JP7175982B2 - Optical measurement device and sample observation method - Google Patents

Description

The present disclosure relates to an optical measurement device and a sample observation method using the same.

Optical measurement devices are devices that can non-destructively acquire information reflecting the surface structure and internal structure of a measurement object, and are used in a wide range of fields. One type of such optical measurement device is optical coherence tomography (OCT).

Since OCT is not invasive to the human body, it is expected to be applied particularly in the medical and biological fields, and in the field of ophthalmology, devices for forming images of the fundus, cornea, etc. are used. In OCT, the light from the light source is divided into signal light that irradiates the measurement target and reference light that is reflected by the reference light mirror without irradiating the measurement target, and the signal light reflected from the measurement target is combined with the reference light. A signal is obtained by making waves interfere with each other.

Recently, attention has also been paid to a technique of applying OCT to obtain time-varying change information of a measurement object. An angiographic OCT is an example of an optical measurement device that utilizes acquisition of time-varying information. In Patent Document 1, light emitted from a light source is divided into two independent polarized beams, and the two polarized beams are simultaneously irradiated onto two different portions on a line along the scanning direction by a galvano mirror to perform scanning. Separate the reflected light into vertical and horizontal components, detect them simultaneously with two detectors, acquire two tomographic images of the same site at different times by one scan, and obtain the two tomographic images A scanning OCT apparatus is disclosed that measures the amount of phase change over time for the same site using an image. According to this device, it is possible to visualize the blood vessel, which is a part of the tissue of the human body that undergoes a large amount of change over time.

In the scanning optical measurement device as described above, in order to obtain information on the change over time of a predetermined portion of the object to be measured, the predetermined portion is measured a plurality of times at intervals of time δt, and the obtained plurality of times A time change amount δS is obtained from the measurement result, and time change information of the predetermined portion is obtained using δt and δS. At this time, the measurement interval .delta.t is the time resolution of the temporal change information. More information can be obtained by measuring with higher temporal resolution.

WO2010/143601

In scanning-type optical measurement devices including scanning-type OCT, it is necessary to increase temporal resolution in order to obtain a large amount of time-dependent change information. However, since the time resolution depends on the scanning cycle, it is difficult to obtain a time resolution shorter than the scanning cycle. Also, if an expensive scanning mechanism with a short scanning cycle is used, the apparatus will be expensive and complicated.

In the angiographic OCT of Patent Document 1, OCT is described in which two signal light beams are applied to a measurement object in order to obtain temporal change information with a time resolution shorter than the scanning period of the beam. In the OCT described above, two polarized beams with different polarization states are applied to two different regions, and the two beams are separated according to the polarization state in order to separately detect information on the two different regions. For this reason, the OCT described in Patent Document 1 requires a beam separation mechanism and further requires an independent detection mechanism for each beam, which increases the size of the device. Further, in the OCT described in Patent Document 1, two beams with different polarization states are used to separate the beams. Therefore, a difference due to a difference in polarization state occurs between the information acquired by the two beams, which may result in a measurement error of the time-varying information.

The present disclosure has been made in view of the above points, and provides a technology capable of measuring temporal change information at low cost and with a temporal resolution shorter than the scanning cycle.

As a means for solving the above problems, the present disclosure includes, for example, a light source, a light branching unit that branches light emitted from the light source into reference light and signal light, and irradiating the signal light to scan an object to be measured. an optical system for combining the signal light reflected or scattered by the measurement object and the reference light to generate interference light; and the interference light generated by the optical system for receiving the interference light. An optical measuring device comprising: a photodetector that converts into an electrical signal; and a signal processor that calculates the intensity of the signal light based on the electrical signal converted by the photodetector, wherein the photodetector detects the signal light by a plurality of photodetection elements respectively associated with a plurality of measurement areas that overlap with the irradiation area of the signal light, and the signal processing unit detects the signal light by each of the plurality of photodetection elements The scanning unit calculates the intensity of the signal light applied to the object to be measured, and calculates the intensity of the signal light applied to the object to be measured. Provided is an optical measurement device that scans the measurement object by moving it so as to overlap another part of the plurality of measurement regions.

Further, for example, a sample observation method using an optical measurement device for acquiring an optical coherence tomographic image, in which a signal light is irradiated onto an object to be measured, and the reflected or scattered signal light and the reference light are synthesized to obtain an interference light. detecting the signal intensity of the interference light at a first time point by a plurality of photodetectors corresponding to each of a plurality of measurement regions overlapping with the irradiation region of the signal light; moving the irradiation region so that a portion of the plurality of measurement regions at a time point and another portion of the plurality of measurement regions at a second time point overlap; and detecting the signal intensity of the interference light at the second time point using the plurality of photodetectors.

According to the present disclosure, temporal change information can be measured at low cost and with a temporal resolution shorter than the scanning period. Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

1 is a schematic diagram illustrating a basic embodiment of an optical metrology device according to the present disclosure; FIG. 4 is a schematic diagram showing the correspondence relationship between the beam spot and the arrangement of the differential detection circuit in the operating state of the optical measurement device of Example 1. FIG. FIG. 4 is a schematic diagram showing how a beam spot irradiated onto a measurement object moves. FIG. 4 is a schematic diagram showing the relationship between the temporal change in the position of the measurement region and the temporal resolution; It is a schematic diagram which shows the structure of the reference optical system which expands the beam diameter described above. FIG. 10 is a diagram illustrating a basic configuration example of an optical measurement device according to a second embodiment; FIG. 10 is a schematic diagram showing the configuration of an optical measurement device of Example 3; FIG. 11 is a schematic diagram showing the configuration of an optical measurement device of Example 4; FIG. 4 is a schematic diagram showing how a beam spot moves on the object to be measured; FIG. 10 is a diagram showing a scanning method in which a plurality of measurement areas are defined in both the x-direction and the y-direction;

Various embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, these examples are merely examples for realizing the present disclosure, and do not limit the technical scope of the present disclosure. In addition, the same reference numerals are given to common configurations in each figure.

<Example 1>
The optical measuring device of Example 1 will be described below with reference to FIGS.
FIG. 1 is a schematic diagram illustrating a basic embodiment of an optical metrology device 1 according to the present disclosure. In FIG. 1, the vertical direction is the z direction, the horizontal direction is the x direction, and the direction perpendicular to the paper surface is the y direction.

