Optical vortex control device and optical vortex control method

Abstract

An optical-vortex control device 1 controls the motion of a microbody in a medium in a sample 90 and includes a light source 10, an optical-vortex generation unit 20, lenses 30-33, an aperture 34, a dichroic mirror 40, a lighting unit 50, an imaging unit 60, and a control unit 70. The objective lens 30 condenses an optical vortex generated by the optical-vortex generation unit 20 and irradiates the microbody in the medium in the sample 90 with the condensed optical vortex to optically trap the microbody. The imaging unit 60 captures an image of the microbody optically trapped and in motion, and outputs image data thereof. The control unit 70 analyzes the motion of the microbody on the basis of the image data, and adjusts the phase distribution of the optical vortex generated by the optical-vortex generation unit 20 on the basis of the result of the analysis, thereby controlling the motion of the microbody. Accordingly, an optical-vortex control device that makes it possible to readily generate a desired optical vortex is realized.

Description

Technical Field

[0001] The present disclosure relates to an optical vortex control device and an optical vortex control method.

Background Art

[0002] A technique of optically trapping microparticles in a medium using an optical vortex is known. An optical vortex has a phase singularity on the propagation axis, has an optical intensity of 0 on the propagation axis, and has a doughnut-shaped optical intensity distribution with a maximum optical intensity at a certain distance from the propagation axis.

[0003] In addition to having a doughnut-shaped optical intensity distribution, an optical vortex is also characterized by having an orbital angular momentum. When a microparticle in a medium is irradiated with an optical vortex having an orbital angular momentum, the microparticle receives angular momentum from the optical vortex and rotates along an orbit with a high optical intensity around the propagation axis. That is, an optical vortex can optically trap a microparticle in a medium and control the movement of the microparticle.

[0004] Depending on the performance of optical components in the optical system from the light source to the microparticle and the adjustment accuracy during the construction of the optical system, the optical vortex irradiated to the microparticle may not be as desired, and the movement of the microparticle may not be as desired. For example, even when it is desired to move a microparticle at a constant speed on a circular orbit, depending on the performance of optical components and the adjustment accuracy during the construction of the optical system, the trajectory of the movement of the microparticle may become elliptical or the speed may fluctuate.

[0005] Non-Patent Documents 1 to 5 describe a technique for estimating the aberration of an optical system based on the intensity information of an optical vortex and improving the accuracy of optical trapping by performing aberration correction based on this estimation result. In the techniques described in Non-Patent Documents 4 and 5, the relationship between the aberration correction amount and the intensity information is learned by machine learning, and the aberration correction amount is obtained from the intensity information.

[0006] In the technique described in Non-Patent Literature 6, a modulation pattern presented on the modulation surface of a spatial light modulator is imaged onto the sample surface, causing a microscopic object on the sample surface to be optically trapped and moved. The modulation pattern is then adjusted based on the intensity information of the optical vortex and the motion information of the microscopic object.

[0007] Specifically, the optical amplitude distribution on the sample surface is adjusted to the desired value by adding a phase grating pattern based on the intensity information of the optical vortex to the modulation pattern presented on the modulation surface of the spatial light modulator. Furthermore, the motion of the micro-body is adjusted to the desired value by adjusting the phase distribution based on the motion information (specifically, the angular velocity distribution) of the micro-body to the modulation pattern presented on the modulation surface of the spatial light modulator (specifically, the orbital angular momentum density distribution (OAM-density) is made uniform). [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] SN Khonina, et al., "Strengthening the longitudinal component of the sharply focused electric field by means of higher-order laser beams", Optics Letters, Vol.38, No.17, pp.3223-3226, 2013 [Non-Patent Document 2] Y. Iketaki, et al., "Investigation of the center intensity of first- and second-order Laguerre-Gaussian beams with linear and circular polarization", Optics Letters, Vol.32, No.16, pp.2357-2359, 2007 [Non-Patent Document 3] Yansheng Liang, et al., "Aberration correction in holographic optical tweezers using a high-order optical vortex", Applied Optics, Vol.57, No.13, pp.3618-3623, 2018 [Non-Patent Document 4] Benjamin P. Cumming, et al., "Direct determination of aberration functions in microscopy by an artificial neural network", Optics Express, Vol.28, No.10, pp.14511-14521, 2020 [Non-Patent Document 5] Jin Li, et al., "Study on Aberration Correction of Adaptive Optics Based on Convolutional Neural Network", Photonics, Vol.8, 377, pp.1-9, 2021 [Non-Patent Document 6] Mingzhou Chen, et al., "Dynamics of microparticles trapped in a perfect vortex beam", Optics Letters, Vol.38, No.22, pp.4919-4922, 2013 [Overview of the project] [Problems that the invention aims to solve]

[0009] The techniques described in Non-Patent Documents 1-5 require high-precision optical equipment and complex post-processing to acquire intensity information of optical vortices generated by high NA objective lenses, making them difficult to implement. The technique described in Non-Patent Document 6 has similar problems to those described in Non-Patent Documents 1-5, and also requires two-stage adjustment of the modulation pattern presented on the modulation surface of the spatial light modulator, making it difficult to implement in this respect as well.

