Light Pressure Force Research Articles

Displacement and localisation of a transparent nanosphere by light-pressure forces in the field of a focused laser beam

We report the results of a numerical simulation of the Langevin equation describing the motion of a transparent nanosphere under the action of a resulting light-pressure force in the field of a continuous focused Gaussian laser beam. The conditions for the localisation of the nanosphere near the focal waist of the beam focused by the lens are determined. An analytical solution of the approximate (truncated) equation of motion is found, which almost exactly coincides with the results of the numerical simulation of the initial equation.

Hepatic morphological changes in experimental acute biliary pancreatitis.

We calculate the temperature of the atoms in the field of counter-propagating stochastic light waves (the chaotic-field model). We show that the temperature of the atomic ensemble depends on the autocorrelation time of the waves, their intensity and the detuning of the carrier frequency of the waves from the atomic transition frequency. The field can form a one-dimensional trap for atoms, as is readily seen from our previous investigation of light-pressure force on an atom in counter-propagating stochastic light waves [V. I. Romanenko, B. W. Shore, L. P. Yatsenko, Opt. Commun. 268 (2006) 121–132]. We carry out numerical simulation of the atomic ensemble using parameters appropriate for sodium atoms. Analyzing the known investigation of the light-pressure force on atoms and their motion in the counter-propagating polychromatic waves, we suggest an hypothesis that any polychromatic counter-propagating waves that have a discrete spectrum, or waves described by a stationary stochastic process, one of which repeats the other, can form a trap for atoms.

Trapping of atoms by the counter-propagating stochastic light waves

We calculate the temperature of the atoms in the field of counter-propagating stochastic light waves (the chaotic-field model). We show that the temperature of the atomic ensemble depends on the autocorrelation time of the waves, their intensity and the detuning of the carrier frequency of the waves from the atomic transition frequency. The field can form a one-dimensional trap for atoms, as is readily seen from our previous investigation of light-pressure force on an atom in counter-propagating stochastic light waves [V. I. Romanenko, B. W. Shore, L. P. Yatsenko, Opt. Commun. 268 (2006) 121–132]. We carry out numerical simulation of the atomic ensemble using parameters appropriate for sodium atoms. Analyzing the known investigation of the light-pressure force on atoms and their motion in the counter-propagating polychromatic waves, we suggest an hypothesis that any polychromatic counter-propagating waves that have a discrete spectrum, or waves described by a stationary stochastic process, one of which repeats the other, can form a trap for atoms.

Approximate analytic method for high-apogee twelve-hour orbits of artificial Earth’s satellites

We propose an approach to the study of the evolution of high-apogee twelve-hour orbits of artificial Earth’s satellites. We describe parameters of the motion model used for the artificial Earth’s satellite such that the principal gravitational perturbations of the Moon and Sun, nonsphericity of the Earth, and perturbations from the light pressure force are approximately taken into account. To solve the system of averaged equations describing the evolution of the orbit parameters of an artificial satellite, we use both numeric and analytic methods. To select initial parameters of the twelve-hour orbit, we assume that the path of the satellite along the surface of the Earth is stable. Results obtained by the analytic method and by the numerical integration of the evolving system are compared. For intervals of several years, we obtain estimates of oscillation periods and amplitudes for orbital elements. To verify the results and estimate the precision of the method, we use the numerical integration of rigorous (not averaged) equations of motion of the artificial satellite: they take into account forces acting on the satellite substantially more completely and precisely. The described method can be applied not only to the investigation of orbit evolutions of artificial satellites of the Earth; it can be applied to the investigation of the orbit evolution for other planets of the Solar system provided that the corresponding research problem will arise in the future and the considered special class of resonance orbits of satellites will be used for that purpose.

Dynamic axial control over optically levitating particles in air with an electrically-tunable variable-focus lens.

