Cantilever for single laser atomic force microscope

Abstract

Cantilever for use in an atomic force microscope comprising an absorption layer provided on the cantilever facing an optical system such that, during use, a first fraction of light emitted by the optical system is absorbed by the absorption layer; wherein the absorption layer has a thickness less than the light absorption depth of the absorption layer such that a second fraction of the light emitted from the optical system during use passes through the absorption layer; and wherein the cantilever is arranged to reflect the second fraction of the light back to the optical system such that at least a part of the light reflected by the cantilever is captured by the optical system during use.

Description

[0001] P137262PC00

[0002] Title: Cantilever for single laser atomic force microscope

[0003] The invention relates to a cantilever and an atomic force microscope comprising such a cantilever.

[0004] An atomic force microscope is a tool that can be used in various scientific and industrial fields to measure and image surfaces at the nanometer scale. A surface can be scanned by a probe that moves across the surface of a sample and detecting forces that act between a probe tip at an end of the probe and the sample. This allows the generation of high- resolution, three-dimensional topographic maps. Such an atomic force microscope typically comprises several key components such as a cantilever with a probe tip at one end and a probe carrier at another end. The probe tip may be a sharp tip that interacts with the sample surface. Additionally key components can be a laser and photodetector system that measures the deflection of the cantilever and a piezoelectric scanner for precise movement of the sample relative to the cantilever, or vice versa. Typically, an atomic force microscope uses a piezo-electric dither to actuate the cantilever. A disadvantage of using a piezo-electric dither for actuating the cantilever is that this may cause significant amounts of parasitic vibrations since the whole mechanical system is vibrating, e.g. the actuator and the probe including the cantilever.

[0005] This can commonly be addressed by used a modulated laser source to actuate the cantilever. By projecting a modulated laser light from the modulated laser source on the cantilever, the laser light may be absorbed by the cantilever. This causes a local temperature gradient in the cantilever, causing modulated bending of the cantilever. This is commonly known as photothermal actuation. Since only the cantilever is vibrating, i.e. by the modulated bending, the parasitic vibrations are much smaller compared to the piezo-electric dither actuated system. Actuating the cantilever using a modulated laser source allows advanced atomic force microscope techniques.

[0006] When a cantilever is actuated using a modulated laser source, commonly a second laser system is provided to measure the deflection of the cantilever. Examples of such a second laser system is an optical beam deflection arrangement. In such an arrangement, a second laser is focused on the cantilever and a position sensing detector is used to capture the reflection of the second laser. The captured reflection can be used to determine the deflection of the cantilever.

[0007] A downside of such a system is that using multiple laser sources, optical systems and auxiliary components such as electronics, cables, housing etc., require a significant amount of space. Thus, it becomes challenging to miniaturize the atomic force microscope. As a result, it also is more difficult to industrialize the system. Furthermore, it is important to understand at which frequency the cantilever was actuated by the modulated laser source. In order to determine this, synchronization between the electronics of the second laser system and the electronics of the modulated laser source needs to be ensured. This adds significantly to the signal processing and hardware complexity of the atomic force microscope.

[0008] The invention aims to counteract the above disadvantages, preferably while retaining the advantages. More specifically, the invention aims to provide for an atomic force microscope that comprises a laser source to actuate the cantilever while simultaneously allowing for the miniaturization of the system and reducing the signal processing and hardware complexity of system. At the same time the atomic force microscope according to the invention allows determination at which frequency the cantilever was modulated.

[0009] Therefore, the invention provides for a cantilever for use in an atomic force microscope, in particular a cantilever according to claim 1. The cantilever comprises an absorption layer provided on the cantilever facing an optical system such that, during use, a first fraction of light emitted by a modulated laser source of the optical system is absorbed by the absorption layer. The absorption layer has a thickness less than the light absorption depth of the absorption layer such that a second fraction of the light emitted by the modulated laser source during use passes through the absorption layer. The cantilever is arranged to reflect the second fraction of the light back to the optical system such that at least a part of the light reflected by the cantilever is detected by the optical system during use.

