No abstract

Electromagnetic momentum carried by light is observable through the mechanical effects radiation pressure exerts on illuminated objects. Momentum conversion from electromagnetic fields to elastic waves within a solid object proceeds through a string of electrodynamic and elastodynamic phenomena, collectively bound by momentum and energy continuity. The details of this conversion predicted by theory have yet to be validated by experiments, as it is difficult to distinguish displacements driven by momentum from those driven by heating due to light absorption. Here, we have measured temporal variations of the surface displacements induced by laser pulses reflected from a solid dielectric mirror. Ab initio modelling of momentum flow describes the transfer of momentum from the electromagnetic field to the dielectric mirror, with subsequent creation/propagation of multicomponent elastic waves. Complete consistency between predictions and absolute measurements of surface displacements offers compelling evidence of elastic transients driven predominantly by the momentum of light.

No abstract

During the interaction of a laser pulse with the surface of a solid object, the object always gains momentum. The delivered force impulse is manifested as propulsion. Initially, the motion of the object is composed of elastic waves that carry and redistribute the acquired momentum as they propagate and reflect within the solid. Even though only ablation- and light-pressure-induced mechanical waves are involved in propulsion, they are always accompanied by the ubiquitous thermoelastic waves. This paper describes 1D elastodynamics of pulsed optical manipulation and presents two diametrical experimental observations of elastic waves generated in the confined ablation and in the radiation pressure regime.

Knowledge of the exact three-dimensional (3D) shape of the feet is extremely important for the footwear industry, since the correct fit between the shoe and the foot is an important comfort factor. Badly fitting shoes are the major cause of pain, foot related diseases and injuries [1] to [4]. 3D feet measurement therefore provides state of the art data for: (i) producing an adaptive design of a standard shoe; (ii) personalizing the shoe to individual foot dimensions; (iii) creating a better fitting for standard mass produced shoes and (iv) determining the best-fitting shoe for customers in a shop selling standard shoes. Traditionally, foot measuring techniques used callipers and measuring tapes. Simple mechanical devices were developed later, such as the Brannock device [5] and [6] or the Ritz stick length measuring device [7], which only measures a few of the most important foot dimensions, such as foot length, arch length and foot width. The next step in the foot measurement evolution are two-dimensional foot scanners, which measure the shape and dimensions of the footwear using a photo capturing in a flat plane [8]. The major drawback of these systems is the lack of foot height measurement. So-called two-and-half-dimension scanners, which measure foot contours from the top and side view [9] to [11] enable extraction of foot's length, width and height in any cross-section. But the girths of the crosssections, their curvature and local foot deformation are still not known.The complete 3D scanning systems are the logical progression to the mentioned limitations of the earlier systems. These systems are mainly based on the laser triangulation principle. One of the first such systems was the measuring system made by the VORUM research corporation [12]. It has four laserline projectors and eight cameras, which measure the lateral cross-section of the foot, defined by the projected light plane. The entire 3D foot shape is further scanned by moving the complete projectorscameras assembly along the longitudinal foot axis (from the toes to the heel). Since the complexity of this system is relatively high due to the many cameras and lasers, which should be actuated during the measurement procedure, the price of the system is rather high. Similar system, but low cost, was later developed by Kouchi and Mochimaru [13]. Such systems are therefore mainly used in research and medical applications [14] to [17].There are many attempts to overcome the economical drawback of above solution, which is still a gold standard in terms of measurement precision. One direction of development was to eliminate the scanning procedure. A representative of this technique is described in [18] where the foot is measured by four stationary measuring modules based on laser multiple line triangulation. The methods based on the fringe projection technique are also presented in [19] to [21]. The major improvement regarding the scanning techniques is the shorter measuring time, which in principle enables the study of the foot shape during walking [1...