A device for suppressing the escape of suspended microspheres in vacuum optical tweezers

Abstract

The present invention discloses a method for inhibiting the escape of suspended microspheres in vacuum optical tweezers. The present invention comprises a laser, a collimating beam expansion module, a photo-induced rotation module, a reflection module and a light block; the laser, the collimating beam expansion module, the photo-induced rotation module and the reflection module are arranged in sequence along the optical axis, the light block is arranged on the side of the photo-induced rotation module, a microsphere is arranged on the optical axis between the photo-induced rotation module and the reflection module, the microsphere is captured by a capture light beam, the optical axis of the circularly polarized light emitted from the photo-induced rotation module is perpendicular to the optical axis of the capture light beam; the light emitted from the laser obtains circularly polarized light after passing through the collimating beam expansion module and the photo-induced rotation module, the circularly polarized light causes the microsphere to rotate around the optical axis of the circularly polarized light, and the reflection module and the light block balance the position of the microsphere. The present method eliminates the influence of the photophoresis phenomenon on the movement of the microspheres in the vacuum optical tweezers, and improves the stability of microsphere capture during vacuum pumping.

Description

Technical Field

[0001] The invention relates to a light trap measuring device in the field of optical engineering, in particular to a device for suppressing the escape of suspended microspheres in vacuum optical tweezers. Background Art

[0002] When photons are incident on the surface of a medium, they are refracted and reflected, and the speed and direction of the photons change, resulting in a change in their momentum vector. From the law of conservation of momentum, it can be deduced that when a light beam is incident on a microsphere, the change in the momentum of the photons is the change in the momentum of the microsphere. Therefore, the light beam exerts a force on the microsphere, which is called light radiation pressure. The light radiation pressure includes the scattering force along the propagation direction of the light beam and the gradient force that always points to the place with stronger light intensity. Under the action of these two forces, the light beam can capture the microsphere in a certain area, that is, stabilize it in a specific position. This area is called a light trap.

[0003] Light trap measurement devices can be used in many fields, such as extremely weak force measurement and light trap accelerometer. When this device works in a vacuum environment, it will greatly reduce thermal noise and obtain higher measurement sensitivity, which has been a research hotspot in recent years.

[0004] A major technical difficulty in the vacuum light trap system is the problem of particle escape. Due to the thermal effect of particles in the light trap, they can easily escape during the vacuum pumping process. It is generally believed that this phenomenon is caused by the photophoretic force generated by the photothermal effect. Driven by this technical difficulty, magnetic trap technology has received widespread attention. For magnetic traps, no light path control is introduced and they are not affected by the photophoretic force caused by heat absorption. Therefore, they can be directly pumped from atmospheric pressure to high vacuum. However, the bandwidth of the magnetic trap is narrow, which is not conducive to improving the detection sensitivity.

[0005] In general, due to defects and impurities in the microspheres, they will absorb part of the captured light, and this part of the energy will be converted into heat. If the gas pressure is low, the gas molecules and the microspheres will not interact enough, and the energy absorbed by the microspheres cannot be dissipated, and the microspheres will be in a state of thermal non-equilibrium. When the microspheres are irradiated with light from one side, a temperature gradient will be generated on the surface of the microspheres. The momentum exchange between the gas molecules and the microspheres in this direction is unbalanced, forming a photophoretic force ( Figure 1 When the pressure in the vacuum chamber drops below a few millibars, the microspheres can easily escape from the light trap without cooling. The cooling system requires a three-axis modulated optical path, which increases the complexity of the entire device and introduces other errors, affecting the practical application of the vacuum light trap system, a device with great potential for ultra-sensitive sensing. Summary of the invention

[0006] The purpose of the present invention is to solve the problem of low efficiency of existing vacuum optical trap experiments and propose a device for suppressing the escape of suspended microspheres in vacuum optical tweezers to improve the stability of microspheres during vacuum pumping.

[0007] The technical solution of the present invention is as follows:

[0008] The invention comprises a laser, a collimating beam expansion module, a photo-induced rotation module, a reflection module and a light block;

[0009] The laser, the collimating beam expansion module, the photo-induced rotation module and the reflection module are arranged in sequence along the optical axis, the light block is arranged on the side of the photo-induced rotation module, a microsphere is arranged on the optical axis between the photo-induced rotation module and the reflection module, the microsphere is captured by the capture light beam, the optical axis of the circularly polarized light emitted from the photo-induced rotation module is perpendicular to the optical axis of the capture light beam; the light emitted from the laser passes through the collimating beam expansion module and the photo-induced rotation module to become the circularly polarized light emitted from the photo-induced rotation module, the circularly polarized light causes the microsphere to rotate around the optical axis of the circularly polarized light, and the reflection module and the light block balance the position of the microsphere.

[0010] The collimating beam expansion module comprises a first lens L1 and a second lens L2; ​​the first lens L1 and the second lens L2 are arranged in sequence along the optical axis, the first lens L1 is arranged close to the laser, and the second lens L2 is arranged close to the photo-induced rotation module.