[0010] Cantilevers for use in an atomic force microscope typically are flexible beams, or beam-shaped, to which a probe tip is attached at one end. The cantilever may bend in response to forces between the probe tip and the surface of a sample that is being scanned. For example, if the surface of the sample has a local high point, e.g. a protrusion protruding outward of the surface of the sample, the tip of the probe positioned on the local high point causes the cantilever to deflect as an upward force is exerted by the local high point on the probe tip. In order to prevent damaging of the surface sample, the cantilever may also be actuated to bend such that the probe tip taps the surface with a predetermined frequency. If the sample is then moved relative to the probe tip, or vice versa, the probe tip does not drag over the surface and possibly damage any features on the surface of the sample. Actuating the cantilever such that it bends, or deflects, and taps the surface at a predetermined frequency can be done using a modulated laser source, using photothermal actuation.

[0011] The cantilever has an absorption layer provided such that, during use in an atomic force microscope, the absorption layer faces an optical system of the atomic force microscope. Specifically, the absorption layer faces a modulated laser source of the atomic force microscope such that, during use, laser light emitted by the modulated laser source hits the absorption layer of the cantilever. Preferably, the absorption layer is arranged such that it can transfer heat relatively easy to the cantilever, in order to locally introduce a temperature gradient in the cantilever when the modulated laser source emits laser light on the absorption layer. Such a temperature gradient may cause the cantilever to deflect, in particular such that the end of the cantilever to which the probe tip is attached, deflects. The absorption layer may be of any shape or size but should have a minimum shape and size that allows for sufficient laser light to be absorbed by the absorption layer to form a temperature gradient in the cantilever. The absorption layer may be provided at any location on the cantilever, preferably near the base of the cantilever to improve the effect the temperature gradient introduced by the modulated laser source has on the deflection of the cantilever. In other words, if the cantilever has a temperature gradient near its base, i.e. the location where the cantilever is attached to the probe carrier, the end of the cantilever that is attached to the probe tip deflects more than when another spot of the cantilever is exposed to the same emitted laser light.

[0012] The absorption layer has a thickness that is less than the light absorption depth of the absorption layer. In the context of the invention, the light absorption depth should be understood as a measure of depth of how deep the emitted laser light penetrates the material. At the light absorption depth, the laser light does not further penetrate the material and all laser light is absorbed. Therefore, since the absorption layer has a thickness that is less than the absorption depth, some of the light emitted by the modulated laser source penetrates, and passes through the material. A first fraction of the emitted light is absorbed by the absorption layer, while a second fraction passes through the absorption layer. It will be clear to the skilled person that the absorption depth is a property of the material of the absorption layer and the wavelength of the light emitted by the laser on the absorption layer. It is commonly known in the art that different wavelengths have different absorption depths.

[0013] The cantilever is arranged to reflect the light passing through the absorption layer back to the optical system during use, such that at least a part of the light reflected by the cantilever is captured by the optical system. The light reflected by the cantilever and subsequently captured by the optical system is indicative for the amount of deflection of the end of the cantilever at the side of the probe tip. Thus it is achieved that, using the above described cantilever, the cantilever is actuated, i.e. deflected, and its deflection measured using a single modulated laser source. Using a single modulated laser source allows for easier miniaturization of the atomic force microscope. Additionally, since the actuation and detection is done at the same frequency, there is no need for synchronization in the signal chain and thus less hardware, software and electronics are needed to achieve the same result compared to an atomic force microscope having a plurality of laser sources.

[0014] The absorption layer can have a thickness such that the light detected by the optical system is between 1% and 50%, e.g. 1% and 30%, 1% and 25%, 1% and 20 % or 1% and less than 20 %, of the power of the light emitted by the optical system during use. Preferably, the amount of light reflected back to the optical system, for measuring the deflection of the cantilever, should be minimized such that enough light is captured for measurement purposes while most of the light is absorbed for introducing a temperature gradient in the cantilever. In other words, the absorption layer should have a thickness such that, in cooperation with the laser light at a predetermined wavelength and the material of the absorption layer, most of the light emitted by the modulated laser source is absorbed while still having the cantilever reflect the sufficient light for detecting the amount of deflection of the probe tip. This optimization may allow for a relatively compact laser source, as the power of the laser light emitted should only be sufficient to actuate the cantilever and measure its deflection and, commonly, the size of the laser increases as the power of the laser increases.

