Maria Luisa Calvo

Neutron optics is a branch of both neutron physics and quantum physics that focuses on the study of the optical properties of slow neutrons and their dual behavior as both waves and particles. In previous research, we developed a mathematical framework based on Dirichlet boundary conditions to describe the propagation of slow neutrons in space. This approach facilitated the creation of an innovative algorithm distinguished by its computational efficiency and versatility. We applied this algorithm to the digital computation of hologram recording and reconstruction for wavelengths typical of thermal neutrons. The results demonstrate that the algorithm provides significant advantages, including rapid computation and broad applicability. It effectively handles scenarios analogous to those encountered in classical holography and shows promise for extension to other areas of physical interest.

The International Commission for Optics (ICO) under the leadership of Prof Anna Consortini: a fruitful period for the optics and photonics world community

The interaction of an incoming slow neutron with a straight semi-infinite material waveguide (physically, a very lengthy one) located in vacuum (clad) in the infinite three-dimensional (3D) space is studied. The waveguide creates an attractive potential on the neutron. The physical quantum-mechanical wave phenomena are: (i) reflection and scattering of the neutron by the waveguide and (ii) its confined propagation along the latter, in specific propagation modes. The direct application of standard scattering integral equations meets several difficulties, arising mainly from the infinite length of the waveguide and (ii). New and more convenient 3D scattering integral equations are proposed and discussed, using suitable Green functions, adequate for the semi-infinite waveguide and accounting for (i) and the above difficulties. Approximate formulae for the probability amplitudes and fluxes for (i) and (ii) are given: in particular, the formulas for slow neutron confined propagation extend the ones given previously for optical waveguides. Some detailed applications and numerical computations for two-dimensional media and waveguides are presented.

In this article we report on the activities in Spain related to the celebration of the International Day of Light (IDL). The Spanish Committee for the IDL was constituted in 2017, as a continuation of the previous Committee for the International Year of Light (2015). This Committee involves different academic, scientific and industrial partners in Spain related to light science and light technologies, and develops actions to promote and disseminate the IDL activities. After the success of the 2018 and 2019 editions, the 2020 IDL celebration has been totally affected by the Covid-19 pandemic, and most of the programmed events were cancelled. Nevertheless, some on-line activities were developed. The aim of this work is to review the IDL impact in Spain in these last three years.

In neutron optics, we analyse the propagation of slow (thermal) neutrons along a semi-infinite waveguide limited by a large repulsive potential (reminding the propagation of light along an optical fibre). We set an ideal case of a straight empty two-dimensional semi-infinite waveguide limited by an infinitely repulsive potential (Dirichlet conditions on its boundaries). The neutron wave function is given through an integral representation involving the incoming wave with energy E, Green’s function and certain functions defined on the boundaries. The latter functions follow from the Dirichlet conditions, thereby proposing a new formalism in neutron optics. We develop various approximations (through Fourier and Hilbert transforms) and numerical computations. We get: (a) the expected extinction of the incoming wave for very large penetration into the waveguide, (b) the generation of propagation modes and their number for suitably large penetration, as E increases, (c) an estimate of the critical angle.

In this chapter we introduce the basic concepts of the neutron as a particle, its description under quantum-mechanical formalism, properties and main phenomena observed according to its wave-particle nature. We introduce, as well, some main current applications under the so-called field of neutron optics.

Neutron optics is the branch of quantum physics devoted to the study of the optical properties of slow neutrons and their behavior as wave-particles. Slow neutrons beams (with typical energy the order of 0.025 eV, known as thermal neutrons, and also smaller) can propagate confined in guides of various transverse dimensions, longitude and geometries, under total internal reflection conditions, like in the case of classical optical waveguides. We study the properties and possible applications of neutron waveguides with small transverse dimensions. In particular, we have implemented a new algorithm to simulate neutron beams as they are confined in particular waveguides. The results, obtained from a new analytical formalism, are compared with standard numerical methods as the FDTD and, then, enhance the feasibility for recreating the beam structure as the later propagates inside the waveguide.

We studied the propagation of slow neutrons and their waveguiding properties in certain suitable thin films where Ti and Si play a key role, having in mind their possible use in Boron Neutron Capture Therapy (BNCT) of small tumors. In PBSi2017 we presented a general overview and some specific proposals for improved focalization of slow neutrons (at and a bit below one micron, with propagation up to about 1 m. with relatively small attenuation), by omitting a good number of quantitative aspects. The present work, based upon our presentation in PBSi2018, extends our previous proposals in PBSi2017 and provides more quantitative descriptions of part of them. Neutron wavelengths versus characteristic dimensions of the waveguides in our proposals typically require quantum-mechanical analysis: specifically, the description of the confined neutrons by means of propagation modes. The confined propagation of incoming waves along waveguides, the evolution of the resulting propagation modes and related issues are investigated. Those features give rise to computational challenges, depending on the smallness of (neutron wavelengths/characteristic dimensions). Approximate analytical formula is provided for the corresponding quantum-mechanical probability. Numerical estimates and the results of some simulations are presented. Consequences of the latter for BNCT will be discussed briefly. Graphical Abstract