CN113380436B - Frequency-adjustable stable rotating device in vacuum optical tweezers system and use method - Google Patents

Frequency-adjustable stable rotating device in vacuum optical tweezers system and use method Download PDF

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CN113380436B
CN113380436B CN202110468911.7A CN202110468911A CN113380436B CN 113380436 B CN113380436 B CN 113380436B CN 202110468911 A CN202110468911 A CN 202110468911A CN 113380436 B CN113380436 B CN 113380436B
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wave plate
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light
linearly polarized
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CN113380436A (en
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胡慧珠
陈铭
苏鹤鸣
陈杏藩
高晓文
李楠
刘承
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Zhejiang University ZJU
Zhejiang Lab
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Zhejiang Lab
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    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
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Abstract

The invention discloses a stable rotating device with adjustable frequency in a vacuum optical tweezers system and a using method thereof. The invention comprises a vacuum cavity, micro-nano particles, a laser source, an objective lens and a polarization control device; the objective lens and the micro-nano particles are placed in the vacuum cavity, and the laser source, the polarization control device, the objective lens and the micro-nano particles are sequentially arranged along the light ray direction; the polarization control device comprises a first half-wave plate, a polarization spectroscope, a second half-wave plate, an electro-optical modulator and a quarter-wave plate; the first half-wave plate, the polarization spectroscope, the second half-wave plate, the electro-optical modulator and the quarter-wave plate are sequentially arranged along the light direction. The invention utilizes the modulation effect of the electro-optical modulator on the polarization of the light beam and combines the interaction characteristic of linearly polarized light and anisotropic polarizability micro-nano particles to realize the function of stably rotating the micro-nano particles in a set frequency in a vacuum optical tweezers system.

Description

Frequency-adjustable stable rotating device in vacuum optical tweezers system and use method
Technical Field
The invention relates to a device for realizing stable rotation of micro-nano particles in vacuum, belonging to the technical field of precision measurement, in particular to a stable rotation device with adjustable frequency in a vacuum optical tweezers system and a use method thereof.
Background
The physical scientists of Ashkin and the like in the seventies of the last century invent an optical tweezers technology by utilizing the property that an object can be subjected to radiation force and gradient force in an optical field, and are used for capturing tiny particles. The technology is widely applied to the research fields of fluid mechanics, thermodynamics and the like. After that, a vacuum optical tweezers technology for capturing particles in vacuum by light has been developed, which can be well decoupled from the environment, resulting in very high measurement accuracy. For example, vacuum optical tweezers may be used to measure non-newtonian attractive forces, cassimel forces, and the like. In addition, if the rotation of the micro-nano particles in the vacuum optical tweezers can be controlled, the method can be applied to measurement of rotation-related physical quantities such as weak moment and the like, and can also eliminate the interference of translational freedom degree. Therefore, the control of the rotation of the micro-nano particles is a valuable research direction.
The existing pure optical control means for the rotational freedom degree of the micro-nano particles in the vacuum optical tweezers system mainly uses circularly polarized light. The method is a method for transferring angular momentum to micro-nano particles by utilizing interaction through the characteristic that circularly polarized light carries non-zero angular momentum. Since the angular momentum transfer gives a continuous angular acceleration to the micro-nano particles, the retardation of the gas increases in proportion to the rotation frequency, and therefore the light applied torque and the retardation of the gas are balanced finally. Therefore, if the method is used for realizing the stable rotation of the micro-nano particles, the rotation speed cannot be adjusted at will, but depends on the retardation coefficient of the surrounding gas. And the rotating speed is controlled by the method of circularly polarized light through the balance of light field drive and gas retardation, so that the rotating speed is easily disturbed by the change of light intensity, airflow and the like, and the line width of the rotating frequency is larger, namely unstable. And the driving of the micro-nano particles in the vacuum optical tweezers to stably rotate at adjustable frequency has important significance for the precise measurement of the physical quantity related to the rotational degree of freedom.
Disclosure of Invention
In order to solve the problems in the background art, the invention provides a stable rotating device with adjustable frequency in a vacuum optical tweezers system.