[0015] The absorption layer may be provided such that the second fraction of light reflected by the cantilever passes through the absorption layer a second time and a third fraction of light can be absorbed by the absorption layer during use, allowing for more emitted light to be absorbed by the absorption layer without increasing the thickness of the absorption layer. Additionally, when the absorption layer is provided such that the second fraction of light passes through the absorption layer a second time, more convenient and thus more cost-efficient designs may be possible. For example, the complete surface facing the modulated laser source may comprise an absorption layer.

[0016] The cantilever can further comprise a reflection layer for reflecting light emitted by the optical system to the optical system during use, for example as a coating or an auxiliary component that may be releasably connected to the cantilever. Thus, it may be possible to produce the cantilever out of a different material than the reflection layer. In such an example, the reflection layer can be provided between the surface of the cantilever and the absorption layer. The reflection layer can be provided over the whole surface of the cantilever facing the absorption layer, or only a part of the surface of the cantilever, for example at the location where the laser light passes through the absorption layer. In other words, the location of the reflection layer may be dependent on the location of where the emitted laser light will hit the cantilever during use, the angle under which it will arrive and the angle of reflection needed for the reflected laser light to be captured by the optical sensing device.

[0017] In an example of the invention, the reflection layer may comprise silicon, the absorption layer may comprise gold and have a thickness of lOnm. In this example, a laser that emits a laser light with a wavelength of about 300nm will partially pass through the coating in a first pass, during which close to half of the light will be absorbed by the absorption layer. At this wavelength, the remainder of the emitted laser light, e.g. the second fraction, may be reflected by the silicon layer. The silicon layer reflects a significant amount of the second fraction, e.g. at a wavelength of 300 nm more than 75% of the light reaching the silicon layer, while the remainder of the second fraction is absorbed by the silicon layer. The reflected light passes through the absorption layer comprising gold for a second time, again absorbing close to half of the reflected light. Alternatively, the reflection layer may comprise aluminum, having a reflectivity of 90-99% at a wavelengths between 200 - 2000 nm or silver, having a reflectivity of about 90% at a wavelength of 500 nm. An alternative absorption layer may be Zinc Oxide having a thickness of 20 nm, as Zinc Oxide has a has an absorption depth of 40 nm at wavelengths between 250 - 350 nm, or carbon with a thickness of 50 nm as carbon has an absorption depth of lOOnm at a wavelength of 500 nm. It is clear to the skilled person that the above combinations of materials and predetermined wavelengths serves merely as an example, and that any combination of materials and wavelengths may be used as long as enough light is absorbed to actuate the probe tip at an end of the cantilever and sufficient light is reflected and captured by the optical system. A combination of materials may be used as well to actuate the cantilever in different modes, e.g. using different wavelengths.

[0018] In a second aspect of the invention an atomic force microscope is provided. The atomic force microscope comprises a cantilever as previously described, and a probe tip attached to an end of said cantilever. The atomic force microscope further comprises a controller and an optical system, wherein the controller is operably connected to the optical system. The optical system comprises a laser source arranged to emit a modulated light pulse at a predetermined wavelength and at a predetermined frequency on the absorption layer of the cantilever, thereby causing the probe tip to vibrate on the surface of a sample. The optical system further comprises an optical beam deflection sensor arranged to detect the part of the light emitted by the laser source that is reflected by the cantilever during use. The controller is arranged to determine the position of the probe tip based on the light detected by the optical beam deflection sensor. The cantilever can thus be actuated by a photothermal effect and vibrate at a frequency equal or close to the predetermined frequency at which the modulated light pulse is emitted by the laser source. The predetermined wavelength can be between 200 nanometer and 2000 nanometer. In particular, the wavelength can be between 200 nanometer and 1000 nanometer such as 250 nanometer and 750 nanometer.

