WO2011128192A1

WO2011128192A1 - Methods and devices for position and force detection in optical tweezers

Info

Publication number: WO2011128192A1
Application number: PCT/EP2011/054427
Authority: WO
Inventors: Reinold Wischnewski; Michael GÖGLER
Original assignee: Carl Zeiss Microimaging Gmbh
Priority date: 2010-04-14
Filing date: 2011-03-23
Publication date: 2011-10-20
Also published as: DE102010027721A1

Abstract

The invention relates to methods and devices, in which a first beam (14) and a second beam (15) are focused in order to form first optical tweezers and second optical tweezers. Light backscattered from a first object (114) captured in the first optical tweezers and light backscattered from a second object (113) captured in the second optical tweezers is decoupled, for example by a beam splitter (110), and separated, for example by a polarizing beam splitter cube (116) on the basis of the polarization. In other variants, the first object and the second object are not captured but rather solely illuminated by the first beam or the second beam.

Description

Description METHOD AND DEVICES FOR THE POSITION AND POWER DETECTION IN OPTICAL TWEEZERS

The present invention relates to methods and apparatus for detecting the position of objects illuminated with a light beam, for example a laser beam, wherein in particular a position relative to the laser beam can be determined. The present invention also relates to methods and apparatus for detecting or measuring a force acting on an object trapped in an optical tweezer or for detecting or measuring forces acting on objects trapped in a plurality of optical tweezers. In such optical tweezers, also referred to as optical traps, an object whose dimensions are typically in the micrometer or nanometer range is held in or near a focus of a highly focused laser beam. The strong focusing of the laser beam generates an electric field with a strong gradient. A dipole induced in the object by the electromagnetic field of the laser beam allows manipulation of the object and, for example, results in a force along the electric field gradient in the direction of the location of maximum light intensity, i. to the focus of the laser beam.

Forces acting on such a trapped object can be detected by evaluating backward or forward scattered light from the object with a detector. Corresponding devices and methods are known, for example, from WO 2008/1451 10 A1 or WO 2009/065519 A1. Similarly, a positional shift of a laser beam, i. be detected by this illuminated, object.

In the above-mentioned WO 2008/1451 10 A1, it is explained in particular how the force can be applied to two objects located in two optical traps by detecting light forwardly scattered by the objects. The use of a structure which uses forward scattered light for detection, however, is disadvantageous in that the accessibility to the objects, or to a sample space, is made more difficult.

It is therefore an object of the present invention to provide methods and apparatus in which the force action on two objects captured in two optical tweezers or position changes of two objects illuminated by two light beams can be detected independently by evaluation of backscattered light. This object is achieved by a method according to claim 1 and a device according to claim 8. The dependent claims define further embodiments.

According to the invention, a method is proposed, comprising:

Generating a first light beam having a first polarization,

Generating a second light beam having a second polarization orthogonal to the first polarization,

Illuminating a first object with the first light beam and a second object with the second light beam,

Decoupling the light backscattered from the first object and the backscattered light from the second object,

Separating the backscattered light from the first object from the backscattered light from the second object based on the polarization, and separately detecting the backscattered light from the first object and the backscattered from the second object light.

By decoupling the backscattered light with subsequent separation on the basis of polarization, a separate detection of a change in position of the first object and the second object in a backscattering geometry can take place, which facilitates, for example, accessibility of a sample space.

The first light beam may be focused to form a first optical tweezer for capturing the first object, and the second light beam may be focused to form a second optical forceps for capturing the second object.

For decoupling, for example, a beam splitter such as a semitransparent mirror can be used. The beam splitter preferably has the same degree of decoupling for the first polarization and for the second polarization. In one embodiment, the generation of the first light beam and the second light beam may be effected by separating two portions of orthogonal polarization based on a single light beam, for example a laser beam. For this purpose, for example a laser with downstream λ / 2 plate and polarizing beam splitter, also referred to as a pole cube, can be used.

For detection, the light backscattered by the first object and the light backscattered by the second object can each be directed to a detector. This can be done via a telescopic arrangement, such as a reduction telescope. In the case of the detectors, an intensity shift or a deflection of a reflex can then be detected and the influence of a force on the respective object can be deduced. The invention will be explained in more detail with reference to the accompanying drawings. Show it:

1 shows a schematic of an optical device according to an exemplary embodiment, FIG. 2 shows a schematic of an optical device according to a further exemplary embodiment,

FIG. 3 is a schematic of an optical device according to another embodiment;

Figure 4 is a schematic of an optical device according to another embodiment and

FIG. 5 shows a flowchart of a method according to an exemplary embodiment.

