JP3568616B2 - Laser trapping device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a laser trapping device that captures a laser beam by condensing the laser beam on a focal point by a condensing optical system and irradiating the particle on a vacuum or a medium in a medium.
[0002]
[Prior art]
2. Description of the Related Art Laser trapping is known as a technique for performing manipulation such as capturing fine particles in a medium in a non-contact and non-destructive manner and transferring the particles to an arbitrary position.
In this method, a laser beam is guided into a microscope, condensed by an objective lens, and irradiates particles to be captured to generate a radiation pressure of light, and the particles are captured by the pressure.
[0003]
In such laser trapping, the trapping force in a plane perpendicular to the optical axis is relatively large, and the trapping force in the optical axis direction is small in comparison with this. The operation of moving particles two-dimensionally has been performed, but recently, by increasing the trapping force in the direction of the optical axis, the particles are three-dimensionally moved not only in a plane perpendicular to the optical axis but also in the direction of the optical axis. A laser trapping device capable of moving has been proposed (see Japanese Patent Application Laid-Open No. 5-93871).
[0004]
This is because, as shown in FIG. 5A, a pair of conical prisms 61 and 62 having the same apex angle and a condenser lens (objective lens) 63 have their optical axes aligned in the optical path B of the laser beam. The laser beam is converted into a light beam that spreads in a conical cylinder when transmitted through the first conical prism 61, and then converted into an annular cylindrical light beam when transmitted through the second conical prism 62. After that, the light is condensed to a focal point by the condenser lens 63, and the particle 64 in the vacuum or the medium is captured at the focal point.
[0005]
At this time, when the particle 64 is irradiated with laser light while being positioned on the focal point, the laser light becomes a conical cylindrical light beam incident at a relatively large angle with respect to the optical axis, and the particle is irradiated inside the light beam. Since there is no light, the force of pushing the particle 64 in the light irradiation direction along the optical axis due to the reflection of the surface of the particle 64 is reduced, and as a result, the force of capturing the particle 64 in the direction opposite to the light irradiation direction is increased. The particles can be lifted against gravity or held at any position in space.
[0006]
[Problems to be solved by the invention]
However, it is extremely difficult to accurately and coaxially arrange the optical axes of the two conical prisms 61 and 62 to form a pair. If the optical axis is tilted or shifted, the laser light is scattered. was there.
For example, when a laser beam having a diameter of about 4 mm is irradiated with the optical axes completely aligned as shown in FIG. 5A, the laser beam at the focal point has a spot having a diameter of about 10 μm as shown in FIG. When the optical axis of the first conical prism 61 is tilted about 2 degrees as shown in FIG. 5B, the laser beam is about 0.2 mm in diameter as shown in FIG. 6B. 5C, and the laser light is shifted from the optical axis of the first conical prism 61 by only 0.10 mm as shown in FIG. There is a problem that the light is scattered to a diameter of about 0.4 mm and cannot be used as an optical system for performing laser trapping.
[0007]
Further, even if the optical axes can be accurately aligned, it is very difficult to precisely process the apex angles of the conical prisms 61 and 62 equally and to form them without distortion. Therefore, a pair of ideal prisms having no distortion must be formed, and their optical axes must be precisely aligned, which increases the manufacturing cost and makes the laser trapping device expensive. There was a problem.
Thus, the present invention reliably collects particles without using a conical prism, which is extremely difficult to manufacture with high accuracy, and without scattering laser light even when the optical axis is slightly inclined or shifted. It is a technical issue to be able to capture.
[0008]
[Means for Solving the Problems]
In order to solve this problem, the present invention provides a laser trapping device that captures laser light by focusing the laser light on its focal point by a focusing optical system and irradiating the particles in a vacuum or a medium with a laser. Along the optical path of the light, a prism for splitting the laser light into a plurality of parallel light beams is provided on the front side of the condensing optical system, and the prism has two or more ends on the incident side and the emission side of the laser light. , And a pair of planes on the incident side and the emission side are formed parallel to each other.