[0010] The embodiment aims to provide an optical vortex control device and an optical vortex control method that can easily generate a desired optical vortex. [Means for solving the problem]

[0011] The embodiment is an optical vortex control device. The optical vortex control device comprises a light source that outputs light, an optical vortex generation unit that generates optical vortices from this light, a focusing optical system that focuses the optical vortices, an imaging unit that images a minute object that is optically trapped and moving by the optical vortices focused by the focusing optical system and outputs image data, and a control unit that analyzes the motion of the minute object based on the image data and adjusts the phase distribution of the optical vortices generated by the optical vortex generation unit based on the analysis results. The control unit calculates an evaluation function that includes an ellipticity evaluation value representing how much the motion trajectory of the micro-body deviates from a perfect circle, and a variance evaluation value representing the degree of variation in the velocity of the motion of the micro-body, and adjusts the phase distribution of the optical vortices generated by the optical vortex generation unit according to the value of the evaluation function. ru.

[0012] The embodiment is an optical vortex control method. The optical vortex control method uses a light source that outputs light, an optical vortex generation unit that generates optical vortices from this light, and a focusing optical system that focuses the optical vortices, and comprises an imaging step in which a minute object that is optically trapped and moving by the optical vortices focused by the focusing optical system is captured by an imaging unit and image data is output, and a control step in which the motion of the minute object is analyzed based on the image data and the phase distribution of the optical vortices generated by the optical vortex generation unit is adjusted based on the analysis results. In the control step, an evaluation function is obtained that includes an ellipticity evaluation value representing how much the motion trajectory of the micro-body deviates from a perfect circle, and a variance evaluation value representing the degree of variation in the velocity of the motion of the micro-body. The phase distribution of the optical vortices generated by the optical vortex generation unit is then adjusted according to the value of the evaluation function. ru. [Effects of the Invention]

[0013] According to the optical vortex control device and optical vortex control method of the embodiment, a desired optical vortex can be easily generated. [Brief explanation of the drawing]

[0014] [Figure 1] FIG. 1 is a diagram showing the configuration of the optical vortex control device 1. [Figure 2] FIG. 2 is a diagram for explaining the optical trapping of the microbody 91 by the optical vortex. [Figure 3] FIG. 3 is a diagram for explaining the optical trapping of the microbody 91 by the optical vortex. [Figure 4] FIG. 4 is a diagram showing an example of the intensity distribution of the optical vortex at the (a) and (b) sample positions. [Figure 5] FIG. 5 is a diagram showing the movement trajectory of the microbody before adjusting the generation of the optical vortex when using the objective lens A, and (b) a diagram showing the movement trajectory of the microbody after adjusting the generation of the optical vortex when using the objective lens A. [Figure 6] FIG. 6 is a graph showing the torque distribution of the microbody before and after adjusting the generation of the optical vortex when using the objective lens A. [Figure 7] FIG. 7 is a diagram showing the movement trajectory of the microbody before adjusting the generation of the optical vortex when using the objective lens B, and (b) a diagram showing the movement trajectory of the microbody after adjusting the generation of the optical vortex when using the objective lens B. [Figure 8] FIG. 8 is a graph showing the torque distribution of the microbody before and after adjusting the generation of the optical vortex when using the objective lens B. [Figure 9] FIG. 9 is a diagram showing the movement trajectory of the microbody before adjusting the generation of the optical vortex when using the objective lens C, and (b) a diagram showing the movement trajectory of the microbody after adjusting the generation of the optical vortex when using the objective lens C. [Figure 10] FIG. 10 is a graph showing the torque distribution of the microbody before and after adjusting the generation of the optical vortex when using the objective lens C. [Figure 11] FIG. 11 is a diagram showing the movement trajectory of the microbody before adjusting the generation of the optical vortex when using the objective lens D, and (b) a diagram showing the movement trajectory of the microbody after adjusting the generation of the optical vortex when using the objective lens D. [Figure 12] FIG. 12 is a graph showing the torque distribution of the microbody before and after adjusting the generation of the optical vortex when using the objective lens D. [Figure 13]Figure 13 shows (a) the motion trajectory of a microorganism before optical vortex generation adjustment when using objective lens E, and (b) the motion trajectory of a microorganism after optical vortex generation adjustment when using objective lens E. [Figure 14] Figure 14 is a graph showing the torque distribution of the micro-body before and after optical vortex generation adjustment when using objective lens E. [Figure 15] Figure 15 shows an example of an adjustment pattern for adjusting optical vortex generation. [Figure 16] Figure 16 is a table summarizing the ellipticity and torque distribution variance values ​​before and after optical vortex generation adjustment for each objective lens A to E. [Modes for carrying out the invention]

[0015] Embodiments of the optical vortex control device and optical vortex control method will be described in detail below with reference to the attached drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted. The present invention is not limited to these examples, but is indicated by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

[0016] Figure 1 shows the configuration of the optical vortex control device 1. The optical vortex control device 1 is a device that controls the movement of minute bodies in a medium in a sample 90, and comprises a light source 10, an optical vortex generation unit 20, lenses 30-33, an aperture 34, a dichroic mirror 40, an illumination unit 50, an imaging unit 60, and a control unit 70.

