JP4542302B2 - Confocal microscope system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is controlled in a confocal microscope system using a photomultiplier tube as the light receiving element, in order to prevent damage to the light-receiving element, the gain of the light receiving element so that the light current of the light receiving element does not exceed the maximum rated current about a confocal microscope system using the gain limiter circuitry for.
[0002]
[Prior art]
In a confocal microscope, light from a sample is received by a light receiving element via a confocal optical system, and information such as a confocal image (hyperfocal depth image) and height distribution of the sample is acquired based on the amount of light received. Is done. For example, when the relative distance between the sample placed on the stage and the objective lens is changed in the optical axis direction, the amount of light incident on the light receiving element via the confocal optical system, that is, the amount of received light changes, The amount of light received is maximized when the surface is in focus. Therefore, the height information of the surface of the sample is calculated from the relative distance between the sample and the objective lens when the maximum amount of received light is obtained, and the height distribution of the surface of the sample is acquired by scanning the surface of the sample with light. be able to.
[0003]
The acquired height distribution is displayed on the screen of the display device by, for example, three-dimensional display. Alternatively, the height distribution replaced with a luminance distribution or a color distribution is displayed on the screen. A CRT (cathode ray tube) or LCD (liquid crystal display device) is used as a display device, and a confocal microscope is connected to a control controller, a display device, a console, and the like to constitute a confocal microscope system.
[0004]
Also, by combining the information on the amount of light received when each point (pixel) on the sample surface is in focus (that is, the maximum luminance information of each pixel), a black and white image of the sample surface with a very deep focal depth can be obtained. Can do. This image is a so-called ultra-deep image.
[0005]
Furthermore, a color image of the sample surface in the same range as the confocal image can be obtained by separating a part of the light from the sample halfway from the confocal optical system and receiving it with the color imaging device. Unlike a confocal image, this color image includes a focused portion and a blurred portion according to the unevenness of the sample surface. It is also possible to obtain a color image that is substantially in focus at each pixel by performing a synthesis process that replaces the luminance signal of the color image with the luminance signal of the confocal image.
[0006]
In the confocal microscope system as described above, a photomultiplier tube (photomultiplier tube) is often used as a light receiving element. A photomultiplier tube is a vacuum tube composed of a photocathode, a secondary electron multiplier mechanism, and an anode. Photoelectrons emitted when light enters the photocathode are multiplied and collected by the anode, and output current is obtained. Take out to the outside. By using a multistage secondary electron emission surface, a large multiplication factor (high light receiving sensitivity) can be obtained.
[0007]
In a light intensity detection circuit such as a confocal microscope system using a photomultiplier tube as a light receiving element, when light exceeding a predetermined level is incident on a photomultiplier tube with high light receiving sensitivity, a photocurrent exceeding the maximum rating is output and the photoelectron is output. There is a risk of damage (damage) to the multiplier. Further, for example, in a confocal microscope system, the above-described confocal image or ultra-deep image is whitened as a result of saturation of the output current of the light amount detection circuit, which is a subsequent circuit, due to the signal from the light receiving element (so-called whiteout) ) Occurs.
[0008]
Therefore, in a conventional confocal microscope system, for example, when the light reflectance of a sample is high, when a saturation phenomenon occurs when light exceeding a predetermined level enters the photomultiplier tube, the measurement is temporarily stopped. Some of them automatically adjust the amount of emitted light and adjust the gain.
[0009]
[Problems to be solved by the invention]
However, if the output light amount adjustment or gain adjustment is automatically entered during the measurement as described above, the user will have to wait until the automatic adjustment is completed, which is felt stressful to the user. In some cases. In addition, when a test measurement for determining measurement conditions is performed before the actual measurement, such automatic adjustment is unnecessary, and it may be annoying. Further, even if the confocal image obtained by the confocal microscope has a whiteout due to saturation almost on the entire surface, image information desired by the user may be obtained on a part of the screen.
[0010]
In view of the above-described conventional problems, the present invention operates the output current limit for protecting the light receiving element without the user being conscious of the measurement, and outputs carelessly for the measurement conditions desired by the user. An object of the present invention is to provide a gain limiter circuit in which current limiting is less effective and a confocal microscope system using the gain limiter circuit.
