JP2007078577A - Optical axis adjusting auxiliary device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical axis adjusting auxiliary device capable of guiding easily and surely an irradiation spot to the center of a light receiving surface on the light receiving surface of a quadripartite photodetector, and facilitating an optical axis adjusting work, in the optical axis adjusting work of a scanning probe microscope or the like equipped with an optical lever type optical detection system. <P>SOLUTION: This optical axis adjusting auxiliary device equipped with a laser light source emitting laser light 16 to a reflecting member, and the photodetector 11 having the light receiving surface 12 receiving the laser light reflected by the reflecting member and comprising a plurality of divided light receiving parts 12a-12d, is used for detecting the incident position of the laser light on the light receiving surface of the photodetector, and is adopted for a position detection device equipped with an optical axis adjusting means. The optical axis adjusting auxiliary device is also equipped with an optical axis adjusting auxiliary tool 14 for converting a relation between the distance of the laser light incident position from the center on the light receiving surface of the photodetector and a detection signal from the photodetector into a relation of monotone increase or monotone decrease. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical axis adjustment auxiliary device, and in particular, an optical axis adjustment auxiliary that facilitates optical axis adjustment from a laser light source to a photodetector in, for example, a scanning probe microscope equipped with an optical lever type optical detection system. Relates to the device.

  As an example of the optical axis adjustment auxiliary device, an example of a scanning probe microscope or the like provided with an optical lever type optical detection system as a position detection device will be described. As an optical axis adjustment auxiliary device in a position detection device of a conventional scanning probe microscope, there is one described in Patent Document 1 previously proposed by the present inventor. A conventional optical axis adjustment assisting device will be described with reference to Patent Document 1 and FIGS.

  An example of how to adjust the optical axis in a scanning probe microscope will be outlined with reference to FIG. It is assumed that the illustrated scanning probe microscope is an atomic force microscope. “Optical axis adjustment” means that the laser beam from the laser light source is appropriately reflected on the back surface of the cantilever and is incident on the photodetector in the optical lever optical detection system of the atomic force microscope. . Conventional optical axis adjustment has been performed manually by an operator. FIG. 12 schematically shows a configuration of a main part of an atomic force microscope including a cantilever and an optical lever type optical detection system.

  A cantilever 103 having a probe 102 at the tip is arranged with respect to the sample 101 to be measured. Reference numeral 104 denotes a part of the cantilever holder. The distance between the probe 102 and the surface of the sample 101 is such a distance that an atomic force acts between them. The measurement of the concavo-convex shape on the sample surface requires the probe 102 to move along the sample surface, and therefore the distance between the probe and the sample surface is held at a constant distance by the control mechanism. The change in the distance between the probe and the sample surface is detected by the displacement due to the bending deformation of the cantilever 103. An optical lever type optical detection system is provided as a mechanism for detecting a displacement due to the bending deformation of the cantilever 103. The optical lever type optical detection system includes a laser light source 105, mirrors 106 and 107 that generate a reflection action, and a quadrant photodetector 108. When the optical axis adjustment of the optical lever type optical detection system is completed and measurement is performed, the laser beam 109 emitted from the laser light source 105 is reflected by the mirror 106, guided to the back surface of the cantilever 103, and reflected by the back surface of the cantilever 103. The laser beam 109 is further reflected by the mirror 107 and guided to the light receiving surface of the quadrant photodetector 108. The displacement of the cantilever 103 is detected as a change in the position of the irradiation (incident) spot of the laser beam 109 on the quadrant photodetector 108. An optical microscope 111 having a TV camera 110 is disposed above the cantilever 103, and the back surface of the cantilever 103 is observed by the optical microscope 111. The detection signal output from the quadrant photodetector 108 is sent to the control device, and the light receiving position of the laser beam can be displayed on the display device by the detection signal. The image observed with the optical microscope 111 is sent to the control device as a video signal by the TV camera 110 and displayed on the display device. In FIG. 12, the illustration of the control device and the display device is omitted for ease of explanation.

  In the above configuration, the mirrors 106 and 107 are provided with a position adjusting mechanism that is manually operated. The optical axis adjustment is performed by the operator who performs measurement operating the position adjustment mechanism of the mirrors 106 and 107. Conventional optical axis adjustments consisted of the following two first and second steps.

  The first step of adjusting the optical axis is to apply an irradiation spot of the laser beam 109 to the reflective surface on the back surface of the cantilever 103. Confirmation of the spot position on the cantilever 103 is performed based on an image obtained by the optical microscope 111.

