Device and method for realizing adjustable distorted light field based on dual-high-order vector light beam coupling

Abstract

The invention relates to the technical field of light field regulation and control, and aims to solve the problems that an existing multifunctional light field is based on modulation of a low-order vector light field, a formed space structure is regular, only regular particles can be stably captured and controlled, and the application of the existing multifunctional light field in the field of biomedicine is limited; the invention provides a device and a method for realizing an adjustable distorted light field based on dual high-order vector light beam coupling, parallel light passes through a beam splitter, two beams of light pass through a spatial light modulator to realize phase modulation, and a vortex wave plate is utilized to perform polarization modulation on light beams carrying phase modulation information; after the two light beams subjected to phase modulation and polarization modulation are coupled, an adjustable and controllable tight focusing light field is generated through an objective lens, and a high-order vector light beam distortion light field achieved through phase modulation and polarization modulation is obtained; the device and the method can be used for researching regulation and control of a multi-target energy flow distortion light field, exploring super-resolution high-order vector vortex light field distribution generated in a sub-wavelength scale of an out-of-focus area, and analyzing a micro mechanism of focusing field distortion under an ultrafast multi-target light field.

Description

Technical Field

[0001] The present invention relates to the technical field of light field control, and more specifically, to a device and method for realizing an adjustable twisted light field based on dual high-order vector light beam coupling. Background Art

[0002] Optical tweezers is an advanced tool that uses light beams to capture and manipulate tiny particles. When a parallel laser beam is focused by a microscope objective, a micro-nanoscale light spot is obtained. When the strong focused light spot excites the particle, it will exert an optical force on it, binding it to the lowest potential energy point in its light field structure. The optical force exerted on a single particle can be divided into the intensity gradient force generated by the electric field intensity gradient, the polarization gradient force generated by the spatial polarization gradient, and the radiation force (including absorption force and scattering force) consistent with the propagation direction. Among them, the intensity gradient force and the polarization gradient force are determined by the intensity and polarization distribution of the focused light field, respectively, while the radiation force is closely related to the energy flux density of the focused light field. In principle, when the intensity gradient force is dominant, stable three-dimensional confinement can be achieved in the optical tweezers, thereby achieving precise manipulation of particles. Optical tweezers technology has been widely used in many research fields such as biology, colloidal physics, chemistry and medicine, such as the study of the mechanical properties of macromolecules or single cells, the interaction between different protein molecules, and the interaction between colloidal particles. In these applications, it is necessary to achieve stable capture and manipulation of particles with different structures, and the key link is to achieve a special structure of light field distribution.

[0003] In this regard, researchers currently mainly achieve polarization-tunable and structurally diverse subwavelength light fields by regulating the amplitude, phase, and polarization of light beams. Tightly focused radially polarized light produces a sub-diffraction longitudinally polarized bright spot, while angularly polarized light produces an angularly polarized hollow light field after tight focusing; when the first-order vortex phase modulates radially (angularly) polarized light, a three-dimensional (transverse) polarized light field is produced after tight focusing; further regulating radially (angularly) polarized light through phase / amplitude filters can form spatial structures such as subwavelength light needles, light chains, and light spot arrays; these specific light field structures can be used to capture or manipulate single and multiple particles with different refractive indices. However, the multifunctional light fields generated above are based on the modulation of low-order vector light fields, and the spatial structures formed are regular, which can only stably capture and manipulate regular particles, so their application in the biomedical field will be limited. For example, to capture and manipulate the double-stranded structure of DNA, it is urgent to realize the twisted light field and energy flow of micro-nano structures. Summary of the invention

[0004] In order to solve the problem of stably capturing and manipulating irregular particles with a light field having a regular spatial structure, the present invention proposes a device and method for realizing an adjustable distorted light field based on the coupling of two high-order vector beams. In the tight beam focusing system, two high-order vector beams with phase control are coherently superimposed to realize light field distortion and energy flow distortion based on the spin-orbit coupling effect. The optical tweezers technology is applied to the manipulation of tiny particles. The degree of light field and energy flow distortion is controlled by changing the defocus position and the topological charge number between the two vortex light beams. The adjustability of the light field distortion structure provides a foundation for the flexible manipulation of irregular particles.

