to the effect that the geometrical optics limit is partly ill-defined in Gödel spacetime; we thereby dissolve the present tension concerning established results on wave propagation and the optical limit.

Numerical Analysis of Optical Trapping Force Affected by Lens Misalignments

Geometrical optics approximation is a classic method for calculating the optical trapping force on particles whose sizes are larger than the wavelength of the trapping light. In this study, the effect of the lens misalignment on optical force was analyzed in the geometrical optics regime. We used geometrical optics to analyze the influence of off-axis placement and the tilt of the lens on the trapping position and stiffness in an optical trap. Numerical calculation results showed that lens tilting has a greater impact on the optical trap force than the off-axis misalignments, and both misalignments will couple with each other and cause a shift of the equilibrium point and the asymmetry of the optical trap stiffness in different ways. Our research revealed the asymmetry in optical traps caused by lens misalignment and can provide guidance for optimize lens placement in future experiments.

Enhancing students collaboration skills in learning geometrical optics trough the ICARE learning model at Kabawo

This study aims to see the improvement of students’ collaboration skills by applying the ICARE learning model to geometrical optics material. The method used is pre-experimental with one group prettest-posttest design. The sample used study were 31 students of class XI IPA2 with random sampling technique. The main instrument in this research is the researcher himself, while the supporting instrument is a written test in the form of an essay test and analyzed using the rubik’s collaboration skills. To find out the improvement of students’ collaboration skills, it was done by comparing the pretest and posttest scores and then analyzed using N-Gain. Based on the results of research using the ICARE learning model in improving students’ collaboration skills based on the N-Gain value, where the average N-Gain value is 40.05. This shows that students’ collaboration skills have increased in the moderate category after applying the ICARE learning model, while to see the implementation of the learning model using an observation sheet with a score of good category. The recommendation in this study is to pay more attention to the time management allocated for each aspect of ICARE so that each stage in ICARE can be carried out properly.

Laue diffraction of X-ray microbeams by multilayers

Laue diffraction theory of X-ray microbeams in multilayers (MLs) is developed. The solution for calculating X-ray reciprocal space maps is obtained. The pendulum (Pendellösung) effect for perfect and imperfect MLs is shown. The numerical simulation of Laue diffraction in Mo/Si multilayers with boundary conditions in the case of geometrical optics and the Fresnel approximation is carried out. It is shown that for X-ray microbeams one should to take into account the diffraction of X-ray waves at the edges of slits (collimators) of the diffraction scheme.

Convex Obstacles from Travelling Times

We consider situations where rays are reflected according to geometrical optics by a set of unknown obstacles. The aim is to recover information about the obstacles from the travelling-time data of the reflected rays using geometrical methods and observations of singularities. Suppose that, for a disjoint union of finitely many strictly convex smooth obstacles in the Euclidean plane, no Euclidean line meets more than two of them. We then give a construction for complete recovery of the obstacles from the travelling times of reflected rays.