  The second step of adjusting the optical axis is to apply an irradiation spot based on the laser beam 109 reflected by the back surface of the cantilever 103 to the center of the light receiving surface of the quadrant photodetector 108. Confirmation of the spot position on the quadrant photodetector 108 is performed based on the detection signal.

  FIG. 13 illustrates the adjustment of the irradiation spot in the quadrant photodetector 108. FIG. 13 shows the movement states (1) to (4) of the irradiation spot 116 of the laser beam 109 on the light receiving surface of the quadrant photodetector 108 and its peripheral region. In the second step, the irradiation spot 116 of the laser beam 109 is finally applied to the center position of the light receiving surface of the quadrant photodetector 108. According to the illustrated configuration, this operation is performed by manually operating the position adjustment mechanism of the mirror 107.

  The configuration of the light receiving surface of the quadrant photodetector 108 will be described. The light receiving surface of the quadrant photodetector 108 is divided into four portions (light receiving portions) a, b, c, and d. When the detection output signals (voltage signals) of the four light receiving parts a to d are Sa to Sd, respectively, the total output signal Ss of the quadrant photodetector 108, the vertical displacement signal component (Y-axis direction signal component) Sv, and the horizontal The displacement signal component (X-axis direction signal component) Sh is obtained as Ss = Sa + Sb + Sc + Sd, Sv = {(Sa + Sb) − (Sc + Sd)} / Ss, Sh = {(Sb + Sd) − (Sa + Sc)} / Ss, respectively. Therefore, in general, the mirror 107 is adjusted so that Ss is maximized and Sv and Sh are minimized. When both Sv and Sh are 0, the irradiation spot 116 of the laser beam 109 is set at the center position of the light receiving surface.

  By executing the first step and the second step as described above, the optical axis adjustment for the optical lever type optical detection system is completed.

  As described above, the conventional optical axis adjustment in the optical lever type optical detection system is performed manually by the measurement operator, and human eyes are indispensable when the irradiation spot is aligned with the cantilever in the first step. Trial and error is often necessary at the initial stage of the second step. In particular, in the first stage of the second step, there are cases where it is possible to detect fortunately by the movement of the irradiation spot by relatively easy trial and error. For example, the irradiation spot is detected by the photodetector due to poor mounting of the cantilever. May be greatly out of the adjustable range of the light receiving surface. In such a case, it can hardly be detected by trial and error. When such an adjustment is impossible, there is no other means to take, and as a result, it is said that “the cause was not understood” using a long time for trial and error.

Therefore, according to the above-described optical axis adjustment auxiliary device of Patent Document 1, in the scanning probe microscope provided with the optical lever type optical detection system, the area is relatively relative to each of the four light receiving portions of the four-divided light receiving surface. The measurement operator determines in what direction the irradiation spot is away from the center of the light receiving surface on the light receiving surface of the quadrant photodetector in the initial stage of the second step of the optical axis adjustment work. We made it easy to know and made it easier to adjust the optical axis.
JP 2000-206125 A

  Further problems in the method of adjusting the optical axis will be described with reference to FIGS. This problem is caused by adjusting the mirror 107 manually while observing the value of a voltage signal Sh ′, which will be described later, with a display device in the latter half of the second step described above, and setting the irradiation spot 116 at the center of the four-divided light receiving surface. It is a problem when moving to.

  In FIG. 14, the four light receiving portions a, b, c, and d on the light receiving surface of the quadrant photodetector 108 are indicated by small squares, and the X axis and the Y axis are defined for the light receiving portions a to d. ing. The intersection point O of the X axis and the Y axis is the origin and the center of the light receiving surface of the quadrant photodetector 108. Further, a black circle element denoted by reference numeral 116 in FIG. 14 indicates the irradiation spot of the laser beam 109 described above. The irradiation spot 116 is moved in the direction of the arrow 201 from the position A toward the center O. FIG. 15 shows the light intensity distribution of the irradiation spot 116 when the irradiation spot 116 is at the position A. FIG. 16 shows that when the irradiation spot 116 moves in the X-axis direction, the voltage signal Sh ′ = (Sb + Sd) for the horizontal displacement signal component (X-axis direction signal component) Sh of the total output signal Ss of the quadrant photodetector 108. )-(Sa + Sc) is a graph showing a change characteristic 203;

  Hereinafter, an example in which the irradiation spot 116 is brought close to the center of the light receiving surface while only observing the change state of the voltage signal Sh ′ will be described.