[0011] The photo-induced rotation module includes a polarization beam splitter PBS, a quarter wave plate and a third lens L3; the polarization beam splitter PBS, the quarter wave plate and the third lens L3 are arranged in sequence along the optical axis, the polarization beam splitter PBS is arranged close to the collimation and expansion module, a light block is arranged on the side of the polarization beam splitter PBS, and a microsphere is arranged on the optical axis between the third lens L3 and the reflection module.

[0012] The reflection module is a fourth lens L4 and a reflector M1; the fourth lens L4 and the reflector M1 are arranged in sequence along the optical axis, and a microsphere is arranged on the optical axis between the photo-induced rotation module and the fourth lens L4.

[0013] The microspheres are optically uniform and transparent microspheres with a size in the μm order.

[0014] The material of the microspheres is polystyrene or silicon dioxide.

[0015] The beneficial effects of the present invention are:

[0016] After capturing the microspheres in the light trap, the present invention uses circularly polarized light perpendicular to the optical axis of the capture light beam to rotate the microspheres at the equilibrium point. The rotating microspheres are evenly heated by the capture light, avoiding asymmetric absorption of light field energy, eliminating asymmetric heating of the microspheres by the capture light, overcoming the influence of photophoretic force on the movement of the microspheres, and inhibiting the escape of the microspheres in the vacuum. Without affecting the equilibrium position of the microspheres in the light trap, the present invention increases the probability of the microspheres maintaining stability during the pressure reduction process of the vacuum suspension system, and improves the stability of microsphere capture during the vacuum pumping process. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the principle of photophoresis.

[0018] Figure 2 It is a structural schematic diagram of the optical path diagram of the device for suppressing the escape of suspended microspheres in vacuum optical tweezers of the present invention.

[0019] Figure 3 The present invention is a light path diagram of a device for suppressing the escape of suspended microspheres in vacuum optical tweezers. DETAILED DESCRIPTION

[0020] Reference Figure 1 When the laser irradiates the microsphere from one side, the microsphere will absorb more heat on the side illuminated by the laser, and the illuminated side has a higher temperature than the backlit side, thereby forming a temperature gradient inside the microsphere, resulting in different strengths of interaction between the two sides of the microsphere and the surrounding air molecules. The illuminated side has a stronger interaction with the air molecules, thereby generating a photophoretic force along the direction of the temperature gradient.

[0021] like Figure 2 and 3 As shown, the present invention includes a laser, a collimating beam expansion module, a photo-induced rotation module, a reflecting module and a light block; the laser, the collimating beam expansion module, the photo-induced rotation module and the reflecting module are arranged in sequence along the optical axis, the light block is arranged on the side of the photo-induced rotation module, a microsphere is arranged on the optical axis between the photo-induced rotation module and the reflecting module, the microsphere is captured by a capture light beam, and the optical axis of the circularly polarized light emitted from the photo-induced rotation module is perpendicular to the optical axis of the capture light beam; the light emitted from the laser passes through the collimating beam expansion module and the photo-induced rotation module to become the circularly polarized light emitted from the photo-induced rotation module, the circularly polarized light causes the microsphere to rotate around the optical axis of the circularly polarized light, thereby eliminating asymmetric heating of the microsphere by the capture light, avoiding the photophoresis phenomenon, and inhibiting the escape of the microsphere; the reflecting module and the light block balance the position of the microsphere.

[0022] The collimation and expansion module is used to ensure the parallelism of the parallel light in the optical path and the focusing effect of the lens behind it, so as to improve the utilization efficiency of the incident light; the photo-induced rotation module is used to generate circularly polarized light, which carries the orbital angular momentum and is transmitted to the microspheres suspended in the vacuum light trap, so that the microspheres rotate along the optical axis of the circularly polarized light; the reflection module is used to reflect the circularly polarized light generated by the photo-induced rotation module for the first time, and the circularly polarized light after the first reflection offsets the scattered light on the microspheres, thereby eliminating the influence of the circularly polarized light on the equilibrium position of the microspheres. The circularly polarized light after the first reflection is incident on the polarization beam splitter PBS and then reflects to form the circularly polarized light after the second reflection. The light shield absorbs the circularly polarized light after the second reflection, and the light beam is discarded to ensure that the other optical path arrangements of the vacuum light trap device are not affected.

[0023] The collimating beam expansion module includes a first lens L1 and a second lens L2; ​​the first lens L1 and the second lens L2 are arranged in sequence along the optical axis, the first lens L1 is arranged close to the laser, and the second lens L2 is arranged close to the polarization beam splitter PBS of the photo-rotation module.

