A photodynamic micro / nano motor based on metal particles

Abstract

This invention discloses a photodynamic micro / nano motor based on metal particles. It involves superimposing two laser beams onto a metal particle on a support platform without a built-in track, driving the particle to rotate around the center of the laser beam. This invention utilizes localized surface plasmon resonance of the metal under light irradiation to achieve off-axis balance and orbital rotation of the particle across the beam cross-section. This results in an ultra-small subwavelength orbital rotation radius and significantly increases the rotational speed of the particle, thus realizing an ultra-small, high-speed photodynamic micro / nano motor.

Description

Technical Field

[0001] This invention relates to the field of photodynamic actuation, and more specifically to a photodynamic micro / nano motor system based on metal particles in a liquid or gaseous environment. Background Technology

[0002] Micromotors are tiny devices that can move at the micro- and nano-scale when given external energy inputs such as chemical, electrical, light, or thermal energy. These devices can perform actions such as translation, contraction, rotation, and orbital motion. Micromotors have significant applications in fields such as drug delivery, nanofabrication, and high-precision microscale measurement.

[0003] Currently, there are several existing micro / nano motor systems or schemes capable of orbital rotation. One method involves using an off-axis vortex beam to capture particles and achieve orbital rotation: Y. Zhao et al. observed orbital rotation with a rotational speed of approximately 1 Hz and a radius of several micrometers in a converged LG01 beam (journal article "Spin-to-orbital angular momentum conversion in a strongly focused optical beam," Phys. Rev. Lett. 99(7), 073901, 2007); A. Lehmuskero et al. placed metal particles in such a beam and achieved a rotational speed of 86 Hz by increasing the topological charge and power, achieving an orbital radius of approximately 2 μm (journal article "Plasmonic particles set into fast orbital motion by an optical vortex beam," Opt. Express 22(4), 4349-4356, 2014). However, due to the diffraction effect of light, the radius of the bright ring cannot be continuously reduced, making it difficult to achieve an ultra-small orbital rotation radius. There are schemes that utilize specifically constructed light fields: X. Chen et al. constructed specific light fields using laterally displaced dual fiber heads, enabling particles to rotate within them (journal article "Dynamics analysis of microsphere inadual-beamfiber-optic trap with transverse offset," Opt. Express 24(7), 7575-7584, 2016). There are schemes that utilize external orbits or auxiliary devices: J. Lu et al. used nano-beams as auxiliary devices, enabling particles to rotate around optical fibers (journal article "Light-Induced Pulling and Pushing by the Synergic Effect of Optical Force and Photophoretic Force," Phys. Rev. Lett. 118(4), 043601, 2017). However, auxiliary orbits or specific devices usually require additional fabrication and limit the flexibility and applicability of the rotation system. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a photodynamic micro / nano motor based on metal particles, which aims to achieve orbital rotation with an ultra-small radius without an external track and to significantly increase the rotational speed of the particle orbit.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0006] The present invention relates to a photodynamic micro / nano motor based on metal particles, characterized in that: a particle containing metal material is set as a rotor on a support platform without built-in track; two laser beams focused by a lens are superimposed on the particle, thereby driving the particle to rotate around the center of the laser beams to form a photodynamic micro / nano motor.

[0007] The optically driven micro / nano motor based on metal particles described in this invention is characterized by the fact that the light sources of both laser beams are quasi-monochromatic light sources, or the light sources of both laser beams are two monochromatic bands in a broadband light source.

[0008] Both incident laser beams are circularly polarized Gaussian beams.

[0009] The particles containing metallic materials are either pure metallic particles or particles of composite materials containing metals.

[0010] The wavelength of the incident laser is set so that the particles are excited to produce localized surface plasmon resonance under the action of the laser.

[0011] The radius of the particle's rotation around the center of the light spot is adjusted by regulating the power of the incident light.

[0012] The rotational speed of the particles around the center of the light spot is adjusted by adjusting the power of the incident light.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] This invention realizes an ultra-small, high-speed, photodynamic-driven micro / nano motor that can drive nanoscale metal particles off-axis and rotate them in an orbit using optical forces in liquid or gas environments. This motor does not require an external track; instead, the incident light provides a ring-shaped optical potential well as the track, resulting in a simple device and easy operation. Since its orbital radius depends on the balance of optical forces between the two beams in the radial direction, its rotational radius is not limited by the optical diffraction limit, thus allowing for a smaller rotational speed. The increased particle scattering cross-section due to the excitation of local surface plasmon resonance by the beam enables very high rotational speeds. This motor has significant application value in fields such as micro / nanomechanics, nanorheology, and high-precision measurement at the micro / nano scale. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a micro / nano motor system driven by photodynamic forces in two laser beams incident in opposite directions on nano-metal particles.