Efficient delivery of viruses, proteins and biological macromelecules into a micrometer-sized focal spot of an XFEL beam for coherent diffraction imaging inspired new development in touch-free particle injection methods in gaseous and vacuum environments. This paper lays out our ongoing effort in constructing an all-optical particle delivery approach that uses piconewton photophoretic and femtonewton light-pressure forces to control particle delivery into the XFEL beam. We combine a spatial light modulator (SLM) and an electrically tunable lens (ETL) to construct a variable-divergence vortex beam providing dynamic and stable positioning of levitated micrometer-size particles, under normal atmospheric pressure. A sensorless wavefront correction approach is used to reduce optical aberrations to generate a high quality vortex beam for particle manipulation. As a proof of concept, stable manipulation of optically-controlled axial motion of trapped particles is demonstrated with a response time of 100ms. In addition, modulation of trapping intensity provides a measure of the mass of a single, isolated particle. The driving signal of this oscillatory motion can potentially be phase-locked to an external timing signal enabling synchronization of particle delivery into the x-ray focus with XFEL pulse train.

К расчету главного вектора и главного момента сил светового давления на солнечный парус

К расчету главного вектора и главного момента сил светового давления на солнечный парус

Ion-trajectory analysis for micromotion minimization and the measurement of small forces

For experiments with ions confined in a Paul trap, minimization of micromotion is often essential. In order to diagnose and compensate micromotion we have implemented a method that allows for finding the position of the radio-frequency (RF) null reliably and efficiently, in principle, without any variation of direct current (DC) voltages. We apply a trap modulation technique and focus-scanning imaging to extract 3d ion positions for various RF drive powers and analyze the power dependence of the equilibrium position of the trapped ion. In contrast to commonly used methods, the search algorithm directly makes use of a physical effect as opposed to efficient numerical minimization in a high-dimensional parameter space. Using this method we achieve a compensation of the residual electric field that causes excess micromotion in the radial plane of a linear Paul trap down to 0.09V/m. Additionally, the precise position determination of a single harmonically trapped ion employed here can also be utilized for the detection of small forces. This is demonstrated by determining light pressure forces with a precision of 135yN. As the method is based on imaging only, it can be applied to several ions simultaneously and is independent of laser direction and thus well-suited to be used with, for example, surface-electrode traps.

The reducibility of linear second-order time-varying systems with control and observation

The possibility of reducing a linear non-autonomous system, containing a control and measurements, to a time-independent form using time-dependent linear transformations of the state, control and observation spaces is investigated. Second-order systems, that is, systems with a second derivative with respect to time, explicitly present in the equations of motion, are examined. The motion of a spacecraft in the neighbourhood of a libration point under the action of a controlling light pressure force is considered as an application, as well as the problem of determining the orientation of an artificial Earth satellite using solar sensing element measurements. In the first problem, controllability and, in the second case, observability is established by reducing the equations to a time-independent form.

Rapid rotations of a satellite with a cavity filled with viscous fluid under the action of moments of gravity and light pressure forces

Rapid rotational motion of a dynamically asymmetric satellite relative to the center of mass is studied. The satellite has a cavity filled with viscous fluid at low Reynolds numbers, and it moves under the action of moments of gravity and light pressure forces. Orbital motions with an arbitrary eccentricity are supposed to be specified. The system, obtained after averaging over the Euler-Poinsot motion and applying the modified averaging method, is analyzed. The numerical analysis in the general case is performed, and the analytical study in the axial rotation vicinity is carried out. The motion in the specific case of a dynamically symmetric satellite is considered.

Sensitive detection of infrared photons using a high-Q microcantilever

A new approach based on microcantilevers is presented to detect infrared photons with high sensitivity. Infrared photons are measured by monitoring the amplitude change of a vibrating microcantilever under light pressure force. The irradiating light is modulated into sinusoidal and pulsed waves, and to be in-phase and anti-phase with the cantilever driving signal. A linear relationship between the amplitude change of the cantilever and the light power distributing on the cantilever was observed. Under a vacuum of 10−4 Pa, an infrared light power of 7.4 nW was detected with the cantilever. The in-phase and anti-phase modulation to the cantilever vibration using a pulsed light results in an enhanced response of the cantilever.