Hereinafter, embodiments of the present invention will be explained in detail with reference to the accompanying drawings. It should be noted that features of various embodiments may be combined with each other unless otherwise stated. It should also be understood that the description of an embodiment having a plurality of elements or features is not to be construed as indicating that all such features are essential to the practice of the invention. Rather, other embodiments may have less than the illustrated features.

A schematic of an optical arrangement according to an embodiment is shown in FIG.

The exemplary embodiment of FIG. 1 comprises as the light source a laser 10, for example an infrared laser, which generates a laser beam 1 1. By a λ / 2 plate 12 and a polarizing beam splitter 13, also referred to as a pole cube, the laser beam 1 1 in a first beam 15 and a second beam 14, which is shown dotted divided. The second beam 14 is directed via a mirror 16 to a polarizing beam splitter 18, while the first beam 15 is directed via a mirror 17 to the polarizing beam splitter 18. The polarizing beam splitter 18 serves to merge the first beam 14 and the second beam 15 in a common light path. By this construction, the first beam 15 and the second beam 14 have mutually orthogonal polarizations. For example, in one embodiment, the orthogonal polarizations of the first beam 15 and the second beam 14 may be s-polarization and p-polarization.

As indicated by an arrow, the mirror 16 and / or the mirror 17 can be movable, as will be explained further below, to change a position of an optical tweezers formed by the first beam 14 and / or by the second beam 15. In other exemplary embodiments, other elements for changing the beam position / beam direction may also be provided, for example an acoustooptic deflector, a spatial spatial modulator (SLM), a galvanometer scanner or another positioning element.

From the beam splitter 18, the first beam 14 and the second beam 15 are separated by a beam splitter 19, e.g. a partially transmissive mirror and a beam splitter 1 10 to a trapping lens 1 1 1 steered, which may be part of a microscope assembly. The trap lens 1 1 1 focuses the first beam 15 and the second beam 14 on a slide 12. On or in the slide 1 12, objects 1 13, 1 14, such as biological objects are located, for example in a liquid. In the illustrated example, the object 1 13 is trapped in an optical tweezer formed by the first beam 15 while the object 14 is trapped in an optical tweezers formed by the second beam 14. By the movable mirrors 16 and / or 17, the locations differ in which the first object 1 13 and the second object 1 14 are trapped in the respective optical tweezers. The slide 1 12 can be illuminated by a further light source (not shown), for example a conventional microscope illumination. The scattered by objects on the slide 1 12 light of this further light source is on the trapping lens 1 1 1 through the beam splitter 1 10 and 19 passes through to a camera 1 19, whereby an optical control is possible. This may assist an operator in controlling the mirrors 16 and / or 17, for example.

The light of the first beam 15 backscattered by the object 1 13 and the light of the second beam 14 backscattered by the object 1 14 is transmitted to the beam via the trap objective 1 1 1. divider 1 10 steered and there coupled out of the light path between the laser 10 and the trap lens 1 1 1 and to a polarization-dependent beam splitter 1 16, for example a pole cube, steered, which directs the backscattered light of the first beam 15 to a first detector 1 17 and the backscattered light of the second beam 14 to a second detector 1 18 directs. The first detector 1 17 and the second detector 1 18 detect changes in the backscattered light, such as changes in the position of an intensity maximum, such changes caused for example by force on the object 1 13 and the object 1 14 and a position shift associated therewith the respective object can be. Thus, by the generation of two mutually orthogonally polarized light beams 14, 15 and by the use of the polarization-dependent beam splitter 1 16, a separate detection of a force acting on the object 1 13 and force acting on the object 1 14 force is possible, in particular in the Figure 1 shown backward scattering geometry. The beam splitter 110, which serves for coupling out the backscattered laser light, can have the same degree of reflection for the two orthogonal polarizations of the first beam 14 and of the second beam 15. The reflectance can be adjusted depending on a required signal strength at the first detector 1 17 and the second detector 1 18. In other embodiments, different reflectivities may be provided for the two orthogonal polarizations.

The position of the beam splitter 1 10, which is shown in Figure 1, is to be understood only as an example; the decoupling can be done in principle at any point of the backscattered beam path, for example, as shown immediately after the trapping lens 1 1 1, but also in the camera 1 19, e.g. at a camera port, in an aperture plane of the beam path, or when the laser light is coupled into a microscope, the microscope e.g. the trap lens 1 1 1 includes.