[0019] At a wavelength within these ranges of wavelengths, e.g. 300 nanometer, light emitted by the modulated laser source may partially be absorbed by the absorption layer and reflected to the optical beam deflection sensor in a preferred reflected to absorbed ratio, e.g. 1:4, 1:9 or 1:99. If the modulated laser source emits the laser light with sufficient power, the cantilever may be actuated, e.g. deflected, while sufficient light is reflected to be captured by the optical beam deflection sensor to determine the position of the probe tip.

[0020] The optical system may further comprise a lens arrangement having at least one lens arranged to focus the emitted pulse light into a predetermined pattern on the cantilever. Such a lens arrangement may further facilitate the use of a single modulated laser to both actuate the cantilever and determine the position of the probe tip. The lens arrangement may be used to make a pattern that corresponds to the absorption layer on the cantilever. For example, if the absorption layer is only provided at the base of the cantilever, i.e. at the end of the cantilever that is connected to the atomic force microscope opposite the end of the cantilever to which the probe tip is connected, the predetermined pattern may be such that the emitted pulse light is aimed at said absorption layer. This may allow the possibility of using multiple different absorption layers, and I or multiple different reflection layers, each layer made of different materials. This may be advantageous if the modulated laser source has to be operated at different wavelengths, as each combination of absorption and reflection layers operates best at different wavelengths. For example, the lens arrangement can comprise a cylindrical lens and the predetermined pattern can be a line that is provided parallel to a longitudinal direction of the cantilever. The line can be provided from end to end of the cantilever, or a section of the longitudinal direction. In the example, multiple absorption layers comprising different materials can be provided adjacent to each other along the longitudinal direction, wherein each absorption layer absorbs sufficient light to actuate the cantilever at different wavelengths. If now a line pattern is projected on the cantilever at a first wavelength by the laser source, only an absorption layer that has a high absorption at that wavelength causes a local temperature gradient for actuating the cantilever and not the other absorption layers. If the laser source now emits at a second wavelength, a different absorption layer may be actuated. In a second example, the predetermined pattern can be at least two points that are provided along a longitudinal direction of the cantilever. The at least two points, or spots, on the cantilever may be created by having a lens arrangement comprising a microlens array, a diffraction lens, a holographic lens or a metasurface lens or any combination thereof. Using said component, at least two spots may be created on the surface of the cantilever while also allowing each spot to have a different wavelength, allowing the possibility for more complex actuation of the cantilever.

[0021] The atomic force microscope can further comprise an optical filter provided between the cantilever and the optical beam deflection sensor arranged to filter the part of the light emitted by the laser source that is reflected by the cantilever during use. Additionally or alternatively, the atomic force microscope can further comprise a polarizing arrangement provided between the laser source and the cantilever arranged to polarize the light emitted by the laser source during use. The optical filter and the polarizing arrangement may be used to ensure that the emitted laser light from the laser source arrives at the absorption layer and the reflected laser light captured by the optical detection sensor are at the preferred wavelength respectively. Thus, the absorption and reflection ratio of the emitted laser light may be further optimized.

[0022] In a third aspect of the invention there is provided for a method of operating an atomic force microscope, comprising the steps of: - providing an atomic force microscope, preferably the atomic force microscope previously described;

[0023] - providing a sample comprising a surface to be scanned such that the surface faces the probe tip of the atomic force microscope;

[0024] - emitting a laser light from the laser source, at a predetermined pulsed interval and at a predetermined wavelength, on an absorption layer of the cantilever such that a first fraction of the emitted laser light is absorbed by the absorption layer;

[0025] - capturing a second fraction of the emitted laser light reflected by the cantilever using an optical beam deflection sensor; and

[0026] - determining the position of the probe tip relative to the surface of the sample based on the captured light using a controller.