The optical measurement device 1 includes a light source unit 190, a polarizing beam splitter 106, a reference optical system 191, a scanning unit 159, a sample stage 139, a cover glass 114, an interference optical system 132, a photodiode array (124, 125, 130 and 131), A differential detection circuit (134 and 135), a signal processing section 136 and a control section 116 are provided.

The light source unit 190 includes a light source 101, a collimator lens 102, a beam shaping prism 103, an ND (Neutral Density) filter 104, and a λ/2 plate 105 whose optical axis direction is adjustable. A laser beam composed of a single wavelength component emitted from the light source 101 is converted into parallel light by the collimating lens 102 . Subsequently, the laser light converted into parallel light is shaped into an elliptical beam cross-sectional shape by the beam shaping prism 103 in which the y direction is longer than the x direction. After that, the intensity of the laser light is reduced by the ND filter 104, and the polarization direction is rotated by the λ/2 plate 105 whose optical axis direction is adjustable. branched.

Scanning unit 159 includes two-dimensional scanner 107 , λ/4 plate 112 , lens 113 and lens actuator 117 . The signal light enters the optical system provided in the scanning unit 159, passes through the two-dimensional scanner 107, and passes through the λ/4 plate 112 whose optical axis direction is set at about 22.5 degrees with respect to the xz plane. Upon transmission, the polarization state is converted from s-polarization to circular polarization. After that, the signal light is condensed by a lens 113 having a numerical aperture of 0.3 or more, passes through a cover glass 114, is irradiated onto a measurement object 115, and forms a beam spot 140 at a condensed position.

Here, since the cross-sectional shape of the beam incident on the lens 113 is an ellipse in which the y direction is longer than the x direction, the numerical aperture is larger in the y direction than in the x direction when the light is condensed. Therefore, the shape of the beam spot 140 on the xy plane is an ellipse in which the x direction is longer than the y direction.

The beam spot 140 is moved in one of the x, y, and z directions by the scanning unit 159 . The control unit 116 controls the lens actuator 117 to move the lens 113 at least in the z-direction, thereby moving the signal light condensing position (measurement position) by the lens 113 .

Further, the movement of the condensing position of the signal light in the xy direction is performed by a two-dimensional scanner 107 including two galvanomirrors 108 and 109 and lenses 110 and 111 provided in the optical path of the signal light. , the object to be measured is scanned according to the condensing position of the signal light.

Signal light reflected or scattered from the object to be measured is converted into parallel light (beam) by the lens 113 . After that, the polarization state of the signal light is converted from circular polarization to p-polarization by the λ/4 plate 112 and enters the polarization beam splitter 106 . By moving the measurement object 115 by moving the sample stage 139, the position of the condensed position of the signal light in the measurement object 115 is roughly moved.

On the other hand, the reference light passes through the λ/4 plate 118 and its polarization state is converted from p-polarized light to circularly polarized light. After that, the reference light is incident on the mirror 119 whose position is fixed and reflected, and then passes through the λ/4 plate 118 again, where the polarization state is converted from circular polarization to s-polarization, and enters the polarization beam splitter 106 . do.

The signal light and the reference light are combined by the polarizing beam splitter 106 to generate combined light. The combined light is directed to interference optics 132 consisting of half beam splitter 120, λ/2 plates (121 and 127), λ/4 plate 126, condenser lenses (122 and 128), and polarizing beam splitters (123 and 129). be killed.

The combined light incident on the interference optical system 132 is split into transmitted light and reflected light by the half beam splitter 120 . The transmitted light passes through a λ/2 plate 121 whose optical axis is set at approximately 22.5 degrees with respect to the xz plane, and then condensed by a condensing lens 122 . After that, the transmitted light is split into two by the polarizing beam splitter 123 to generate a first interference light 144 and a second interference light 145 having a phase relationship different from each other by 180 degrees.

The first interference light 144 is condensed by the condensing lens 122 to form an image 153 of the beam spot 140 at the position of the photodiode array 124 . The photodiode array 124 is arranged such that the image 153 of the beam spot 140 is superimposed with a plurality of photodetecting elements (photodiodes) 148 .

Similarly, the second interference light 145 is condensed by the condensing lens 122 to form an image 154 of the beam spot 140 at the photodiode array 125 . The photodiode array 125 is composed of a plurality of photodetecting elements 149 each functioning as a photodetector, and is arranged so that the plurality of photodetecting elements 149 overlap the image 154 of the beam spot 140 .

Each of the first interference light 144 and the second interference light 145 is detected by the photodiode arrays 124 and 125 and the differential detection circuit 134 of the corresponding elements of the plurality of photodetection elements 148 and the plurality of photodetection elements 149. The outputs are combined and subjected to current differential detection, and a signal 137 proportional to the difference in intensity between the two interference lights is output. Here, the mutually corresponding elements of the plurality of photodetecting elements 148 and the plurality of photodetecting elements 149 are, for example, in the example shown in FIG. and the leftmost photodetector among the plurality of photodetectors 149 correspond to each other.

On the other hand, the reflected light reflected by the half beam splitter 120 passes through the λ/4 plate 126 whose optical axis is set at approximately 45 degrees with respect to the xz plane, and then the optical axis is approximately 22.5 degrees with respect to the xz plane. The light is transmitted through the λ/2 plate 127 set to 100 degrees and condensed by the condensing lens 128 . After that, the reflected light is split into two by the polarizing beam splitter 129 to generate a third interference light and a fourth interference light having a phase relationship different from each other by 180 degrees. Each of the third interference light and the fourth interference light is subjected to current differential detection by photodiode arrays 131 and 130 and a differential detection circuit 135, and a signal 138 proportional to the difference in intensity of the two interference lights is output. be done.

The third interference light 146 is condensed by the condensing lens 128 to form an image 155 of the beam spot 140 on the photodiode array 131 . The photodiode array 131 is arranged such that a plurality of photodetecting elements (photodiodes) 150 overlap an image 155 of the beam spot 140 .