[0017] The medium in sample 90 is either a liquid or a gas. The shape of the microorganisms in the medium is arbitrary and may be, for example, a sphere, a cube, or a cone. The material of the microorganisms is also arbitrary and may be, for example, polystyrene beads, glass, or quartz. The microorganisms have a size and weight such that they can be optically trapped by optical vortices in the medium.

[0018] The light source 10 outputs light. Preferably, the light source 10 is a laser light source that generates coherent light. Preferably, the light output from the light source 10 has a wavelength that causes little thermal absorption by the medium in the sample 90.

[0019] The optical vortex generation unit 20 is optically connected to the light source 10. The optical vortex generation unit 20 receives light output from the light source 10, generates an optical vortex, and outputs it. The optical vortex generated by the optical vortex generation unit 20 is an optical beam with a helical wavefront, such as a Laguerre-Gauss beam or a Bessel beam. A diffractive optical element or a spatial light modulator is preferably used as the optical vortex generation unit 20.

[0020] A spatial light modulator has multiple pixels arranged in a two-dimensional array and can modulate and output at least the phase of light at each pixel. The spatial light modulator may also be capable of modulating the amplitude of light at each pixel. If such a spatial light modulator is used as the optical vortex generation unit 20, various forms of optical vortices can be easily generated according to the set modulation pattern without changing the optical system, and various evaluations of the optical trap state of a minute body can be performed.

[0021] The spatial light modulator used as the optical vortex generation unit 20 may be a transmissive type or a reflective type, and in the latter case, it may be an LCOS-SLM (Liquid Crystal on Silicon - Spatial Light Modulator). Figure 1 shows a reflective spatial light modulator as the optical vortex generation unit 20. In Figure 1, the light output from the light source 10 is incident obliquely on the optical vortex generation unit 20, but the light may also be incident on the optical vortex generation unit 20 at an angle closer to perpendicular.

[0022] Lens 31, aperture 34, lens 32, dichroic mirror 40, and objective lens 30 constitute a focusing optical system that guides the optical vortices output from the optical vortex generation unit 20 to the microorganisms in the medium of the sample 90.

[0023] The rear focal position of lens 31 and the front focal position of lens 32 coincide with each other. The aperture 34 has an opening at the rear focal position of lens 31. Lenses 31 and 32 are positioned so that the modulation plane of the optical vortex generation unit 20 and the pupil plane of the objective lens 30 are conjugate to each other, and the image of the optical vortex output from the optical vortex generation unit 20 is imaged near the pupil plane of the objective lens 30.

[0024] The dichroic mirror 40 reflects the light arriving from the lens 32 to the objective lens 30. The objective lens 30 focuses the optical vortex onto the microorganisms in the medium of the sample 90, thereby optically trapping the microorganisms. The rotational shape (circular, elliptical) of the microorganisms can also be controlled by placing a λ / 4 plate or a λ / 2 plate in the optical path of the optical vortex before it enters the objective lens 30.

[0025] The illumination unit 50 is located on the side opposite the objective lens 30, with the sample 90 in between, and outputs illumination light to the sample 90. Preferably, the illumination unit 50 outputs light of a different wavelength than the light output from the light source 10. A white light source, a mercury lamp, a laser light source, etc., can be used as the illumination unit 50.

[0026] The imaging unit 60 captures images of a minute object that is light-trapped and moving, illuminated by the illumination unit 50, via the objective lens 30, dichroic mirror 40, and lens 33, and outputs image data. A CCD camera, CMOS camera, etc., can be used as the imaging unit 60. The dichroic mirror 40 transmits light from the sample 90 illuminated by the illumination unit 50.

[0027] The control unit 70 analyzes the motion of the micro-body based on the image data output from the imaging unit 60. Based on the analysis results, the control unit 70 controls the motion of the micro-body by adjusting the phase distribution of the optical vortices generated by the optical vortex generation unit 20. A computer or the like is used as the control unit 70.

[0028] The control unit 70 includes a processing unit, such as a CPU or FPGA, for analyzing the motion of microorganisms and adjusting the generation of optical vortices; a display unit, such as a liquid crystal display, for displaying the motion of microorganisms captured by the imaging unit 60, as well as modulation patterns for optical vortex generation and adjustment patterns for adjustment; an input unit, such as a keyboard or mouse, for receiving adjustment conditions for optical vortex generation and instructions to start adjustment; and a storage unit, such as a hard disk drive or RAM, for storing programs for processing performed by the processing unit and various data.

