VORTEX-PAIR BEAM BASED OPTICAL TWEEZER SYSTEM

Abstract

The present disclosure discloses a vortex-pair beam based optical tweezer system, including a laser device (1), a collimating beam expanding system, a spatial light modulator (6), a confocal beam shrinking system, a sample table (12), and an observation unit arranged according to a light path. The spatial light modulator (6) continuously loads different vortex-pair beam phase diagrams in real time, and manipulates and rotates a particle in real time by using a single vortex-pair beam. The optical tweezer system can realize precise regulation, control, and positioning of two spherical particles at any positions in a plane, and any controllable rotation operation of a rod-shaped particle in the plane, which makes application objects of the optical tweezer system richer, and effectively solves the problem that the rod-shaped particle is difficult to be controlled by the existing optical tweezer system.

Claims

1. A vortex-pair beam based optical tweezer system, comprising a laser device, a collimating and beam expanding system, a spatial light modulator, a confocal beam shrinking system, a sample table, and an observation unit arranged according to a light path, wherein the spatial light modulator continuously loads different vortex pair phase diagrams, and outputs a single vortex-pair beam to realize real-time manipulation of a particle; a vortex pair phase diagram is calculated through formula (1): $\begin{array}{cc}\varphi \left(u,v\right)={\left(\frac{u-a+\mathrm{iv}}{\sqrt{{\left(u-a\right)}^2+v^2}}\right)}^{m_1}{\left(\frac{u+a+\mathrm{iv}}{\sqrt{{\left(u+a\right)}^2+v^2}}\right)}^{m_2}& \left(1\right)\end{array}$ wherein, ϕ represents a phase, m.sub.1, m.sub.2 are any two equal integers, called topological charges; a represents the off-axis distance of phase singularities of double vortices, and is any real number; u represents a horizontal coordinate; v represents a longitudinal coordinate; i represents an imaginary unit.

2. The vortex-pair beam based optical tweezer system according to claim 1, wherein a is 0.1 to 1 time the waist radius of an incident beam of the spatial light modulator.

3. The vortex-pair beam based optical tweezer system according to claim 1, wherein a horizontal coordinate and a longitudinal coordinate in the vortex pair phase diagram are calculated according to formula (2): $\begin{array}{cc}\{\begin{array}{c}u=u_0\cos \theta \left(t\right)+v_0\sin \theta \left(t\right)\\ v=-u_0\sin \theta \left(t\right)+v_0\cos \theta \left(t\right)\end{array}& \left(2\right)\end{array}$ wherein, u represents the horizontal coordinate; v represents the longitudinal coordinate; u.sub.0 represents an initial horizontal coordinate; v.sub.0 represents an initial longitudinal coordinate; θ(t) represents a rotation angle, and is a time function; t represents a time parameter.

4. The vortex-pair beam based optical tweezer system according to claim 3, wherein the range of θ(t) is 0 to 360°, and the maximum rotational angular speed is 60° per second.

5. The vortex-pair beam based optical tweezer system according to claim 1, wherein the collimating and beam expanding system comprises a half-wave plate, a polarization beam splitting prism, a high-reflectivity mirror, and a beam expanding lens system in sequence according to the setting of the light path; the confocal beam shrinking system comprises a first lens, a second lens, a beam splitter, and an objective lens in sequence according to the setting of the light path; the observation unit comprises a visible light source, a focusing lens, and a CCD detector.

6. The vortex-pair beam based optical tweezer system according to claim 5, wherein the half-wave plate can rotate around an optical axis.

7. The vortex-pair beam based optical tweezer system according to claim 1, wherein the spatial light modulator superposes a blazed grating phase diagram, and a diaphragm is arranged behind the spatial light modulator.

8. The vortex-pair beam based optical tweezer system according to claim 1, wherein the output power of the laser device is more than 400 mW; the wavelength of the laser device is 533 to 1064 nm.

9. The vortex-pair beam based optical tweezer system according to claim 1, wherein the wave band of the modulated light of the spatial light modulator is 450 to 1064 nm.