Three-dimensional localization of atoms in the polychromatic optical superlattice

Quasiclassical kinetic theory of the light pressure force has been applied to describe the localization of atoms (or ions) with the transition F = 1 → F = 0 in the three-dimensional (3D) dissipative optical superlattice of a new type. Its action is based on the effect of the gradient force rectification in the polychromatic field: superposition of the three color far-off-resonant field and partially coherent resonant field. An approximate explicit solution of the kinetic equation for 3D motion of atoms in such a (multicolor) field has been achieved. This solution demonstrates the capability of the polychromatic superlattice to provide efficient cooling and strong spatial localization of the particles and to form an atomic (or ionic) grating with highly controllable characteristics.

Atom optics and its applications

Atom optics began to develop as an independent physics discipline only in the mid-1990s. This occurred because effects of laser radiation’s light pressure forces on the progressive movement of atoms were found. A meeting of the RAS Presidium was devoted to prospects for the development of a new trend in the optics of material particles. The article published below is based on the paper heard at this meeting.

Calculation of resultant vector and principal moment of light pressure forces acting upon the spacecraft with a solar sail

Two methods of calculating the resultant vector and principal moment of light pressure forces, having an effect on a spacecraft with a composite solar sail, are compared. The first method is based on analytical formulas obtained without regard to shading of some parts of the sail by others. The second method uses a detailed geometrical model of the sail, which allows one to take such shading into account. Some part of photons falling on a sail is supposed to be reflected from it in a mirror manner, while the others are completely absorbed. The range of variation of sail orientation parameters with respect to incident solar light streams, where the first method turns out to be accurate enough, is found.

Using Magnetic Fluids as a Versatile Method for Manipulating and Sorting Unlabeled Nonmagnetic Particles in a Flow

Sorting and detection technologies have become an important part of industrial and medical practice. Recently, innovation in lab-on-a-chip technologies promises smaller, less expensive, and more portable devices for these applications. Labeling efficiency, specificity and throughput are challenges that must be overcome in developing such technologies. We introduce a continuous-flow magnetic flow focusing, sorting and detection scheme for unlabeled particles on the size order of cells. Unlabeled particles are focused and sorted by size in the apparatus using the magnetophoretic force in a specially crafted high-gradient magnetic field. The magnetic scheme is orthogonal to other sorting techniques, allowing other physical properties to be explored. We demonstrate using the light pressure force from a laser to actively sort a focused stream of flowing particles and use the balance between the light pressure force and the magnetic force as an additional physical axis on which particles can be sorted. We show that the positions and distribution of the particles conform to their theoretical expectations, and use the theory to explore the limitations of this technology in practice.

Theoretical study of the light pressure force acting on a spherical dielectric particle of an arbitrary size in the interference field of two plane monochromatic electromagnetic waves

The light pressure force acting on a spherical dielectric particle in the interference field of two plane monochromatic electromagnetic waves is studied in detail for different particle radii and angles of incidence of waves.

Two-level atoms moving in strong biharmonic and monochromatic counterpropagating fields

The polarization and power spectra of radiation of two-level atoms moving in a field of biharmonic and monochromatic counterpropagating waves are computer simulated. It is shown that, as the frequencies of the counterpropagating waves are scanned with respect to the central frequency of the Doppler contour in the intensity distribution of groups of atoms moving at velocities that satisfy the resonance conditions for multiphoton transitions between quasi-energy levels, apart from well-known sub-Doppler resonances, narrow peaks appear. Such resonances should also occur for the stimulated light pressure force.