[0005] In order to realize the above-mentioned distorted light field and energy flow distribution, the invention provides the following technical solutions:

[0006] A device for realizing adjustable twisted light field based on dual high-order vector beam coupling comprises a femtosecond laser, a plurality of reflectors, a polarization converter, a vortex wave plate, a spatial light modulator, and a photoelectric coupling detector, wherein: a reflector 1 is arranged at the pulse light output end of the femtosecond laser, the output end of the reflector 1 is split by a beam splitter, the first beam of light passes through a reflector 2, a spatial light modulator 1, a reflector 4, a reflector 5, a polarization converter 1, a vortex wave plate 1, a reflector 6, a reflector 7 in sequence to a focusing objective lens; the second beam of light passes through a reflector 3, a spatial light modulator 2, a reflector 8, a reflector 9, a polarization converter 2, a vortex wave plate 2, a reflector 10, a reflector 11 to a focusing objective lens; the two beams of light are focused by the focusing objective lens and then received by a photoelectric coupling detector.

[0007] Furthermore, the numerical aperture NA of the focusing objective lens is 0.95; the light source of the femtosecond laser has a pulse width of 330fs, a wavelength of 532nm, and a repetition frequency of 1MHz; and both spatial light modulators are reflective spatial light modulators.

[0008] Furthermore, it also includes a display terminal for displaying the operation process.

[0009] A method for realizing an adjustable twisted light field based on dual high-order vector light beam coupling. Based on the above-mentioned adjustable twisted light field device, the pulse light emitted by a femtosecond laser is reflected by a reflector to change the propagation direction of the light path, and is divided into two beams of light by a beam splitter. After each beam of light is modulated by a spatial light modulator in an independent light path, it carries different topological charges and amplitudes. The light beam is converted into horizontal polarized light by a polarization converter, and the horizontal polarized light is modulated into vector polarized light by a vortex wave plate to realize polarization order regulation of the light beam and generate a vector light field of corresponding polarization order. The two beams of light are independently modulated with different parameters through two light paths. After each light path changes its propagation direction through two reflectors, the two beams of light carrying different amplitudes, phases and polarization information are coupled, and after being focused by a focusing objective lens, a tightly focused light field with adjustable light field distortion and adjustable energy flow distortion is generated. The vortex order of the vector light field is controlled by the spatial light modulator to realize the energy flow shape and distortion degree under different topological charges and polarization orders.

[0010] Furthermore, the two beams of light split by the beam splitter are high-order vector polarized Laguerre-Gaussian vortex lights:

[0011]

[0012] Among them, r 0 and denote the radial coordinate and polar coordinate of the incident plane, σ is the waist size of the Laguerre-Gaussian beam, l 1 With l 2 are the topological charges of the two incident lights, m and are the polarization order and initial polarization angle of the high-order vector beam, e x With e y are orthogonal unit vectors.

[0013] Furthermore, the electric field and magnetic field distribution of the high-order vector polarized Laguerre-Gaussian vortex light superimposed on the focal plane after being focused by the focusing objective lens is expressed as:

[0014]

[0015] in

[0016]

[0017] (r,ψ,z) represents the cylindrical coordinate system in the focusing plane, θ represents the focusing angle of the high numerical aperture objective, k r With k z are the transverse wave vector and the longitudinal wave vector respectively.