In the embodiment of Figure 1, the detectors 1 17, 1 18 may be positioned, for example, in the rear focal plane of the arrangement. In order to detect a force effect, a shift of an intensity maximum of the beam incident on the respective detector 1 17, 1 18 can then be detected.

In other embodiments, a telescopic arrangement may be provided to cause a deflection of the incident on the respective beam beam in response to a force acting on the respective object 1 13, 1 14 force. Such telescoping arrangements can also be used independently of the use of two differently polarized beam optical tweezers as described with reference to FIG become. Various examples of such telescopic arrangements will be explained in more detail below.

In this regard, Figure 2 shows an optical device according to another embodiment of the present invention.

In the exemplary embodiment of FIG. 2, a laser 20 generates a laser beam 21, which is directed via a mirror 22 and a beam splitter 23 through a beam splitter 24 to a trap objective 25. The trapping objective 25 focuses the laser beam onto an object carrier 216 and thus forms optical tweezers with which an object 217 can be caught.

As in the embodiment of FIG. 1, the slide 216 can be illuminated with a light source (not shown), thus allowing optical control via a camera 215 corresponding to the camera 1 19 of FIG.

Laser light backscattered by the object 217 is decoupled by the beam splitter 24 after passing through the trap lens 25 and directed to a detection device 218. In the detection unit 218, the decoupled laser beam is directed through a reduction telescope, of which a lens 29 and a lens 21 1 are shown, onto a first detector 213.

The reduction telescope 29, 21 1 is preferably configured in such a way that a divergent beam strikes the first detector 213. In other words, the beam, which is usually substantially parallel to the reduction telescope 29, 21 1, is converted into a divergent beam. In this case, for example, be the distance of the lenses 29, 21 1 in a range of 0.5-0.9, preferably 0.6-0.8 times the lens spacing for a collimated beam after passing through the reduction telescope.

The distance of the first detector 213 to the lens 21 1 can then be selected such that the reflection generated by the incident beam illuminates only a part of the detector surface, for example between 40% and 90% of the detector surface, for example about 80% of the detector surface. For example, at a focal length of the lens 29 of about 80mm and a focal length of the lens 21 1 of about -16mm the distance to the detector be about 75mm and the distance of the lenses 29, 21 1 can be about 45-52mm, in this For example, at 62mm lens pitch, a collimated, ie parallel, beam would strike the first detector 213. A telescope actuator of the reduction telescope formed by the lenses 29 and 21 1 can be between 2x and 10x, for example between 4x and 5x.

However, the above numerical values are to be understood as examples only, and other values are possible.

The use of such a reduction telescope is possible not only in the detection of a single beam, but also in the use of multiple beams to form a plurality of optical tweezers. In particular, the use of a reduction telescope is also feasible when using two orthogonally polarized beams to form two tweezers as explained with reference to FIG. For this purpose, for example, a polarization-dependent beam splitter 210 corresponding to the polarization-dependent beam splitter 1 16 of FIG. 1 can optionally be provided in the detection device 218, which performs a polarization separation and directs a first beam with a first polarization onto the first detector 213, while a directs second beam with a second polarization to a second detector 214. This polarization-dependent beam splitter 210 can be arranged as shown in Figure 2 between the lenses 29 and 21 1. A further lens 212 forms, together with the lens 29, a further reduction telescope with which the second beam is imaged on the second detector 214. In this case, the reduction telescope and the further reduction telescope thus share the lens 29, while the lenses 21 1 and 212 are provided separately. For the distance of the lens 212 to the lens 29 and the distance of the second detector 214 to the lens 212, the above statements apply to the lenses 29, 21 1 and the detector 213 accordingly. Two beams polarized orthogonally to one another can thereby be produced with a λ / 2 plate and a polarizing beam splitter as explained with reference to FIG. 1, but it is also possible to generate two orthogonally polarized beams by means of two separate light sources or by means of other types of polarizers, for example, by splitting a single beam with a non-polarizing beam splitter and subsequent polarizers. In other embodiments, the beams may also differ in characteristics other than polarization, for example, in terms of wavelength, and the separation may then take place, for example, by means of corresponding filters instead of by the beam splitter 210. In embodiments in which one or more optical tweezer beams are movable, eg displaceable, eg as explained with reference to FIG. 1, such as the first beam 15 or the second beam 14 of the embodiment of FIG. 1 by moving the mirror 17 or 16, moving the beam may cause ren that a corresponding reflex is no longer centrally incident on a detector such as the first detector 213 or the second detector 214 and thus generates an undefined behavior when a force is applied to an object located in the corresponding optical tweezers, for example a deflection oblique to the force effect a detection of the acting force difficult.