10. The vortex-pair beam based optical tweezer system according to claim 5, wherein the half-wave plate is fixed to a rotatable optical lens frame; the polarization direction of incident laser is changed by rotating the half-wave plate around the optical axis; the polarization beam splitting prism reflects light s and enables light p to pass through a dielectric beam splitting film to separate polarized light s from polarized light p; the optical power of output light is changed by rotating the half-wave plate and combining the polarization beam splitting prism; the high-reflectivity mirror is used for changing the light path, and reflecting the beam to the beam expanding lens system; the beam expanding lens system expands the radius of a light spot of the beam and realizes the collimation of the beam; the spatial light modulator is connected to a computer, and loads different vortex pair phase diagrams for the spatial light modulator through a control program of the computer to realize precise regulation, control, and positioning of the particle; a first lens, a second lens, and a beam splitter are used for shrinking the light spot of the vortex-pair beam generated by the modulation of the spatial light modulator, so that the light spot can completely enter the aperture of the objective lens; the objective lens is used for focusing the shrinked light spot onto the sample table; the sample table is a two-dimensional electric control displacement table; a light filter is arranged in front of the focusing lens and is used for filtering incident laser.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] To describe the technical solutions in the embodiments of the present disclosure or in the prior art more clearly, the following briefly describes the accompanying drawings required for describing the embodiments. Apparently, the accompanying drawings in the following description show merely some embodiments of the present disclosure, and those of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts.

[0038] FIG. 1 is a light path diagram of an optical tweezer system of the embodiments of the present disclosure.

[0039] FIG. 2 is a vortex pair phase diagram when a=0.45 mm, m.sub.1=6, and m.sub.2=6;

[0040] FIG. 3 is a vortex pair phase diagram when a=0.9 mm, m.sub.1=6, and m.sub.2=6;

[0041] FIG. 4 is a trapping effect diagram of the optical tweezer system on two spherical particles, where in (a), a=0.45 mm; in (b), a=0.9 mm;

[0042] FIG. 5 is a theoretical light intensity distribution diagram of a vortex-pair beam after being focused through a lens with the focal length of 500 mm on a focal plane, m.sub.1=6, m.sub.2=6, and a=0.9 mm;

[0043] FIG. 6 is a vortex pair phase diagram after the vortex-pair beam is rotated 120°, a=0.9 mm, m.sub.1=6, m.sub.2=6, and θ(t)=120°;

[0044] FIG. 7 is a trapping effect diagram of the optical tweezer system on a rod-shaped particle, where in (a), a=0.9 mm, m.sub.1=6, m.sub.2=6, and θ(t)=0°; in (b), a=0.9 mm, m.sub.1=6, m.sub.2=6, and θ(t)=120°.

[0045] Reference signs in drawings: 1—laser device; 2—half-wave plate; 3—polarization beam splitting prism; 4—high-reflectivity mirror; 5—beam expanding lens system; 6—spatial light modulator, 7—diaphragm; 8—first lens; 9—second lens; 10—beam splitter; 11—objective lens; 12—sample table; 13—visible light source; 14—light filter; 15—focusing lens; 16—CCD detector; 17—computer.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] The technical solutions in the embodiments of the present disclosure will be clearly and completely described herein below with reference to the accompanying drawings in the embodiments of the present disclosure. Apparently, the described embodiments are merely part rather than all of the embodiments of the present disclosure. On the basis of the embodiments of the present disclosure, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present disclosure.

[0047] The objective of the present disclosure is to provide a vortex-pair beam based optical tweezer system, which solves the problems in the prior art that relative positions of two particles cannot be regulated and controlled, and directional rotation of specially structural, such as strip-shaped, particles cannot be realized. The optical tweezer system can realize precise regulation, control, and positioning of two spherical particles at relative positions in a plane, and any controllable rotation operation of a rod-shaped particle in the plane, which makes the application objects of the optical tweezer system richer, and effectively solves the problem that the rod-shaped particle is difficult to be controlled by the existing optical tweezer system.

[0048] In order to make the above objective, features, and advantages of the present disclosure more apparent and more comprehensible, the present disclosure is further described in detail below with reference to the accompanying drawings and specific vortex-pair beam in emergent light of the spatial light modulator.

[0049] The vortex-pair beam emitted from the spatial light modulator 6 passes through the diaphragm 7 to pick out the first order diffraction light and block other orders of light. The first order diffraction light is the vortex-pair beam of a target, and radius of the beam is reduced through the first lens 8 and the second lens 9, so that the light spot completely enters the aperture of the objective lens 11. Then, the vortex-pair beam is reflected to the objective lens 11 through the reflection of the beam splitter 10. The vortex-pair beam is focused to a sample to be tested on the sample table 12 through the objective lens 11. The sample table 12 is a two-dimensional electric control table, which can precisely move and position the particle that needs to be trapped.

