Method and apparatus for detecting position/variance of input light

Abstract: An apparatus for detecting position/variance of input light is disclosed which comprises a photoelectric conversion device receiving input light constituted of a first resistive layer formed of a first photoelectric conversion material and a second resistive layer formed of a second photoelectric conversion material connected with the first resistive layer through a depletion layer or directly, wherein the first resistive layer is provided with uniform resistivity throughout its surface so that a linear output proportional to the average of the distances between one end of the photoelectric conversion device and positions of the input light is detected and the second resistive layer is provided with resistivity dependent upon the distance from its one end so that a quadratic output proportional to the average of the squares of the distances between one end of the photoelectric conversion device and positions of the input light is detected.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position sensitive detector (PSD) for detecting position of an incident beam of light (light input) employing a photoelectric conversion device, and more particularly, to a method and apparatus for detecting position/variance of input light suitable for use, for example, in detection of surface flaws, surface roughness, or surface shape of metallic materials and the like utilizing a beam of light or detection of defocusing produced in a measuring instrument which uses a beam of light. 2. Description of the Prior Art Fig. 18 is a side view of a prior art position sensitive detector, for example, as described in a paper entitled "An Application of PSD to Measurement of Position", by Kazuo Kurasawa, pp. 730 - 737, Precision Instrument, Vol. 51, No. 4, 1985. In this prior art position sensitive detector, a flat silicon substrate is provided as shown in Fig. 18 with a first resistive layer 51 formed of a p-type semiconductor (photoelectric conversion material) to receive a light input and a second resistive layer 52 formed of an n-type semiconductor (photoelectric conversion material) connected with the first resistive layer 51 through a depletion layer 53, in which the first resistive layer 51 is provided with uniform resistivity throughout its surface. And, in order to detect the one-dimensional position and light energy of a beam of light incident on the first resistive layer 51, there are provided electrodes 54, 55 attached to both ends of the first resistive layer 51. Further, in the center of the second resistive layer 52, there is connected a bias electrode 56. With such a position sensitive detector, when a beam of light impinges on the first resistive layer 51 as shown by the arrow a in Fig. 18, its one-dimensional position and light energy is obtained in the following way. In this case, the coordinate system is set up such that the middle point of the electrodes 54, 55 is taken as the origin, the coordinate of the position of incidence with respect to the origin is represented by x, and the positive direction is taken to the right on Fig. 18. When the beam of light impinges on the first resistive layer 51 as indicated by the arrow a, there are generated electrons and positive holes proportional to the light energy at the position of incidence. The generated positive holes flow through the first resistive layer 51 and are detected as current values I₁₀, I₂₀ from the electrodes 54, 55, respectively. The generated electrons flow through the depletion layer 53 into the second resistive layer 52 and are taken out from the bias electrode 56. At this time, the flow of the positive holes, i.e., the photoelectric current, is distributed in inverse proportion to the distances from the position of incidence to the electrodes 54, 55 on account of the uniform resistivity of the first resistive layer 51. Accordingly, representing the total length of the first resistive layer 51 by 2L, we obtain I₁₀/(L - x) = I₂₀/(L + x) = k (1) where k is a quantity depending on the light energy, not on the position of incidence x. Then, if (I₁₀ - I₂₀)/(I₁₀ + I₂₀) in connection with the measured values I₁₀, I₂₀ is obtained from equation (1), it is expressed as and therefore, the position of incidence x can be measured regardless of the light energy according to x = L·(I₁₀ - I₂₀)/(I₁₀ + I₂₀) (3) And, since (I₁₀ + I₂₀) is equal to 2k·L, the quantity k depending on the light energy is detected regardless of the position of incidence k according to k = (I₁₀ + I₂₀)/(2L) (4) As described above, the one-dimensional position of the beam of light incident on the first resistive layer 51 and the quantity k depending on the light energy can be obtained from the current values I₁₀, I₂₀ measured with the position sensitive detector according to equations (3), (4). Incidentally, the two-dimensional position of the beam of light can also be measured on the same principle as utilized in the above described measurement of the one-dimensional position. In such case, a position sensitive detector as shown in Fig. 19 or Fig. 21 is