The technical scheme adopted by the invention is as follows:
1. stable rotating device with adjustable frequency in vacuum optical tweezers system
The stable rotation device comprises a laser source LS, a polarization control device, a vacuum cavity VC, an objective lens OL and micro-nano particles MS; an objective lens OL and a micro-nano particle MS are placed in a vacuum cavity VC, and a laser source LS, a polarization control device, the objective lens OL and the micro-nano particle MS are sequentially arranged along the light ray direction;
the polarization control device comprises a first half-wave plate HWP1, a polarization beam splitter PBS, a second half-wave plate HWP2, an electro-optical modulator EOM and a quarter-wave plate QWP; the first half-wave plate HWP1, the polarization beam splitter PBS, the second half-wave plate HWP2, the electro-optical modulator EOM and the quarter-wave plate QWP are arranged in sequence along the light direction;
the laser source LS emits original laser, the original laser sequentially transmits through the first half-wave plate HWP1, the polarizing beam splitter PBS, the second half-wave plate HWP2, the electro-optical modulator EOM and the quarter-wave plate QWP and then enters the vacuum cavity VC, the objective lens OL focuses linearly polarized light entering the vacuum cavity VC to form an optical trap capturing area, micro-nano particles MS are released from the upper portion of the optical trap capturing area, and then the micro-nano particles MS do free falling body movement downwards under the action of gravity and reach the optical trap capturing area to be captured.
The original laser sequentially passes through a first half-wave plate HWP1, a polarization beam splitter PBS and a second half-wave plate HWP2 to become linearly polarized light with adjustable intensity, and the linearly polarized light with adjustable intensity passes through modulation of an electro-optical modulator EOM and a quarter-wave plate QWP to become linearly polarized light with the polarization direction rotating at variable frequency;
the optical axis direction of the first half-wave plate HWP1 is rotated around the light ray direction to control the light intensity of the linearly polarized light emitted from the polarization beam splitter PBS, the optical axis direction of the second half-wave plate HWP2 is rotated around the light ray direction to enable the polarization direction of the linearly polarized light emitted from the second half-wave plate HWP2 and the optical axis direction of the electro-optical modulator EOM to form an included angle of 45 degrees, and the optical axis direction of the quarter-wave plate QWP is the same as the polarization direction of the linearly polarized light emitted from the second half-wave plate HWP 2.
The variation frequency omega of the modulation voltage V applied on the electro-optical modulator EOM satisfies omega < omega c ，ω c Is a critical frequency, a critical frequency omega c The setting is made by the following formula:
Figure BDA0003044564520000021
wherein Δ α is a difference Δ α = α between the components of the polarizability of the micro-nano particle MS in the axial direction and the direction perpendicular to the axial direction || -α ⊥ ，α || Is the polarizability in the axial directionAmount, α ⊥ E is an amplitude of an electric field component of light irradiated to the micro-nano particles MS, and γ represents a retardation coefficient of residual gas in the vacuum chamber VC.
And a light-transmitting optical window for light beam transmission/passing is formed on the cavity wall of the vacuum cavity VC close to the quarter-wave plate QWP.
The polarizability tensor of the micro-nano particle MS
Figure BDA0003044564520000022
The anisotropic condition is satisfied; specifically, the micro-nano particles MS are made of birefringent crystals or ordinary non-spherical materials.
2. Use method of frequency-adjustable stable rotating device in vacuum optical tweezers system
The using method comprises the following steps:
1) Starting a laser source LS, and enabling the light intensity of linearly polarized light transmitted through a polarization beam splitter PBS to reach a preset value by adjusting the rotation of the optical axis direction of a first half-wave plate HWP1 around the light ray direction;
2) Adjusting the rotation of the optical axis direction of the second half-wave plate HWP2 around the light direction, so that the polarization direction of the linearly polarized light emitted by the second half-wave plate HWP2 forms an angle of 45 degrees with the optical axis direction of the electro-optical modulator EOM;
3) Setting the modulation voltage V of the electro-optical modulator EOM as zero volt, adjusting the optical axis direction of the quarter-wave plate QWP to be the same as the polarization direction of linearly polarized light emitted by the second half-wave plate HWP2, and converging the linearly polarized light emitted from the quarter-wave plate QWP through the objective lens OL to form an optical trap capturing area;
4) Releasing a micro-nano particle from the upper part of the optical trap capturing area, and allowing the micro-nano particle MS to make free falling body movement downwards under the action of gravity to reach the optical trap capturing area to be captured;
5) The electro-optical modulator EOM is added with a sinusoidal modulation voltage V with a variable frequency omega, so that linearly polarized light is emitted from the polarization control device, and the polarization direction of the linearly polarized light emitted by the polarization control device rotates at the variable frequency omega and drives the micro-nano particles MS to rotate stably.