[0018] Furthermore, the energy flux distribution on the focusing plane is:

[0019]

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention proposes a method for realizing tunable twisted light field structure and energy flow by coupling and superposition of dual high-order vector vortex beams, wherein the construction, propagation and phase modulation of the controllable vector vortex light field with energy flow twist are realized by phase modulation of the spatial light modulator and the vector vortex wave plate, the light field structure and degree of twist are made more diverse by coupling and superposition of two vector vortex beams, the tight focusing and defocus distance control of the light field are realized by the high NA objective system, and finally the light field morphology and degree of twist are realized by the control of phase modulation and defocus distance; the present invention adds the control of electric field distortion and energy flow distortion on the basis of traditional vector light field control, and adds a new degree of freedom to light field control, optical tweezers technology and particle control technology. The present invention can be used to study the control of multi-target energy flow twisted light field, explore the super-resolution high-order vector vortex light field distribution in the sub-wavelength scale of the defocus area, and analyze the microscopic mechanism of focusing field distortion under ultrafast multi-target light field. Based on the vector diffraction theory, the present invention realizes the control of light field distortion and energy flow distortion by tight focusing of dual vector vortex femtosecond vortex pulse light. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram of the optical path principle of the device of the present invention;

[0023] Figure 2 The tightly focused light field intensity distribution of the double high-order vector vortex beam under the condition that the sum of the topological charges is zero in the embodiment of the present invention;

[0024] Figure 3 The intensity distribution and distortion of the tightly focused light field of the double high-order vector vortex beam under the condition that the sum of the topological charges is not zero in the embodiment of the present invention;

[0025] Figure 4 In the embodiment of the present invention, energy flow distortions of different shapes corresponding to the topological charge are achieved by utilizing a dual high-order vector vortex light field.

[0026] In the figure: 1, femtosecond laser, 2, mirror 1, 3, beam splitter, 4, mirror 2, 5, mirror 3, 6, spatial light modulator 1, 7, mirror 4, 8, mirror 5, 9, polarization converter 1, 10, vortex wave plate 1, 11, mirror 6, 12, mirror 7, 13, spatial light modulator 2, 14, mirror 8, 15, mirror 9, 16, polarization converter 2, 17, vortex wave plate 2, 18, mirror 10, 19, mirror 11, 20, focusing objective lens, 21 photoelectric coupled detector (CCD). Figures 2 to 4 The corresponding topological charges are marked in . DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] like Figure 1 As shown, an example of the present invention provides a device for realizing an adjustable distorted light field based on dual high-order vector beam coupling, including a femtosecond laser 1, wherein the pulsed light emitted by the femtosecond laser 1 is divided into two beams of light through a reflector 1 2 and a beam splitter 3, wherein each beam of light undergoes independent amplitude, phase and polarization modulation, and the first beam of light passes through a reflector 2 4, a spatial light modulator 1 6, a reflector 4 7, a reflector 5 8, a polarization converter 1 9, a vortex wave plate 1 10, a reflector 6 11, and a reflector 7 12 in sequence to a focusing objective lens 20; the second beam of light passes through a reflector 3 5, a spatial light modulator 2 13, a reflector 8 14, a reflector 9 15, a polarization converter 2 16, a vortex wave plate 2 17, a reflector 10 18, and a reflector 11 19 to a focusing objective lens 20, and the two beams of light are focused by the focusing objective lens 20 and received by a photoelectric coupling detector 21.

[0029] Taking the outgoing light of the reflector 24, i.e., the first beam of light, as an example, after beam expansion and collimation, the outgoing light is modulated by the spatial light modulator 6, carrying different topological charges and amplitudes, and the light beam is converted into horizontal polarized light by the polarization converter, and then the horizontal polarized light is modulated into vector polarized light by the vortex wave plate to achieve polarization order regulation of the light beam, so as to complete the amplitude, phase and polarization modulation of the two beams of light after the incident light is split, and each light path changes the propagation direction through two reflectors, and the two beams of light carrying different amplitude, phase and polarization information are coupled, and the two beams of light can be independently modulated with different parameters. The coupled light formed by the superposition of the two beams of light is incident on the focusing objective 20 to obtain an adjustable high-order tightly focused light field, which is received by the photoelectric coupling detector 21.