[0009]
[Action]
According to the present invention, a prism for splitting a laser beam into a plurality of parallel light beams is provided on the front side of the converging optical system, and the prism has two or more ends on the incident side and the emission side of the laser beam. Are formed with the same number of planes, and the planes forming the pair on the entrance side and the exit side are formed in parallel to each other, so that it is not necessary to form a complicated curved surface, and the prism can be formed very simply and accurately. Can be processed and formed.
[0010]
When laser light is incident from the ridgeline or vertex where the planes on the incident side of the prism converge, the laser light is refracted on each plane and split into luminous fluxes corresponding to the number of the planes, and again on the plane on the exit side. Refracted.
At this time, since the paired planes of the incident side and the exit side are formed in parallel, even if the optical axis of the prism is slightly inclined with respect to the optical axis of the condensing optical system, The light beam is always emitted as a plurality of light beams parallel to the optical axis around the focusing optical system without being scattered.
Therefore, these light beams can be condensed at the focal point by the condensing optical system, and each light beam is condensed at a relatively large angle with respect to the optical axis, so that particles are captured on the focal point.
[0011]
【Example】
Hereinafter, the present invention will be specifically described based on embodiments shown in the drawings.
FIG. 1 is a schematic explanatory view showing a laser trapping device according to the present invention, FIGS. 2A to 2E show prisms used in the laser trapping device, respectively, and FIGS. 4A and 4B are schematic diagrams showing the optical system when the optical axis is inclined and when the optical axis is deviated, respectively.
[0012]
In the drawing, reference numeral 1 denotes a laser trapping device that captures a particle 2 in a vacuum or a medium by irradiating the particle 2 with the laser light, and divides the laser light into a plurality of parallel light beams along the optical path. A prism 3 for emitting light and a condensing optical system 5 composed of two lenses 4a and 4b for converging a parallel light beam on a focal point are arranged.
The prism 3 has two or more equal-numbered planes 6A, 6B, 7A, and 7B at both ends on the incident side and the emission side of the laser beam, and the planes 6A and 7A, 6B and 7B are formed parallel to each other.
[0013]
Specifically, for example, as shown in FIG. 2 (a), a square pillar 8 is formed with mountain-shaped slopes at both ends, and as shown in FIG. 2 (b), a square pyramid-shaped slope is formed at both ends of a square prism 9 2 (c), a regular hexagonal prism 10 is formed at both ends of a regular hexagonal prism 10 as shown in FIG. 2 (c), and a regular octagonal prism 11 is formed at both ends of a regular octagonal prism 11 as shown in FIG. 2 (d). Can be used.
[0014]
Further, the present invention is not limited to the case where an even number of planes are formed as described above, but may be a cylinder having a regular triangular pyramid-shaped slope formed on a cylinder 12 as shown in FIG. The shape is not limited to a regular polygonal pyramid, but may be a simple pyramid as long as the planes forming the pair on the side are formed in parallel to each other.
Furthermore, if there is a ridge or vertex P where the planes are gathered on the incident side, such a ridge or vertex may not be provided on the output side.
[0015]
The prism 3 and the lenses 4a and 4b can be made of any material. However, the prism 3 of this example uses glass having a refractive index n _d = 1.51, and the lens 4a is made of SK11 (refractive index n _d = 1. 5638), and the lens 4b uses SF5 (refractive index n _d = 1.6727) glass.
[0016]
The above is an example of the configuration of the present invention, and its operation will be described next with reference to an example in which the prism shown in FIG. 2B is used.
The prism 3 has a square pyramid-shaped slope formed at both ends of a square prism 9, and not only the slopes that form a pair on the incident side and the emission side, but also the entire peripheral surface of the prism 3 is formed of a parallel plane. Therefore, processing can be performed easily and accurately.
[0017]
Then, the prism 3 formed in this way is arranged coaxially with the optical axis of the condensing optical system 5, and when a laser beam is incident along the optical axis from the vertex P on the incident side of the prism 3, the prism 3 on the incident side The laser light is refracted in four directions by the four slopes of the regular square pyramid, and is refracted again by the four slopes of the square pyramid on the emission side to be emitted as four parallel lights.