For compensation, in some embodiments of the invention, one or more movable optical elements may be provided. A corresponding embodiment is shown in FIG.

The embodiment of Figure 3 is in many parts a combination of the embodiments of Figures 1 and 2.

In the embodiment of Figure 3, as in the embodiment of Figure 1 with a laser 30, a λ / 2 plate 319 and a polarizing beam splitter 33 generates a first beam and a second beam, wherein in the embodiment in Figure 3, an additional (optional) mirror 32 is provided in the beam path. The first beam and the second beam can be moved, for example displaced, by mirrors 34, 35 which in their function correspond to the mirrors 16, 17 of FIG. 1 and are transmitted via a polarizing beam splitter 36 and a beam splitter 37 through a beam splitter 38 a trajectory lens 39 is directed, wherein the function of the elements 36-39 corresponds to the function of the elements 18, 19, 1 10 and 1 1 1 of Figure 1. As an example of an object trapped in one of the optical tweezers thus formed, an object 310 is shown in FIG. However, as explained with reference to Figure 1, two optical tweezers may be formed by the first beam and the second beam, in which two objects are captured accordingly. The object 310 may be located in or on a slide as explained with reference to FIGS. 1 and 2. For observation of the object, a camera 318 is provided as in the embodiments of FIGS. 1 and 2. The light backscattered by one or more trapped objects is decoupled by the beam splitter 38 as in the previous embodiments and directed to a detection device. This comprises a polarization-dependent beam splitter 312 for separating the beams as described with reference to FIG. 1 and lenses 31 1, 313 and 315 which form a first reduction telescope 31 1, 313 and a second reduction telescope 31 1, 315, corresponding to FIG 2 described for the lenses 29, 21 1 and 212. As already explained with reference to FIG. 2, a first detector 314 and a second detector 316 detect those from the first reduction telescope or from the first second reduction telescope emitted light beams to detect a force on one or more objects trapped in optical tweezers.

In the embodiment of Figure 3, the lens 313 is movable, in particular perpendicular to the optical axis, to compensate for moving the first beam through the movable mirror 35 and to ensure, for example, that the beam emitted by the first reduction telescope 31 1, 313 is always substantially centered on the detector 314 falls as long as no force acts on the respective captured object. Additionally or alternatively, the lens 315 may be movable to compensate for moving the second beam through the movable mirror 34. The movement of the lenses 313, 315 is controlled by a controller 317 in the embodiment of FIG.

The controller 317 may, for example, be coupled to the control of the mirrors 35 and / or 34 or directly control the mirrors 35 and / or 34 and move the lens 313 and / or 315 in response to the control of the mirrors 35 and / or 34.

For this purpose, for example, a calibration can be performed and for each position of the mirror 34 a corresponding position of the lens 315 and for each position of the mirror 35 a position of the lens 313 are stored, for example in a table in the controller 317 and in operation then the Lenses 313 and 315 according to this table in response to the control of the mirror 35 and 34 are moved.

In another embodiment, the detector signal and / or an image of the camera 318 may be used to control the lens 313 and the lens 315. In still other embodiments, the control may be manual by a user.

In the exemplary embodiments of FIGS. 1 -3, backscattered light is used by one or more objects to detect a force effect. In other embodiments, forward scattered light may also be used. An example of detection of forward scattered light is shown in FIG. The embodiment of Figure 4 is as it were a version of the embodiment of Figure 3, in which instead of the backscattered light forward scattered light is used to detect a force effect. However, a corresponding use of the forward scattered light is also possible, for example, for the embodiment of Figure 2.

In the embodiment of Figure 4 correspond to the functions of a laser 40, a mirror 41, a λ / 2 plate 420, a polarizing beam splitter 42, of mirrors 43 and 44, a polarizing beam splitter 45, a beam splitter 46, a trapping objective 47 and a camera 419 of the already described function of the laser 30, the mirror 32, the Abplatte 319, the polarizing beam splitter 33, the mirrors 34 and 35, the polarizing beam splitter 36, the beam splitter 37, the tracer lens 39 and the camera 318 of Figure 3 and will therefore not be explained again in detail.