[0030] In an embodiment of the present invention, a spatial light modulator is used to perform amplitude and phase modulation on a collimated light beam so that the light beam carries phase information after passing through the spatial light modulator; the phase-modulated pulse light is polarized by a polarization converter and a vortex wave plate with a specific order, thereby generating a vector light field with a specific polarization order.

[0031] Specifically, in this embodiment, the photoelectric coupled detector CCD21. The light source used by the femtosecond laser has a pulse width of 330fs, a wavelength of 532nm, and a repetition frequency of 1MHz, and the two spatial light modulators are reflective spatial light modulators. The focusing lens 20 is specifically a high numerical aperture lens, and the numerical aperture NA=0.95. The light beam after amplitude, phase, and polarization modulation is focused by the focusing lens 20 to generate a tightly focused light field with adjustable light field distortion and adjustable energy flow distortion. The tightly focused light field of the focusing lens 20 is collected by the photoelectric detection device 21, so as to be clearly displayed on the display terminal.

[0032] In the embodiment of the present invention, based on the vector diffraction theory of dual high-order vector vortex beams, the control of high-order vector vortex light field is studied. A linearly polarized femtosecond laser is used as the light source, with a pulse width of 330fs and a wavelength of 532nm. Based on the vortex order of the spatial light modulator coded beam, the polarization of the phase-coded femtosecond vortex beam is controlled by selecting a vortex wave plate of an order that meets the use requirements according to actual needs.

[0033] The two incident high-order vector polarized Laguerre-Gaussian vortex lights are expressed as:

[0034]

[0035] where r 0 and denote the radial coordinate and polar coordinate of the incident plane, σ is the waist size of the Laguerre-Gaussian beam, l 1 With l 2 are the topological charges of the two incident lights, m and are the polarization order and initial polarization angle of the high-order vector beam, e x With e y are orthogonal unit vectors, constituting the transverse component of the plane wave (perpendicular to the propagation direction). When two beams of light are transmitted in the same direction and superimposed, their total light field in the pupil plane is:

[0036] After the two superimposed high-order vector polarized Laguerre-Gaussian vortex lights are focused by a high numerical aperture focusing objective 20, the electric field and magnetic field distributions in the focal plane are obtained based on the vector diffraction theory and are expressed as follows:

[0037]

[0038] in

[0039]

[0040] In formula (3) to formula (8), (r, ψ, z) represents the cylindrical coordinate system in the focusing plane, θ represents the focusing angle of the high numerical aperture objective lens, and k r With k zare the transverse wave vector and the longitudinal wave vector respectively. Based on the electric field and magnetic field distribution of the focusing plane, the energy flow distribution of the focusing plane is obtained as:

[0041]

[0042] The device of the present invention uses MATLAB numerical analysis to analyze the light field structure distribution and energy flow distortion under non-paraxial approximation conditions, and simulates and verifies the light field distortion structure to confirm the correctness of the experimental results. The experimental results are as follows: Figures 2 to 4 As shown: Figure 2 The figure shows the distribution of the light field structure after the superposition of two high-order vector beams is completed and a tightly focused light field is formed. The figure shows the light field distribution with topological charges of (0,0), (2,-2), and (3,-3). It can be seen from the figure that when the topological charge number changes, different structural distributions will be formed. When the sum of the topological charges is zero, the light field structure is not distorted.

[0043] Figure 3 The structure of the tightly focused light field after superposition of another set of two high-order vector beams with different topological charges is shown. The topological charges are (3,3), (1,-5), and (-1,-7). It can be seen from the figure that when the sum of the topological charges is not zero, the structure of the light field is obviously distorted.

[0044] Figure 4 The total light field (S) and energy flux distribution (S) under different topological charges are shown. z ) comparison chart. At this time, the energy flux distribution is mainly contributed by the longitudinal field. The distortion of the energy flux is similar to the light field structure distribution. The difference is that the energy flux in the three cases of topological charge (3, -3), (1, -5), and (-1, -7) is 12-petal type, corresponding to twice the difference in topological charge number.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0046] The matters not described in detail in the present invention are all known technologies to those skilled in the art.