[0029] Figures 2 and 3 illustrate the optical trapping of microorganisms 91 by an optical vortex. Figure 2 shows the optical vortex L viewed perpendicular to its propagation axis. Figure 3 shows the optical vortex L viewed along its propagation axis, with hatching indicating the donut-shaped region of high light intensity within the optical vortex L. When the optical vortex L is focused and shone onto a sample 90, it can optically trap the microorganisms 91 in the medium 92 within the sample 90, causing the microorganisms 91 to rotate around their propagation axis. The rotational motion of the microorganisms 91 can be, for example, circular or elliptical.

[0030] Figures 4(a) and (b) show an example of the intensity distribution of optical vortices at the sample location. This figure shows the light intensity on a plane perpendicular to the propagation axis using shades of gray, with lighter shades indicating higher light intensity.

[0031] As shown in this figure, the optical vortex has a donut-shaped optical intensity distribution where the optical intensity is maximum at a certain radial distance from the propagation axis. Both the optical intensity distributions in Figures 4(a) and (b) are intended to generate a perfectly circular optical intensity distribution where the optical intensity is maximum at a certain radial distance from the propagation axis, thereby intended to move the optically trapped microorganism along a perfectly circular orbit.

[0032] However, the light intensity distribution shown in Figure 4(a) has lower circularity compared to the light intensity distribution shown in Figure 4(b), and as a result, the motion trajectory of the light-trapped micro-object differs significantly from a perfect circle. The reason why the light intensity distribution differs from the desired one is thought to be due to aberrations in the optical system caused by limitations in the performance of the optical components constituting the optical system of the optical vortex control device and the adjustment precision during the construction of the optical system.

[0033] In this embodiment, the optical system aberrations are corrected based on the motion information of the optically trapped microorganisms, thereby bringing the light intensity distribution at the sample position closer to the desired one. The optical vortex control method of this embodiment comprises an imaging step and a control step.

[0034] In the imaging step, the imaging unit 60 captures images of the moving micro-objects trapped by light and outputs image data. In the control step, the motion of the micro-objects is analyzed based on the image data, and the phase distribution of the optical vortices generated by the optical vortex generation unit 20 is adjusted based on the analysis results.

[0035] The optical vortex generation unit 20 may include one spatial light modulator, or it may include two spatial light modulators connected in optical series. If the optical vortex generation unit 20 includes one spatial light modulator, the adjustment pattern (phase distribution) for adjusting optical vortex generation, obtained based on the analysis results of the motion of the micro-body, is superimposed on the modulation pattern for optical vortex generation before adjustment, and the resulting superimposed modulation pattern is presented to the single spatial light modulator.

[0036] Furthermore, if the optical vortex generation unit 20 includes two spatial light modulators, the modulation pattern for optical vortex generation before adjustment can be presented to one spatial light modulator, and the adjustment pattern (phase distribution) for optical vortex generation adjustment, obtained based on the analysis results of the motion of the micro-body, can be presented to the other spatial light modulator.

[0037] In the control step, the control unit 70 preferably analyzes one of the following as the motion of the microorganism: the motion trajectory, position distribution, and torque distribution of the microorganism. Alternatively, the sum of the squares of the differences between the motion trajectory of the microorganism and a desired trajectory may be analyzed as the motion of the microorganism, allowing for the analysis of any parameter related to motion.

[0038] Furthermore, in the control step, the control unit 70 analyzes the motion of the microorganism, preferably either the velocity distribution or the angular velocity of the microorganism. Furthermore, in the control step, the control unit 70 analyzes the motion of the microorganism, preferably based on a function in which the motion trajectory, position distribution, velocity distribution, angular velocity, and torque distribution of the microorganism are variables.

[0039] In analyzing the motion trajectory of a microorganism, for example, the motion trajectory of the microorganism obtained based on image data is approximated by an ellipse, and the ellipticity, which is the ratio of the minor axis to the major axis of the ellipse, is determined. In analyzing the positional distribution of a microorganism, for example, the circumferential direction around the propagation axis is divided into multiple sections at fixed angles, and the positional distribution of the microorganism in the circumferential direction around the propagation axis is determined by finding out which of these sections the microorganism is located in for each frame of the image data.

[0040] Furthermore, in the analysis of the torque distribution of microorganisms, for example, the circumferential direction around the propagation axis is divided into multiple sections at regular angle intervals, and the torque of the microorganisms in each of these sections is determined based on image data, thereby determining the torque distribution of the microorganisms in the circumferential direction around the propagation axis.

[0041] When a small object is undergoing rotational motion, there is a relationship between the mean angular velocity ω, torque N, and viscous drag coefficient Γ, as shown in equation (1) below. The viscous drag coefficient Γ is determined from the statistical variance of the angular velocity according to the Fluctuation Dissipation Theorem of Brownian motion.

number

[0042] A statistical set of angular velocity information {ω} of a small object exhibiting Brownian motion in a circular orbit under a constant rotational force. i Given}(i=1,2,…,M), the fluctuation-dissipation theorem is expressed by equations (2) and (3) below, where T is the absolute temperature and k B Δω is the Boltzmann constant, and Δω is the angular velocity variance. Note that a correction may be applied to calculate the correct angular velocity variance from the experimental data.

number

number

[0043] The imaging unit 60 acquires image data at a constant frame rate using a plurality of pixels arranged in two dimensions on an imaging surface that receives light from the micro-body. Since motion information of the micro-body is acquired based on this image data, it is preferable that there is the following relationship between the exposure time of each frame and the motion of the micro-body.