In the illustration of Figure 4, an object 48 is trapped in optical tweezers. Light scattered forward by the object 48 is picked up by an objective 49 and directed via a mirror 410 to a detection arrangement 41 1 -417. The detection arrangement 41 1 -417 corresponds in its operation to the detection arrangement 31 1 -317 of FIG. 3, and corresponding elements carry the same reference symbols apart from the left-most 3 or left-hand 4 (element 31 1 corresponds to element 41 1 etc.). Therefore, the detection device will not be described again. In particular, lenses 413, 415 can also be moved by the controller 417 in the exemplary embodiment of FIG. 4 in order to compensate for movements of the beams used to generate optical tweezers by moving the mirrors 43, 44.

FIG. 5 shows a flow diagram of an exemplary embodiment of a method according to the invention, wherein this method can be implemented essentially as already described above in the exemplary embodiments of FIGS. 3 and 4, but can also be used independently of these specific exemplary embodiments.

In step 50, an object is illuminated or captured with a laser beam, in particular a focused laser beam forming an optical tweezers. In step 51, scattered light, for example forward or backward scattered light, is directed from the object through a reduction telescope to a detector so as to be able to detect forces acting on the object.

In step 52, the laser beam is moved, and in step 53, an optical element, for example a lens, of the reduction telescope is moved to compensate for the movement of the laser beam from step 52 and to allow consistent detection with the detector.

It should be noted that the embodiments described above are merely examples and a variety of variants and modifications are possible. Some of these variations are explained in more detail below. As explained for the embodiment of Figure 2, the embodiments of Figures 3 and 4 can be realized only for a single beam and thus a single optical tweezers. In this case, for example, in the detection of the polarization-dependent beam splitter 312, the lens 315 and the detector 316 in the case of Figure 3 or the polarization-dependent beam splitter 412, the lens 415 and the detector 416 omitted in the case of Figure 4, and the division of the laser beam emitted by the laser 30 or 40 into two beams with orthogonal polarization can be omitted.

While in the illustrated embodiments, a camera is provided for receiving an image of an object plane, this can also be omitted in other embodiments, or it can be alternatively or additionally provided an optical control by a microscope without a camera.

The use of mirrors, such as mirrors 22, 32, 41 and 410, for directing beams depends on the relative position of the various elements desired in each specific implementation, and depending on the desired position mirrors can be omitted, additional mirrors can be provided or Mirrors are placed differently. In addition, additional optical elements such as lenses may be provided, for example a telescope for expanding the beam emitted by the laser 10, 20, 30 or 40.

The laser used may each be an infrared laser, but lasers of other wavelengths are also possible.

Whereas in the exemplary embodiments illustrated, the detection is effected by means of a single detector for each beam forming an optical tweezers, in other embodiments a further division of the respective beam can be provided, for example a division of the beam into the lens 21 1 of FIG. for example, for separate detection for different spatial directions. In a further splitting can be detected independently, for example, in the Z direction.

The described reduction telescopes can be realized, for example, as Galileitel telescopes with a first plano-convex lens (lens 29, 31 1 or 41 1) and a second plano-concave lens (lenses 21 1, 212, 313, 315, 413, 415). Thus, it can be achieved that no focal point in the second lens and when using a Polwürfels for beam splitting is no focus point in the pole cube.

While in the embodiments of Figures 2-4, a first reduction telescope and a second reduction telescope have been described which a common first lens and Having separate second lenses, in other embodiments, for example, completely separate reduction telescopes can be arranged according to the respective polarization-dependent beam splitter. In embodiments which use a single beam, the outcoupling in the case of backward scattering can also take place with the aid of a pole cube instead of with the aid of a beam splitter, such as the beam splitter 24 or 38.

As detectors, for example, quadrant diodes or linear detectors can be used. Such a linear detector can be configured one-dimensionally or two-dimensionally. The detectors may be adjustable, for example the position of the detectors may be displaceable.

For the quantitative measurement of the acting force, the position of the beam emitted by the reduction telescope can be determined on the detector and, for example, converted into a force on the basis of a previously performed calibration.

While a second lens of the reduction telescopes has been described as being movable in the exemplary embodiments of FIGS. 3 and 4, the first lens may additionally or alternatively be movable. In other embodiments, instead of a dual lens design, other optical structures, such as a three lens optical assembly, may be used, and accordingly, one or more of these optical elements may be movable. To compensate for moving the laser beam, the optical elements can then be displaceable in particular perpendicular to the optical axis. In addition, such optical elements can also be displaceable in the direction of the optical axis, for example in order to change a size of the beam on the respective detector.

