JP3386643B2 - Two beam trapping method and apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser trapping device, and more particularly to a two-beam trapping method and device for independently trapping fine particles using a plurality of light beams.

[0002]

2. Description of the Related Art When a fine particle is irradiated with a laser beam focused by a microscope objective lens or the like, the fine particle can be caught near the spot of the laser beam by the radiation pressure of light.
This phenomenon was introduced in 1986 by Ashkin at Bell Laboratories.
It was discovered by the company and is called the laser trapping method, and applied research such as cell manipulation and cell fusion is being actively conducted. In this laser trapping method, 1
One laser beam can capture one particle, and a plurality of laser beams can be used to independently capture a plurality of particles.

The laser trapping method of interest here is a two-beam trapping method using two laser beams. In the case of using two laser beams, conventionally, one beam is split by a half mirror, each split laser beam is deflected by a deflection mirror, and then the half mirror again returns the beam to the same optical path to capture the situation. It was introduced into the microscope for observation. The configuration will be described with reference to FIG.

The laser beam 45 is split into two beams 46 and 47 by the half mirror 41, these laser beams 46 and 47 are deflected by the deflection mirrors 42 and 43, respectively, and are returned to the same optical path by the half mirror 44 again. However, at that time, one of the branched laser beams 4
6 is split into beams 48 and 49 by the half mirror 44,
The other laser beam 47 is also split into laser beams 50 and 51. Of these branched laser beams, only one of the laser beams 48 and 50 was guided to the microscope and used for laser trapping, and the other laser beams 49 and 51 could not be used.

Further, the above-mentioned deflection mirrors 42 and 43 are
It is used when moving trapped (trapped) particles in the microscope visual field during laser trapping, but in order to move freely in the visual field, two axes (X axis, Y axis) are used for one beam. A means for moving the shaft is required. There is a galvano-mirror method that has been often used in the past, but because of the structure of the galvano-mirror attached to one axis, it is not possible to give one mirror the functions of two axes, so two galvano-mirrors are used. Was.
An example thereof will be described with reference to FIG.

The laser beam 4 is transmitted by the galvano mirror 52.
0 is deflected in the X-axis direction, and its laser beam 40 is 1
Galvano mirror 55 with a pair of pupil transfer lenses 53 and 54
It is returned to the center of rotation (center of the mirror). Next, it is polarized in the Y-axis direction by the galvanometer mirror 55, and again by another pair of pupil transfer lenses 56 and 57, the pupil position 5 of the objective lens 59.
Collected in 8. This method requires two sets of pupil transfer lenses for one laser beam, so that four sets of pupil transfer lenses are required to form a two-beam trapping device, and laser beam splitting and combining are also required. The system becomes complicated.

There is also a configuration in which the pair of pupil transfer lenses 53 and 54 between the galvano mirror 52 and the galvano mirror 55 are omitted from the configuration described in FIG. This is shown in FIG. This structure does not become so complicated when forming two beams, but it is the galvano-mirror 52 and the galvano-mirror 55 that are conjugate with the pupil position 58 of the objective lens 59 by the pupil transfer lenses 56 and 57. It becomes the midpoint 60. However, since the laser beam is actually deflected by the mirror surfaces of the galvano mirror 52 and the galvano mirror 55, when the laser beam is largely deflected, the pupil position 58
Therefore, there is a part that cannot be incident on the objective lens 59 because it is not collected.

[0008]

The conventional beam trapping device described above has the following problems.

(1) Since a half mirror is used to obtain two beams from one laser beam, more than half of the light amount cannot be used, and a laser light source with a large output is required accordingly. .

(2) Fine particles having different weights cannot be captured. For example, in biotechnology, there is a demand for capturing and manipulating fine particles of different weights, but since the two beams split by the half mirror have a constant light amount division ratio and cannot be changed, they capture fine particles of different weights. Can not do it. Conventionally, a laser beam is incident on a polarizing beam splitter through a λ / 4 wavelength plate (Japanese Patent Laid-Open No. 4-354532). However, when a λ / 4 wavelength plate is used, the laser beam is circularly polarized. Therefore, the amount of light split by the polarization beam splitter becomes equal, and the split ratio cannot be changed.

(3) X-axis and Y-axis for one laser beam
Since two galvanometer mirrors that move the axis are used,
When the two-beam trapping device is configured, the device becomes complicated, and it becomes difficult to adjust the movement amount, and when the two beams are moved within the microscope field, the light amount is reduced, so that the fine particles cannot be captured.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a two-beam trapping method capable of independently trapping fine particles having different weights.

Another object of the present invention is to provide a two-beam trapping device which does not require a large output to a laser light source and can independently capture fine particles having different weights.