[0011]
A confocal microscope system according to a first aspect of the present invention includes a light source and a light receiving element that outputs a photocurrent value corresponding to a received light amount and a predetermined gain, and scans a sample with light from the light source. The light receiving element receives light or reflected light from the sample at each point within the scanning range via a confocal optical system, and the surface of the sample is received based on light reception information of the light receiving element. A confocal microscope system for acquiring height information and light amount information,
A digital value corresponding to the photocurrent value from the light receiving element is output, and when the photocurrent value exceeds a predetermined saturation current value smaller than the maximum rated current value of the light receiving element, the digital value is saturated and constant. A light amount detection circuit that outputs a digital value of
A control unit for acquiring height information and light amount information of the surface of the sample at each point within the scanning range based on the digital value;
In order to prevent damage to the light receiving element due to the photocurrent value exceeding the maximum rated current value, a threshold value that is smaller than the maximum rated current value and within a range greater than the saturation current value; comparing the photocurrent value from the light receiving element, when the photocurrent value is smaller than the threshold value so as not to affect the gain of the previous SL light receiving element, the photocurrent value is the threshold value lower the gain of the light receiving element to limit a further increase of the photocurrent value upon reaching, the when the photocurrent value gain down of the light receiving element becomes rather smaller than the threshold value so as to maintain the photocurrent value to the threshold value greater than the saturation current value, the gain limiter circuit for controlling the gain of the light receiving element,
It is characterized by having.
[0012]
The confocal system according to claim 2 of the present invention is the confocal microscope system according to claim 1, wherein the gain limiter circuit includes a reference voltage value corresponding to the threshold value and the light receiving element. An operational amplifier that outputs a control signal for controlling the gain in accordance with a result of comparing the signal voltage value according to the photocurrent value from, and a diode provided at a subsequent stage of the operational amplifier, The diode is installed in a direction in which the operational amplifier and the light receiving element are not electrically connected when the signal voltage value is smaller than the reference voltage value, and the gain limiter when the signal voltage value is smaller than the reference voltage value. The circuit does not affect the gain of the light receiving element .
[0013]
According to the gain limiter circuit of the electron multiplier having the above-described configuration and the confocal microscope system using the same, the threshold at which the gain limiter circuit operates is smaller than the maximum rated current, and the light amount detection circuit Since it is set within a range larger than the saturation current, the current limit to prevent damage to the electron multiplier works reliably, while flexibly responding to the measurement conditions desired by the user and limiting the output current during the measurement Work less carelessly. For example, even if the confocal image obtained with a confocal microscope has whiteout due to saturation almost entirely, the output current is limited as long as the output current of the light receiving element does not exceed a threshold value greater than the saturation current. Will not work. Therefore, measurement can be continued even under measurement conditions in which whiteout due to saturation occurs on almost the entire confocal image, and desired image information can be obtained on a part of the screen.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0015]
FIG. 1 shows a schematic configuration of a confocal microscope system according to an embodiment of the present invention. The confocal microscope system 1 includes a confocal microscope having a confocal optical system 2 and a non-confocal optical system 3, a controller including a laser driving circuit 44, a confocal signal processing circuit 41, a control unit 46, and the like, and is connected to the controller. The display device 47 and the input device 48 are provided.
[0016]
First, the confocal optical system 2 of the confocal microscope and its signal processing will be described. The confocal optical system 2 includes a light source 10 for irradiating a sample wk with monochromatic light (for example, laser light), a first collimating lens 11, a polarizing beam splitter 12, a quarter wavelength plate 13, a horizontal deflection device 14a, and vertical deflection. A device 14b, a first relay lens 15, a second relay lens 16, an objective lens 17, an imaging lens 18, a pinhole plate 9, a light receiving element 19 and the like are included.
[0017]
As the light source 10, for example, a semiconductor laser that emits red laser light is used. The laser light emitted from the light source 10 driven by the laser driving circuit 44 passes through the first collimating lens 11, the optical path is bent by the polarization beam splitter 12, and passes through the quarter wavelength plate 13. Thereafter, the light is deflected in the horizontal (lateral) direction and the vertical (longitudinal) direction by the horizontal deflecting device 14a and the vertical deflecting device 14b, passes through the first relay lens 15 and the second relay lens 16, and is sampled by the objective lens 17. The light is condensed on the surface of the sample wk placed on the stage 30.
[0018]
The horizontal deflection device 14a and the vertical deflection device 14b are each configured by a galvanometer mirror, and scan the surface of the sample wk with the laser light by deflecting the laser light in the horizontal and vertical directions. For convenience of explanation, the horizontal direction is referred to as the X direction, and the vertical direction is referred to as the Y direction. The objective lens 17 is driven in the Z direction (optical axis direction) by the objective lens moving mechanism 40. Thereby, the relative position of the focal point of the objective lens 17 and the sample wk in the optical axis direction can be changed.