The electro-optical modulator EOM is a birefringent crystal with adjustable refractive index, and the optical axis direction of the birefringent crystal is parallel to the incident plane. Light incident thereon can be decomposed into linearly polarized light o polarized perpendicular to the optical axis 1 Light and linearly polarized light e polarized parallel to the optical axis 1 Light, the pair e of which can be varied by applying different modulation voltages thereto 1 The refractive index of the light. O transmitted through the EOM of the electro-optic modulator 1 Light and e 1 A phase difference modulated by the voltage V is added between the lights.
The quarter-wave plate QWP is a birefringent crystal with its optic axis oriented parallel to the plane of incidence, into which light can be decomposed into o polarized perpendicular to the optic axis 2 Light and parallel-axis polarized e 2 Light. O transmitted through quarter-wave plate QWP 2 Light and e 2 One quarter period will be added between the lights, i.e. one quarter period is added between the lights
Figure BDA0003044564520000031
The phase difference of (1).
The method comprises the steps of sequentially placing an electro-optical modulator EOM and a quarter-wave plate QWP on a light propagation path, enabling the optical axis direction of the quarter-wave plate QWP to form an angle of 45 degrees with the optical axis direction of the electro-optical modulator EOM, and then enabling a linearly polarized light beam with the same polarization direction as the optical axis direction of the QWP to enter the EOM, wherein the optical axis direction of the QWP is the same as the polarization direction of the light entering the EOM, and after the electro-optical modulator EOM and the QWP are modulated, emergent light is an elliptically polarized light beam with large elliptical eccentricity and can be regarded as the linearly polarized light beam in practical application. The polarization direction of the emerging light is related to the voltage V applied to the EOM. By applying a sinusoidal modulation voltage with frequency ω to the EOM, a linearly polarized light with polarization direction rotated by ω can be obtained.
Considering the electric field of linearly polarized light at the micro-nano particles
Figure BDA0003044564520000032
Electric dipole moment excited by it
Figure BDA0003044564520000033
Wherein
Figure BDA0003044564520000034
Is the polarizability tensor of the micro-nano particles. For the micro-nano particles with asymmetric structures or birefringence, the polarizability tensor is anisotropic, and the excited electric dipole moment and the electric field direction are different. Moment tau of light to micro-nano particles is
Figure BDA0003044564520000041
When the rotation frequency omega of the polarization direction of the light beam is less than the critical frequency omega c When the light beam is polarized, the micro-nano particles rotate at the same frequency omega, and the rotation of the micro-nano particles relative to the polarization direction of the light beam lags behind by a phase delta phi. Critical frequency omega c The definition of (A) is:
Figure BDA0003044564520000042
wherein Δ α is the difference between the components of the polarizability of the micro-nano particles in the axial and perpendicular axial directions Δ α = α || -α ⊥ And E is the amplitude of the electric field component of the light, and γ represents the retardation coefficient of the residual gas in the cavity. And the lag phase Δ φ is defined as:
Figure BDA0003044564520000043
when the rotation frequency of the polarization direction of the light beam is larger than the critical frequency omega c The micro-nano particles can not rotate at a stable rotating speed, so that the rotating frequency omega < omega of the polarization direction of the light beam is ensured when the device is used c 。
According to the invention, original laser is output by a laser source, the polarization direction of emergent linearly polarized light is rotated at a set frequency through a polarization control device, an optical trap capturing area is formed in a vacuum cavity through an objective lens, and micro-nano particles are captured and driven to rotate by the linearly polarized light of which the polarization direction is rotated at the set frequency.
The invention provides a frequency-adjustable stable rotation device in a vacuum optical tweezers system, which utilizes the easy controllability of an electro-optical modulator on the polarization state of light and drives the stable rotation of micro-nano particles in the vacuum optical tweezers system through the interaction of linearly polarized light on the micro-nano particles with anisotropic polarizability.