  As shown in FIG. 14, when the irradiation spot 116 of the laser beam 109 is at position A, the light intensity distribution is as indicated by D200 in FIG. At that time, the voltage signal Sh 'is zero. When the mirror 107 is moved and the irradiation spot 116 moves in the direction of the arrow 201, the light intensity distribution becomes as indicated by a dotted line D202, and the base of the light intensity distribution is applied to the light receiving part d. At this time, the voltage signal Sh ′ takes a value in the range K3 shown in FIG. When the mirror 107 is further moved to move the irradiation spot 116 in the direction of the center O, the voltage signal Sh ′ changes in a direction increasing in the section K3. Further, when the irradiation spot 116 approaches the center O, the signal changes in the range of the section K2. Further, when the irradiation spot 116 is brought closer to the center O, it is included in the range of the section K1. When the irradiation spot 116 is located at the center O, the voltage signal Sh ′ becomes zero.

  In the above, the position of the irradiation spot 116 is adjusted so as to approach the center O while observing the change state of the voltage signal Sh ′ with the display device. In this case, since the voltage signal Sh ′ approaches 0 when approaching the center (O) in the section K1 from the section K2, it can be determined that the voltage signal Sh ′ is approaching the center O. However, even when the irradiation spot 116 moves within the range of the section K3, the change in the voltage signal Sh ′ decreases as it moves away from the center O. Therefore, it is easy to give a misunderstanding that the direction is toward the center O. Further, since the section K2 includes the flat portion 203a, when the irradiation spot 116 moves on the flat portion 203a, it is difficult to confirm the change with the voltage signal Sh ′, and it is possible to determine whether or not the irradiation spot 116 is moving toward the center O. It becomes very difficult.

  As described above, according to the conventional optical axis adjustment method, the mirror 107 is manually adjusted while observing the value of the voltage signal Sh ′ on the display device in the latter half of the second step described above, and the irradiation spot 116 is adjusted. When moving to the center O of the quadrant light receiving surface, is it moving in the section K3 where the voltage signal Sh ′ decreases or is moving toward the center O of the light receiving surface of the quadrant photodetector 108? It was difficult to distinguish. Therefore, there is a problem that adjustment is very difficult.

  Although the example of the optical axis adjustment of the scanning probe microscope has been described above, the problem of the optical axis adjustment described above is not limited to the optical lever optical detection system of the scanning probe microscope.

  In view of the above problems, the object of the present invention is to adjust the optical axis in a scanning probe microscope or the like equipped with an optical lever type optical detection system, with the irradiation spot at the center of the light receiving surface on the light receiving surface of the quadrant photodetector. An object of the present invention is to provide an optical axis adjustment auxiliary device that can be guided easily and reliably and can facilitate the optical axis adjustment operation.

  The optical axis adjustment auxiliary device according to the present invention is configured as follows to achieve the above object.

  The first optical axis adjustment auxiliary device (corresponding to claim 1) has a laser light source that emits laser light to the reflecting member, and a light receiving surface on which the laser light reflected by the reflecting member is incident, and this light receiving surface is And a photodetector that is divided into a plurality of light receiving sections, detects the incident position of the laser beam on the light receiving surface of the photodetector, and is applied to a position detecting device that further includes an optical axis adjusting means. This optical axis adjustment auxiliary device is a correction means for converting the relationship between the distance of the laser light incident position from the center of the light receiving surface of the photodetector and the detection signal from the photodetector into a monotonically increasing or monotonically decreasing relationship. Optical axis adjustment aid).

  According to the optical axis adjustment auxiliary device described above, since the correction means having conversion characteristics such as monotonic increase is provided on the front surface of the light receiving surface of the photodetector, the incident position (irradiation spot position) of the laser beam is surely secured on the light receiving surface. Can be moved to the center position of the light receiving surface. Accordingly, the measurement operator can easily guide the irradiation spot to the center of the light receiving surface on the light receiving surface of the four-divided photodetector, and the optical axis adjustment work can be facilitated.

  In the second optical axis adjustment assisting device (corresponding to claim 2), in the above-mentioned configuration, preferably, the correction means includes a convex lens disposed on the front surface of the light receiving surface, and light from the central portion toward the peripheral portion. And an optical filter that increases the transmittance.

  In the third optical axis adjustment assisting device (corresponding to claim 3), in the above configuration, preferably, the correction means is disposed on the front surface of the light receiving surface, and the light transmittance increases from the central portion toward the peripheral portion. It is characterized by being a convex lens.

  In the third configuration described above, the fourth optical axis adjustment assisting device (corresponding to claim 4) is preferably configured such that the convex lens is thicker toward one or both sides of the convex lens and from the central part to the peripheral part of the convex lens. A metal thin film is deposited so as to be thin.