Another object of the present invention is that the device is simple,
It is an object of the present invention to provide a two-beam trapping device capable of efficiently guiding a laser beam to an optical system such as an objective lens and simultaneously capturing a plurality of fine particles.

[0015]

In order to solve the above problems, the present invention is configured as follows.

The first aspect of the present invention is that fine particles having different weights from each other.
A single light beam so that
The two divided into light intensity ratio according to the weight of each particle, at each light beam bisected, it is obtained so as to capture the fine particles independently. If the light intensity ratios are equal,
Fine particles having the same weight can be independently captured.

A second invention is a two-beam trapping device for irradiating two particles of light with fine particles and trapping the particles independently by each light beam, as shown in FIG. Of the first polarization beam splitter 7 for splitting the light beam 15 of the two light beams into two, and 2 for deflecting the respective split light beams 19 and 20.
A pair of deflection mirrors 8 and 9, a second polarization beam splitter 10 for combining the deflected light beams again, and an optical system 16 for irradiating the combined light beams to the particles to capture the particles. , By rotating the optical axis, the deflection direction of the light beam 15 incident on the first polarization beam splitter 7 is changed, and the light quantity division ratio of the light beam split by the first polarization beam splitter 7 is adjusted. / 2 wavelength plate 6
It is equipped with and.

The light beam 15 is first split into two by the first polarization beam splitter 7 into an S-polarized beam 19 on the reflecting side and a P-polarized beam 20 on the transmitting side. The respective beams are deflected by the deflecting mirrors 8 and 9, but the polarization state is preserved at that time, so that the second polarizing beam splitter 10 is used.
Causes the S-polarized beam 19 to be totally reflected and the P-polarized beam 2 to be reflected.
0 transmits the entire amount of light, and it becomes possible to efficiently return the two beams to the same optical path. When the λ / 2 wave plate 6 is rotated about the optical axis, the polarization direction of the light beam 15 incident on the first polarization beam splitter 7 changes, so that the S polarization component and the P polarization component in the polarization beam splitter 7 are changed. The division ratio changes, and it becomes possible to independently capture fine particles having a weight corresponding to the division ratio.

In a third aspect of the present invention, in the second aspect, the two deflection mirrors can be deflected in the X-axis and Y-axis directions with respect to one light beam as shown in FIG. It is composed of deflection mirrors 8 and 9 each having an axial tilting function, and the two axes of the two deflection mirrors 8 and 9 are provided between the second polarization beam splitter 10 and the optical system, for example, the objective lens 14. A pupil transfer optical system, such as a pupil transfer lens 11, for condensing the light beam, which is deflected in the X-axis and Y-axis directions by the tilt function and synthesized by the second polarization beam splitter 10, at the pupil position 25 of the objective lens 14. It is equipped with 12. Here, the biaxial tilt function is a function capable of deflecting one light beam in the X-axis direction and the Y-axis direction by one mirror.

The two deflecting mirrors are composed of the deflecting mirrors 8 and 9 each having a biaxial tilt function capable of deflecting one light beam in the X-axis and Y-axis directions. In the case of configuring a two-beam trapping device, since the light beam can be deflected in the X-axis direction and the Y-axis direction by the deflecting mirror of 1 and one pupil transfer lens 11 and 12 is sufficient for one light beam. , The common pupil transfer lens 11,
12 is sufficient, and the configuration is simple, such as a light beam branching and combining system.

By using the pupil transfer lenses 11 and 12, the light beam 21 inclined by the deflection mirror 8 by the angle θ ₁ and the light beam 22 inclined by the deflection mirror 9 by the angle θ ₂ are positioned at the pupil position of the objective lens 14. Since it can be passed through 25, the amount of light does not decrease even if it is moved within the field of view of the microscope, and efficient light trapping is possible.

In a fourth aspect of the invention, in the second and third aspects of the invention, the light beam to be incident on the first polarization beam splitter from the light source is transmitted by the polarization maintaining fiber 4.

In the two-beam trapping device using the polarization beam splitters 7 and 10, it is necessary to guide the light beam to the polarization beam splitter 7 while preserving the polarization plane. Since the light beam can be guided to the polarization beam splitter 7 while the wavefront is preserved, the light source system is composed of the λ / 2 wavelength plate 6 and the polarization beam splitter 7, and the main body of the device is composed of the latter-stage optical components. The device can be easily handled.

In the present invention, the mutually different fine particles include a fine particle group, and a case where a plurality of fine particles are collectively captured by one beam is also included.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS.

