Influence of the measurement configuration on the results of Raman microspectroscopy of human hair

Increasing interest in spectroscopic studies of human hair raises the question about the accuracy of measurement of their spectra and requires optimisation of experimental facilities. An original method of obtaining transverse hair sections without using a microtome and chemical influence is proposed. The results obtained by confocal Raman microspectroscopy of human hair differently oriented with respect to the optical axis of the measuring setup are compared. It is shown that, in addition to expected changes in the spectra measured at different distances from the hair periphery in the direction to its centre, the spectra measured in the case of hair excitation perpendicular and parallel to its axis are also considerably different.

Angular responsivity of ground and space-based direct solar irradiance radiometers

The angular response setup of PMOD/WRC was modified to facilitate measurements of the narrow field of view of radiometers for direct solar irradiance. First, The pointing of the JTSIM-DARA radiometer was measured four times during its construction in the optic laboratory of PMOD/WRC. The final offset of the pointing before shipping relative to the optical axis, defined by a removable alignment cube, is 1.07° / 0.67° (β/γ-axis) for the four-quadrant sensor and 0.095°/-0.017° for the radiometer cavity A. Next to JTSIM-DARA the DARA for the occulter of the satellite Proba-3 was characterised at PMOD/WRC. First tests of the pointing have been carried out and the final pointing characterization will be carried out in summer 2021. Finally, the angular response setup was also used the angular responsivity of solar direct irradiance filter radiometers. The first test was carried out using Precision Filter Radiometer (PFR) F-064.

Terahertz microscope with oblique subwavelength illumination: design principle

It is shown that the image contrast in the air when using a microscope based on dielectric microparticles with a size of the order of wavelength can be significantly enhanced with the help microparticles that provide the formation of the radiation localisation region at an angle to the direction of radiation incidence (at an angle to the optical axis). For this purpose, a screen is placed in front of the particle, which blocks part of the incident beam, forming a photonic hook or a photonic jet (terajet) with oblique illumination in the near field.

Flux profile at focal area of concentrating solar dishes

We analytically, experimentally and computationally explore the solar radiation flux distribution in the interior region of a spherical mirror and compare it to that of a paraboloidal one with the same aperture area. Our investigation has been performed in the framework of geometrical optics. It is shown that despite one can assign a quasi focus, at half the radius, to a spherical mirror, the light concentration occurs as well on an extended line region which starts at half-radius on the optical axis. In contrast to a paraboloidal concentrator, a spherical mirror can concentrate the radiation parallel to its optical axis both in a point-focus and in a line-focus manner. The envelope of the reflected rays is also obtained. It is shown that the flux distribution has an axial symmetry. The radial dependence of the flux on a flat circular receiver is obtained. The flux longitudinal dependence is shown to exhibit three distinctive regions in the interval [0, R] (R is mirror radius). We obtain the radiational (optical) concentration ratio characteristics and find the optimal location of the flat receiver of a given size at which the concentration ratio is maximised. In contrast to a parabolic mirror, it is shown that this location depends on the receiver size. Our findings offers that in spherical mirrors one can alternatively use a line receiver and gains a considerable thermal energy harvest. Our results are supported by Monte Carlo ray tracing performed by Zemax optical software. Experimental validation has been performed in lab with a silver-coated lens as the spherical mirror.

Evaluate the impact of optical axis stability on the exoplanet detection

For detecting exoplanets with high precision, using the angular distance between the two stars to detect the periodic motion of the star will be a better choice. This approach can avoid importing the position error of the reference catalog in the process that using the traditional photographic plate to derive the star position. At the precision level of microarcseconds, the error caused by optical axis deviation is not negligible. In this paper, we evaluate the impact of the stability of the optical axis on the relative angular distance measurement from the aspects of theoretical analysis and numerical simulation. When the angular distance error limit of 1~microarcsecond is given, the upper limit of optical axis deviation is estimated to be 68~milliarcsecond. In addition, when limiting the deviation of the optical axis, we give the corresponding error allowance of angular distance measurement. Moreover, we also discuss the way to resolve the problem of CCD distortion and focal length change on the measurement of angular distance. The work in this paper is of guiding significance to the design of the telescope.