At this time, since the circular spot of the laser light beam is divided into four by the four slopes of the regular square pyramid, the cross section of each light beam has a shape of a quarter circle as shown in FIG.
[0018]
When this parallel light beam is condensed by the condensing optical system 5, each light beam converges at a large angle with respect to the optical axis, and a laser spot of about 10 μm is formed as shown in FIG. Capture the particles at their focal point.
At this time, since there is no laser light applied to the particles inside the angle between the light flux and the optical axis, the force of pushing the particles in the light irradiation direction along the optical axis by reflection of the surface of the particles is reduced, As a result, the force of capturing along the optical axis in the direction opposite to the light irradiation direction increases, and the particles can be lifted against gravity or held at an arbitrary position in space.
[0019]
Further, when the prisms 3 are arranged, as shown in FIG. 4A, even if the optical axis of the prism 3 is inclined with respect to the optical axis of the condensing optical system 5, each light beam is parallel to the optical axis. Is maintained, the light is not scattered. For example, when the inclination of the optical axis is 2 degrees, the laser spot of about 10 μm is also focused on the focal point of the condenser lens 4 as shown in FIG. Is formed, the particles 2 can be reliably captured.
[0020]
Further, as shown in FIG. 4B, even if the optical axis of the prism 3 is shifted with respect to the optical axis of the condenser lens 4, only the energy intensity of each parallel light incident on the condenser lens 4 is different. There is no scattering of light. For example, when the deviation of the optical axis is 0.1 mm, a laser spot of about 10 μm is also focused at the focal point of the condenser lens 4 as shown in FIG. Since the particles 2 are formed, the particles 2 can be reliably captured in this case as well.
[0021]
In the embodiment, the case where the prism having the slopes of the regular quadrangular pyramid formed at both ends is used.However, a prism having two pairs of mountain-shaped planes formed at both ends or a prism having a pyramid-shaped inclined surface formed at both ends is used. The same operation and effect can be obtained.
However, when the prism 3 formed in a pyramid shape is used, the processing becomes troublesome as the number of planes increases, so it is preferable to process one end side to about eight surfaces.
[0022]
【The invention's effect】
As described above, according to the present invention, all of the surfaces on the entrance side and the exit side of the prism can be constituted by planes, so that processing can be performed easily and accurately, and the unit price of the prism decreases. In addition, the manufacturing cost of the entire device can be reduced, and since the paired surfaces of the incident side and the outgoing side are formed by parallel surfaces, light is scattered even if the optical axis is tilted or shifted. Since the light is condensed at the focal point without performing the above operation, it has an excellent effect that particles can be reliably captured.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory view showing an example of a laser trapping device according to the present invention. FIG. 2 is a perspective view showing an example of a prism used therein. FIG. 3 is an explanatory view showing a light beam and a laser spot.
FIG. 4 is a schematic explanatory view showing a state where the optical axis is tilted and shifted. FIG. 5 is a schematic explanatory view showing a conventional apparatus. FIG. 6 is an explanatory view showing a laser spot at a focal point of the conventional apparatus.
DESCRIPTION OF SYMBOLS 1 ... Laser trapping apparatus 2 ... Particle 3 ... Prism 5 ... Condensing optical system 6A, 7A ... Plane 6B, 7B which becomes a pair of an incident side and an outgoing side Outgoing side paired plane

Claims (1)

An optical path of the laser light in a laser trapping device that captures the laser light by condensing the laser light on its focal point by a light condensing optical system (5) and irradiating the particle (2) in a vacuum or a medium with the laser light A prism (3) for splitting the laser beam into a plurality of parallel light beams is disposed in front of the condensing optical system (5), and the prism (3) is arranged on the incident side and the emission side of the laser beam. Are formed by two or more equal numbers of planes (6A, 6B, 7A, 7B), and planes (6A, 7A, 6B, and 7B) forming a pair on the incident side and the exit side are formed in parallel to each other. A laser trapping device.

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