  In the third configuration, the fifth optical axis adjustment assisting device (corresponding to claim 5) is preferably characterized in that the convex lens is formed of a material that absorbs laser light at a predetermined absorption rate. And

  According to the present invention, on the front surface of the light receiving surface of the photodetector, the relationship between the distance of the laser light incident position from the center of the light receiving surface of the photodetector and the detection signal from the photodetector is monotonously increased or decreased monotonously. In order to correct the laser beam incident position on the light receiving surface using this relationship, the measuring operator can adjust the optical axis of the position detector. In this case, the irradiation spot can be easily guided to the center of the light receiving surface, and the optical axis adjustment work can be facilitated.

  DESCRIPTION OF EMBODIMENTS Preferred embodiments (examples) of the present invention will be described below with reference to the accompanying drawings.

  In this embodiment, an example of a position detection device to which the optical axis adjustment auxiliary device is applied is a light detector of an optical lever type optical detection system in a scanning probe microscope. 1 and 2 show an example of a photodetector used in the optical lever type optical detection system of the scanning probe microscope according to the present invention. As an example, the photodetector has a configuration in which the light receiving surface is divided into four. Have. 1 is a front view and FIG. 2 is a side view.

  The scanning probe microscope assumes the atomic force microscope shown in FIG. 12 for the prior art. Since the atomic force microscope has been described in the background art section, reference is made to the above description, and illustration and description are omitted here. Further, as described above, the optical lever type optical detection system is composed of a laser light source, a cantilever having a probe at the tip and a reflecting portion on the back, the photodetector, and a necessary reflection mirror.

  Since the configuration and operation of the optical lever type optical detection system are also described in the background art section, reference is made to the above description, and illustration and description thereof are omitted here. Since the light receiving surface of the photodetector is divided into four parts, it is hereinafter referred to as “four-part photodetectors”. As shown in FIG. 1, a square light receiving surface 12 is formed on the upper surface of the quadrant photodetector 11. The light receiving surface 12 is composed of four small light receiving portions (or light receiving sections) 12a, 12b, 12c and 12d which preferably have a square shape. The light receiving surface 12 has, for example, a square shape as a whole, and the light receiving surface having the square area is formed of light receiving portions 12a to 12d that are divided from each other and have small partial areas that are independent from each other. The light receiving portions 12a, 12b, 12c, and 12d correspond to the light receiving portions a, b, c, and d described with reference to FIGS. 13 and 14, respectively.

  As the quadrant photodetector 12, a commercially available one is usually used. For example, a multi-element type Si photodiode (S5981) manufactured by Hamamatsu Photonics is used. As such a photodetector, one having a large light receiving surface area is commercially available, but one having a relatively small area is used from the viewpoint of miniaturization. The square light receiving surface 12 has a side of about 3 mm.

  As shown in FIGS. 1 and 2, the head 11a of the quadrant photodetector 11 is formed of a metal container (sensor package) having a flat cylindrical shape in appearance. Inside, an amplifier that converts the laser light received by each of the light receiving portions 12a to 12d of the light receiving surface 12 into electricity and amplifies it to a predetermined level is incorporated. As shown in FIG. 2, a plurality of pin-shaped electric wires 13 led out from the lower surface of the head portion 11 a are provided below the quadrant photodetector 11. The number of electrical wirings 13 is arbitrary and is not particularly limited. When the quadrant photodetector 11 is provided as part of an optical lever optical detection system of an atomic force microscope, the quadrant photodetector is disposed obliquely above the cantilever and the probe, and its light receiving surface 12 is Arranged to face the back of the cantilever.

  In FIG. 1, the X axis and the Y axis are defined for the light receiving portions 12 a to 12 d on the square light receiving surface 12. The intersection of the X axis and the Y axis is the origin O and the center of the light receiving surface 12.

  3 and 4 show the configuration of the main part of the optical axis adjustment assisting device according to the present invention, and show the configuration in which the optical axis adjustment assisting tool is provided in the aforementioned four-divided photodetector 11. 3 is a front view and FIG. 4 is a side view. 3 corresponds to FIG. 1, and FIG. 4 corresponds to FIG. FIG. 6 is a diagram for explaining the operation of the optical axis adjustment assisting device. Hereinafter, the optical axis adjustment assisting tool is simply referred to as an assisting tool for convenience of explanation.

  The auxiliary tool 14 includes a convex lens 14a installed on the front surface of the light receiving surface 12 of the quadrant photodetector 11, an optical filter 14b whose transmittance increases from the central portion toward the peripheral portion, and the convex lens 14a and the optical filter 14b. It consists of a holder 14c that is fixed in a positional relationship. The front shape of the auxiliary tool 14 is circular, and has a larger diameter than the circular shape of the head portion 11a of the quadrant photodetector 11 as shown in FIG. Therefore, the convex lens 14a is installed in a shape spreading outward from the square area of the light receiving surface 12. The convex lens 14a installed in this way functions to condense the laser light arriving at a position outside the light receiving surface 12 onto the light receiving surface 12, as shown in FIG.

