A method for measuring the waist distance of the optical axis direction of a dual-beam optical tweezer

Abstract

The present application belongs to the field of precision measurement technology, and relates to a kind of double-beam optical tweezers optical axis direction beam waist spacing measurement method.The method comprises the following steps: step one, build a measuring device;Step two, adjust the position of the imaging plate;Step three, measure the relative position of one trapping objective lens beam waist;Step four, adjust the position of the imaging plate;Step five, measure the relative position of the other trapping objective lens beam waist;Step six, calculate the double-beam optical tweezers beam waist spacing.The present application combines the imaging principle of the objective lens in the optical tweezers, measures the critical position of the probe completely blocking the laser beam, realizes the judgment and distance measurement of the double-beam beam waist.Using the present application to align the beams in the double-beam optical tweezers has the advantages of high alignment efficiency, high precision, good repeatability and strong practicality, and has good application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of precision measurement, and relates to a method for measuring the waist distance of a double-beam optical tweezer in the optical axis direction. BACKGROUND

[0002] A double-beam optical tweezer is a precision optical device for binding and suspending micro-nano particles by using two counter-propagating Gaussian laser beams. When the waists of the two Gaussian laser beams coincide or substantially coincide, optical forces generated by the momentum of light will generate an optical potential well at the waist coincidence position, which is called a double-beam optical trap. The double-beam optical trap can measure various physical quantities such as acceleration, extremely weak force, charge quantity and electric field by using the suspended micro-nano particles therein, and has wide application prospects in the field of precision measurement.

[0003] The double-beam optical tweezer mainly utilizes the mechanical effect of light to bind the suspended micro-nano particles in the double-beam optical trap, and mainly utilizes the radial gradient force and the scattering force along the optical axis direction of the Gaussian beam to bind the micro-nano particles. In the double-beam optical tweezer, the beams propagate in opposite directions, the scattering forces cancel each other out, and the gradient force always points to the maximum of the optical cavity, thereby realizing radial suspension. Generally, in order to realize stable capture of the suspended micro-nano particles by the double-beam optical tweezer, the counter-propagating double beams need to be strictly aligned, and the waist positions of the counter-propagating double beams need to satisfy a specific relationship, otherwise multiple potential wells will be formed or the gradient force will be too small to suspend. Therefore, it is necessary to accurately determine the waist positions of the counter-propagating double beams.

[0004] The traditional double-beam alignment scheme mainly uses the observation of scattering light brightness to determine the waist position, but this scheme is highly dependent on the surface roughness and cleanliness of the probe object. When the surface roughness of the probe object is high, different brightness scattering spots will be formed at different irradiation positions. On the other hand, when the NA value of the applied capture objective lens is small, the Rayleigh distance of the Gaussian beam is long, and the scattering light brightness cannot be determined by the scattering light brightness. Moreover, the double-beam alignment scheme using micro-holes cannot accurately determine the waist position in the optical axis direction, and when the NA value of the capture objective lens is different, multiple types of micro-hole alignment plates need to be prepared. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, the present application provides a method for measuring the waist distance of a double-beam optical tweezer in the optical axis direction. The present application does not involve multiple types of alignment devices, and can accurately measure by using the principle of optical imaging, thereby having the advantages of simple structure, high precision and strong practicality.

[0006] The technical scheme adopted by the present application is as follows:

[0007] A method for measuring the waist distance of a double-beam optical tweezer in the optical axis direction, mainly comprising the following steps:

[0008] Step one, build the measuring device: a displacement table is used to fix a probe, the displacement table can make the probe move back and forth along the optical axis direction and the probe direction between the two capture objectives of the double-beam optical tweezers, so that the probe is always perpendicular to the optical axis, and the needle tip of the probe is at the lower edge of the Gaussian beam, and the relative position reading of the probe in the optical axis direction can be given, the needle tip radius of the probe is larger than the waist radius of the Gaussian beam, a piece of imaging plate is inserted into the beam input end of one capture objective, the imaging plate is perpendicular to the optical axis, the center axis coincides with the optical axis, and the size is larger than the light spot formed by the beam;

[0009] Step two, adjust the position of the imaging plate: the double-beam optical tweezers is powered on, the position of the probe is moved back and forth along the optical axis direction between the two capture objectives, and the position of the imaging plate is adjusted, so that all the images of the probe on the imaging plate are clear and visible;