[0019]
However, the relative position in the optical axis direction between the focal point of the objective lens 17 and the sample wk can be changed by other methods. For example, instead of driving the objective lens 17 in the Z-axis direction, the sample stage 30 may be driven in the Z-axis direction. Or the structure which moves the focus of the objective lens 17 to a Z-axis direction by inserting the lens from which a refractive index changes between the objective lens 17 and the sample wk is also possible. The sample stage 30 can be displaced in the X, Y and Z directions by manual operation.
[0020]
The laser beam reflected by the sample wk follows the above optical path in reverse. That is, it passes through the objective lens 17, the second relay lens 16, and the first relay lens 15, and again passes through the quarter wavelength plate 13 through the horizontal deflection device 14a and the vertical deflection device 14b. As a result, the laser beam passes through the polarization beam splitter 12 and is collected by the imaging lens 18. The condensed laser light passes through the pinhole of the pinhole plate 9 disposed at the focal position of the imaging lens 18 and enters the light receiving element 19.
[0021]
As the light receiving element 19, a photomultiplier tube (photomultiplier tube) is used. A photomultiplier tube is a vacuum tube composed of a photocathode, a secondary electron multiplier mechanism, and an anode. Photoelectrons emitted when light enters the photocathode are multiplied and collected by the anode, and output current is obtained. Take out to the outside. By using a multistage secondary electron emission surface, a large multiplication factor (high light receiving sensitivity) can be obtained. An electrical signal corresponding to the amount of received light is given to the control unit 46 as a digital value through a confocal signal processing circuit 41 including an output amplifier, a gain limiter circuit, an AD converter, and the like.
[0022]
With the confocal optical system 2 configured as described above, the height (depth) information of the surface of the sample wk can be acquired. The principle will be briefly described below.
[0023]
As described above, when the objective lens 17 is driven in the Z direction (optical axis direction) by the objective lens moving mechanism 40, the relative distance between the focal point of the objective lens 17 and the sample wk in the optical axis direction changes. Then, when the focal point of the objective lens 17 is focused on the surface of the sample wk, the laser light reflected on the surface of the sample wk is condensed by the imaging lens 18 through the above optical path, and almost all the laser light is collected. Passes through the pinhole of the pinhole plate 9. Therefore, at this time, the amount of light received by the light receiving element 19 is maximized. On the contrary, in a state where the focus of the objective lens 17 is deviated from the surface of the sample wk, the laser light collected by the imaging lens 18 is focused at a position deviated from the pinhole plate 9, so that some lasers Only light can pass through the pinhole. As a result, the amount of light received by the light receiving element 19 is significantly reduced.
[0024]
Therefore, if the received light amount of the light receiving element 19 is detected while driving the objective lens 17 in the Z direction (optical axis direction) at any point on the surface of the sample wk, the objective lens 17 when the received light amount becomes maximum. The position in the Z direction (the relative position of the focal point of the objective lens 17 and the sample wk in the optical axis direction) can be uniquely determined as height information.
[0025]
Actually, each time the objective lens 17 is moved by one step (one pitch), the surface of the sample wk is scanned by the horizontal deflection device 14a and the vertical deflection device 14b to obtain the amount of light received by the light receiving element 19. When the objective lens 17 is moved in the Z direction from the lower end to the upper end of the measurement range, received light amount data that changes according to the position in the Z direction is obtained for each point (pixel) in the scanning range.
[0026]
FIG. 2 is a graph showing an example of received light amount data that changes in accordance with the position of the objective lens 17 in the Z direction. Based on such received light amount data, the maximum received light amount and the position in the Z direction at that time are obtained for each point (pixel). Therefore, the distribution of the surface height of the sample wk on the XY plane is obtained. This process is executed by the control unit 46 using a microcomputer.
[0027]
The obtained surface height distribution information can be displayed on the monitor screen of the display device 47 by several methods. For example, the height distribution (surface shape) of the sample can be displayed three-dimensionally by three-dimensional display. Alternatively, it can be displayed as a two-dimensional distribution of brightness by converting the height data into luminance data. By converting the height data into color difference data, the height distribution can also be displayed as a color distribution.