[0044] The centroid of a microorganism is determined by performing centroid calculations on the image of the microorganism in each frame. However, if the exposure time for each frame is too long, the distance the microorganism moves during that exposure becomes long, and the image of the microorganism stretches in the direction of movement, making it difficult to accurately determine the centroid of the microorganism.

[0045] Therefore, in order to accurately determine the centroid position of a micro-body, it is preferable that the distance the micro-body moves within the exposure time on each frame of the image is smaller than the size of the micro-body image. The centroid calculation allows for obtaining positional information of the micro-body with an accuracy below the diffraction limit. Note that the distance the micro-body moves within the exposure time depends on the amount of optical vortex light.

[0046] Furthermore, the velocity vector of the microorganism can be determined based on the position of the centroid of the microorganism in the image of the frame at a certain time t1 and the frame at the following time t2, and the circumferential velocity vector distribution of the microorganism can also be determined. However, if the difference between time t1 and time t2 is too large, it becomes difficult to distinguish the direction of rotation of the microorganism (clockwise / counterclockwise).

[0047] Therefore, in order to distinguish the direction of rotation of the micro-body, it is preferable that the product of the average angular velocity of the rotational motion of the micro-body and the exposure time of each frame is less than 180°.

[0048] In the control step, the control unit 70 uses one or more of these analysis results. When using one analysis result, it adjusts the optical vortex generation by the optical vortex generation unit 20 so that the evaluation value based on that analysis result is minimized. When using multiple analysis results, for example, the linear sum of the evaluation values ​​based on each analysis result is used as an evaluation function, and the optical vortex generation by the optical vortex generation unit 20 is adjusted so that the value of this evaluation function is minimized.

[0049] For example, if we want to move a microscopic body at a constant speed along a perfectly circular orbit, we calculate an ellipticity evaluation value A, which represents how much the trajectory of the microscopic body deviates from a perfect circle, based on ellipticity, and we calculate a variance evaluation value B, which represents the degree of variation in the speed of the microscopic body's motion, based on the variance of the positional distribution or torque distribution of the microscopic body. We also calculate an evaluation function expressed by the equation αA + βB using coefficients α and β. Then, we adjust the optical vortex generation by the optical vortex generation unit 20 so that the value of this evaluation function is minimized.

[0050] In the control step, when the control unit 70 determines an adjustment pattern for adjusting the optical vortex generation by the optical vortex generation unit 20 based on the analysis results, it is preferable to express the adjustment pattern using a Zernike polynomial, and it is also preferable to determine the adjustment pattern using an optimization method.

[0051] Zernike polynomials are orthogonal polynomials defined on the unit circle, expressed by two exponents (non-negative integers n and integers m) and two variables (radius ρ and argument φ). Zernike polynomials are particularly used in the field of optics to analytically treat axially symmetric optical aberrations based on diffraction theory. They can also be used to represent aberration correction patterns.

[0052] For optimization, methods such as annealing, genetic algorithms, or blind search can be used. When the aberration correction amount is expressed as a linear sum of multiple aberration components, the coefficients of each aberration component can be determined using optimization methods.

[0053] In the control step, the control unit 70 superimposes an adjustment pattern for optical vortex generation adjustment, obtained based on the analysis results of the motion of the micro-body, onto the modulation pattern for optical vortex generation before adjustment, and causes the optical vortex generation unit 20 to present the resulting modulation pattern. This allows the control unit 70 to control the motion of the micro-body by adjusting the optical vortex generation by the optical vortex generation unit 20. The adjustment pattern may include both amplitude distribution and phase distribution, but may include only phase distribution.

[0054] Next, an example will be described. In the example, in the configuration of the optical vortex control device 1 shown in Figure 1, the motion trajectory and torque distribution of the minute bodies were determined for each of the five objective lenses A to E used as the objective lens 30, both before and after optical vortex generation adjustment.

[0055] Of the five objective lenses A through E, the optical system of the optical vortex control device 1 was constructed by the same person using four objective lenses B through E, but the optical system of the optical vortex control device 1 was constructed by a different person using the other objective lens A. Furthermore, of the five objective lenses A through E, four objective lenses A through D had the same specifications, but the other objective lens E had different specifications.

[0056] The four objective lenses A-D are plan-semi-apochromatic objective lenses corrected for chromatic aberration and field curvature, and have high transmittance across a wide bandwidth from the ultraviolet to the near-infrared region. Plan-semi-apochromatic objective lenses are higher-spec than achromatic objective lenses and are suitable for use in optical vortex generation. Objective lens E is an achromatic objective lens corrected for chromatic aberration in the visible range and is the most common type. Achromatic objective lenses are considered unsuitable for photography because focusing on the center of the field of view causes blurring at the edges.