  The optical filter 14b has a transmittance change characteristic as shown in FIG. 5 from the central portion toward the peripheral portion. In FIG. 5, the horizontal axis indicates the X axis as an example, which means the distance from the center of the optical filter 14b, and the vertical axis means the transmittance. A curve C10 indicates a change characteristic of the transmittance with respect to the distance from the center. In the optical filter 14b, the transmittance is lower at the center and higher as it is closer to the periphery. In FIG. 5, D10 and D11 indicate the light intensity distribution of the irradiation spot related to the laser light after passing through the optical filter 14b. The laser light transmitted near the periphery of the optical filter 14b has a higher light intensity, and the laser light transmitted near the center of the optical filter 14b has a lower light intensity. Such an optical filter 14b can be manufactured, for example, by performing deposition while changing the thickness of aluminum stepwise.

  The holder 14c having the convex lens 14a and the optical filter 14b has a gap of an appropriate distance at the front surface position of the light receiving surface 12 of the quadrant photodetector 11 according to the focal length of the convex lens 14a, as shown in FIGS. The position is fixed. In the figure, the fixing structure is not shown, but any fixing structure can be adopted.

  The ratio of the area of each light receiving part forming the light receiving surface 12 to the area of the corresponding convex lens 14a and optical filter 14b is arbitrarily determined as necessary. That is, as to how large the convex lens 14a and the optical filter 14b are provided with respect to the light receiving surface 12, an appropriate size that enables easy optical axis adjustment based on empirically obtained knowledge. The convex lens 14a and the optical filter 14b are determined. As a preferable dimension of the convex lens 14a and the optical filter 14b, an upper limit is about 10 mm.

  FIG. 6 shows an operation of a combination of the convex lens 14a and the optical filter 14b as an example. FIG. 7 is a graph showing the relationship between the incident position of the laser beam and the detection signal intensity of the photodetector 11 (the aforementioned voltage signal Sh ′). In FIG. 6, the horizontal axis is the X axis, and the vertical axis is the direction perpendicular to the light receiving surface 12 (Z-axis direction). In FIG. 7, the horizontal axis indicates the horizontal distance from the origin O in the X-axis direction, and the vertical axis indicates the voltage signal Sh ′.

  In FIG. 7, a curve C <b> 11 indicates a change characteristic of the detection voltage signal Sh ′ with respect to the distance from the center O in the horizontal direction with respect to the quadrant photodetector 11 provided with the auxiliary tool 14. The voltage signal Sh ′ indicated by the curve C <b> 11 has a characteristic of increasing monotonously and linearly from the central part to the peripheral part. Note that the change characteristic of the detection voltage signal Sh ′ can be made as a characteristic so as to monotonously and linearly decrease from the central part to the peripheral part.

  5, 6, and 7, the horizontal axis is shown in the X-axis direction, but the characteristics shown in each figure include the Y-axis direction in the light receiving surface 12 of the four-split photodetector 11. This is a characteristic that holds in all diameter directions passing through the origin O.

  Even when the position of the laser beam 16 is outside the light receiving surface 12 of the quadrant photodetector 11 when the laser beam 16 is reflected by the back surface of the cantilever and arrives at the quadrant detector 11 side. If it is in the range of the auxiliary tool 14 and, for example, enters the peripheral portion of the optical filter 14b, the optical filter 14b has high transmittance, so that the light intensity is not attenuated so much and enters the convex lens 14a (FIG. 6). Middle arrow A10). The light incident on the convex lens 14a is refracted toward the light receiving portions 12c and 12d and is incident on these light receiving portions (arrow A11 in FIG. 6). Thereby, the voltage signal level Sh′20 shown in FIG. 7 is detected.

  Next, for example, consider the case where the above-described mirror 107 described with reference to FIG. At that time, the optical filter 14b attenuates the light intensity and enters the convex lens 14a (arrow A12 in FIG. 6) than when the laser light is incident on the peripheral portion. The laser light incident on the convex lens 14a is refracted and incident on the light receiving portion of the light receiving surface 12 (arrow A13 in FIG. 6). At that time, the detected electrical signal Sh'21 becomes weaker than when it enters from the peripheral portion. Furthermore, when approaching the center of the light receiving surface 12, the voltage signal becomes weaker more rapidly as shown in FIG. 7, and the voltage signal value decreases rapidly toward the center (origin) O. Therefore, for example, when the adjustment is performed by moving the mirror 107, the adjustment may be made in such a direction that the electric signal becomes weaker, so that the optical axis can be easily adjusted.