[0028]
Further, a surface image (black and white image) of the sample wk is obtained from a luminance signal having the received light amount obtained for each point (pixel) in the XY scanning range as luminance data. If a luminance signal is generated using the maximum amount of light received at each pixel as luminance data, an image having a very deep focal depth in focus at each point having a different surface height, a so-called hyperfocus depth image can be obtained. In addition, when the height (Z-direction position) at which the maximum light reception amount is obtained at any target pixel is fixed, the light reception amount of the pixel of the target pixel portion and the portion having a large difference in height is significantly reduced. A bright image is obtained only at the same height.
[0029]
Next, the non-confocal optical system 3 provided in the confocal microscope and its signal processing will be described. The non-confocal optical system 3 includes a white light source 20, a second collimating lens 21, a first half mirror 22, a second half mirror 23, and a color for irradiating the sample wk with white light (illumination light for photographing a color image). A CCD (image sensor) 24 and the like are included. Further, the non-confocal optical system 3 shares the objective lens 17 of the confocal optical system 2, and the optical axes of the two optical systems 1 and 2 partially coincide.
[0030]
For example, a white lamp is used as the white light source 20, but a dedicated light source may not be provided, and natural light or room light may be used. White light emitted from the white light source 20 passes through the second collimating lens 21, the optical path is bent by the first half mirror 22, and is condensed on the surface of the sample wk placed on the sample stage 30 by the objective lens 17. .
[0031]
The white light reflected by the sample wk passes through the objective lens 17, the first half mirror 22, and the second relay lens 16, is reflected by the second half mirror 23, and enters the color CCD 24 to form an image. The color CCD 24 is provided at a position conjugate to or close to the conjugate with the pinhole of the pinhole plate 9 of the confocal optical system 2. The color image picked up by the color CCD 24 is read out by the CCD drive circuit 43 and is given to the control unit 46 through the color image signal processing circuit 42. The color image thus obtained is displayed on the monitor screen of the display device 47 as an enlarged color image for observing the sample wk.
[0032]
In addition, by combining an image with a deep focal depth obtained by the confocal optical system 2 and a normal color image obtained by the non-confocal optical system 3, a color having a deep focal depth that is substantially in focus at all pixels. Images can also be generated and displayed. For example, a color confocal image can be easily generated by replacing the luminance signal constituting the color image obtained by the non-confocal optical system 3 with the luminance signal of the confocal image obtained by the confocal optical system 2. be able to.
[0033]
The controller including the control unit 46 also controls the processing related to the color image as described above. An input device 48 such as a console (console console) and a display device 47 such as a CRT (cathode ray tube) or LCD (liquid crystal display device) are connected to the controller. A pointing device such as a mouse is also connected as the input device 48.
[0034]
The user can set various measurement parameters using the input device 48 in accordance with the guidance displayed on the screen of the display device 47. For example, the Z direction movement range (measurement range) and movement pitch of the objective lens 17 are set. Alternatively, the light receiving sensitivity (PMT gain) of the light receiving element 19 and the attenuation amount by the ND filter are set according to the light reflectance of the surface of the sample wk, so that the brightness of the confocal image becomes appropriate. . The shutter speed, gain, and white balance for obtaining a color image by the color CCD 24 are set.
[0035]
FIG. 3 is a block diagram showing the configuration of the confocal signal processing circuit 41 that processes the output signal of the light receiving element 19. The confocal signal processing circuit 41 includes an amplifier 51, a gain limiter circuit 52, and an AD converter 53. The signal voltage Vsig output from the light receiving element 19 which is a photomultiplier tube is amplified by the amplifier 51 of the confocal signal processing circuit 41, converted into a digital signal by the AD converter 53, and given to the control unit 46. The signal voltage Vsig from the light receiving element 19 is also input to the gain limiter circuit 52, and the output signal Vcont of the gain limiter circuit 52 is configured to control the gain of the light receiving element (PMT) 19.
[0036]
FIG. 4 is a diagram illustrating a circuit configuration example of the gain limiter circuit 52. The signal voltage Vsig from the light receiving element 19 is input to the inverting input side of the comparator (operational amplifier) 55 through a low-pass filter including a resistor R1 and a capacitor C1. A reference voltage Vref which is a threshold value is input to the non-inverting input side.
[0037]
When the signal voltage Vsig is lower than the reference voltage Vref, the output of the operational amplifier 55 is at the H level, and the diode D1 is cut off. At this time, the output Vcont of the gain limiter circuit 52 is in an open state (high impedance) and does not affect the light receiving element (PMT) 19.