Similarly, fourth interference light 147 is condensed by condensing lens 128 to form image 156 of beam spot 140 at photodiode array 130 . The photodiode array 130 is composed of a plurality of photodetecting elements 151 each functioning as a photodetector, and is arranged so that the plurality of photodetecting elements 151 overlap an image 156 of the beam spot 140 .

Third interfering light 146 and fourth interfering light 147 are detected by the photodiode arrays 130 and 131 and the differential detection circuit 135 of the corresponding elements of the plurality of photodetecting elements 150 and the plurality of photodetecting elements 151, respectively. The outputs are combined and current-differentially detected to output a signal 138 proportional to the difference in intensity between the two interfering lights. The meaning of "elements corresponding to each other" is as explained above.

The signal 137 and the signal 138 generated as described above are input to the signal processing unit 136 and calculated to obtain a signal proportional to the amplitude of the signal light. Specifically, when the combined light enters the interference optical system 132, E _sig is the amplitude of the signal light component, E _ref is the amplitude of the reference light component, I is the intensity of the signal 137, and Q is the intensity of the signal 138. , a signal proportional to the absolute value of the amplitude of the signal light, independent of the phase, is obtained by performing the calculation of the following equation 1 in the signal processing unit 136 .
|E _sig |·|E _ref |={I ² +Q ² } ^1/2 (Formula 1)

Here, the signals 137 and 138 are output by the number of photodetecting elements 148, 149, 150, 151 of the photodiode arrays 124, 125, 130, 131. A corresponding number of signals proportional to the amplitude of the signal light are obtained (four in the example shown in FIG. 1). In this embodiment, three or more interfering lights with different phase relationships are detected, so by performing calculations on these detection signals, a stable signal independent of the interfering phase can be obtained.

FIG. 2 is a schematic diagram showing the correspondence relationship between the beam spot 140 and the differential detection circuit 134 in the operating state of the optical measurement device 1 of Example 1. As shown in FIG.

The shape of the beam spot 140 on the measurement object 115 on the xy plane is an ellipse in which the x direction is longer than the y direction, as described above. The signal light reflected by the measurement object 115 is combined with the reference light to become interference light 144, 145, 146, 147, and passes through the optical system of the apparatus to the light receiving surfaces of the photodiode arrays 124, 125, 130, 131. Above, they are connected as images 153, 154, 155 and 156, respectively.

FIG. 2 shows the positional relationship between the photodiode arrays 124 and 125 and the images 153 and 154 corresponding to the first interference light and the second interference light. The positional relationship between the photodiode arrays 130, 131 and the images 155, 156 corresponding to the third and fourth interference lights is also the same as for the first and second interference lights.

An image 153 formed by the interference light 144 has an elliptical shape elongated in the direction 301 in which the four photodetector elements 148 (D ₁₁ , D ₁₂ , D ₁₃ , D ₁₄ ) of the photodiode array 124 are arranged. The image 153 spans four photodetector elements 148, and each photodetector element outputs a current proportional to the intensity of the component of the interfering light 144 that strikes the respective detector element. In FIG. 2, the direction 301 in which the four photodetectors 148 are arranged is drawn to match the direction corresponding to the x direction on the measurement object 115 on the image 153 .

An image 154 formed by the interference light 145 has an elliptical shape elongated in the direction 302 in which the four photodetector elements 149 (D ₂₁ , D ₂₂ , D ₂₃ , D ₂₄ ) of the photodiode array 125 are arranged. The image 154 spans four photodetector elements 149, and each photodetector element outputs a current proportional to the intensity of the component of the interfering light 145 that strikes the respective detector element. In FIG. 2, the direction 302 in which the four photodetectors 149 are arranged is drawn to match the direction corresponding to the x direction on the measurement object 115 on the image 154 .

The relative positional relationship between the image 153 and the four photodetector elements 148 is matched with the relative positional relationship between the image 154 and the four photodetector elements 149, and the four photodetector elements 148 (D ₁₁ , D ₁₂ , D ₁₃ , D ₁₄ ) and the four photodetector elements 149 (D ₂₁ , D ₂₂ , D ₂₃ , D ₂₄ ) together form four measurement areas 303 (A ₁ , A ₂ ) on the measurement object 115 . , A ₃ , A ₄ ) are optically conjugate. Here, assuming that the interval between the photodetectors is δx and the magnification of the optical system is M, the interval δx' between the four measurement regions 303 is δx'=M×δx.

The current outputs of the four photodetector elements 148 ( _D11 , _D12 , _D13 , _D14 ) and the _four photodetector elements 149 ₍ D21, _D22 , _D23 , D24) are Four sets of signals obtained by combining the outputs of _{( D11} and D21, _D12 and _D22 , _D13 and _D23 , _D14 and _D24 ) are input to differential detection circuits 304, 305, 306 and 307, respectively. are differentially detected and input to the signal processing unit 136 as a signal 137 that is a set of four signals.

As for the third interference light and the fourth interference light, similarly to the first interference light and the second interference light, the four photodetection elements 150 and the four photodetection elements 151 are both detected by the measurement object 115. It is positioned optically conjugate with the upper four measurement areas 303 (A ₁ , A ₂ , A ₃ , A ₄ ). The outputs of the corresponding photodetectors are combined, and four sets of signals are input to four differential detection circuits and differentially detected. As a result, a signal 138 that is a set of four signals is input to the signal processing section 136 .

The signal processing unit 136 performs the calculation of Equation 1 above four times with the signals 137 and 138 as inputs, and the signal light reflected by the four measurement areas 303 (A ₁ , A ₂ , A ₃ , A ₄ ) is Four signals (S ₁ , S ₂ , S ₃ , S ₄ ) proportional to the amplitude of each component of are calculated. As mentioned above, signal measurements for the four measurement areas 303 (A ₁ , A ₂ , A ₃ , A ₄ ) can be performed simultaneously.

The operation of the optical measuring device 1 of the present embodiment when scanning the measurement object 115 with the beam spot 140 to acquire time-varying change information will be described below with reference to FIGS. 3 and 4. FIG.

FIG. 3 is a schematic diagram showing how the beam spots 140, 157, and 158 irradiated onto the measurement object 115 move.