The invention has the beneficial effects that:
the invention provides a method for driving micro-nano particles to stably rotate at a set frequency by utilizing the modulation of an electro-optic modulator on photoelectric polarization and the interaction of linearly polarized light on the micro-nano particles with anisotropic polarizability in a vacuum optical tweezers system for the first time.
Since the electro-optic modulator is modulated by the modulation voltage applied thereto. Therefore, the polarization of light can be accurately and rapidly regulated and controlled by utilizing mature circuit technology.
And because the rotation of the micro-nano particles is driven by the linearly polarized light which rotates at a certain frequency in the polarization direction, the rotation frequency of the micro-nano particles can be accurately controlled.
The invention provides a novel means for measuring physical quantities related to weak rotation in vacuum, such as moment and angular momentum. Has important significance for basic scientific research and precise measurement.
Drawings
FIG. 1 is a schematic view of the apparatus of the present invention;
FIG. 2 is a flow chart of the use of the present invention;
FIG. 3 is a schematic view of polarization control of the polarization control apparatus of the present invention;
fig. 4 is a schematic diagram of the rotation driving of the micro-nano particles of the invention.
Detailed Description
The invention is further illustrated by the following examples in conjunction with the accompanying drawings:
as shown in fig. 1, the invention comprises a laser source LS, a polarization control device, a vacuum cavity VC, an objective lens OL, and micro-nano particles MS; the objective lens OL and the micro-nano particles MS are placed in the vacuum cavity VC, and the laser source LS, the polarization control device, the objective lens OL and the micro-nano particles MS are sequentially arranged along the light ray direction; the direction of the light is the direction of propagation of the light. The laser source LS provides a laser for trapping and driving the particle rotation. The polarization control device is used for controlling the polarization state of the light beam. The vacuum cavity VC provides a measuring environment close to vacuum for the micro-nano particles, and a light-transmitting optical window for light beam transmission/passing is formed on the cavity wall of the vacuum cavity VC close to the quarter-wave plate QWP. The objective lens OL is used for converging light beams, and the micro-nano particles MS are driven to rotate.
The polarization control device comprises a first half-wave plate HWP1, a polarization beam splitter PBS, a second half-wave plate HWP2, an electro-optical modulator EOM and a quarter-wave plate QWP; the first half-wave plate HWP1, the polarization beam splitter PBS, the second half-wave plate HWP2, the electro-optical modulator EOM and the quarter-wave plate QWP are arranged in sequence along the light direction;
the laser source LS emits original laser, the original laser sequentially transmits through the first half-wave plate HWP1, the polarizing beam splitter PBS, the second half-wave plate HWP2, the electro-optical modulator EOM and the quarter-wave plate QWP and then enters the vacuum cavity VC, the objective lens OL focuses linearly polarized light entering the vacuum cavity VC to form an optical trap capturing area, micro-nano particles MS are released from the upper portion of the optical trap capturing area, and then the micro-nano particles MS do free falling body movement downwards under the action of gravity and reach the optical trap capturing area to be captured.
The original laser sequentially passes through a first half-wave plate HWP1, a polarization beam splitter PBS and a second half-wave plate HWP2 to become linearly polarized light with adjustable intensity, and the linearly polarized light with adjustable intensity passes through modulation of an electro-optical modulator EOM and a quarter-wave plate QWP to become linearly polarized light with the polarization direction rotating at variable frequency;
the optical axis direction of the first half-wave plate HWP1 rotates around the light direction as required to control the light intensity of the linearly polarized light emitted from the polarization beam splitter PBS, the optical axis direction of the second half-wave plate HWP2 rotates around the light direction to enable the polarization direction of the linearly polarized light emitted from the second half-wave plate HWP2 and the optical axis direction of the electro-optical modulator EOM to form an included angle of 45 degrees, and the optical axis direction of the quarter-wave plate QWP is the same as the polarization direction of the linearly polarized light emitted from the second half-wave plate HWP 2. The optical axis directions of the first half-wave plate HWP1, the second half-wave plate HWP2, the quarter-wave plate QWP, and the electro-optical modulator EOM are all intrinsic directions of themselves. In the first half-wave plate HWP1, the second half-wave plate HWP2, the quarter-wave plate QWP or the electro-optical modulator EOM, the light direction is perpendicular to the plane in which the polarization direction and the optical axis direction lie.