[0010] Step three, measure the relative position of the waist of one capture objective: move the probe along the optical axis direction to a critical position where the light on the imaging plate is completely blocked by the probe, record the relative position of the probe at this moment Z 11 , move the probe along the optical axis direction to another critical position where the light on the imaging plate is completely blocked by the probe, record the relative position of the probe at this moment Z 12 , calculate the relative position of the waist of this capture objective ;

[0011] Step four, adjust the position of the imaging plate: insert the imaging plate into the beam input end of the other capture objective, the imaging plate is perpendicular to the optical axis, the center axis coincides with the optical axis, move the position of the probe back and forth along the optical axis direction between the two capture objectives, and adjust the position of the imaging plate, so that all the images of the probe on the imaging plate are clear and visible;

[0012] Step five, measure the relative position of the waist of the other capture objective: move the probe along the optical axis direction to a critical position where the light on the imaging plate is completely blocked by the probe, record the relative position of the probe at this moment Z 21 , move the probe along the optical axis direction to another critical position where the light on the imaging plate is completely blocked by the probe, record the relative position of the probe at this moment Z 22 , calculate the relative position of the waist of this capture objective ;

[0013] Step six, calculate the waist distance of the double-beam optical tweezers: the distance between the waists of the double-beam optical tweezers .

[0014] Further, the displacement table can move the probe back and forth along a direction perpendicular to the optical axis and the probe direction, and can give a reading of the relative position of the probe in the direction.

[0015] Further, the diameter of the probe gradually decreases from the end to the needle tip, and the diameter of the needle tip of the probe is in the order of microns, and the precision of the displacement table in moving the position of the probe reaches the order of microns.

[0016] Further, the imaging plate can form a clear visible image on infrared light.

[0017] The beneficial effects of the present application are:

[0018] The present application combines the imaging principle of the objective lens in the optical tweezers, measures the critical position of the probe completely blocking the laser beam, realizes the judgment and distance measurement of the waist of the double-beam, and has the advantages of high alignment efficiency, high precision, good repeatability and strong practicability in the alignment of the double-beam optical tweezers. In addition, the present application is not limited to the type of optical trap and the structure of optical path, and has a very wide range of application. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The basic idea of the present application is shown in the figure.

[0020] Figure 2 The structure of the device in the embodiment of the present application is shown in the figure.

[0021] Figure 3 The imaging change on the imaging plate caused by the displacement of the probe in the embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0022] The present application will be described in detail below with reference to the accompanying drawings, but the protection scope of the present application should not be limited thereby.

[0023] As shown in the figure, a method for measuring the waist spacing of the optical axis direction of the double-beam optical tweezers mainly includes the following steps: Figure 1

[0024] Step one, build a measuring device: fix a probe with a displacement table, the displacement table can move the probe back and forth along the optical axis direction and the probe direction between the two capture objective lenses of the double-beam optical tweezers, so that the probe is always perpendicular to the optical axis, and the needle tip of the probe is at the lower edge of the Gaussian beam, and a reading of the relative position of the probe in the optical axis direction can be given, the radius of the needle tip of the probe is greater than the waist radius of the Gaussian beam, and an imaging plate is inserted at the input end of the beam of one capture objective lens, the imaging plate is perpendicular to the optical axis, the center axis coincides with the optical axis, and the size is greater than the light spot formed by the beam;

[0025] ​Step two, adjusting the position of the imaging plate: energize the dual-beam optical tweezers, move the position of the probe back and forth along the optical axis between the two trapping objectives, adjust the position of the imaging plate so that all the images of the probe on the imaging plate are clearly visible;

[0026] Step three, measuring the relative position of the waist of one trapping objective: move the probe to a critical position along the optical axis where the light on the imaging plate is completely blocked by the probe, record the relative position of the probe at this moment Z 11 move the probe to another critical position along the optical axis where the light on the imaging plate is completely blocked by the probe, record the relative position of the probe at this moment Z 12 calculate the relative position of the waist of this trapping objective ;