When scanning the measurement object 115 with the beam spot 140, the beam spot 140 on the measurement object 115 moves in the x direction at a constant speed. FIG. ₃ shows the position at time t1 of the beam spot 140 moving at a constant scanning speed v in the scanning direction 152, and _four measurement areas 303 (A1, _A2 , A3 _{, A4} ) at the same time. shows the position of The distance between the four measurement areas 303 (A ₁ , A ₂ , A ₃ , A ₄ ) is a value (δx′) determined by the distance between the photodetectors and the characteristics of the optical system as described above. is constant regardless of In FIG. ₁ , the expected positions of the beam spot 140 at times .delta.t and 2.times..delta.t after time t1 are indicated by reference numerals 157 and 158, respectively. Here, the time .delta.t is a value given by the following equation.
δt=δx′/v (Formula 2)
In other words, the distance traveled by the beam spot 140 at time δt is v·δt=δx′, which is equal to the distance between the measurement regions.

FIG. 4 is a schematic diagram showing the relationship between the temporal change in the position of the measurement region and the time resolution (that is, the sampling interval). In the graph of FIG. 4, the horizontal axis indicates time t, and the vertical axis indicates the position of the measurement area 303 in the x direction. In FIG. 4, the locations of four measurement areas 303 (A ₁ , A ₂ , A ₃ , A ₄ ) are shown as traces 401, 402, 403, 404 respectively. The solid-line portion of each trace represents the measurement period, and the dashed-line portion represents the period during which no measurement was performed, but simply moved. In the example shown in FIG. 4, measurements are taken only while the measurement area 303 is moving in the positive x direction, and not while it is moving in the negative x direction (returning to the start position of the scan). not

At time t ₁ , the position of one A ₁ of the measurement areas 303 is x ₁ , and the positions of the other three A ₂ , A ₃ , and A ₄ are x ₁ −δx′, x ₁ −2δx′, x _1-3δx '. After that, since the measurement area 303 moves at a speed v, the times when _each measurement area 303 reaches the position x1 are as follows.
A ₂ : t ₁ + δt
A ₃ : t ₁ +2δt
A ₄ : t ₁ +3δt

Therefore, for the four signals (S ₁ , S ₂ , S ₃ , S ₄ ) obtained in the four measurement regions 303, if the signal value at time t in the n-th measurement region is written as S _n (t), S ₁ (t ₁ ), S ₂ (t ₁ + δt), S ₃ (t ₁ + 2δt), S ₄ (t ₁ + 3δt) are time-series measured values of the position x ₁ acquired every time δt from time t ₁ becomes.

More generally, the time-series measured value Y(x ₀ , n) of the position x ₀ through which the m-th measurement region passes at a certain time t ₀ is obtained as S _m+n (t ₀ +n·δt), and this Time-series measurements can be used to obtain time-varying information for position _x0 . Furthermore, the time-series measured value Y(x 0 ₊ x', n) at the position x' in the positive direction from the position x ₀ is obtained as S _{m + n} (t ₀ + x'/v + n·δt). In this manner, by scanning one scanning line on the measurement object 115 with the four measurement regions 303 only once, it is possible to acquire time-series measurement values at each point on the scanning line at each time δt.

Here, if the scanning amplitude in the x direction of the measurement area 303 is X _A and the scanning period 405 is T _x , X _A =v·T _x because the movement during scanning is at a constant speed. Also, since the scanning amplitude is sufficiently large (δx'<<X _A ) with respect to the interval between the measurement regions, δt=δx'/v=(δx'/X _A )·T _x <<T _x . In other words, the optical measurement device 1 of the present embodiment can acquire time-varying change information of a certain position on the measurement object 115 by executing the above operation, and the time resolution δt is sufficiently larger than the scanning period 405T _x . can be shortened to

In addition, by setting the time resolution (AD conversion frequency and response frequency) of the differential detection circuits 134 and 135 and the photodiode arrays 124, 125, 130, and 131 to the same or less than δt, the measured value at the intended point of time can be obtained. Furthermore, by setting the time resolution to be .delta.t/2 or less, it is possible to obtain information with the intended time resolution while satisfying the sampling theorem. Further, by setting the time resolution to δt/10 or less, measurement can be performed without being affected by the state of the measurement object 115 at adjacent points of time, and change information over time can be accurately detected.

As described above, according to the present disclosure, a plurality of detectors provided in a direction corresponding to the scanning direction can measure a predetermined portion of an object to be measured at different times, and a plurality of obtained measurement results can be used to measure the predetermined portion. It is possible to acquire information on changes over time of the site. That is, the optical measurement device 1 of the present disclosure can measure temporal change information with a time resolution shorter than the scanning period without using two signal light beams.

In the optical measurement device 1 of Example 1, the photodiode arrays 148, 149, 150, and 151 each have two or more photodetector elements, thereby acquiring signals between two or more points in time. and the amount of change over time can be calculated. More preferably, the number of photodetectors on each photodiode array is three or more. In this case, it is possible to make the time resolution variable or acquire information at a plurality of time resolutions at once. Specifically, among the three signals S ₁ , S ₂ , and S ₃ obtained using a photodiode array having three photodetectors, information with a time resolution δt can be obtained by using S ₁ and S ₂ . Therefore, by using S ₁ and S ₃ , information with a time resolution of 2δt can be obtained.

In the optical measurement device 1 of the present embodiment, for the photodiode arrays 148, 149, 150, and 151, the minimum value δx _min and the maximum value δx _max of the spacing between arbitrary photodetecting elements on each photodiode array, the optical system Assuming that the magnification is M and the scanning speed of the beam spot 140 is v, change information over time can be obtained with a time resolution δt in the range of (δx _min /M)/v ≤ δt ≤ (δx _max /M)/v. It is possible. Here, the minimum value δx _min is, for example, the interval between adjacent photodetectors, and the maximum value δx _max is, for example, (the number of photodetectors−1)×δx _min .

Also, in FIG. 3, the shape of the beam spot 140 has been described as having a size that fits within the plurality of measurement regions 303 . The shape (irradiation area) of the beam spot 140 may be a shape including the measurement area 303 . By doing so, the intensity of the signal light irradiated to each measurement area (A ₁ , A ₂ , A ₃ , A ₄ ) can be made uniform, and the accuracy of change information over time can be improved.