[0038]
When a signal voltage Vsig higher than the reference voltage Vref is input, the output of the operational amplifier 55 is inverted and becomes L level, and the diode D1 becomes conductive. At this time, the control voltage Vcont, which is the output of the gain limiter circuit 52, works to lower the gain (PMT gain) of the light receiving element 19. As a result, the photocurrent extracted from the light receiving element (photomultiplier tube) 19 is limited.
[0039]
In the confocal microscope system 1 of the present embodiment, the reference voltage (threshold value) Vref is set so that the above limitation is applied with a photocurrent (sufficiently) smaller than the maximum rated current of the light receiving element 19. Thereby, even if the sample wk having a high light reflectance such as a mirror surface is repeatedly measured, there is no possibility that the light receiving element (photomultiplier tube) 19 is deteriorated or damaged.
[0040]
Further, the reference voltage (threshold) Vref is set so that the above-described restriction is applied with a photocurrent that is (sufficiently) larger than the photocurrent that becomes the saturation current in the light amount detection circuit that is a subsequent circuit after the amplifier 51. As a result, even when almost all of the obtained confocal image has whiteout due to saturation, the output current of the light receiving element 19 is larger than the saturation current of the light amount detection circuit, which is the subsequent circuit. The output current limit does not work unless the value is exceeded. That is, measurement can be continued even under measurement conditions in which whiteout due to saturation occurs on substantially the entire confocal image, and desired image information can be obtained on a part of the screen.
[0041]
FIG. 5 and FIG. 6 are diagrams illustrating an example in the case where measurement is performed under measurement conditions desired by the user. FIG. 5 shows a state when measured with a normal PMT gain, and FIG. 6 shows a state when the PMT gain is increased from the conditions of FIG. In the confocal image 60 shown in FIG. 5A, a black island 62 is displayed in a white background 61. The change in the amount of received light along the horizontal line L1 in the horizontal direction of the screen is as shown in FIG. The amount of light received at the black island 62 is very small, and the amount of light received at the white background 61 is close to the saturation light amount. At this time, the graph of the amount of received light that changes in accordance with the Z-direction position of the objective lens 17 shown in FIG. 2 is shown by a solid line in FIG. 65 indicates the amount of light received by the white background 61, and 66 indicates the amount of light received by the black island 62.
[0042]
In FIG. 5A, the black islands 62 appear to be uniform, but when the PMT gain is increased, it can be seen that there are darker spots 63 in the black islands 62 as shown in FIG. 6A. It is assumed that there is a portion that the user wants to observe in detail in this portion. In FIG. 6A in which the PMT gain is increased, the change in the amount of received light along the straight line L1 is as shown in FIG. 6B, and the amount of received light exceeds the saturation light amount in the white background 61 portion.
[0043]
In the confocal microscope system 1 of the present embodiment, since the reference voltage (threshold value) Vref is set so as to be limited by a photocurrent (sufficiently) larger than the saturation current of the photomultiplier tube 19, FIG. It is possible to measure and observe the sample wk even in the state shown.
[0044]
Further, in the PMT gain of the confocal image shown in FIG. 5, the Z-direction position (focused position) Z1 that is the maximum light reception amount is found from the change 65 of the light reception amount of the white background 61 as shown in FIG. However, it is difficult to find the position in the Z direction that is the maximum light reception amount from the change 66 of the light reception amount of the black island 62. On the other hand, in the state where the PMT gain is increased as in the confocal image shown in FIG. 6, the change in the amount of received light of the black island 62 is amplified from the solid line 66 to the broken line 66 ′ in FIG. It becomes possible to easily find the Z direction position (position in focus) Z2 that is the maximum amount of received light.
[0045]
As described above, according to the confocal microscope system 1 of the present embodiment, when it is desired to observe in detail a portion that becomes dark due to a small amount of received light with a normal PMT gain, the PMT is increased until the peripheral portion exceeds the saturation light amount. Since the gain can be increased, detailed observation of the part can be performed. Also, it is easy to focus on a specific location included in the portion.
[0046]
As mentioned above, although embodiment of this invention was described along drawing, this invention is not restricted to said embodiment, It can implement with a various form. For example, in order to acquire the height information of the surface of the sample wk by the confocal optical system 2, the stage 30 may be moved up and down instead of moving the objective lens 17 in the Z direction (up and down movement).