  As for the configuration of the optical axis adjustment assisting tool 14, a modification as shown in FIG. 8 or FIG. 9 can be used.

  FIG. 8 shows an auxiliary tool in which a convex lens is provided with a filter function. 8A shows a side sectional view of the auxiliary tool 30, and FIG. 8B shows a transmittance distribution in the X-axis direction of the auxiliary tool 30. FIG. In FIG. 8B, the horizontal axis indicates the distance from the center of the auxiliary tool 30 in the X-axis direction, and the vertical axis indicates the transmittance. A curve C30 shows the distribution characteristic of transmittance. In FIG. 8A, aluminum or the like is vapor-deposited stepwise on the flat surface 30b of the plano-convex lens 30a, and a thin film 30c is provided in which the central portion is thickened and becomes thinner toward the peripheral portion. Note that FIG. 8A exaggerates the thickness. As shown in FIG. 8B, the auxiliary tool 30 has a lower transmittance at the center thereof, and the transmittance increases as it approaches the peripheral portion. As a result, as in the case of using the auxiliary tool 14, a detection voltage signal Sh ′ that is monotonously increasing or monotonically decreasing according to the distance from the center as shown in FIG. 7 can be obtained, and the optical axis adjustment is facilitated. be able to. In the above example, a thin film is provided on one side of the lens, but it is also possible to provide a thin film on both sides of the lens.

  FIG. 9 is a diagram showing an auxiliary tool composed of a convex lens manufactured using a material having an appropriate absorption rate for laser light. 9A shows a side cross-sectional view of the auxiliary tool 40, and FIG. 9A shows the transmittance distribution of the auxiliary tool 40 in the X-axis direction. In FIG. 8A, the horizontal axis represents the distance from the center of the auxiliary tool 40 in the X-axis direction, and the vertical axis represents the transmittance change characteristic. A curve C40 shows the transmittance distribution. In FIG. 9A, the plano-convex lens 40a is thicker at the center and thinner toward the periphery. Therefore, the closer the thickness is to the center, the more the laser beam that is transmitted is absorbed, and the intensity of the transmitted light is weakened. Therefore, as shown in FIG. 9 (B), the auxiliary tool 40 has a lower transmittance at the center portion and a higher transmittance as it approaches the peripheral portion. As a result, similarly to the case where the auxiliary tool 14 is used, a detection voltage signal Sh ′ that increases monotonously or decreases according to the distance from the center as shown in FIG. 7 is obtained, and the optical axis adjustment can be facilitated. .

  Next, with reference to FIG. 10, a method of adjusting the optical axis in the four-divided photodetector 11 that typically includes the auxiliary tool 14 will be described.

  The entire optical axis adjustment work in the optical probe optical detection system of the scanning probe microscope provided with the optical lever optical detection system is as described in the background art section. In summary, the first step is to first guide the laser light emitted from the laser light source while controlling the position of the laser light and hit the reflection area formed on the back surface of the cantilever, and the laser light reflected on the back surface of the cantilever. In the second step of adjusting the position of the laser beam so that it enters the light receiving surface of the quadrant photodetector. When the first step is completed and the second step is performed, the laser light reflected by the back surface of the cantilever is irradiated in the vicinity of the light receiving surface 12 of the quadrant photodetector 11.

  On the other hand, as described above, the convex lens 14a and the optical filter 14b constituting the auxiliary tool 14 are attached to the front surface of the light receiving surface 12 of the quadrant photodetector 11 according to the present embodiment. Therefore, the laser beam that has arrived by reflection from the cantilever is generally captured by the optical filter 14 b of the auxiliary tool 14 even if it is off the light receiving surface 12. In the example shown in FIG. 10, irradiation spots (16-1, 16-2, 16-3) of the laser beam 16 are shown.