Also, as shown in FIG. 3, when the shape of the beam spot 140 is elliptical, there is a possibility that the irradiation amount of the signal light differs between both ends and the center of the plurality of measurement regions 303 . In this case, the difference in irradiation amount (difference in signal intensity) between both ends and the center of the plurality of measurement regions 303 is measured in advance, and the signal processing unit 136 calculates the intensity of the signal light corresponding to each of the plurality of measurement regions 303. It may be calculated after calibration. By doing so, the measurement accuracy of the temporal change information of the measurement object 115 is improved.

Next, a scanning method for acquiring a two-dimensional image and a three-dimensional image of the measurement object 115 will be described. A two-dimensional image (zx image) of the measurement object 115 is obtained by scanning a two-dimensional area of the measurement object 115 with the beam spot 140 . For example, the control unit 116 controls the two-dimensional scanner 107 constituting the scanning unit 159 to move the galvanomirror 108 (first scanning unit) to repeatedly scan in the x direction, and the galvanomirror 108 reaches the folding position. Each time, the control unit 116 operates the lens actuator 117 to move the lens 113 (second scanning unit) by a predetermined amount (approximately the diameter of the focused beam spot 140 in the z direction) in the z direction. A two-dimensional image (zx image) can be obtained. Note that, for example, scanning in the x direction moves the beam spot 140 (irradiation area) faster than scanning in the z direction.

The three-dimensional image of the object to be measured can be obtained by repeating the procedure of moving the lens 113 in the y direction by a predetermined amount (approximately the spot diameter of the focused signal light) after obtaining the zx image by the scanning method described above. can be done. Alternatively, after acquiring the zx image by scanning the galvanomirror 108 and the lens 113, the procedure of moving the measurement object 115 or the entire optical measurement apparatus 1 in the y direction by an electric stage or the like may be repeated. In this embodiment, z-scanning is performed by scanning the lens 113. For example, at least one lens is further inserted in front of the lens 113, and the focal position is scanned by scanning the lens. Alternatively, the two-dimensional scanner 107 may be used to move in the y direction.

As described above, the optical measurement device 1 of the present disclosure uses the lens actuator 117 and the two-dimensional scanner 107 to scan a two-dimensional region or a three-dimensional region, and acquire time-dependent change information of the region. It is also possible to output as a two-dimensional or three-dimensional image having the acquired amount of change over time in the luminance value of each pixel.

The numerical aperture of the lens 113 that collects the signal light to form the beam spot 140 in the measurement object 115 is preferably 0.3. Further, when the numerical aperture of the lens 113 is increased to 0.4 or more, high resolution in the Z direction can be obtained. Further, when the numerical aperture of the lens 113 is set to 0.3 to 0.4, the depth of focus of the lens can be increased, so that the measurable depth range in the measurement object 115 can be expanded.

For the light source 101, a laser light source is used in which the coherence length of the emitted laser light is longer than the change in the optical path length of the signal light generated by the scanning of the lens 113 in the optical axis direction. By doing so, even if an optical path length difference occurs between the signal light and the reference light when the lens 113 is scanned in the optical axis direction, a decrease in interference amplitude can be suppressed. Therefore, by driving the lens 113 in the z-direction, it becomes possible to move the position of the beam spot 140 in the z-direction.

The shape of beam spot 140 may be circular, elliptical, linear, rectangular, or the like. When the circular beam spot 140 is used, a normal optical system configuration can be used, so the device configuration of the optical measurement device 1 can be constructed simply. A linear or rectangular beam spot can be realized by using a cylindrical lens or the like, and since the signal light intensity in the beam spot 140 hardly changes in the x direction, it is easy to obtain a stable signal during scanning.

Also, the size of the beam spot 140 in the x direction is at least two or more in the image formed by the optical system on the photodiode arrays 148, 149, 150, and 151 in the direction corresponding to the x direction. is the size including the photodetector element. That is, where M is the magnification of the optical system, L _max is the distance between the most distant photodetecting elements used for detection in each photodiode array, and D _x is the size of the beam spot 140 in the x direction, D _x ≧L _max /M.

Also, the size of the beam spot 140 in the y direction may be smaller than the size in the x direction. Desirably, the size in the y direction is such that in the image formed by the optical system on the photodiode arrays 148, 149, 150, 151, the size in the direction corresponding to the y direction is within the light receiving surface of the photodetector. It's size. That is, D _y ≦L _y /M where M is the magnification of the optical system, L _y is the width of the photodetector in the direction corresponding to the y direction, and D _y is the size of the beam spot 140 in the y direction. In this case, the information about the intensity of the signal light contributes to the detected signal thoroughly, so that a signal with a high SN ratio can be obtained.

Such an elliptical beam spot 140 is obtained by making the signal light incident on the lens 113 as a beam with an elliptical cross section. If the cross-sectional shape of the beam incident on the lens 113 is an ellipse with the y direction longer than the x direction, the numerical aperture at the time of condensing is greater in the y direction than in the x direction, and the shape of the beam spot 140 on the xy plane is It becomes an ellipse with the x direction longer than the y direction. By changing the y-direction diameter and the x-direction diameter of the elliptical beam of the signal light, the elliptical diameter of the beam spot 140 in the x-direction and the y-direction can also be changed. Adjustment of the elliptical beam shape is made possible by a beam shaping prism 103 inserted in the optical path of the signal light.

Moreover, if an element that outputs an elliptical beam, such as a semiconductor laser, is used as the light source 101, the beam shaping prism 103 can be omitted. Further, when the elliptical beam spot 140 is formed by this method, even if the x direction of the beam spot 140 is enlarged, defocusing of the beam spot in the z direction can be suppressed, and the beam spot can be enlarged. It is possible to minimize the deterioration of spatial resolution during measurement caused by

Ideally, the signal light incident on and reflected from the measurement object 115 becomes a beam having the same diameter as the incident signal light. , which may result in a beam with a larger diameter than at the time of incidence. By making the beam diameter of the reference light larger than the beam diameter of the signal light, all components of the reflected signal light can contribute to interference and signal generation even in such a case. As a result, the SN ratio is improved by increasing the amount of signal light, and the resolution is improved by increasing the effective numerical aperture.