The variation frequency omega of the modulation voltage V applied on the electro-optical modulator EOM satisfies omega < omega c ，ω c The change frequency omega of the modulation voltage V applied on the electro-optical modulator EOM is adjusted as the critical frequency, and the polarization direction of the linearly polarized light emitted from the polarization control device rotates at the change frequency omega; critical frequency omega c The setting is made by the following formula:
Figure BDA0003044564520000061
wherein Δ α is a difference Δ α = α between the components of the polarizability of the micro-nano particle MS in the axial direction and the direction perpendicular to the axial direction || -α ⊥ ，α || Is a component of polarizability in the axial direction, alpha ⊥ E is an amplitude of an electric field component of light irradiated to the micro-nano particles MS, and γ represents a retardation coefficient of residual gas in the vacuum chamber VC.
Polarizability tensor of micro-nano particle MS
Figure BDA0003044564520000062
The anisotropic condition is met, namely the components of the polarizability of the micro-nano particles MS in the axial direction are not equal to the components in the direction vertical to the axial direction; specifically, the micro-nano particles MS are made of birefringent crystals or ordinary non-spherical materials. Common materials are silicon dioxide or silicon, and the non-spherical shape is cylindrical, ellipsoidal, and the like.
As shown in fig. 2, the method of use comprises the steps of:
1) Starting a laser source LS, wherein the light intensity of original laser emitted by the laser source LS is stable and is larger than a preset value, the wavelength of the original laser is unchanged, the light intensity of linearly polarized light transmitted through a polarizing beam splitter PBS reaches the preset value by adjusting the rotation of the optical axis direction of a first half wave plate HWP1 around the light ray direction, the preset value is the light intensity capable of capturing micro-nano particles, and the value depends on specific experimental parameters such as the size of the micro-nano particles and the aperture of an objective lens;
2) Adjusting the rotation of the optical axis direction of the second half-wave plate HWP2 around the light direction to ensure that the polarization direction of linearly polarized light emitted by the second half-wave plate HWP2 forms an angle of 45 degrees with the optical axis direction of the electro-optical modulator EOM;
3) Setting the modulation voltage V of the electro-optical modulator EOM as zero volt, adjusting the optical axis direction of the quarter-wave plate QWP to be the same as the polarization direction of linearly polarized light emitted by the second half-wave plate HWP2, and converging the linearly polarized light emitted from the quarter-wave plate QWP through the objective lens OL to form an optical trap capturing area;
4) Releasing a micro-nano particle from the upper part of the optical trap capturing area, and allowing the micro-nano particle MS to make free falling body movement downwards under the action of gravity to reach the optical trap capturing area to be captured;
5) The electro-optical modulator EOM is added with a sinusoidal modulation voltage V with a variable frequency omega, so that linearly polarized light is emitted from the polarization control device, and the polarization direction of the linearly polarized light emitted by the polarization control device rotates at the variable frequency omega and drives the micro-nano particles MS to rotate stably.
The electro-optical modulator EOM is a birefringent crystal with adjustable refractive index, and the optical axis direction of the birefringent crystal is parallel to the incident plane. Light incident thereon can be decomposed into linearly polarized light o polarized perpendicular to the optical axis 1 Light and linearly polarized light e polarized parallel to the optical axis 1 Light, the pair e of which can be varied by applying different modulation voltages thereto 1 The refractive index of the light. O transmitted through the EOM of the electro-optic modulator 1 Light and e 1 A phase difference modulated by the voltage V is added between the lights.
The quarter-wave plate QWP is a birefringent crystal with its optic axis oriented parallel to the plane of incidence, into which light can be decomposed into o polarized perpendicular to the optic axis 2 Light and parallel-axis polarized e 2 Light. O transmitted through quarter-wave plate QWP 2 Light and e 2 One quarter period will be added between the lights, i.e. one quarter period is added between the lights
Figure BDA0003044564520000071
Of the phase difference.