used. The position sensitive detector as shown in Fig. 19 is of a surface division type, in which two pairs of electrodes 57, 58 and electrodes 54, 55 are disposed at both ends of a first resistive layer 51 in the directions at right angles to each other. In such a position sensitive detector, while the x coordinate is obtained based on equation (3) from current values I₁₀, I₂₀ detected from the electrodes 54, 55, respectively, the y coordinate is obtained from current values I₃₀, I₄₀ detected from the electrodes 57, 58, respectively. Incidentally, Fig. 20 is an equivalent circuit diagram of the position sensitive detector as shown in Fig. 19, and referring to the figure, P denotes a power source, D denotes an ideal diode, C j denotes junction capacitance, R sh denotes a resistor in parallel, and R p denotes the positioning resistor. The position sensitive detector as shown in Fig. 21 is of a double-side division type, in which the electrodes 57, 58 are disposed at both ends of the second resistive layer 52 at right angles to the direction between the electrodes 54, 55. In this case, the second resistive layer 52 is also provided with uniform resistivity throughout its surface. Also with such a position sensitive detector, the x coordinate is obtained from the current values I₁₀, I₂₀ detected from the electrodes 54, 55, while the y coordinate is obtained from the current values I₃₀, I₄₀ detected from the electrodes 57, 58. Here, Fig. 22 is an equivalent circuit diagram of the position sensitive detector as shown in Fig. 21. Besides the position sensitive detector using the photoelectric conversion device as described above, there are apparatus for detecting position of light using an imaging device (image pick-up tube, solid state imaging element such as CCD camera) or photodiodes. In the apparatus using an imaging device, an image of a beam of light is picked up by the imaging device and the image is converted into a digital image by analog-to-digital conversion, and the digital image is then processed by signal processing circuits as shown in Fig. 23 and Fig. 25 whereby the position of the beam of light and its spread (variance) are detected, respectively. The signal processing circuit for detecting the position of a beam of light is, as shown in Fig. 23, made up of a timing pulse generator 60 for outputting an operation instructing signal, a comparator 61 in response to a scan signal of an image from an imaging device 59 for detecting that the signal has exceeded a predetermined threshold value, a pulse generator 62 for generating pulses over the period from the time point when the scanning is started to the time point when the detection signal from the comparator 61 is output, and a counter 63 for counting the number of pulses output from the pulse generator 62 to detect and output the count value as the position of the beam of light. Therefore, in detecting the position of the beam of light, as shown in Fig. 24, when at first the timing pulse generator 60 has output the operation instructing signal, the imaging device 59 starts scanning and simultaneously the pulse generator 62 starts to output the pulse. Then, upon the detection by the comparator 61 of the position of a light signal P₁ exceeding the predetermined threshold value in the scan signal from the imaging device 59, the pulse generator 62 stops its operation. In the meantime, the number of pulses from the pulse generator 62 are counted by the counter 63, and the count value is provided as the position of the beam of light. The signal processing circuit for detecting the spread (variance) of the beam of light is, as shown in Fig. 25, made up of a comparator 61 in response to a scan signal of an image from an imaging device 59 for detecting that the signal has exceeded a predetermined threshold value, a pulse generator 64, an AND gate 65 performing a logical multiply operation on the pulse signal from the pulse generator 64 and the detection signal from the comparator 61, and a counter 66 for counting the number of pulses passed through the AND gate 64 to detect and output the count value as the spread (variance) of the beam of light. Accordingly, in detecting the spread (variance) of a beam of light, as shown in Fig. 26, the comparator 61 detects the period during which there exists a light signal P₂ exceeding a predetermined threshold value in the scan signal from the imaging device 59, and since the pulses from the pulse generator 64 have been passed through the AND gate 65 during that period, the number of the passed pulses is counted by the counter 63 and this count value is provided as the spread (variance) of the beam of light. In the apparatus using photodiodes or the like, a plurality of such photodiodes or phototransistors, not shown, are disposed in a line, and it is detected to which photodiode or the like a beam of light impinges on, whereby the position and spread (variance) of the beam of light are detected. Now, the incident beam of light is not a ray but has some spread. The degree of spread, when the beam of light is a reflected beam of light from a surface as an object of