<Modification of Example 1>
FIG. 5 is a schematic diagram showing the configuration of the reference optical system 500 that expands the beam diameter described above. In FIG. 5, the vertical direction is the z direction, the horizontal direction is the x direction, and the direction perpendicular to the paper surface is the y direction. A laser beam emitted from the light source 101 is split into an s-polarized signal beam and a p-polarized reference beam by the polarization beam splitter 501 . The reference light has its beam diameter expanded by a beam expander 506 consisting of two lenses 502 and 503, is reflected by mirrors 504 and 505 to change direction, and is converted from p-polarized light to s-polarized light by a λ/2 plate 507. , enter the polarizing beam splitter 106 . After passing through the polarization beam splitter 106, the signal light returns through an optical system similar to that shown in FIG. 1 and is combined with the reference light at the polarization beam splitter 106 to generate combined light. Since the subsequent operations are the same as those in FIG. 1, description thereof is omitted.

<Example 2>
FIG. 6 is a diagram showing a basic configuration example of the optical measurement device 2 according to the second embodiment. In FIG. 6, the vertical direction in the drawing is the z direction, the horizontal direction is the x direction, and the direction perpendicular to the plane of the drawing is the y direction.

The optical measuring device 2 of the second embodiment has a configuration in which the laser light emitted from the light source 101 is split into the signal light and the reference light, and the combined light is generated by recombining the light. Same as 1. The optical measuring device 2 of the second embodiment differs from the optical measuring device 1 of the first embodiment in that it uses the photodiode array 607 in which a plurality of photodetectors are arranged in a line to output a current proportional to the intensity of the interference light. different.

In the optical measurement device 2 of the second embodiment, the generated combined light is first split into ±1st-order diffracted lights by the diffraction grating 602 to generate the first split combined light and the second split combined light. . These synthesized lights are arranged such that the phase difference between the s-polarized component and the p-polarized component of the first branched synthesized light and the phase difference between the s-polarized component and the p-polarized component of the second branched synthesized light are different by 90 degrees. pass through the phase plate 603 .

Thereafter, the first branched combined light and the second branched combined light have their polarization directions rotated by the λ/2 plate 604 set at approximately 22.5 degrees with respect to the xz plane, and are polarized by the Wollaston prism 605. The separation produces four interfering beams whose phases of interference differ from each other by approximately 90 degrees. These interfering lights are condensed by condensing lens 606 and form images of beam spots 140 on four regions 608 , 609 , 610 , 611 each consisting of a plurality of photodetectors on photodiode array 607 . As a result, each of the interfering lights is converted into a current by each photodetector, and a pair of currents from regions corresponding to the interfering lights with a phase relationship different by 180 degrees are differentially detected by the differential detection circuits 134 and 135 .

The detection signal is calculated by the signal processing unit 136 to obtain a signal proportional to the absolute value of the amplitude of the signal light, independent of the phase. Since the function of the interference optical system 601 is the same as that of the interference optical system 132 of Example 1, description thereof is omitted here. As described above, by adopting a configuration in which a single photodiode array 607 receives and detects a plurality of the four interference lights with different interference phases, the number of parts can be reduced.

That is, the optical measurement device 2 of the second embodiment is smaller than the optical measurement device 1 of the first embodiment because it has fewer parts in the interference optical system and is smaller. Become.

<Example 3>
FIG. 7 is a schematic diagram showing the configuration of the optical measurement device 3 of Example 3. As shown in FIG. In FIG. 7, the vertical direction in the figure is the z direction, the horizontal direction is the x direction, and the direction perpendicular to the paper surface is the y direction. The same members as those shown in FIG. 2 are denoted by the same reference numerals, and descriptions thereof are omitted.

The optical measurement device 3 of Example 3 is different in type from the OCT device of Example 1, and is obtained by applying the technology of the present disclosure to a type of OCT device that uses a low coherence light source. Light emitted from a light source 701, which is a low-coherence light source such as an SLD (Super Luminescence Diode), is converted into parallel light by a collimating lens 702, and a beam shaping prism 703 forms a cross-sectional shape of the beam into an elliptical shape in which the y direction is longer than the x direction. , and split into a signal light and a reference light by a beam splitter 706 .

The signal light is condensed by a lens 713 to form an elliptical beam spot 740 at the condensed position on the measuring object 115 held by the sample stage 739 . Here, since the cross-sectional shape of the beam incident on the lens 713 is an ellipse whose y direction is longer than that of the x direction, the numerical aperture at the time of condensing is greater in the y direction than in the x direction, and the beam spot 740 on the xy plane is The shape of is an ellipse with the x direction longer than the y direction.

The signal light reflected or diffused by the measurement object 715 is beamed by the lens 713 and returned to the beam splitter 706 . The reference light is reflected by the mirror 719 and similarly returns to the beam splitter 706, where it is multiplexed with the signal light and interferes to generate combined light. The combined light is condensed by condensing lens 722 and forms image 753 of beam spot 740 on photodiode array 724 . The image 753 is detected by a plurality of photodetector elements 748 of the photodiode array 724 and a plurality of detected signals 737 are sent to the signal processing section 736 .

In the optical measurement device 3 of the third embodiment, a low coherence light source is used, and only the components having the same optical path length as the reference light among the components included in the signal light interfere to give the signal 737. can be obtained using the z-position of . The optical measurement device 3 performs z-scanning of the measurement point by driving the actuator 760 by the control unit 716 and scanning the mirror 719 during measurement. Also, the optical measurement device 3 performs xy scanning with a two-dimensional scanner 759 controlled by the control unit 716 . A two-dimensional image or a three-dimensional image of the measurement object 715 can be acquired by combining the above operations.

In the optical measurement device 3 of Example 3, the two-dimensional scanner 759 scans in the x direction during measurement, and the signals from the plurality of photodetectors are compared in the same manner as in Example 1, thereby scanning in the x direction. Time-dependent change information can be obtained with a time resolution shorter than the period. Also, the optical measurement device 3 of the third embodiment can achieve the same functions as those of the first embodiment with a smaller number of parts than the optical measurement device 1 of the first embodiment, and can provide a more compact device. .

<Example 4>
FIG. 8 is a schematic diagram showing the configuration of the optical measurement device 4 of Example 4. As shown in FIG. In FIG. 8, the vertical direction in the drawing is the z-direction, the horizontal direction is the x-direction, and the direction perpendicular to the plane of the drawing is the y-direction. The same members as those shown in FIG. 2 are denoted by the same reference numerals, and descriptions thereof are omitted.