[0027] Further advantageous aspects of the invention are set out in the description and appended claims.

[0028] The technical features described in the paragraphs and sentences above can be isolated from the context, and the isolated technical features from the different paragraphs and sentences can be combined. Such combinations are herewith specifically disclosed in this description.

[0029] The invention will further be elucidated on the basis of exemplary embodiments which are represented in the drawings. The exemplary embodiments are given by way of non-limitative illustration of the invention.

[0030] In the drawings:

[0031] Figs. 1A and IB depicts a schematic side view of an example of a cantilever for use in an atomic force microscope and a detail of the cantilever respectively;

[0032] Figs. 2A and 2B depicts a schematic side view of a further example of a cantilever for use in an atomic force microscope and a detail of the further example of a cantilever respectively;

[0033] Fig. 3 depicts a schematic side view of an atomic force microscope according to an example of the invention; Figs. 4A and 4B show two further examples of an atomic force microscope according to the invention.

[0034] In this description embodiments of the invention will be described with reference to the drawings by way of example only. These embodiments should by no means be understood as limiting the scope of the disclosure. At least all combinations of aspects, elements and features of the embodiments shown and discussed are also considered to have been disclosed herein. In this description the same or similar elements and features will be referred to by the same or similar reference signs. The drawings are not necessarily to scale, and can show exaggerations in order to more clearly show features of the claimed invention.

[0035] In this description wording like substantially and generally should be understood as meaning that relatively small deviations from the feature or value they refer to are also considered to be covered, for example deviations of 20% or less, such as 15% or less or 10% or less, unless specified differently.

[0036] Fig. 1A shows a schematic side view of a probe 10 comprising a cantilever 1 according to the invention, Fig. IB shows a detail A from Fig. 1A. At a first end of the cantilever 1 a probe tip 5 has been attached, said probe tip 5 is arranged to scan the surface of a sample (not depicted) during use. The cantilever 1 can be used in an atomic force microscope (not depicted), through which it is connected by a probe carrier 6. The cantilever 1 comprises an absorption layer 2, provided as a coating, on the cantilever 1 facing an optical system during use such that a first fraction of light emitted by the modulated laser source of the optical system is absorbed by the absorption layer 2.

[0037] This is schematically represented in Fig. IB as the emitted light 3 by a modulated laser source (not depicted) being a relatively broad arrow that is aimed towards the cantilever 1, specifically towards the absorption layer 2 of the cantilever 1. The reflected light 4 by the cantilever 1 is represented by a relatively small arrow aimed away from the cantilever 1. The width of both arrows, representing emitted light 3 and reflected light 4, is a schematic indication of the magnitude of the power of the light. Specifically, the broader the arrow, the more power the light comprises in that depicted direction. Thus, in Fig. IB, the emitted light 3 by the modulated laser source has more power than the reflected light 4. The difference in power between the emitted light 3 and the reflected light 4 is absorbed by the cantilever 1, which may cause a local temperature gradient that can cause a deflection of the cantilever 1 during use. In order to facilitate light being reflected by the cantilever 1, the absorption layer 2 has a thickness D that is less than the light absorption depth of the absorption layer 2 such that a second fraction of the light emitted from the optical system passes through the absorption layer 2. The cantilever 1 is arranged to reflect the second fraction of the light back to the optical system of the atomic force microscope (not depicted) such that a part of the light reflected by the cantilever 1 is captured by the optical system during use. In the shown example, this is done by making the cantilever 1 out of silicon.