A linearly polarized laser beam emitted from a laser oscillator 1 as a light source is a λ / 2 wave plate 2
The direction of the polarized light is determined by and is narrowed down to the diffraction limit by the aberrated condenser lens 3. The laser beam can be introduced into the fiber 4 by accurately positioning the end face of the polarization-preserving fiber 4 on the incident side at the converging position. At that time, it is necessary to match the polarization direction of the laser beam with the polarization axis of the polarization-maintaining fiber 4, but the polarization direction of the laser beam can be easily adjusted by rotating the λ / 2 wave plate 2 about the optical axis. It is possible. Since the core diameter of the polarization-maintaining fiber 4 is almost equal to the diffraction limit, the emitted laser beam can be regarded as an ideal point light source.

The laser beam emitted from the polarization-maintaining fiber 4 is collimated by the aplanatic lens 5 to obtain λ /
The first polarization beam splitter 7 passes through the two-wave plate 6 and splits it into an S-polarized beam and a P-polarized beam. The λ / 2 wave plate 6 has a function of changing (rotating) the polarization direction of the incident linearly polarized light beam, and determines the angle between the polarization direction of the incident linearly polarized light beam and the crystal optical axis direction of the λ / 2 wave plate. When θ is set, the deflection direction of the outgoing linearly polarized beam is 2θ with respect to the incident linearly polarized beam. By changing the polarization direction with the λ / 2 wavelength plate 6, the light quantity division ratio of the S polarization component and the P polarization component in the first polarization beam splitter 7 can be changed. By changing the light quantity division ratio, it becomes possible to independently capture fine particles having different weights.

Each of the divided beams is deflected by the deflecting mirrors 8 and 9 in which one mirror is provided with the biaxial tilt function by the piezo, and the second polarizing beam splitter 1
0 returns to the same optical path. As shown in FIG.
Since the laser beam of the book is tilted by the deflection mirrors 8 and 9 by the angles θ ₁ and θ ₂ , respectively, at a distance f from the mirror, the laser beam is separated from the optical axis to a distance ftan θ. The pupil transfer lens 11 makes the two laser beams parallel to the optical axis, and the pupil transfer lens 12 causes the objective lens 1 of the microscope 17 to move.
Collected towards the 4th pupil. The dichroic mirror 13 provided between the pupil transfer lens 12 and the objective lens 14 is used to be introduced into the optical path of the commercially available microscope 17.

[0029] When the focal length of the pupil transfer lenses 11 and 12 and f _1, f _2, pupil transfer lens 11 at a distance of f ₁ from the deflection mirror 8 and 9, further pupil transfer lens at a distance of f ₁ + f ₂ 12, Further, it is arranged so as to be at the pupil position 25 of the objective lens 14 at a distance of f ₂ . With this arrangement, the beam reflecting position 23 of the deflecting mirror 8 and the beam reflecting position 24 of the deflecting mirror 9 are optically conjugate with the pupil position 25 of the objective lens 14. As a result, even if the deflection mirrors 8 and 9 are swung at a large angle to deflect the beams 19 and 20,
It can be collected at the pupil position 25 and can be made incident on the objective lens 14.

By the way, two fine particles having different weights are used.
When capturing each independently with a beam, for example, when trying to capture the lighter fine particles with a beam having the same light amount as the laser beam in which the light amount is adjusted to capture the heavier fine particles,
The radiation pressure becomes too large, and the lighter particles are scattered and cannot be captured. On the contrary, if you try to capture the heavier particles with a beam of the same light quantity as the laser beam with the same light quantity to capture the lighter particles,
Since the radiation pressure is small, heavier particles cannot be captured. In this respect, in the present embodiment, by rotating the λ / 2 wavelength plate 6, the light quantity division ratio divided by the first polarization beam splitter 7 is changed to emit a beam matched to the weight of the fine particles. Therefore, even if the weights are different from each other, the fine particles can be reliably captured.

The device body is composed of optical components including the polarization beam splitter after the aplanatic lens 5. The laser oscillator 1 and the polarization-maintaining fiber 4 are used for the device body using this polarized light. Since the laser oscillator 1 can be separated from the main body of the device, the device can be easily handled.

FIG. 4 is a plan view showing an example of a deflecting mirror in which one mirror is provided with the above-mentioned biaxial tilt function by the piezo. An inner disk having a triple circular structure of an inner side, a center, and an outer side is a mirror 31, and this mirror 31 is supported by a central circle holder 32 that rotates around a Y axis 36, and the central circle holder 32. It is designed to rotate with the rotation of. The central circle holder 32 is further supported by an outer circle holder 33 that rotates around the X-axis 37, and rotates as the outer circle holder 33 rotates.