[0027] Step four, adjusting the position of the imaging plate: insert the imaging plate into the light beam input end of the other trapping objective, the imaging plate is perpendicular to the optical axis, the center axis coincides with the optical axis, move the position of the probe back and forth along the optical axis between the two trapping objectives, adjust the position of the imaging plate so that all the images of the probe on the imaging plate are clearly visible;

[0028] Step five, measuring the relative position of the waist of the other trapping objective: move the probe to a critical position along the optical axis where the light on the imaging plate is completely blocked by the probe, record the relative position of the probe at this moment Z 21 move the probe to another critical position along the optical axis where the light on the imaging plate is completely blocked by the probe, record the relative position of the probe at this moment Z 22 calculate the relative position of the waist of this trapping objective ;

[0029] Step six, calculating the distance between the waists of the dual-beam optical tweezers: the distance between the waists of the dual-beam optical tweezers .

[0030] Preferably, the displacement table can move the probe back and forth along a direction perpendicular to the optical axis and the direction of the probe, and can give the relative position reading of the probe in this direction.

[0031] Preferably, the diameter of the probe gradually decreases from the end to the needle tip, and the diameter of the needle tip of the probe is in the order of microns, and the displacement table moves the position of the probe with an accuracy of microns.

[0032] Preferably, the imaging plate can form clear and visible images of infrared light.

[0033] The device of the specific embodiment of the application is as follows Figure 2As shown, the dual-beam optical tweezers include a trapping laser 1, a polarizing beam splitter 2, a first reflecting mirror 3, a second reflecting mirror 4, a third reflecting mirror 5, a first trapping objective lens 6, and a second trapping objective lens 7. The trapping laser 1 emits a trapping laser beam, which is split into clockwise propagating beams by the polarizing beam splitter 2. a and counterclockwise propagating beam b .beam a The light beam is incident on the second capturing objective lens 7 through the first reflecting mirror 3 and the second reflecting mirror 4. b The light is incident on the first capturing objective lens 6 through the third reflecting mirror 5; the device in a specific embodiment of the present invention also includes a displacement stage 8, a probe 9 and an imaging plate 10.

[0034] The specific measurement process is as follows: First, according to... Figure 2 Set up the measuring device. Turn on the capturing laser 1 to output appropriate power, and adjust the first reflector 3 and the second reflector 4 to propagate the beam clockwise. a It passes through the second capture objective 7, probe 9 and the first capture objective 6 in sequence.

[0035] The second step is to adjust the third reflecting mirror 5 to propagate the light beam counterclockwise. b The light trap is formed by passing the first capturing objective 6, the probe 9, and the second capturing objective 7 in sequence. The probe 9 is fixed on the displacement stage 8 and placed vertically into the light trap along the direction of gravity, with the tip of the probe positioned at the lower edge of the Gaussian beam.

[0036] The next step is to measure the clockwise propagating beam. a The beam waist position is determined by focusing through the second capturing objective 7. The imaging plate 10 is placed along the optical axis direction of the beam. a Move probe 9 in the direction of propagation until the light spot on the imaging plate is completely blocked, then record the reading of displacement stage 8. Z 11 Along the optical axis, against the direction of the beam. a When the probe 9 is moved in the direction of propagation and the light spot on the imaging plate is again completely blocked, the reading of the displacement stage 8 is recorded. Z 12 The light beam propagates clockwise. a The waist position after focusing through the second capturing objective lens 7 is: .

[0037] The next step is to measure the counterclockwise propagating beam. b The beam waist position is obtained after focusing through the first capturing objective 6. The imaging plate 10 is inserted into the input end of the second capturing objective 7, along the optical axis direction... b Move probe 9 in the direction of propagation until the light spot on imaging plate 10 is completely blocked, then record the reading on displacement stage 8. Z 21Along the optical axis, against the direction of the beam. b Move probe 9 in the propagation direction until the light spot on imaging plate 10 is completely blocked again, then record the reading on displacement stage 8. Z 22 The light beam then propagates counterclockwise. b The waist position after focusing by the first capturing objective lens 6 .

[0038] Finally, through calculation The beam waist spacing of the two beams propagating in opposite directions in the double-beam optical trap is obtained.