[0016] Figure 2 This is a schematic diagram of a micro / nano motor system driven by photodynamics in two laser beams incident in the same direction on nano-metal particles.

[0017] The numbers in the diagram are: 1. Laser, 2. Laser, 3. Substrate, 4. Nanoscale metal particles, 5. Converging lens, 6. Converging lens. Detailed Implementation

[0018] In this embodiment, a photodynamic micro / nano motor based on metal particles is described, such as... Figure 1 As shown, in a liquid or gas environment, a particle 4 containing metallic material of appropriate size is placed on a support platform 3 without a built-in track. Laser beams 1 and 2, in circularly polarized Gaussian mode and of appropriate wavelength, are converged by lenses 5 and 6 respectively and then illuminate the particle 4. The selected laser beam 2, on the cross-section of the beam ( Figure 1 The radial optical force exerted on the particle (in the xy plane) points towards the center of the laser spot; the selected laser beam 1, because its wavelength is in the band that can excite plasmonic resonance on the particle surface, exerts a radial optical force on the appropriately sized metal particle on the cross-section of the beam that points away from the center of the beam. The resultant force of these two forces allows the metal particle 4 to be captured by the beam at a position off the center of the laser spot (i.e., the optical axis). Since the incident beam is a circularly polarized beam and is focused by a lens, the light field near the focal point has orbital angular momentum, which can drive the particle to move in the angular direction within the cross-section of the beam. That is, the particle will simultaneously act as a rotor, rotating around the center of the laser spot to form a photodynamic micro-nano motor. By adjusting the power of the incident light, the distance of the metal particle from the center of the laser spot will change, that is, the radius of rotation will change; at the same time, the rotational speed of the particle's orbit will also change.

[0019] In this embodiment, laser beam 1 and laser beam 2 can also be incident in the same direction, such as... Figure 2 As shown: Both laser beam 1 and laser beam 2 are focused by lens 5 and then shine onto particle 4. Other implementation steps are the same. Figure 1 .

[0020] The principle behind the off-axis trapping and orbital rotation of nanoscale metal particles is briefly described below:

[0021] By utilizing the localized surface plasmon resonance of metals, a negative real part of polarizability appears within a certain wavelength range, while it is positive at other wavelengths. When a particle is in a light beam, the gradient force along the radial direction is positive when the real part of the polarizability is negative, and negative when the real part of the polarizability is positive. Therefore, in this invention, two different wavelengths are selected: one wavelength generates a positive radial force, and the other wavelength generates a negative radial force, thereby capturing the particle off-axis. Simultaneously, because the incident circularly polarized light beam is focused by a lens with a high numerical aperture, the light field near the particle possesses orbital angular momentum along the angular direction, which can drive the particle to rotate along the angular direction.

[0022] The present invention will be described in detail below with reference to implementation examples, but the present invention is not limited thereto.

[0023] The environment is water, and gold particles with a radius of 60 nm are used. Laser 1 is a right-handed circularly polarized Gaussian beam with a wavelength of 532 nm, and laser 2 is a left-handed circularly polarized Gaussian beam with a wavelength of 1064 nm. Laser 1 has a power of 60 mW, and laser 2 has a power of 100 mW. The beam of laser 1 is focused using a converging lens 5 with NA = 1.0, and the beam of laser 2 is focused using a converging lens 6 with NA = 1.2, so that the focal spots of the two focused beams overlap and fall on the gold particles. The gold particles are captured at a distance of approximately 110 nm from the center of the spot and rotate around the center of the spot, with a maximum rotation speed of 3255 revolutions per second.

[0024] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A photodynamic micro / nano motor based on metal particles, characterized in that: A particle containing metallic material is placed on a support platform without a built-in track as a rotor. Two laser beams focused by a lens are superimposed and irradiated onto the particle. The wavelength of the incident laser is set so that the particle is excited by local surface plasma resonance under the action of the laser, thereby driving the particle to rotate around the center of the laser spot to form a photodynamic micro-nano motor. The two incident laser beams are circularly polarized Gaussian beams.

2. The photodynamic micro / nano motor based on metal particles as described in claim 1, characterized in that: Both laser beams are sourced from quasi-monochromatic light sources, or from two monochromatic bands within a single broadband light source.

3. The photodynamic micro / nano motor based on metal particles as described in claim 1, characterized in that: The particles containing metallic materials are either pure metallic particles or particles of composite materials containing metals.

4. The photodynamic micro / nano motor based on metal particles as described in claim 1, characterized in that: The radius of the particle's rotation around the center of the light spot is adjusted by regulating the power of the incident light.

5. The photodynamic micro / nano motor based on metal particles as described in claim 1, characterized in that: The rotational speed of the particles around the center of the light spot is adjusted by adjusting the power of the incident light.

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