[0038] In the shown example, the absorption layer 2 is provided such that the section fraction of light reflected by the cantilever 1 passes through the absorption layer 2 a second time such that a third fraction of the light is absorbed by the absorption layer 2. Thus, on the first pass through the absorption layer 2 by the emitted laser light 3, a part of the light is absorbed by the absorption layer 2 while a second part of the light is absorbed during the second pass through the absorption layer 2. In total, the thickness D of the absorption layer 2 is such that the light captured by the optical system has a power that is 20% of the power of the light emitted by the optical system. In other words, 80% of the power of the light emitted 3 is absorbed by the absorption layer 2 during the first and second pass through the absorption layer 2 combined. This may, for example, be achieved by providing an absorption layer 2 made out of gold, having a thickness of 10 nm. If the emitted light 3 has a wavelength of, for example, 300 nm, 80% of the power of the emitted light 3 can be absorbed by the absorption layer 2. The remaining 20% may be reflected by the cantilever 1, for example by a silicon cantilever 1.

[0039] Turning to Figs. 2A and 2B, a further example of a probe 20 comprising a cantilever 1 according to the invention is shown. The cantilever 1 of the probe 20 differs at least from the cantilever 1 of the probe 10 depicted in Figs. 1A and IB by having a reflection layer 7. The reflection layer 7 is for reflecting the emitted light 3 by the optical system, i.e. the laser source, to the optical system, e.g. the optical beam deflection sensor. The reflection layer 7 is provided between the surface of the cantilever 1, specifically the surface of the cantilever 1 that faces the optical system during use, and the absorption layer 2. In the shown example, the reflection layer 7 is made out of silicon. The cantilever 1 itself can be made of any other material suitable for the production of cantilevers, without being limited to the reflective properties of the material.

[0040] Turning to Fig. 3, a schematic view of an atomic force microscope 30 comprising a cantilever 1 according to the invention is depicted. The atomic force microscope 30 comprises a probe 10 that has a cantilever 1 with a probe tip 5 attached to an end of the cantilever 1. Furthermore, the atomic force microscope 30 comprises a controller (not depicted) and an optical system 31. The controller is operably connected to the optical system 31. The optical system 31 comprises a laser source 32 arranged to emit a modulated laser pulse 5 at a predetermined wavelength and at a predetermined frequency on the absorption layer 2 of the cantilever 1. In the shown example, the predetermined wavelength is between 200 nm and 2000 nm, specifically 300 nm. If the laser light is emitted as a modulated pulse, at a predetermined frequency, the probe tip 5 will vibrate on a surface of a sample 33 as a result of photothermal actuation at a frequency close or equal to the predetermined frequency at which the laser light is emitted. The optical system 31 further comprises an optical beam deflection sensor 34 arranged to capture the part of the emitted light 5 by the laser source 32 that is reflected by the cantilever 1 during use. The controller is arranged to determine the position of the probe tip 5 based on the light captured by the optical beam deflection sensor 34. In the example, an optical filter 37 has been provided to filter the reflected light 4 such that the optical beam deflection sensor 34 only measures the reflected light 4, thereby reducing noise and increasing accuracy in position detection.

[0041] Turning to Figs. 4A and 4B, further examples of an atomic force microscope 30 are shown. The further examples comprise the same features as presented in the example of Fig. 3. In the shown examples, the optical system 31 further comprises a lens arrangement 35 that has at least one lens that is arranged to focus the emitted light pulse 4 into a predetermined pattern on the cantilever 1. Turning to the example of Fig. 4A, the lens arrangement 35 comprises a cylindrical lens that causes the emitted light pulse 4 to have a predetermined pattern that is a line that is provided parallel to the longitudinal direction of the cantilever 1, however other lenses or lens configurations may be used. Turning to another example depicted in Fig. 4B, the lens arrangement 35 comprises lenses that are arranged to cause the emitted light 3 to be split in two light bundles each having a separate focal point on the absorption layer 2 of the probe 10. In other words, the predetermined pattern is two points that are provided along the longitudinal direction of the cantilever 1. In both examples of Fig. 4A and Fig. 4B, an optical filter 37 has been provided between the cantilever 1 and the optical beam deflection arrangement 34. The optical filter 37 is arranged to filter the part of the light emitted by the laser source that is reflected by the cantilever 1 during use. Additionally, in the shown examples, a polarizing arrangement 38 is provided between the laser source 32 and the cantilever 1. The polarizing arrangement 38 is arranged to polarize light emitted by the laser source 2 passing through the polarizing arrangement 38 during use such that the wavelength of the emitted light 3 is at the preferred wavelength, e.g. 300 nm.