As shown in FIG. 8, the optical measuring device 4 of the fourth embodiment differs from the light of the first embodiment in that the optical observation unit 801 and the light detection unit 804 are connected by a polarization-maintaining optical fiber bundle 803 . It differs from the measuring device 1 . The polarization-maintaining optical fiber bundle 803 is detachably fixed to the fiber connection portion 807 of the optical observation unit 801 and the fiber connection portion 808 of the light detection unit 804 .

The optical measuring device 4 of Example 4 has the same configuration and functions as those of Example 1 until the laser light emitted from the light source 101 is split into two and combined again to generate combined light. The generated combined light forms an image 809 at the incident end of the polarization-maintaining optical fiber bundle 803 by a condenser lens 802 and is coupled to the polarization-maintaining optical fiber bundle 803 . The spatial distribution information of the combined light image 809 is transmitted by the polarization-maintaining optical fiber bundle 803 to the photodetection unit 804 and presented as an image 810 at the output end of the polarization-maintaining optical fiber bundle 803 . The combined light emitted from the image 810 is converted into parallel light by the collimator lens 805 and then enters the interference optical system 132 . Since the subsequent configuration and functions are the same as those of the first embodiment, the description thereof is omitted.

As described above, in the optical measurement device 4 of Example 4, the photodetection unit 804 and the optical observation unit 801 are connected by the polarization maintaining fiber bundle 803 . Therefore, when measuring a large object such as a human body, the measurement can be facilitated by bringing only the optical observation unit 801 closer to the object 115 to be measured. Also, the polarization-maintaining optical fiber bundle 803 can be easily attached and detached. Therefore, for example, when the photodetection unit 804 fails, it is possible to replace only the photodetection unit 804, and it is not necessary to replace the entire apparatus. Therefore, the running cost of the optical measuring device 4 is reduced.

<Example 5>
FIG. 9 is a schematic diagram showing movement of beam spots 940, 957, and 958 on the object to be measured. Elements that are the same as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted.

The optical measuring device of Example 5 is realized by the same member configuration as the optical measuring device 1 of Example 1, but differs from Example 1 in that the installation angle of the beam shaping prism 103 is rotated by 90 degrees. In this case, the cross-sectional shape of the beam incident on the lens 113 is an ellipse in which the x direction is longer than the y direction. Therefore, the numerical aperture in the x direction when light is condensed is larger than in the y direction, and as shown in FIG. Longer oval shape.

A beam spot 940 scans a two-dimensional area of the measurement object 115 to acquire a two-dimensional image (xy image) of the measurement object 115 . While repeatedly scanning in the scanning direction 152 at a constant scanning speed v and a scanning period Tx, when the turn-around position 901 in the scanning direction 152 is reached, the beam spot 940 is moved in the sub-scanning direction 952, here in the _y direction, with a scanning line width δy. only move. As a result, beam spot 940 follows trajectory 902 . A solid line portion of the trajectory 902 represents a section scanned while measuring, and a broken line section represents a section scanned without measuring. A beam spot 940 located at the hatched position at time t ₁ is located at a planned position 957 at time t ₁ +T _x and at a planned position 958 at time t ₁ +2T _x . Thus, in the scanning method of the fifth embodiment, the scanning returns to the same x position (here, _{x 1} ) every scanning period Tx.

In the example shown in FIG. 9, scanning is performed so that the scanning line width .delta.y and the interval .delta.x' between the four measurement areas 903 match. In this case, the position measured by A ₁ in the measurement area at time t ₁ is measured by A ₂ in the measurement area at time t ₁ +T _x , and A ₃ in the measurement area at time t ₁ +2T _x . Thus, it is possible to acquire temporal change information with a time resolution equal to the scanning period _Tx . Furthermore, in this case, for example, by comparing the measurement result of A ₁ of the measurement area at time t ₁ with the measurement result of A ₃ of the measurement area at time t ₁ +2T _x , the elapsed time equal to n times the scanning period T _x Change information can also be acquired.

When the scanning line width δy and the interval δx′ between the _four measurement areas 903 are δy=δx′ _/ m, the position measured by A1 in the measurement area at time t1 is measured again by _A2 in the measurement area. The time to do so is time t ₁ +mT _x , and the time resolution is mT _x .

When the scanning line width δy and the interval δx′ between the four measurement areas 903 are δy=δx′×m (= _{2), the position measured by A1 in the measurement area at time t 1 is time t 1 + T x} The position measured by A ₃ in the measurement area at t ₁ and A ₂ in the measurement area at time t 1 will be measured by A ₄ in the measurement area at time t ₁ +T _x , respectively, and the time resolution is T _x However, since δy can be increased m times, the time required to scan and measure a predetermined area can be shortened.

As described above, by using the beam spot 940 having a long diameter in the direction perpendicular to the scanning direction 152 and a plurality of detectors provided in the direction corresponding to the direction perpendicular to the scanning direction 152, the scanning period T Information can be obtained with a temporal resolution longer than _x .

Also, by arranging the ellipse so that the long axis direction is inclined (for example, 45 degrees) with respect to the scanning direction 152, it is possible to obtain a time resolution other than an integer multiple of the scanning period _Tx .

<Modification of Example 5>
FIG. 10 is a diagram showing a scanning method in which a plurality of measurement areas are defined in both the x-direction and the y-direction. FIG. 10 shows measurement areas 1003 (A ₁₁ , A ₁₂ , A ₁₃ , A ₁₄ , A ₂₁ , A ₂₂ , A ₂₃ , A ₂₄ ) are shown. By performing a scan similar to the scan described above, in this example, time-varying information with both temporal resolution shorter and longer than the scanning period _Tx can be acquired simultaneously.