The optical axis directions of the EOM and the QWP are placed at an angle of 45 degrees, and then a beam of linearly polarized light with the polarization direction forming an angle of 45 degrees with the optical axis direction of the EOM is incident into the EOM, wherein the optical axis direction of the QWP is the same as the polarization direction of the light incident into the EOM, as shown in FIG. 3, after modulation of the EOM and the QWP, emergent light is a beam of elliptically polarized light with large elliptical eccentricity, and can be regarded as linearly polarized light in practical application. The polarization direction of the emerging light is related to the voltage V applied to the EOM. By applying a sinusoidal modulation voltage with frequency ω to the EOM, a linearly polarized light with polarization direction rotated by ω can be obtained. As shown in fig. 3, the left column is the polarization of the light incident on the EOM, the middle column is the polarization of the light exiting the EOM, and the right column is the polarization of the light exiting the QWP. Wherein a) indicates that the modulation voltage applied to the EOM is in the 0 phase of the sinusoidal cycle, b) indicates that the modulation voltage applied to the EOM is in the sinusoidal cycle
Figure BDA0003044564520000072
Phase, c) indicates that the modulation voltage applied to the EOM is in a pi phase of the sinusoidal cycle, d) indicates that the modulation voltage applied to the EOM is in a pi phase of the sinusoidal cycle
Figure BDA0003044564520000073
Phase, when the modulation voltage of the EOM is in phase 2 pi of the sinusoidal cycle, i.e. in phase 0 of the next cycle, the polarization state of the light beam is returned to the state shown in a). As can be seen from the figure, the light incident on the EOM is linearly polarized light, and the light emitted after modulation by the EOM and the QWP is also linearly polarized light, but the polarization direction thereof is rotated at a certain frequency.
As shown in FIG. 4, consider the electric field of linearly polarized light at the micro-nano particle
Figure BDA0003044564520000074
Electric dipole moment excited by it
Figure BDA0003044564520000075
Wherein
Figure BDA0003044564520000076
Is the polarizability tensor of the micro-nano particles, alpha || And alpha ⊥ Is its component in the axial and vertical axes, and E || And E ⊥ Then are the components of the electric field in both directions. For micro-nano particles with anisotropic polarizability, excited electric dipole moment
Figure BDA0003044564520000077
And electric field
Figure BDA0003044564520000078
The directions are different. Moment tau of light to micro-nano particles is
Figure BDA0003044564520000079
When the rotation frequency omega of the polarization direction of the light beam is less than the critical frequency omega c When the light beam is polarized, the micro-nano particles rotate at the same frequency omega, and the rotation of the micro-nano particles relative to the polarization direction of the light beam lags behind by a phase delta phi. Critical frequency omega c The definition of (A) is as follows:
Figure BDA0003044564520000081
wherein Δ α is the difference between the components of the polarizability of the micro-nano particles in the axial and perpendicular axial directions Δ α = α || -α ⊥ And E is the amplitude of the electric field component of the light, and γ represents the retardation coefficient of the residual gas in the cavity. And the lag phase Δ φ is defined as:
Figure BDA0003044564520000082
when the rotation frequency of the polarization direction of the light beam is larger than the critical frequency omega c The micro-nano particles can not rotate at a stable rotating speed, so that the rotating frequency omega of the polarization direction of the light beam is ensured when the device is used＜ω c 。
Therefore, the implementation shows that the stable rotation of the micro-nano particles in the vacuum optical tweezers at the set frequency can be driven by the interaction of the linearly polarized light and the micro-nano particles with anisotropic polarizability by utilizing the easy controllability of the electro-optical modulator on the polarization state of the light.