[0024] The photo-rotation module includes a polarization beam splitter PBS, a quarter wave plate and a third lens L3; the polarization beam splitter PBS, the quarter wave plate and the third lens L3 are arranged in sequence along the optical axis, the polarization beam splitter PBS is arranged close to the second lens L2 of the collimating beam expansion module, a light block is arranged on the side of the polarization beam splitter PBS, and a microsphere is arranged on the optical axis between the third lens L3 and the fourth lens L4 of the reflection module. The light emitted by the laser passes through the collimating beam expansion module and then through the polarization beam splitter PBS to obtain linear polarization, and the linear polarization passes through the quarter wave plate to obtain circular polarization, which is focused on the microsphere by the third lens L3.

[0025] The reflection module is a fourth lens L4 and a reflector M1; the fourth lens L4 and the reflector M1 are arranged in sequence along the optical axis, and a microsphere is arranged on the optical axis between the third lens L3 and the fourth lens L4 of the photo-rotation module. The vertically incident circularly polarized light is collimated by the lens L4, and then reflected by the reflector M1, which offsets the incident scattered light of L3, thereby ensuring that the stable point position in the light trap remains unchanged while the particles are rotated. In addition, the light reflected by the reflector M1 is reflected on the polarization beam splitter PBS, and this part of the light is blocked by a light block to avoid affecting other light paths.

[0026] The microspheres are optically uniform and transparent microspheres with a size of μm, which can be stably captured by the captured light in the corresponding environment. The material of the microspheres is polystyrene or silicon dioxide.

[0027] Before rotating the microsphere, the microsphere must be stably captured in the vacuum chamber. First, the pressure of the vacuum chamber is reduced to the order of 10 mbar, and the microsphere is thrown into the light trap area using piezoelectric ceramics to stably capture the microsphere in the gas.

[0028] During the experiment, the microspheres are first stably captured in a vacuum chamber, and then circularly polarized light is introduced to make the microspheres rotate. The chamber is then further evacuated and the pressure drops to a predetermined value, blocking the circularly polarized light so as not to affect subsequent operations and measurements.

[0029] The suspended microspheres are in a closed vacuum chamber, and the light emitted from the photo-rotation module and the reflection module can be incident perpendicular to the capture light beam.

[0030] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention and should be included in the scope of the claims of the present invention.

Claims

1. A device for suppressing the escape of suspended microspheres in vacuum optical tweezers, characterized in that: It includes a laser, a collimating beam expansion module, a photo-induced rotation module, a reflection module and a light block; The laser, the collimating beam expansion module, the photo-induced rotation module and the reflection module are arranged in sequence along the optical axis, the light block is arranged on the side of the photo-induced rotation module, a microsphere is arranged on the optical axis between the photo-induced rotation module and the reflection module, the microsphere is captured by the capture light beam, and the optical axis of the circularly polarized light emitted from the photo-induced rotation module is perpendicular to the optical axis of the capture light beam; the light emitted from the laser passes through the collimating beam expansion module and the photo-induced rotation module to become the circularly polarized light emitted from the photo-induced rotation module, the circularly polarized light causes the microsphere to rotate around the optical axis of the circularly polarized light, and the reflection module and the light block balance the position of the microsphere; The reflection module is used for reflecting the circular polarized light generated by the photo-induced rotation module for the first time. The circular polarized light after the first reflection is used to offset the scattered light on the microsphere. The circular polarized light after the first reflection is incident on the polarization beam splitter PBS in the photo-induced rotation module and then reflected to form the circular polarized light after the second reflection. The light block absorbs the circular polarized light after the second reflection.

2. The device for suppressing the escape of suspended microspheres in vacuum optical tweezers according to claim 1, characterized in that: The collimating beam expansion module comprises a first lens L1 and a second lens L2; ​​the first lens L1 and the second lens L2 are arranged in sequence along the optical axis, the first lens L1 is arranged close to the laser, and the second lens L2 is arranged close to the photo-induced rotation module.

3. The device for suppressing the escape of suspended microspheres in vacuum optical tweezers according to claim 1, characterized in that: The photo-induced rotation module includes a polarization beam splitter PBS, a quarter wave plate and a third lens L3; the polarization beam splitter PBS, the quarter wave plate and the third lens L3 are arranged in sequence along the optical axis, the polarization beam splitter PBS is arranged close to the collimation and expansion module, a light block is arranged on the side of the polarization beam splitter PBS, and a microsphere is arranged on the optical axis between the third lens L3 and the reflection module.

4. The device for suppressing the escape of suspended microspheres in vacuum optical tweezers according to claim 1, characterized in that: The reflection module is a fourth lens L4 and a reflector M1; the fourth lens L4 and the reflector M1 are arranged in sequence along the optical axis, and a microsphere is arranged on the optical axis between the photo-induced rotation module and the fourth lens L4.

5. The device for suppressing the escape of suspended microspheres in vacuum optical tweezers according to claim 1, characterized in that: The microspheres are optically uniform and transparent microspheres with a size in the μm order.

6. The device for suppressing the escape of suspended microspheres in vacuum optical tweezers according to claim 1, characterized in that: The material of the microspheres is polystyrene or silicon dioxide.

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