  (A), (B), and (C) of FIG. 10 show that the irradiation spot of the laser beam incident on the outer position of the auxiliary tool 14 (optical filter 14b) is adjusted in position, and (A) to (C). In this way, the state of being guided to the center position of the light receiving surface 12 is shown. Further, symbols Sh′20, Sh′21, etc. in FIG. 7 indicate the level (sensitivity) of the detection voltage signal Sh ′ of the quadrant photodetector 11 corresponding to the position of the irradiation spot. The irradiation spot positions 16-1, 16-2, and 16-3 in FIG. 10 correspond to A10, A12, and A0 in FIG. 7, respectively. As is clear from FIG. 7, when the irradiation spot hits the center position of the light receiving surface 12, the level is 0 and the change characteristic of the voltage signal Sh 'becomes remarkable. The voltage signal Sh ′ increases monotonously as the irradiation spot approaches the peripheral edge, and the voltage signal Sh ′ decreases monotonously as the irradiation spot approaches the center. Therefore, the position of the irradiation spot of the laser beam 16 in the X-axis direction (generally in the radial direction) can be known by examining the level of the voltage signal Sh ′ relating to the light receiving surface 12 of the four-split photodetector 11. It can also be seen that the weaker voltage signal level is closer to the center. In other words, by obtaining the level of the voltage signal Sh ′ output from the quadrant photodetector 11 and its change state, when the laser light 16 enters the optical filter 14b, the laser light 16 is moved inward from the incident position, Furthermore, it is possible to easily adjust to the center position of the light receiving surface 12 of the quadrant photodetector 11. The characteristics of the detection voltage signal described above are the same even in the horizontal direction with respect to other directions such as the Y-axis direction.

  When the laser beam 16 is captured by the optical filter 14b or the like of the auxiliary tool 14, it is normally captured at the peripheral portion of the optical filter 14b as shown in FIG. At that time, since the transmittance of the optical filter 14b is high, the detection output is strong. Thereafter, the laser beam 16 can be moved in the direction of the position of the center O of the light receiving surface 12 by manually adjusting the optical axis so that the detection output becomes weak using the monotonically decreasing change characteristic C11. It becomes possible. Arrows 51 and 52 shown in FIG. 7 indicate the moving direction of the irradiation spot of the laser beam 16 in manual adjustment of the optical axis. In this way, adjustment is performed so that the voltage signal Sh ′ which is the detection output finally becomes zero. When the detection output of the quadrant photodetector 11 becomes zero, the optical axis adjustment operation is completed.

  As described above, by attaching the auxiliary tool 14 to the light receiving surface 12 of the quadrant photodetector 11 based on the above-described configuration, the irradiation spot of the laser beam 16 reflected from the back surface of the cantilever can be relatively set. Then, the laser beam 16 is easily moved to the center position of the light receiving surface 12 while observing the output characteristic (voltage signal Sh ′) from the four-split photodetector 11. Thus, the optical axis adjustment operation can be completed easily and in a short time.

  Compared with the conventional method of adjusting the optical axis, the method according to the present embodiment requires little or no trial and error process, so the part depending on experience is reduced, and it is easily performed even by an unskilled operator. be able to.

  In addition, after the optical axis adjustment is completed, measurement with an atomic force microscope is performed using an optical lever type optical detection system. In this measurement, the auxiliary tool 14 used for adjusting the optical axis is usually removed from the quadrant photodetector 11. Accordingly, the auxiliary tool 14 is detachably provided with respect to the quadrant photodetector 11. This also applies to the auxiliary tools 30 and 40.

  Although the atomic force microscope has been described in the above embodiment, the present invention is not limited to this, and it is needless to say that the optical axis adjustment auxiliary device according to the present invention can be applied to a scanning probe microscope having an optical lever type optical detection system. Further, it can be used for other position detection devices. Although the optical axis adjustment auxiliary device is used for the four-divided photodetector, the present invention is not limited to this, and it is needless to say that the optical axis adjustment assisting device can be modified and used for photodetectors of other division numbers. Such an optical axis adjustment auxiliary device can substantially expand the light receiving area of the multi-element photodetector.

  Further, in the above-described embodiment, the auxiliary tool 14 and the like are provided detachably, but the auxiliary tool may be fixed to the quadrant photodetector 11. In this case, the characteristics of the auxiliary tools in the light receiving portions 12a to 12d on the light receiving surface 12 are adjusted so that the detection characteristics of the four-split photodetector 11 are not affected.

  Further, in the above embodiment, the optical axis adjustment is performed by adjusting the irradiation spot of the laser beam 16 on the light receiving surface 12 of the quadrant photodetector 11 by adjusting the posture related to the reflection direction of the mirror 107. Instead of the mirror 107, the optical axis adjustment can be performed using an optical axis adjustment mechanism 61 as shown in FIG. In the optical axis adjustment mechanism 61, a mounting base 63 having a triangular shape is provided on a base member 62 with a fulcrum support portion 64 and two adjustment screws 65 and 66. The fulcrum support portion 64 is provided at one apex portion of the mounting base 63, and the two adjustment screws 65 and 66 are attached to the other two apex portions, respectively. The above-described quadrant photodetector 11 is provided on the mounting base 63. The light receiving surface 12 of the quadrant photodetector 11 faces upward, and laser light 16 is incident on the light receiving surface 12. The aforementioned auxiliary tool 14 and the like are arranged on the front surface of the light receiving surface 12 of the quadrant photodetector 11. In FIG. 11, illustration of the auxiliary tool 14 and the like is omitted.