inspection, bears information on flaws on or roughness of the surface or shape of it, or in the case of a measuring instrument, the degree of spread bears information about defocusing produced in the instrument. However, with position sensitive detectors using a photoelectric conversion device of the prior art, one can only obtain the position (or, to be more exact, the center-of-gravity position) of the beam of light. Therefore, in order to detect the spread of a beam of light under existing conditions, it is required to take an image of the beam with an imaging device (such as an image pick-up tube, CCD camera) and subject it to analog-to-digital conversion, and to calculate, from the obtained digital image, the spread of the beam of light by means of of the signal processing circuit as described above (Fig. 25). Thus, there have been such problems that the apparatus becomes considerably large and quite expensive and laborious steps of procedure must be taken. With the apparatus employing photodiodes or the like, high resolution is not achievable because a large number of such elements cannot be used, and therefore, such an apparatus has not been useful when high accuracy is desired. It is also known from U.S. 3 246 161 a photoelectric conversion device having a junction providing an output signal proportional to the distance between one end of the device and the position of the input light. SUMMARY OF THE INVENTION The present invention was made to solve such problems as mentioned above and has an object to provide a method and apparatus for detecting position/variance of input light which is compact and economical and yet capable of providing information on position and spread (variance) of the beam of light with high response and accuracy. A first apparatus for detecting position/variance of input light according to the present invention is defined in claim 1. A second apparatus for detecting position/variance of input light according to the present invention is defined in claim 2. With the first apparatus, while the linear output is detected from the current values obtained from both ends of the first resistive layer, the quadratic output is detected from the current values obtained from both ends of the second resistive layer, and the average position (center-of-gravity position) and the variance (spread) of the input light can be obtained from the results of the detections. With the second apparatus, while the linear output is detected from the current values obtained from both ends of the odd-numbered slip-formed resistive layer segments of the first resistive layer, the quadratic output is detected from the current values obtained from both ends of the even-numbered slip-formed resistive layer segments of the first resistive layer, and therefrom are obtained the average position and the variance of the input light. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1 - 3 are for showing an apparatus for detecting position/variance of input light as a first embodiment of the present invention, of which Fig. 1(a) is a side view and Fig. 1(b) is a plan view of the same, Fig. 2 is a graph showing an example of intensity distribution of a beam of light incident on the first resistive layer of the same, and Fig. 3 is a block diagram showing structure of a computing element for calculating intensity, average position, and variance of the beam of light from current values detected by the above apparatus for detecting position/variance of input light; Fig. 4 is a perspective view showing an apparatus for detecting position/variance of input light as a second embodiment of the present invention; Fig. 5 is a perspective view showing an apparatus for detecting position/variance of input light as a third embodiment of the present invention; Figs. 6 - 9 are for showing an apparatus for detecting position/variance of input light as a fourth embodiment of the present invention, of which Fig. 6 is a side view of the same, Figs. 7(a) and (b) are plan views showing forms of a first and a second shielding masks, respectively, Figs. 8(a) and (b) are graphs showing the relationships between detected current values obtained from the photoelectric conversion devices covered by the first and second shielding masks, respectively, and positions on the photoelectric conversion devices, and Fig. 9 is a side view showing a variance of the apparatus of the present embodiment; Fig. 10 is a side view showing an apparatus for detecting position/variance of input light as a fifth embodiment of the present invention; Figs. 11 and 12 are for showing an apparatus for detecting position/variance of input light as a sixth embodiment of the present invention, of which Fig. 11(a) is a plan view and Fig. 11(b) is a front view of the same, and Fig. 12 is a side view showing an example of the arrangement of the same; Figs. 13(a) and (b) are for showing an apparatus for detecting position/variance of input light as a seventh embodiment of the present invention, of which Fig. 13(a) is a plan view and Fig. 13(b) is a side view of the same; Figs. 14(a) and (b) are for showing an apparatus for