Claims

1. A device for realizing adjustable twisted light field based on dual high-order vector beam coupling, characterized in that: The invention comprises a femtosecond laser (1), a plurality of reflectors, a polarization converter, a vortex wave plate, a spatial light modulator, and a photoelectric coupling detector (21), wherein: a reflector 1 (2) is arranged at the pulse light output end of the femtosecond laser (1), the output end of the reflector 1 (2) is split by a beam splitter (3), and the first beam of light passes through a reflector 2 (4), a spatial light modulator 1 (6), a reflector 4 (7), a reflector 5 (8), a polarization converter 1 (9), a vortex wave plate 1 (10), a reflector 6 (11), a reflector 7 (12) in sequence to a focusing objective lens (20); The second beam of light passes through a reflector three (5), a spatial light modulator two (13), a reflector eight (14), a reflector nine (15), a polarization converter two (16), a vortex wave plate two (17), a reflector ten (18), and a reflector eleven (19) to a focusing lens (20); The two beams of light are focused by a focusing objective lens (20) and then received by a photoelectric coupling detector (21).

2. The device for realizing adjustable twisted light field based on dual high-order vector beam coupling according to claim 1, characterized in that: The numerical aperture NA of the focusing objective lens (20) is 0.95; the light source of the femtosecond laser (1) has a pulse width of 330 fs, a wavelength of 532 nm, and a repetition frequency of 1 MHz; and both spatial light modulators are reflective spatial light modulators.

3. The device for realizing adjustable twisted light field based on dual high-order vector beam coupling according to claim 1, characterized in that: It also includes a display terminal for displaying the operation process.

4. A method for realizing an adjustable twisted light field based on dual high-order vector beam coupling, based on the device for an adjustable twisted light field according to any one of claims 1 to 3, characterized in that: The pulse light emitted by a femtosecond laser (1) is reflected by a reflector (2) to change the propagation direction of the optical path, and is then split into two beams of light by a beam splitter (3). After each beam of light is modulated by a spatial light modulator in an independent optical path, it carries different topological charges and amplitudes. The light beam is converted into horizontally polarized light by a polarization converter, and the horizontally polarized light is modulated into vector polarized light by a vortex wave plate to achieve polarization order control of the light beam and generate a vector light field of corresponding polarization order. The two beams of light are independently modulated with different parameters through two optical paths. After each optical path changes its propagation direction through two reflectors, the two beams of light carrying different amplitudes, phases and polarization information are coupled, and after being focused by a focusing objective lens (20), a tightly focused light field with adjustable light field distortion and adjustable energy flow distortion is generated. The vortex order of the vector light field is controlled by the spatial light modulator to achieve energy flow shapes and distortion degrees under different topological charges and polarization orders.

5. The method for realizing adjustable twisted light field based on dual high-order vector beam coupling according to claim 4, characterized in that: The two beams of light split by the beam splitter (3) are high-order vector polarized Laguerre-Gaussian vortex lights: Among them, r0 and denote the radial coordinate and polar coordinate of the incident plane, σ is the waist size of the Laguerre-Gaussian beam, l1 and l2 are the topological charges of the two incident beams, and m and are the polarization order and initial polarization angle of the high-order vector beam, e x With e y are orthogonal unit vectors.

6. The method for realizing adjustable twisted light field based on dual high-order vector beam coupling according to claim 5, characterized in that: The electric field and magnetic field distribution of the high-order vector polarized Laguerre-Gaussian vortex light superimposed on the focal plane after being focused by the focusing objective lens (20) is expressed as follows: in (r,ψ,z) represents the cylindrical coordinate system in the focusing plane, θ represents the focusing angle of the high numerical aperture objective, k r With k z are the transverse wave vector and the longitudinal wave vector respectively.

7. The method for realizing adjustable twisted light field based on dual high-order vector beam coupling according to claim 6, characterized in that: The energy flow distribution of the focusing plane is:

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