[0047]
The scanning of the sample with light is not limited to two-dimensional scanning by horizontal deflection and vertical deflection, and various scanning methods can be considered. For example, if a cylindrical lens is used to generate light that is elongated in the X direction (slit light) and is deflected in the Y direction, two-dimensional scanning is possible.
[0048]
The confocal microscope of the above embodiment is a reflection type microscope, but the present invention can also be applied to a transmission type confocal microscope. In the case of a transmission type microscope, laser light from a confocal optical system and white light from a non-confocal optical system are irradiated from the back surface of the sample.
The light source of the confocal optical system may include not only a monochromatic light source including a laser light source but also a plurality of wavelengths. The light source of the non-confocal optical system can be replaced with natural light or room light.
[0049]
【The invention's effect】
As described above, according to the gain limiter circuit and the confocal microscope system of the photomultiplier tube of the present invention, the threshold at which the gain limiter circuit operates is smaller than the maximum rated current and the light amount detection circuit is saturated. Since it is set within a range larger than the current, the current limit to prevent damage to the electron multiplier works reliably, while flexibly responding to the measurement conditions desired by the user, the output current limit is limited during the measurement. Work less carelessly. For example, even if the confocal image obtained with the confocal microscope has a whiteout due to saturation in almost the entire surface, the output current of the light receiving element does not exceed a threshold value greater than the saturation current of the light amount detection circuit. As long as the output current limit does not work.
Therefore, measurement can be continued even under measurement conditions in which whiteout due to saturation occurs on substantially the entire confocal image, and desired image information can be obtained on a part of the screen.
[Brief description of the drawings]
FIG. 1 shows a schematic configuration of a confocal microscope system according to an embodiment of the present invention.
FIG. 2 is a graph showing an example of received light amount data that changes in accordance with the position of the objective lens in the Z direction.
FIG. 3 is a block diagram illustrating a configuration of a confocal signal processing circuit that processes an output signal of a light receiving element.
FIG. 4 is a diagram illustrating a circuit configuration example of a gain limiter circuit.
FIG. 5 is a diagram illustrating an example in the case where measurement is performed under measurement conditions desired by a user.
6 is a diagram showing a state when a PMT gain is increased from the condition of FIG. 5. FIG.
7 is a graph showing an example of the amount of received light that changes in accordance with the position of the objective lens in the Z direction in the measurement examples of FIGS. 5 and 6. FIG.
[Explanation of symbols]
1 Confocal microscope system 19 Photomultiplier tube (light receiving element)
52 Gain limiter circuit

Claims (2)

A light source and a light receiving element that outputs a photocurrent value corresponding to the amount of light received and a predetermined gain, scans the sample with light from the light source, and within the scanning range via a confocal optical system In this confocal microscope system, transmitted light or reflected light from the sample at each point is received by the light receiving element, and height information and light amount information on the surface of the sample are acquired based on light reception information of the light receiving element. And
A digital value corresponding to the photocurrent value from the light receiving element is output, and when the photocurrent value exceeds a predetermined saturation current value smaller than the maximum rated current value of the light receiving element, the digital value is saturated and constant. A light amount detection circuit that outputs a digital value of
A control unit for acquiring height information and light amount information of the surface of the sample at each point within the scanning range based on the digital value;
In order to prevent damage to the light receiving element due to the photocurrent value exceeding the maximum rated current value, a threshold value that is smaller than the maximum rated current value and within a range greater than the saturation current value; comparing the photocurrent value from the light receiving element, when the photocurrent value is smaller than the threshold value so as not to affect the gain of the previous SL light receiving element, the photocurrent value is the threshold value lower the gain of the light receiving element to limit a further increase of the photocurrent value upon reaching, the when the photocurrent value gain down of the light receiving element becomes rather smaller than the threshold value so as to maintain the photocurrent value to the threshold value greater than the saturation current value, the gain limiter circuit for controlling the gain of the light receiving element,
A confocal microscope system characterized by comprising: The gain limiter circuit is
An operational amplifier that outputs a control signal for controlling a gain according to a result of comparing a reference voltage value corresponding to the threshold value and a signal voltage value corresponding to the photocurrent value from the light receiving element;
A diode provided at a subsequent stage of the operational amplifier,
The diode is installed in a direction in which the operational amplifier and the light receiving element are not electrically connected when the signal voltage value is smaller than the reference voltage value, and the gain limiter when the signal voltage value is smaller than the reference voltage value. The confocal microscope system according to claim 1, wherein the circuit does not affect the gain of the light receiving element.

Images