[0057] A spatial light modulator was used as the optical vortex generation unit 20, and the hologram to be displayed was designed using the Kirk-Jones method. The design parameters were a declination index of 2, a radial index of 0, and a beam size radius of 2.00 mm. It is preferable that the radius of the optical vortex generated on the pupil plane of the objective lens is 20% or more of the radius of the pupil plane.

[0058] In this embodiment, sample 90 used polystyrene beads with a diameter of 0.40 μm as the micro-body 91 and pure water as the medium 92. An annular spacer was sandwiched between two glass plates, and the micro-body and medium were placed in the space formed by these. The micro-body (polystyrene beads) suspended in the medium (pure water) was then optically trapped by an optical vortex focused by an objective lens.

[0059] With the goal of moving a micro-body at a constant speed along a perfectly circular orbit, the optical vortex generation by the optical vortex generation unit 20 was adjusted so that the value of the evaluation function, which is expressed as a linear sum of the ellipticity evaluation value A and the variance evaluation value B, is minimized. Before and after the optical vortex generation adjustment, the centroid position of the micro-body in each frame of the image data was plotted as a point on the xy plane, the motion trajectory of the micro-body was approximated by an ellipse, and the ellipticity, which is the ratio of the minor axis to the major axis of the ellipse, was determined. Based on this ellipticity, the ellipticity evaluation value A was determined.

[0060] Furthermore, before and after optical vortex generation adjustment, the circumferential direction around the propagation axis was divided into 72 sections at fixed angles of 5 degrees each, and the torque of the microorganisms in each section was determined based on image data to obtain the torque distribution of the microorganisms in the circumferential direction around the propagation axis. Based on the variance of this torque distribution, a variance evaluation value B was calculated.

[0061] Figure 5(a) shows the motion trajectory of the microorganism before optical vortex generation adjustment when using objective lens A. Figure 5(b) shows the motion trajectory of the microorganism after optical vortex generation adjustment when using objective lens A. Figure 6 is a graph showing the torque distribution of the microorganism before and after optical vortex generation adjustment when using objective lens A.

[0062] Figure 7(a) shows the motion trajectory of the microorganism before optical vortex generation adjustment when using objective lens B. Figure 7(b) shows the motion trajectory of the microorganism after optical vortex generation adjustment when using objective lens B. Figure 8 is a graph showing the torque distribution of the microorganism before and after optical vortex generation adjustment when using objective lens B.

[0063] Figure 9(a) shows the motion trajectory of the microorganism before optical vortex generation adjustment when using objective lens C. Figure 9(b) shows the motion trajectory of the microorganism after optical vortex generation adjustment when using objective lens C. Figure 10 is a graph showing the torque distribution of the microorganism before and after optical vortex generation adjustment when using objective lens C.

[0064] Figure 11(a) shows the motion trajectory of the microorganism before optical vortex generation adjustment when using objective lens D. Figure 11(b) shows the motion trajectory of the microorganism after optical vortex generation adjustment when using objective lens D. Figure 12 is a graph showing the torque distribution of the microorganism before and after optical vortex generation adjustment when using objective lens D.

[0065] Figure 13(a) shows the motion trajectory of the microorganism before optical vortex generation adjustment when using objective lens E. Figure 13(b) shows the motion trajectory of the microorganism after optical vortex generation adjustment when using objective lens E. Figure 14 is a graph showing the torque distribution of the microorganism before and after optical vortex generation adjustment when using objective lens E.

[0066] Figures 5(a), 5(b), 7(a), 7(b), 9(a), 9(b), 11(a), 11(b), 13(a), and 13(b) each plot the centroid position of the microorganism in each frame of the image data as a point on the xy plane, with the density of the points indicated by the intensity of the grayscale. Figures 6, 8, 10, 12, and 14 are graphs with the horizontal axis representing the circumferential angular position around the propagation axis and the vertical axis representing torque.

[0067] Figure 15 shows an example of an adjustment pattern for optimizing optical vortex generation. This adjustment pattern is a phase distribution represented by a Zernike polynomial.

[0068] Figure 16 is a table summarizing the ellipticity and variance of the torque distribution before and after optical vortex generation adjustment for each of the objective lenses A to E. As shown in the results of the example, after optical vortex generation adjustment, the ellipticity could be brought closer to 1 compared to before adjustment, and the motion trajectory of the micro-body could be brought closer to a perfect circle. In addition, after optical vortex generation adjustment, the variance of the torque distribution of the micro-body in the circumferential direction around the propagation axis could be reduced compared to before adjustment, and the speed of motion of the micro-body could be brought closer to a constant value.

[0069] According to this embodiment, regardless of the performance of the optical components constituting the optical system or the adjustment precision during the construction of the optical system, it is possible to easily generate and adjust optical vortices that can bring the motion of a light-trapped minute object closer to a desired state.