Generating a 3D optical needle array with prescribed characteristics

Unlike the general optical needle along the optical axis, we propose a method to generate a three-dimensional (3D) array formed by optical needles with prescribed length and polarization direction. Moreover, the geometric model of the created array can be specified. With the aid of antenna array pattern synthesis theory and time reversal technology, a virtual uniform line source (ULS) antenna array arranged regularly near the confocal region of two high numerical apertures objectives is employed to obtain the required illumination in the pupil plane for creating the desired focal fields. Numerical results demonstrate that there is a one-to-one correspondence between the focal field and the virtual ULS antenna array elements. The length and polarization direction of the optical needles depends on the length and spatial direction of the virtual ULS antenna. The peculiarities of the focal field array, such as the polarization, length, number, spatial position and array structure, can be customized according to application requirements. The created optical needle array can be used for such application as 3D synchronous particle acceleration and manipulation, 3D parallel fabrication.

Effect of Corneal Tilt on the Determination of Asphericity

To quantify the effect of levelling the corneal surface around the optical axis on the calculated values of corneal asphericity when conic and biconic models are used to fit the anterior corneal surface. This cross-sectional study starts with a mathematical simulation proving the concept of the effect that the eye’s tilt has on the corneal asphericity calculation. Spherical, conic and biconic models are considered and compared. Further, corneal asphericity is analysed in the eyes of 177 healthy participants aged 35.4 ± 15.2. The optical axis was determined using an optimization procedure via the Levenberg–Marquardt nonlinear least-squares algorithm, before fitting the corneal surface to spherical, conic and biconic models. The influence of pupil size (aperture radii of 1.5, 3.0, 4.0 and 5.0 mm) on corneal radius and asphericity was also analysed. In computer simulations, eye tilt caused an increase in the apical radii of the surface with the increase of the tilt angle in both positive and negative directions and aperture radii in all models. Fitting the cornea to spherical models did not show a significant difference between the raw-measured corneal surfaces and the levelled surfaces for right and left eyes. When the conic models were fitted to the cornea, changes in the radii of the cornea among the raw-measured corneal surfaces’ data and levelled data were not significant; however, significant differences were recorded in the asphericity of the anterior surfaces at radii of aperture 1.5 mm (p < 0.01). With the biconic model, the posterior surfaces recorded significant asphericity differences at aperture radii of 1.5 mm, 3 mm, 4 mm and 5 mm (p = 0.01, p < 0.01, p < 0.01 & p < 0.01, respectively) in the nasal temporal direction of right eyes and left eyes (p < 0.01, p < 0.01, p < 0.01 & p < 0.01, respectively). In the superior–inferior direction, significant changes were only noticed at aperture radii of 1.5 mm for both right and left eyes (p = 0.05, p < 0.01). Estimation of human corneal asphericity from topography or tomography data using conic and biconic models of corneas are affected by eyes’ natural tilt. In contrast, the apical radii of the cornea are less affected. Using corneal asphericity in certain applications such as fitting contact lenses, corneal implant design, planning for refractive surgery and mathematical modelling when a geometrical centre of the eye is needed should be implemented with caution.

Spiraling light: from donut modes to a Magnus effect analogy

The insight that optical vortex beams carry orbital angular momentum (OAM), which emerged in Leiden about 30 years ago, has since led to an ever expanding range of applications and follow-up studies. This paper starts with a short personal account of how these concepts arose. This is followed by a description of some recent ideas where the coupling of transverse orbital and spin angular momentum (SAM) in tightly focused laser beams produces interesting new effects. The deflection of a focused light beam by an atom in the focus is reminiscent of the Magnus effect known from aerodynamics. Momentum conservation dictates an accompanying light force on the atom, transverse to the optical axis. As a consequence, an atom held in an optical tweezer will be trapped at a small distance of up to λ/2π away from the optical axis, which depends on the spin state of the atom and the magnetic field direction. This opens up new avenues to control the state of motion of atoms in optical tweezers as well as potential applications in quantum gates and interferometry.