101, 701 Light sources 102, 702 Collimating lenses 103, 703 Beam shaping prism 104 ND filter 105 λ/2 plates 106, 706 Polarizing beam splitter 107 Two-dimensional scanners 108, 109 Galvanometer mirrors 110, 111 Lenses 112, 118 λ/4 plate 113 , 713 lens 114 cover glass 115, 715 measurement object 116, 716 control unit 117 lens actuator 119, 719 mirror 120 half beam splitter 121, 127 λ/2 plate 122, 128, 722 condenser lens 123, 129 polarization beam splitter 124 , 125, 130, 131, 724 photodiode array 126 λ/4 plate 132 interference optical system 134, 135 differential detection circuits 136, 736 signal processing units 137, 138, 737 signals 139, 739 sample stages 140, 740, 940, 1040 beam spot 141 signal light 142 reflected signal light 143, 743 reference light 144, 145, 146, 147 interference light 148, 149, 150, 151, 748 photodetector 152 scanning direction 153, 154, 155, 156, 753 Images 157, 158, 957, 958, 1057, 1058 Planned positions of future beam spots 159, 759 Scanning units 190, 790 Light source units 191, 791 Reference optical systems 301, 302 Directions 303, 903, 1003 in which photodetectors are arranged Measurement Regions 304, 305, 306, 307 Differential detection circuits 401, 302, 403, 404 Measurement region position trace 500 Reference optics for expanding beam diameter 501 Polarizing beam splitters 502, 503 Lenses 504, 505 Mirrors 506 Beam expander 507 λ/2 plate 601 Interference optical system 602 Diffraction grating 603 Phase plate 604 λ/2 plate 605 Wollaston prism 606 Condensing lens 607 Photodiode array 608, 609, 610, 611 Area 760 consisting of a plurality of photodetecting elements Actuator 801 Light Observation unit 802 Condensing lens 803 Polarization-maintaining optical fiber bundle 804 Light detection unit 805 Collimating lens 807 Fiber connecting parts 809 and 810 Image

Claims (14)

a light source;
an optical splitter that splits light emitted from the light source into reference light and signal light;
a scanning unit that irradiates the signal light to scan an object to be measured;
an optical system that combines the signal light reflected or scattered by the measurement object and the reference light to generate interference light;
a photodetector that receives the interference light generated by the optical system and converts it into an electrical signal;
a signal processing unit that calculates the intensity of the signal light based on the electrical signal converted by the photodetector;
An optical measurement device comprising
wherein the photodetector detects the signal light by means of a plurality of photodetection elements associated with each of a plurality of measurement regions overlapping an irradiation region of the signal light;
The signal processing unit calculates the intensity of the signal light detected by each of the plurality of photodetection elements,
The scanning unit changes the irradiation area of the signal light with which the measurement object is irradiated to a part of the plurality of measurement areas at a first time point and another part of the plurality of measurement areas at a second time point. scanning the measurement object by moving it so as to overlap with
Optical measurement device. In the optical measurement device according to claim 1,
The optical measurement device includes a plurality of optical elements,
The scanning unit scans the measurement object along a direction in which each of the plurality of measurement regions is arranged,
Each of the plurality of optical elements is arranged in an optically conjugate positional relationship with the plurality of measurement regions,
Optical measurement device. In the optical measurement device according to claim 1,
The signal processing unit controls the intensity of the signal light detected by the photodetector corresponding to a part of the plurality of measurement regions at the first time point and another one of the plurality of measurement regions at the second time point. processing the intensity of the signal light detected by the photodetector corresponding to the part as time-series information of the same part of the measurement object;
Optical measurement device. In the optical measurement device according to claim 3,
The time interval between the first time point and the second time point is the interval between a part of the plurality of measurement areas and another part of the plurality of measurement areas, and the scanning unit moves the irradiation area. is the value divided by the velocity,
Optical measurement device. In the optical measurement device according to claim 2,
The scanning unit comprises: a first scanning unit that scans the measurement object in a first direction that is a direction in which the plurality of measurement regions are arranged; A second scanning unit that scans in a different second direction,
The first scanning unit moves the irradiation area faster than the second scanning unit,
Optical measurement device. In the optical measurement device according to claim 1,
The shape of the irradiation region is such that the diameter in the scanning direction in which the measurement object is scanned is larger than the diameter in the direction perpendicular to the scanning direction.
Optical measurement device. In the optical measurement device according to claim 6,
At least one point on the optical path in the scanning unit, the shape of the beam of the signal light is such that the diameter in the scanning direction is smaller than the diameter in the direction perpendicular to the scanning direction.
Optical measurement device. In the optical measurement device according to claim 1,
wherein the irradiation area includes the plurality of measurement areas;
Optical measurement device. In the optical measurement device according to claim 1,
The signal processing unit calibrates and calculates the intensity of the signal light corresponding to each of the plurality of measurement regions.
Optical measurement device. In the optical measurement device according to claim 1,
a plurality of the photodetectors;
an interference optical system that disperses the interference light into three or more interference lights having mutually different interference phases;
with
The phase difference between the interference phases of the signal light and the reference light in the plurality of photodetectors of the three or more interference lights is an integer multiple of approximately 90 degrees, and the phase difference is approximately 180 degrees. the pair of output currents corresponding to the light are input to a differential detection circuit that performs current differential detection;
Optical measurement device. In the optical measurement device according to claim 10,
The number of the photodetectors is four,
The interference optical system splits the interference light into four interference lights having different interference phases,
Each pair of interference light having a phase difference of approximately 180 degrees between the two sets of interference phases is input to the differential detection circuit.
Optical measurement device. In the optical measurement device according to claim 1,
further equipped with a fiber optic bundle,
The optical system that generates the interference light causes the combined interference light to enter an optical fiber connection portion to which one end of the optical fiber bundle is connected.
Optical measurement device. In the optical measurement device according to claim 1,
The photodetector detects the signal light with three or more of the photodetectors,
Optical measurement device. A sample observation method using an optical measurement device that acquires an optical coherence tomogram,
irradiating an object to be measured with signal light, and synthesizing the reflected or scattered signal light and reference light to generate interference light;
a step of detecting the signal intensity of the interference light at a first point in time using a plurality of photodetectors corresponding to each of a plurality of measurement regions overlapping the irradiation region of the signal light;
moving the irradiation region so that a portion of the plurality of measurement regions at the first time point and another portion of the plurality of measurement regions at a second time point overlap;
detecting the signal intensity of the interference light at the second time point by the plurality of photodetection elements corresponding to each of the plurality of measurement regions;
Sample observation method including.

Images