Claims (5)

1. The utility model provides a stable rotary device of frequency adjustable among vacuum optical tweezers system which characterized in that: the device comprises a laser source LS, a polarization control device, a vacuum cavity VC, an objective lens OL and micro-nano particles MS; the objective lens OL and the micro-nano particles MS are placed in the vacuum cavity VC, and the laser source LS, the polarization control device, the objective lens OL and the micro-nano particles MS are sequentially arranged along the light ray direction;
the polarization control device comprises a first half-wave plate HWP1, a polarization beam splitter PBS, a second half-wave plate HWP2, an electro-optical modulator EOM and a quarter-wave plate QWP; the first half-wave plate HWP1, the polarization beam splitter PBS, the second half-wave plate HWP2, the electro-optical modulator EOM and the quarter-wave plate QWP are arranged in sequence along the light direction;
emitting original laser from a laser source LS, wherein the original laser sequentially transmits through a first half-wave plate HWP1, a polarizing beam splitter PBS, a second half-wave plate HWP2, an electro-optical modulator EOM and a quarter-wave plate QWP and then enters a vacuum cavity VC, an objective lens OL focuses linearly polarized light entering the vacuum cavity VC to form a light trap capturing area, micro-nano particles MS are released from the upper part of the light trap capturing area, and then the micro-nano particles MS do free falling body movement downwards under the action of gravity and reach the light trap capturing area to be captured;
the variation frequency omega of the modulation voltage V applied on the electro-optical modulator EOM satisfies omega < omega c ，ω c Is a critical frequency, a critical frequency omega c The setting is made by the following formula:
Figure FDA0003812793740000011
wherein Δ α is a difference Δ α = α between the components of the polarizability of the micro-nano particle MS in the axial direction and the direction perpendicular to the axial direction || -α ⊥ ，α || Is a component of polarizability in the axial direction, alpha ⊥ E is an amplitude of an electric field component of light irradiated to the micro-nano particles MS, and γ represents a retardation coefficient of residual gas in the vacuum chamber VC.
2. The stable rotating device with adjustable frequency in the vacuum optical tweezers system according to claim 1, wherein:
the original laser sequentially passes through a first half-wave plate HWP1, a polarization beam splitter PBS and a second half-wave plate HWP2 to become linearly polarized light with adjustable intensity, and the linearly polarized light with adjustable intensity passes through modulation of an electro-optical modulator EOM and a quarter-wave plate QWP to become linearly polarized light with the polarization direction rotating at variable frequency;
the optical axis direction of the first half-wave plate HWP1 rotates around the light direction to control the light intensity of the linearly polarized light emitted from the polarization beam splitter PBS, the optical axis direction of the second half-wave plate HWP2 rotates around the light direction to enable the polarization direction of the linearly polarized light emitted from the second half-wave plate HWP2 to form an included angle of 45 degrees with the optical axis direction of the electro-optical modulator EOM, and the optical axis direction of the quarter-wave plate QWP is the same as the polarization direction of the linearly polarized light emitted from the second half-wave plate HWP 2.
3. The stable rotating device with adjustable frequency in the vacuum optical tweezers system according to claim 1, wherein:
and a light-transmitting optical window for light beam transmission is formed on the cavity wall of the vacuum cavity VC close to the quarter-wave plate QWP.
4. The stable rotating device with adjustable frequency in the vacuum optical tweezers system according to claim 1, wherein:
the polarizability tensor of the micro-nano particle MS
Figure FDA0003812793740000021
The anisotropic condition is satisfied; specifically, the micro-nano particles MS are composed of birefringent crystalsOr may be formed of a common material that is not spherical.
5. Use of a stable rotation device with adjustable frequency in a vacuum optical tweezers system according to any of claims 1-3, comprising the steps of:
1) Starting a laser source LS, and enabling the light intensity of linearly polarized light transmitted through a polarization beam splitter PBS to reach a preset value by adjusting the rotation of the optical axis direction of a first half-wave plate HWP1 around the light ray direction;
2) Adjusting the rotation of the optical axis direction of the second half-wave plate HWP2 around the light direction, so that the polarization direction of the linearly polarized light emitted by the second half-wave plate HWP2 forms an angle of 45 degrees with the optical axis direction of the electro-optical modulator EOM;
3) Setting the modulation voltage V of the electro-optical modulator EOM as zero volt, adjusting the optical axis direction of the quarter-wave plate QWP to be the same as the polarization direction of linearly polarized light emitted by the second half-wave plate HWP2, and converging the linearly polarized light emitted from the quarter-wave plate QWP through the objective lens OL to form an optical trap capturing area;
4) Releasing a micro-nano particle from the upper part of the optical trap capturing area, and allowing the micro-nano particle MS to make free falling body movement downwards under the action of gravity to reach the optical trap capturing area to be captured;
5) The electro-optical modulator EOM is added with a sinusoidal modulation voltage V with a variable frequency omega, so that linearly polarized light is emitted from the polarization control device, and the polarization direction of the linearly polarized light emitted by the polarization control device rotates at the variable frequency omega and drives the micro-nano particles MS to rotate stably.
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