Piezos 34, 3 whose length changes when an electric current is applied
Two 5 are provided, and one piezo 34 is pressed against the central circle holder 32, and the central circle holder 32 is pushed in the direction perpendicular to the paper surface by changing the length, and the central circle holder 32 is moved to Y The shaft 36 is rotated. The other piezo 35 is pressed against the outer circle holder 33, and the length thereof changes to push the outer circle holder 33 in the direction perpendicular to the plane of the drawing, so that the outer circle holder 33 is centered on the X axis 37. It is designed to rotate. By applying an electric current to each piezo 34, 35, the piezo expands according to the electric current, and the holders 32, 33 rotate about their respective axes by an angle corresponding to the expanded amount. Two axes can be moved. The means for rotating the holder is not limited to the piezo. Any means such as screws, hydraulic cylinders and air cylinders can be adopted.

In the above embodiment, the pupil transfer lens is composed of a set of two lenses, but it may be composed of three or more lenses or an optical system other than the lenses. Further, the light beam is not limited to the laser beam, and any other light beam may be used as long as it can capture the particles by radiation pressure.

[0035]

EXAMPLE Two-beam trapping of 1 μm polystyrene beads was actually carried out under the following conditions.

Laser oscillator: (CWNd YAG laser) Product name Spectra Physics 7910-Y3-106 Wavelength 1064 nm Output 250 mW Polarization preserving fiber: Product name Fujikura 0.85 μm polarization preserving fiber deflection mirror : Product name Sigma Koki TFM-20C03-1064 Microscope: Product name Nikon Diaphoto TDM300 Objective lens magnification: 100 × Focal length of pupil transfer lens: f ₁ = 150 f ₂ = 150 As a result, two laser beams are used as a microscope Even if the particles were moved within the visual field, the two particles could be independently captured by the two laser beams. Further, by rotating the λ / 2 wavelength plate arranged on the incident side of the first polarization beam splitter, the light quantity division ratio could be changed to 0: 100 to 50:50.

[0037]

According to the invention described in claim 1, since one light beam can be divided into two light amount ratios according to the weight of each fine particle, fine particles having mutually different weights are simultaneously captured. can do.

According to the second aspect of the present invention, since the polarization beam splitter is used for the two-beam splitting / combining, it is possible to theoretically secure twice the amount of light as compared with the conventional half mirror. It has become possible to perform two-beam trapping with the previously used laser with 1/2 output. Further, by utilizing the polarized light, the beam splitting ratio can be adjusted by the λ / 2 wavelength plate, and fine particles having different weights can be simultaneously captured.

According to the third aspect of the present invention, the pupil transfer optical system is provided and the biaxial tilting function is provided for one deflecting mirror.
Beam trapping can be performed.

According to the invention described in claim 4, since the light source can be separated from the main body of the device by using the polarization-maintaining fiber, the device can be easily handled.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a two-beam trapping device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a beam branching / combining unit using the polarization beam splitter of the present invention.

FIG. 3 is an explanatory diagram of a pupil transfer unit according to the present embodiment.

FIG. 4 is a schematic configuration diagram of a deflecting mirror having a biaxial tilt function according to the present embodiment.

FIG. 5: Beam splitting using a conventional half mirror
It is explanatory drawing of a synthetic | combination part.

FIG. 6 is an explanatory diagram of a beam branching / combining unit using two galvano mirrors and two sets of pupil transfer lenses of a conventional example.

FIG. 7 is an explanatory diagram of a beam branching / combining unit using two galvano mirrors and a set of pupil transfer lenses of a conventional example.

[Explanation of symbols]

1 Laser oscillator 4 Polarization maintaining fiber 6 λ / 2 wave plate 7 First polarization beam splitter 8 deflection mirror 9 Deflection mirror 10 Second polarization beam splitter 11 Pupil transfer lens 12 pupil transfer lens 14 Objective lens 25 pupil position

Claims (4)

(57) [Claims] 1. It is possible to simultaneously capture fine particles having different weights.
To kill manner, one light beam, and divided into two light quantity ratio according to the weight of each particle, 2 split the light beam
Then, a two-beam trapping method in which the particles are independently captured . 2. A light source, a first polarization beam splitter for splitting a light beam from the light source into two, two deflection mirrors for deflecting each of the split light beams, and the deflected light. A second polarization beam splitter for recombining the beams, an optical system for converging the combined light beam, and light incident on the first polarization beam splitter by rotating about the optical axis. Change the polarization direction of the beam,
A two-beam trapping device, comprising: a λ / 2 wavelength plate that adjusts a light amount division ratio of a light beam divided by a first polarization beam splitter. 3. The two deflecting mirrors are constituted by deflecting mirrors each having a biaxial tilting function capable of deflecting one light beam in the X-axis and Y-axis directions. 3. The pupil transfer optical system according to claim 2, further comprising a pupil transfer optical system for condensing a light beam synthesized by a second polarization beam splitter between the polarization beam splitter of 1) and the optical system at a pupil position of the optical system. Beam trapping device. 4. A two-beam trapping device according to claim 2, wherein a light beam made incident on said λ / 2 wave plate from a light source is transmitted by a polarization-maintaining fiber.