As already mentioned, two orthogonally polarized beams, for example an s-polarized and a p-polarized beam, can be generated not only by means of a λ 2 plate and subsequent polarizing beam splitter, but also in other ways.

In the above exemplary embodiments, it has been described how a force effect on an object trapped in an optical tweezer can be detected, in particular via a detection of a positional shift by means of a detector and a corresponding calibration with which a corresponding force can be assigned to the detected positional shift. With the devices explained also a mere detection of a position shift is possible. For example, a beam intensity can be chosen so that the forces acting in or at the focus of the laser beam are insufficient, which respectively illuminated Capture object. The described detection can then be used to detect positional shifts of the object and then, for example, to readjust a position of the beam in order to be able to track the movement of the object (particle tracking) Embodiments described modifications are also applicable to the other embodiments, unless otherwise noted.

Claims

claims

1 . Method for detecting a change in position of two objects (1 13, 1 14), comprising:

Generating a first light beam (14) having a first polarization,

Generating a second light beam (15) having a second polarization orthogonal to the first polarization,

Illuminating a first object (1 14) with the first light beam (14),

Illuminating a second object (1 13) with a second light beam (15),

Decoupling light backscattered from the first object (1 14) and backscattered light from the second object (1 13),

Separating the light backscattered from the first object by light backscattered from the second object (1 13) based on the polarization and

separately detecting the backscattered light from the first object (1 14) and the backscattered light from the second object (1 13).

2. The method of claim 1, further comprising:

Focusing the first light beam (14) to produce a first optical tweezer and the second light beam (15) to produce a second optical tweezer.

3. The method of claim 1 or 2, wherein the decoupling comprises decoupling with a beam splitter (1 10; 24; 38), wherein the beam splitter (1 10; 24; 38) for the backscattered from the first object (1 14) light has the same degree of decoupling as for the backscattered by the second object (1 13) light.

4. The method of claim 1, wherein generating the first light beam and generating the second light beam generate original light beam and directing the source light beam through a polarizing beam splitter to surround the first light beam and the second light beam To generate light beam (15) comprises.

5. The method according to any one of claims 1-4, wherein the decoupling takes place after the beam backscattered by the first object and the beam scattered backward by the second object has passed through an objective (1 1 1) used for the focusing.

The method of any of claims 1-5, further comprising directing the extracted backscattered beam from the first object and the beam backscattered from the second object through a telescope assembly (29, 21 1, 214, 31 1, 313, 315).

7. The method of claim 1, further comprising splitting the light backscattered from the first object and / or the backscattered light beam from the second object after separation for separate detection in different spatial directions.

8. A device for detecting a change in position of two objects (1 13, 1 14), comprising:

a light source arrangement (10, 12, 13) for generating a first light beam (14) having a first polarization and a second light beam (15) having a second polarization orthogonal to the first polarization,

a focusing lens (1 1 1) for focusing the first light beam (14) and focusing the second light beam (15),

a decoupling device (1 10) for decoupling light backscattered from a first object (1 14) illuminated by the first light beam (14) and a backscattered light from a second object (1 13) illuminated by the second light beam (15),

one of the decoupling device (1 10) downstream separation device (1 16) for separating the backscattered from the first object (1 14) light from the second object (1 13) backscattered light based on the polarization,

a first detection device (17) for detecting the light backscattered by the first object (1 14), and

a second detection means (1 18) for detecting the backscattered from the second object (1 13) light.

9. Apparatus according to claim 8,

wherein the light source assembly (10, 12, 13) and the focusing lens (1 1 1) are adapted to form a first optical tweezer based on the first light beam (14) and a second optical tweezer based on the second light beam (15).

10. Apparatus according to claim 8 or 9, wherein the decoupling means (1 10) for the first polarization and the second polarization has the same coupling-out.

1 1. Device according to one of claims 8-10, wherein the separating device comprises a polarizing beam splitter (1 16).

12. Device according to one of claims 8-11, wherein the decoupling device is arranged immediately after the focusing device (111).

13. Device according to one of claims 8-12, further comprising between the coupling-out device (110) and the first and second detector means (117, 118) arranged telescopic arrangement (29, 211, 214, 311, 313, 315).

14. Device according to one of claims 8-13, wherein the device for carrying out the method according to one of claims 1-7 is configured.