[0070] In the techniques described in Non-Patent Documents 1 to 6, high-precision optical devices and complex post-processing are required to acquire optical vortex intensity information, making it difficult to adjust the generation of optical vortices. In contrast, in this embodiment, it is not necessary to acquire optical vortex intensity information, making it easy to adjust the generation of optical vortices.

[0071] In the technique described in Non-Patent Literature 6, the adjustment of the modulation pattern presented to the spatial light modulator is performed in two stages: amplitude distribution adjustment and phase distribution adjustment, making it difficult to adjust the generation of optical vortices. In contrast, in this embodiment, only phase distribution adjustment is required, making the adjustment of optical vortex generation easy. Furthermore, this embodiment is preferable because only phase distribution adjustment is required, thus suppressing light loss.

[0072] The optical vortex control device and optical vortex control method are not limited to the embodiments and configuration examples described above, and various modifications are possible.

[0073] The optical vortex control device according to the first embodiment described above comprises a light source that outputs light, an optical vortex generation unit that generates optical vortices from this light, a focusing optical system that focuses the optical vortices, an imaging unit that images a minute object that is optically trapped and moving by the optical vortices focused by the focusing optical system and outputs image data, and a control unit that analyzes the motion of the minute object based on the image data and adjusts the phase distribution of the optical vortices generated by the optical vortex generation unit based on the analysis results.

[0074] In the optical vortex control device of the second embodiment, the optical vortex generation unit may be configured to include a spatial light modulator having a plurality of pixels arranged in two dimensions, and at least the phase of light at each pixel is modulated and output.

[0075] In the optical vortex control device of the third embodiment, in the configuration of the second embodiment, the control unit may be configured to superimpose an adjustment pattern for adjusting optical vortex generation onto the modulation pattern for optical vortex generation, and then present the resulting modulation pattern to the spatial light modulator.

[0076] In the optical vortex control device of the fourth embodiment, the control unit may be configured to determine the adjustment pattern as a phase distribution, in the configuration of the third embodiment.

[0077] In the optical vortex control device of the fifth embodiment, in the configuration of the third or fourth embodiment, the control unit may be configured to determine the adjustment pattern using Zernike polynomials.

[0078] In the optical vortex control device of the sixth embodiment, in any of the configurations of the third to fifth embodiments, the control unit may be configured to determine the adjustment pattern using an optimization method.

[0079] In the optical vortex control device of the seventh embodiment, in any configuration of the first to sixth embodiments, the control unit may be configured to analyze one of the following as the motion of a micro-body: the motion trajectory of the micro-body, the position distribution, and the torque distribution.

[0080] In the optical vortex control device of the eighth embodiment, in any of the configurations of the first to sixth embodiments, the control unit may be configured to analyze either the velocity distribution or the angular velocity of a micro-body as the motion of a micro-body.

[0081] In the optical vortex control device of the ninth embodiment, in any of the configurations of the first to sixth embodiments, the control unit may be configured to analyze the motion of a micro-body based on a function in which one of the following variables is the motion trajectory, position distribution, velocity distribution, angular velocity, and torque distribution of the micro-body.

[0082] The optical vortex control method according to the first embodiment described above uses a light source that outputs light, an optical vortex generation unit that generates optical vortices from this light, and a focusing optical system that focuses the optical vortices, and comprises an imaging step in which a minute body that is optically trapped and moving by the optical vortices focused by the focusing optical system is imaged by an imaging unit and image data is output, and a control step in which the motion of the minute body is analyzed based on the image data and the phase distribution of the optical vortices generated by the optical vortex generation unit is adjusted based on the analysis results.

[0083] In the optical vortex control method of the second embodiment, the optical vortex generation unit may be configured to include a spatial light modulator having a plurality of pixels arranged in two dimensions, and at least the phase of light at each pixel is modulated and output.

[0084] In the optical vortex control method of the third embodiment, in the configuration of the second embodiment, in the control step, an adjustment pattern for adjusting optical vortex generation may be superimposed on the modulation pattern for optical vortex generation, and the resulting modulation pattern may be presented to the spatial light modulator.

[0085] In the optical vortex control method of the fourth embodiment, in the configuration of the third embodiment, the adjustment pattern may be determined as a phase distribution in the control step.

[0086] In the fifth embodiment of the optical vortex control method, in the configuration of the third or fourth embodiment, the control step may involve determining the adjustment pattern using a Zernike polynomial.

[0087] In the optical vortex control method of the sixth embodiment, in any of the configurations of the third to fifth embodiments, the control step may involve determining the adjustment pattern using an optimization method.

[0088] In the optical vortex control method of the seventh embodiment, in any of the configurations of the first to sixth embodiments, the control step may involve analyzing one of the motion trajectory, position distribution, or torque distribution of the micro-body as the motion of the micro-body.

[0089] In the optical vortex control method of the eighth embodiment, in any of the configurations of the first to sixth embodiments, the control step may involve analyzing either the velocity distribution or angular velocity of the microorganism as the motion of the microorganism.