[0039] like Figure 3 As shown, this is a beam of light propagating clockwise. a The example is determined by the position of the beam waist after focusing by the second capturing objective lens 7. The beam propagates clockwise. a The light is incident on probe 9 through the second capturing objective lens 7 and on imaging plate 10 through the first capturing objective lens 6. When the probe is at positions 9a-9e, the images on imaging plate 10 are 9f-9j, respectively. When probe 9 moves to 9d and 9e, the diameter of probe 9 is exactly equal to the diameter of the light spot, and the light spot is completely blocked. At this time, probe 9 is at two critical positions on the imaging plate where the light is completely blocked, and the images on imaging plate 10 are as shown in 9i and 9j, respectively. Record the readings of the displacement stage 8 at 9d and 9e. Z 11 and Z 12 Then it can be determined whether the light beam is propagating clockwise. a The waist position after focusing through the second capturing objective lens 7 .

[0040] This invention can also be used to determine the beam waist position and measure the spacing in the radial direction of the optical axis. Using this invention for beam alignment in dual-beam optical tweezers offers advantages such as high alignment efficiency, high precision, good repeatability, and strong practicality. Furthermore, this invention is not limited to optical trap types and optical path structures, and has a very wide range of applications.

Claims

1. A method for measuring the waist distance of the optical axis direction of a dual-beam optical tweezer, characterized in that, The method comprises the following steps: Step one, building a measuring device: a displacement table is used to fix a probe, the displacement table can make the probe move back and forth along the optical axis direction and the probe direction between two trapping objectives of a double-beam optical tweezers, so that the probe is always perpendicular to the optical axis, and the needle tip of the probe is at the lower edge of the Gaussian beam, and the relative position reading of the probe in the optical axis direction can be given, the radius of the needle tip of the probe is larger than the waist radius of the Gaussian beam, and an imaging plate is inserted into the beam input end of one trapping objective, the imaging plate is perpendicular to the optical axis, the center axis coincides with the optical axis, and the size is larger than the light spot formed by the beam; Step two, adjusting the position of the imaging plate: the double-beam optical tweezers is powered on to work, the position of the probe is moved back and forth along the optical axis direction between the two trapping objectives, and the position of the imaging plate is adjusted, so that all the images of the probe on the imaging plate are clear and visible; Step three, measuring the relative position of the beam waist of the objective lens: moving the probe to a critical position on the imaging plate where the light is completely blocked by the probe in the direction of the optical axis, and recording the relative position of the probe at this moment Z 11 moving the probe to another critical position on the imaging plate where the light is completely blocked by the probe in the direction of the optical axis, and recording the relative position of the probe at this moment Z 12 calculating the relative position of the beam waist of the objective lens ; Step four, adjusting the position of the imaging plate: the imaging plate is inserted into the beam input end of the other trapping objective, the imaging plate is perpendicular to the optical axis, the center axis coincides with the optical axis, the position of the probe is moved back and forth along the optical axis direction between the two trapping objectives, and the position of the imaging plate is adjusted, so that all the images of the probe on the imaging plate are clear and visible; Step five, measuring the relative position of another capture objective beam waist: moving the probe to a critical position on the imaging plate where the light is completely blocked by the probe in the direction of the optical axis, and recording the relative position of the probe at this moment Z 21 moving the probe to another critical position on the imaging plate where the light is completely blocked by the probe in the direction of the optical axis, and recording the relative position of the probe at this moment Z 22 calculating the relative position of this capture objective beam waist ; Step six, calculate the distance between the beam waists of the dual beam optical tweezer: the distance between the beam waists of the dual beam optical tweezer .

2. The method of measuring the waist distance of the optical axis direction of the dual-beam optical tweezers according to claim 1, wherein, The displacement table can make the probe move back and forth along the direction perpendicular to the optical axis and the probe direction, and the relative position reading of the probe in this direction can be given.

3. The method of measuring the waist distance of the optical axis direction of the dual-beam optical tweezers according to claim 2, wherein, The diameter of the probe gradually decreases from the end to the needle tip, and the diameter of the needle tip of the probe is in the order of microns, and the accuracy of the displacement table in moving the position of the probe reaches the order of microns.

4. The method of measuring the waist distance of the optical axis direction of the dual-beam optical tweezers according to any one of claims 1-3, characterized in that, The imaging plate can form clear and visible images for infrared light.

Images