[0050] The sample to be tested on the sample table 12 is illuminated through the visible light source 13, and the light of the light source is focused and imaged on the CCD detector 16 by the focusing lens 15 after being filtered through the light filter 14. The light filter 14 is arranged in front of the focusing lens 15 and is used for filtering the incident laser, so as to prevent the incident laser from affecting the imaging of the CCD detector 16.

[0051] In the following embodiments, the laser device 1 is a high-power semiconductor continuous laser device with the wavelength of 533 nm, and has the maximum output power of 2 W. The power can meet the requirement of enough trapping force when trapping the particle. The laser device adopts the laser device with the model number of MW-GL-532/2000 mW-16060208 of Changchun Leishi Photoelectric Technology Co., LTD.

[0052] The beam expanding lens system 5 adopts a GCO-25 series contact zoom beam expanding lens of Daheng Photoelectric Technology Company, and has the model number of GCO-2503.

[0053] The spatial light modulator 6 adopts a spatial light modulator with the model number of PLUTO-2-VIS-056 of Holoeye Company. The wave band of the modulated light is 450 to 650 nm, and the reflectivity is greater than 93%.

[0054] The objective lens 11 has the aperture NA=1.25, and the magnification of 100. The objective lens adopts the lens with the model number of CFI Achromat 100× OilA N.A.1.25 of Nikon Corporation. The light filter adopts the light filter with the model number of Thorlab FD1M.

Embodiment 1

[0055] The laser device 1 emits a linearly polarized beam with the wavelength of 533 nm. After the linearly polarized beam passes through the half-wave plate 2 and the polarization beam splitting prism 3, the polarization direction of the beam is horizontally polarized, and the light intensity suitable for trapping the particle is regulated by rotating the half-wave plate 2. The beam passes through the high-reflectivity mirror 4 to change its propagation direction and enters the beam expanding lens system 5; the beam size is expanded twice by the beam expanding lens system 5; the diameter of the spot after the beam is expanded is about 3 mm, which can cover a liquid crystal panel of the spatial light modulator 6.

[0056] The beam expanded by the beam expanding lens system 5 enters the spatial light modulator 6. The spatial light modulator 6 is controlled to load a vortex pair phase diagram in real time by the computer 17. The vortex-pair beam modulated by the spatial light modulator 6 passes through the diaphragm 7 to pick out the first order diffraction light. The beam is shrinked by the first lens 7 and the second lens 8, where the beam shrinking ratio is 80%.

[0057] The shrinked vortex-pair beam is reflected to enter the objective lens 11 by the beam splitter 10. The laser is focused in the sample to be tested on the sample table 12. The particle can be moved and trapped by moving the sample table 12. The visible light source 13 illuminates the sample to be tested on the sample table 12, the light passes through the light filter 14 to filter the laser with the wavelength of 533 nm, and then is focused on the CCD detector 16 through the focusing lens 15.

[0058] The spatial light modulator 6 is controlled by the computer 17 to load an initial phase diagram of the vortex-pair beam and superposes the blazed grating phase diagram. The first order diffraction light is picked out through the diaphragm 7, and the diffracted first order diffraction beam is the vortex-pair beam that we need. Precise control and rotation of two particles can be realized by loading the vortex pair phase diagram in real time. The vortex pair phase diagram is calculated through formula (1):

[00003]$\begin{array}{cc}\varphi \left(u,v\right)={\left(\frac{u-a+\mathrm{iv}}{\sqrt{{\left(u-a\right)}^2+v^2}}\right)}^{m_1}{\left(\frac{u+a+\mathrm{iv}}{\sqrt{{\left(u+a\right)}^2+v^2}}\right)}^{m_2}& \left(1\right)\end{array}$

[0059] Where, ϕ represents a phase, m.sub.1, m.sub.2 are any two equal integers, called topological charges; a represents the off-axis distance of phase singularities of double vortices, and is any real number, u represents a horizontal coordinate; v represents a longitudinal coordinate; i represents an imaginary unit.