[0090] In the optical vortex control method of the ninth embodiment, in any of the configurations of the first to sixth embodiments, the control step may involve analyzing the motion of a micro-body based on a function in which one of the following variables is the motion trajectory, position distribution, velocity distribution, angular velocity, and torque distribution of the micro-body. [Industrial applicability]

[0091] The embodiments can be used as an optical vortex control device and optical vortex control method that can easily generate a desired optical vortex. [Explanation of Symbols]

[0092] 1...Optical vortex control device, 10...Light source, 20...Optical vortex generation unit, 30-33...Lens, 34...Aperture, 40...Dichroic mirror, 50...Illumination unit, 60...Imaging unit, 70...Control unit, 90...Sample, 91...Microbody, 92...Medium.

Claims

1. A light source that emits light, A light vortex generating unit that generates a light vortex from the aforementioned light, A focusing optical system that focuses the aforementioned optical vortex, An imaging unit that captures images of a minute object that is light-trapped and moving by an optical vortex focused by the aforementioned light-collecting optical system and outputs image data, A control unit that analyzes the motion of the micro-body based on the image data and adjusts the phase distribution of the optical vortex generated by the optical vortex generation unit based on the analysis results, Equipped with, The control unit determines an evaluation function that includes an ellipticity evaluation value representing how much the motion trajectory of the micro-body deviates from a perfect circle, and a variance evaluation value representing the degree of variation in the speed of motion of the micro-body, and adjusts the phase distribution of the optical vortex generated by the optical vortex generation unit according to the value of the evaluation function, and is an optical vortex control device.

2. The optical vortex control device according to claim 1, wherein the optical vortex generating unit includes a spatial light modulator having a plurality of pixels arranged in two dimensions and outputting at least the phase of light at each pixel.

3. The optical vortex control device according to claim 2, wherein the control unit superimposes an adjustment pattern for adjusting optical vortex generation onto a modulation pattern for generating optical vortices, and causes the spatial light modulator to present the resulting superimposed modulation pattern.

4. The optical vortex control device according to claim 3, wherein the control unit determines the adjustment pattern as a phase distribution.

5. The optical vortex control device according to claim 3, wherein the control unit determines the adjustment pattern using a Zernike polynomial.

6. The optical vortex control device according to claim 3, wherein the control unit determines the adjustment pattern using an optimization method.

7. The optical vortex control device according to any one of claims 1 to 6, wherein the control unit analyzes the motion of the micro-body as any one of the motion trajectory, position distribution, and torque distribution of the micro-body.

8. The optical vortex control device according to any one of claims 1 to 6, wherein the control unit analyzes either the velocity distribution or the angular velocity of the microorganism as the motion of the microorganism.

9. The optical vortex control device according to any one of claims 1 to 6, wherein the control unit analyzes the motion of the micro-body based on a function in which any of the following variables are the motion trajectory, position distribution, velocity distribution, angular velocity, and torque distribution of the micro-body.

10. Using a light source that outputs light, an optical vortex generating unit that generates an optical vortex from the light, and a focusing optical system that focuses the optical vortex, The imaging step involves capturing images of a minute object that is light-trapped and moving by an optical vortex focused by the aforementioned light-gathering optical system, and outputting image data, A control step of analyzing the motion of the micro-body based on the image data and adjusting the phase distribution of the optical vortex generated by the optical vortex generation unit based on the analysis results, Equipped with, An optical vortex control method comprising: in the control step, determining an evaluation function that includes an ellipticity evaluation value representing how much the motion trajectory of the micro-body deviates from a perfect circle, and a variance evaluation value representing the degree of variation in the speed of motion of the micro-body; and adjusting the phase distribution of the optical vortex generated by the optical vortex generation unit according to the value of the evaluation function.

11. The optical vortex control method according to claim 10, wherein the optical vortex generation unit includes a spatial light modulator having a plurality of pixels arranged in two dimensions and modulating at least the phase of light at each pixel for output.

12. The optical vortex control method according to claim 11, wherein in the control step, an adjustment pattern for adjusting optical vortex generation is superimposed on a modulation pattern for optical vortex generation, and the resulting modulation pattern is presented to the spatial light modulator.

13. The optical vortex control method according to claim 12, wherein in the control step, the adjustment pattern is determined as a phase distribution.

14. The optical vortex control method according to claim 12, wherein the adjustment pattern is determined using a Zernike polynomial in the control step.

15. The optical vortex control method according to claim 12, wherein in the control step, the adjustment pattern is determined using an optimization method.

16. The optical vortex control method according to any one of claims 10 to 15, wherein in the control step, the motion of the micro-body is analyzed as any one of the motion trajectory, position distribution, and torque distribution of the micro-body.

17. The optical vortex control method according to any one of claims 10 to 15, wherein in the control step, the velocity distribution and angular velocity of the microorganism are analyzed as the motion of the microorganism.

18. The optical vortex control method according to any one of claims 10 to 15, wherein in the control step, the motion of the micro-body is analyzed based on a function in which any of the motion trajectory, position distribution, velocity distribution, angular velocity, and torque distribution of the micro-body are variables.

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