[0042] These and other such alternatives are considered to fall within the scope of the appending claims.

Claims

Claims1. Cantilever for use in an atomic force microscope comprising an absorption layer provided on the cantilever facing an optical system, during use, such that a first fraction of light emitted by a modulated laser source of the optical system is absorbed by the absorption layer; wherein the absorption layer has a thickness less than the light absorption depth of the absorption layer such that a second fraction of the light emitted from the modulated laser source during use passes through the absorption layer; and wherein the cantilever is arranged to reflect the second fraction of the light back to the optical system such that at least a part of the light reflected by the cantilever is captured by the optical system during use.

2. Cantilever according to claim 1, wherein the absorption layer has a thickness such that the light captured by the optical system has a power that is between 1% and 50% of the power of the light emitted by the optical system during use.

3. Cantilever according to claim 1 or 2, wherein the absorption layer is provided such that the second fraction of light reflected by the cantilever passes through the absorption layer a second time and a third fraction of light is absorbed by the absorption layer during use.

4. Cantilever according to any of the preceding claims, further comprising a reflection layer for reflecting light emitted by the optical system to the optical system during use.

5. Cantilever according to claim 4, wherein the reflection layer is provided between a surface of the cantilever and the absorption layer.

6. Cantilever according to claim 4 or 5, wherein the reflection layer comprises silicon.

7. Cantilever according to any of the preceding claims, wherein the absorption layer comprises gold.

8. Cantilever according to claim 7, wherein the absorption layer has a thickness of lOnm.

9. Atomic force microscope comprising:- a cantilever according to any of the preceding claims and a probe tip attached to an end of said cantilever;- a controller and an optical system, wherein the controller is operably connected to the optical system;- wherein the optical system comprises a laser source arranged to emit a modulated light pulse at a predetermined wavelength and at a predetermined frequency on the absorption layer of the cantilever for causing the probe tip to vibrate at the predetermined frequency on the surface of a sample;- wherein the optical system further comprises an optical beam deflection sensor arranged to capture the part of the light emitted by the laser source that is reflected by the cantilever during use; and- wherein the controller is arranged to determine the position of the probe tip based on the light captured by the optical beam deflection sensor.

10. Atomic force microscope according to claim 9, wherein the predetermined wavelength is between 200 nm and 2000 nm.

11. Atomic force microscope according to claim 9 or 10, wherein the optical system further comprises a lens arrangement having at least onelens arranged to focus the emitted light pulse into a predetermined pattern on the cantilever.

12. Atomic force microscope according to claim 11, wherein the lens arrangement comprises a cylindrical lens and the predetermined pattern is a line that is provided parallel to a longitudinal direction of the cantilever.

13. Atomic force microscope according to claim 11, wherein the predetermined pattern is at least two points that are provided along a longitudinal direction of the cantilever.

14. Atomic force microscope according to any of the claims 11-13, further comprising an optical filter provided between the cantilever and the optical beam deflection sensor arranged to filter the part of the light emitted by the laser source that is reflected by the cantilever during use.

15. Atomic force microscope according to any of the claims 9-14, further comprising a polarizing arrangement provided between the laser source and the cantilever arranged to polarize the light emitted by the laser source during use.

16. Method of operating an atomic force microscope, comprising the steps of:- providing an atomic force microscope, preferably the atomic force microscope according to any of the claims 9-15;- providing a sample comprising a surface to be scanned such that the surface faces the probe tip of the atomic force microscope;- emitting a laser light from the laser source, at a predetermined pulsed interval and at a predetermined wavelength, on an absorption layer of the cantilever such that a first fraction of the emitted laser light is absorbed by the absorption layer;- capturing light a second fraction of the emitted laser light reflected by the cantilever using an optical beam deflection sensor; and- determining the position of the probe tip relative to the surface of the sample based on the captured light using a controller.

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