[0060] The initial phase diagram of the vortex-pair beam is as shown in FIG. 2, where a=0.45 mm, m.sub.1=6, and m.sub.2=6. The phase diagram of the vortex-pair beam is as shown in FIG. 3 by keeping m.sub.1, m.sub.2 unchanged and continuously increasing the off-axis distance parameter a to a=0.9 mm, where a=0.9 mm, m.sub.1=6, and m.sub.2=6.

[0061] In the phase diagram loaded by the spatial light modulator, when m.sub.1=6, m.sub.2=6, and a=0.45 mm, the trapping effect diagram of the optical tweezer system on a spherical particle is as shown in (a) of FIG. 4, and controllable distance operation of the two spherical particles in the transverse direction can be realized by adjusting 8 in the phase diagram. When m.sub.1=6, m.sub.2=6, and a=0.9 mm, the trapping effect diagram of the optical tweezer system on a spherical particle is as shown in (b) of FIG. 4, and the transverse distance between two spherical particles is shortened.

[0062] FIG. 5 is a theoretical light intensity distribution diagram of a vortex-pair beam on a focal plane after being focused through a lens with the focal length of 500 mm, the parameters are that m.sub.1=6, m.sub.2=6, and a=0.9 mm.

Embodiment 2

[0063] By using the same optical tweezer system as Embodiment 1, the vortex pair phase diagram loaded by the spatial light modulator is calculated through formula (1):

[00004]$\begin{array}{cc}\varphi \left(u,v\right)={\left(\frac{u-a+\mathrm{iv}}{\sqrt{{\left(u-a\right)}^2+v^2}}\right)}^{m_1}{\left(\frac{u+a+\mathrm{iv}}{\sqrt{{\left(u+a\right)}^2+v^2}}\right)}^{m_2}& \left(1\right)\end{array}$

[0064] Where, ϕ represents a phase, m.sub.1, m.sub.2 are any two equal integers, called topological charges; a represents the off-axis distance of phase singularities of double vortices, and is any real number, u represents a horizontal coordinate; v represents a longitudinal coordinate; i represents an imaginary unit.

[0065] The horizontal coordinate and the longitudinal coordinate in the vortex pair phase diagram are calculated according to formula (2):

[00005]$\begin{array}{cc}\{\begin{array}{c}u=u_0\cos \theta \left(t\right)+v_0\sin \theta \left(t\right)\\ v=-u_0\sin \theta \left(t\right)+v_0\cos \theta \left(t\right)\end{array}& \left(2\right)\end{array}$

[0066] Where, u represents the horizontal coordinate; v represents the longitudinal coordinate; u.sub.0 represents an initial horizontal coordinate; v.sub.0 represents an initial longitudinal coordinate; θ represents a rotation angle, and is a time function; t represents a time parameter.

[0067] By taking the phase diagram in which m.sub.1=6, m.sub.2=6, a=0.9 mm, and θ(t)=0° as the initial phase diagram, the trapping effect diagram of the optical tweezer system on a rod-shaped particle is as shown in (a) of FIG. 7. The rod-shaped particle is horizontal and transverse;

[0068] the rotation angle in formula (2) is adjusted, and when θ(t)=120°, and other parameters are unchanged, the rotated vortex pair phase diagram is as shown in FIG. 6; controllable directional rotation of the rod-shaped particle is realized, as shown in (b) of FIG. 7, the rod-shaped particle is rotated 120° counterclockwise.

[0069] The range of θ(t) is 0 to 360°. Any rotation of the vortex-pair beam at 360°, including external rotational angular speed, or the rotation of a specially structural, such as non-spherical, particle at any angle in 360° can be realized. The maximum rotational angular speed is 60° per second. The phase diagrams at different rotation angles can be prepared by changing the time parameter t, so as to realize speed-controllable rotation of the rod-shaped particle. The optical tweezer system has extremely high precision, high stability, and convenience in operation.

[0070] Various embodiments in the present specification are described in a progressive manner. Each embodiment focuses on differences from other embodiments, and the same and similar parts of various embodiments may be referred to one another.

[0071] Herein, specific examples are used to describe the principle and implementation manners of the present disclosure. The description of the embodiments above is merely intended to help understand the method and its core idea of the present disclosure. In addition, those of ordinary skill in the art may make modifications based on the idea of the present disclosure with respect to the specific implementation manners and the application scope. In conclusion, the contents of the present specification shall not be construed as a limitation to the present disclosure.