  According to the optical axis adjustment mechanism 61 described above, by appropriately adjusting one of the two adjustment screws 65 and 66, the incident position of the laser beam 16 on the light receiving surface 12 is changed, and the optical axis is adjusted.

  The configurations, shapes, sizes, and arrangement relationships described in the above embodiments are merely schematically shown to the extent that the present invention can be understood and implemented. Therefore, the present invention is not limited to the described embodiments, and can be variously modified without departing from the scope of the technical idea shown in the claims.

  INDUSTRIAL APPLICABILITY The present invention is used as an optical axis adjustment auxiliary device such as a quadrant photodetector in an optical lever type optical detection system in a scanning probe microscope.

It is a front view of the 4-part dividing photodetector to which the optical axis adjustment auxiliary device concerning the present invention is applied. FIG. 2 is a side view of the quadrant photodetector shown in FIG. 1. It is the front view which applied the optical axis adjustment auxiliary tool which concerns on this embodiment to the 4 division | segmentation photodetector shown in FIG. FIG. 4 is a side view of the quadrant photodetector shown in FIG. 3. It is a graph which shows the transmittance | permeability characteristic of the optical filter contained in the optical axis adjustment auxiliary tool which concerns on this embodiment. It is a figure which shows the effect | action of the combination of the convex lens and optical filter which are contained in the optical axis adjustment auxiliary tool which concerns on this embodiment. It is a graph which shows the relationship between the incident position of the laser beam of the 4 division | segmentation photodetector provided with the optical axis adjustment auxiliary tool which concerns on this embodiment, and the voltage signal Sh '. It is a figure which shows the other Example of the optical axis adjustment auxiliary tool which concerns on this embodiment, (A) is side surface sectional drawing, (B) is a graph which shows the transmittance | permeability distribution. It is a figure which shows the other Example of the optical axis adjustment auxiliary tool which concerns on this embodiment, (A) is side surface sectional drawing, (B) is a graph which shows the transmittance | permeability distribution. It is a figure for demonstrating the method of the optical axis adjustment based on the optical axis adjustment auxiliary | assistance apparatus which concerns on this embodiment. It is a perspective view which shows the other example of an optical axis adjustment mechanism. It is a schematic side view for demonstrating an example of the conventional optical axis adjustment. It is a figure which shows the control state which moves the spot position of a laser beam to the center of a light-receiving surface on the light-receiving surface of a 4-part dividing photodetector. It is a typical front view when the irradiation spot of a laser beam exists on the light-receiving surface of a 4-part dividing photodetector. It is the typical side view which showed the state in FIG. 14 from the side with light intensity. It is a graph which shows the change state of voltage signal Sh 'when the irradiation spot of a laser beam is moved on the X-axis of the light-receiving surface of a 4-part dividing photodetector.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 4 division | segmentation photodetector 12 Light-receiving surface 12a-12d Light-receiving part 14, 30, 40 Optical axis adjustment auxiliary tool 14a Convex lens 14b Optical filter 14c Holder 16 Laser light

Claims (5)

A laser light source that emits laser light to a reflecting member; and a photodetector that has a light receiving surface on which the laser light reflected by the reflecting member is incident and is divided into a plurality of light receiving portions. In the position detection device that detects an incident position of the laser beam on the light receiving surface of the photodetector, and further includes an optical axis adjustment unit,
An optical axis adjustment assist, comprising correction means for converting the relationship between the distance of the laser beam incident position from the center of the light receiving surface and the detection signal from the photodetector into a monotonically increasing or monotonically decreasing relationship. apparatus.   The optical axis according to claim 1, wherein the correction unit includes a convex lens disposed on the front surface of the light receiving surface and an optical filter whose light transmittance increases from a central portion toward a peripheral portion. Adjustment auxiliary device.   2. The optical axis adjustment assisting device according to claim 1, wherein the correcting means is a convex lens that is disposed in front of the light receiving surface and increases in light transmittance from a central portion toward a peripheral portion.   4. The optical axis adjustment according to claim 3, wherein the convex lens has a metal thin film deposited on one or both sides of the convex lens so that the thickness thereof decreases from the central portion toward the peripheral portion of the convex lens. Auxiliary device. 4. The optical axis adjustment assisting device according to claim 3, wherein the convex lens is formed of a material that absorbs the laser light at a predetermined absorption rate.

Images