Interaction of plane gravitational waves with a Fabry-Perot cavity in the local Lorentz frame

We analyze the interaction of the plane `$+$'-polarized gravitational waves with a Fabry-Perot cavity in the local Lorentz frame of the cavity's input mirror outside of the range of long-wave approximation with the force of radiation pressure taken into account. The obtained detector's response signal is represented as a sum of two parts: (i) the phase shift due to displacement of a movable mirror under the influence of a gravitational wave and the force of light pressure, and (ii) the phase shift due to the direct interaction of a gravitational wave with light wave inside the cavity. We obtain the formula for the movable mirror's law of motion paying close attention to the phenomena of optical rigidity, radiative friction, and direct coupling of a gravitational wave to light wave. Some issues concerning the detection of high-frequency gravitational waves and the role of optical rigidity in it are discussed. We also examine in detail special cases of optical resonance and small detuning from it and compare our results with the known ones.

Particle image velocimetry for visualizing laser-induced motion of nanoparticles

The pressure of electromagnetic waves, experimentally discovered in the early twentieth century,1 produces forces that affect objects scattering or absorbing light. With ordinary light sources these forces are feeble indeed and were considered unimportant before the invention of lasers in the 1960s. In the early 1970s, Arthur Ashkin demonstrated that a focused laser beam provides light pressure sufficient to displace and even levitate microscopic objects.2 This work eventually led to the development of ‘optical tweezers’3 employed for motion control of microscopic objects in physics, chemistry, and biology.4 Applying the concept of light pressure force to nanoparticle and laser technologies represents a further instrumental advance. In the past decade, noble metal nanoparticles have found broad application in biotechnology and nanomaterials.5 But the displacement of nanoparticles by light pressure requires much less intensity than is required to trap it in ’optical tweezers’. Laser-driven nanoparticles have a variety of potiential uses in nanofluidics, nanobiotechnology, and biomedicine. Although the possibility of optically trapping gold nanoparticles was demonstrated in 1994,6 developing tweezers for nanoparticles is not straightforward. The gradient forces that are responsible for trapping, fall off with particle size. Moreover, the non-negligible absorption by particles leads to a dramatic temperature rise at high power, destablizing single beam optical traps.7 Recently we visualized nanoparticles moving along a laser beam under light pressure by micron-resolution particle image velocimetry (PIV).8 PIV records images of two successive moving particles, separated by a known time delay. Each image Figure 1. The microscope-based experimental setup. Inset shows the illumination geometry: A – microscope objective; B – laser beam; C – light scattered by nanoparticles; D – micro cell with nanoparticles colloidal solution; E – illuminating light; Fdark field condenser.

Capped colloids as light-mills in optical traps

Custom-designed colloidal particles in optical tweezers act as light-mills in a fluid. In particular, aqueous suspensions of capped silica colloids, in which half of the surface is covered with metal layers, are investigated. Due to their asymmetry, the capped colloids can act as rotators when exposed to intense laser fields. Particles of 4.7 μm in diameter are observed rotating around the focus of a laser beam. For low intensities, particles become trapped close to the spot of highest laser intensity. Above a threshold value of about 4 mW in total beam intensity, the particles move away from the centre of the focus and start to rotate at frequencies of about 1 Hz. The balance of forces due to light pressure and hydrodynamic forces gives a constant rotation rate. The speed of the spinning particle increases linearly with laser power to above 2 Hz until the particles are ejected from the focus for intensities higher than 7 mW. Magnetic caps introduce further possibilities to tune the rotation rates.

Focusing of an atomic beam by a two-dimensional magneto-optical trap

A method for focusing neutral atoms based on the light-pressure force in a nonuniform magnetic field is proposed and analyzed. Its particular scheme is realized by means of a two-dimensional magneto-optical trap using a thermal beam of Rb atoms. A feature of this focusing method is the linear dependence of the focal length on the longitudinal velocity of atoms in contrast to the quadratic dependence in the known methods of focusing material-particle beams. The minimum size of the waist of the focused atomic beam is equal to 270 µm. Owing to focusing by means of the two-dimensional magneto-optical trap, the velocity monochromatization of a thermal atomic beam is realized: the width of the distribution of the longitudinal atomic velocities in the beam is reduced from 350 to 60 m/s.