detecting position/variance of input light as a eighth embodiment of the present invention, of which Fig. 14(a) is a plan view and Fig. 14(b) is a side view of the same; Fig. 15 is a plan view showing an apparatus for detecting position/variance of input light as a ninth embodiment of the present invention; Figs. 16 and 17 are for showing an apparatus for detecting position/variance of input light as a tenth embodiment of the present invention, of which Fig. 16 is a side view of the same, and Fig. 17 (a) and (b) are graphs showing transmittance properties of a linear characteristic ND filter and a quadratic characteristic ND filter, respectively; Fig. 18 is a side view showing a position sensitive detector of the prior art; Figs. 19 and 20 are for showing a position sensitive detector of the prior art of a surface division type, of which Fig. 19 is a side view of the same and Fig. 20 is its equivalent circuit diagram; Figs. 21 and 22 are for showing a position sensitive detector of the prior art of a double-side division type, of which Fig. 21 is a side view of the same and Fig. 22 is its equivalent circuit diagram; Figs. 23 and 24 are for showing a position sensitive detector using an imaging device of the prior art, of which Fig. 23 is a block diagram of the same and Fig. 24 is a timing chart therefor; Figs. 25 and 26 are for showing a light variance (spread) detector using an imaging device, of which Fig. 25 is a block diagram of the same and Fig. 26 is a timing chart therefor; and Fig. 27 is a block diagram showing an application example of the apparatus for detecting position/variance of input light of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS To begin with, the method for detecting position/variance of input light according to the present invention and its principle will be briefly described with a case of one dimensional detection taken as an example. In order to detect the variance of input light, if the average of the positions (center-of-gravity position) of the input light, x , and the average of the squares of the positions, , are obtained, then the variance σ ² is statistically calculated and detected as - x². Therefore, in the method of the present invention, a photoelectric conversion device is used which, upon receipt of input light, outputs a predetermined current corresponding to the intensity of the input light by photoelectric conversion, and firstly the intensity of the light, ∫ ρ (x)dx (where ρ represents intensity distribution of the input light), the average of the positions x of the input light weighted by the intensity of the light, ∫ x·ρ (x)dx, and the average of the squares of the positions of the input light similarly weighted by the intensity of the light, ∫ x²·ρ (x)dx, are obtained as current values. Then, from the detected current values, K₁₀·∫x·ρ (x)dx/ ∫ ρ (x)dx is obtained as a linear output proportional to the average value (center-of-gravity position) x of the distances between one end of the photoelectric conversion device and the positions of the input light and K₂₀·∫ x²·ρ (x)dx/ ∫ ρ (x)dx is obtained as a quadratic output proportional to the average of the squares of the distances between the end of the photoelectric conversion device and the positions of the input light (where K₁₀, K₂₀ are constants), and based on those outputs, the position (center-of-gravity position) x of the input light is detected as ∫ x·ρ (x)dx/ ∫ ρ (x)dx , and the variance σ ² of the input light is detected as ∫ x²·ρ (x)dx/ ∫ ρ (x)dx - [∫ x·ρ (x)dx/ ∫ ρ (x)dx]². Now, practical embodiments of the apparatus for detecting position/variance of input light capable for detecting the above mentioned linear output and quadratic output and applicable to the method of the present invention will be described with reference to the accompanying drawings. 1. First Embodiment of the Present Invention: Figs. 1 - 3 show an apparatus for detecting position/variance of input light as a first embodiment of the present invention, in which Fig. 1(a) is a side view and Fig. 1(b) is a plan view of the same, Fig. 2 is a graph showing an example of intensity distribution of a beam of light incident on (input light to) a first resistive layer, and Fig. 3 is a block diagram showing structure of a computing element for calculating intensity, average position, and variance of the beam of light from current values detected by the apparatus of the present embodiment. The first embodiment of the present invention is based on the invention defined in claim 3 and is that for obtaining one-dimensional average position (center-of-gravity position), intensity (light energy), and variance (spread) of a beam of light. The same as in the prior art, the photoelectric conversion device is constituted, as shown in Figs. 1 (a) and (b), of a first resistive layer 1 formed of a P type semiconductor as a first photoelectric conversion material and a second resistive layer 2 formed of an N type semiconductor as a second photoelectric conversion material connected with the first resistive layer 1 through a depletion layer 3, in which the first resistive layer 1 is provided with uniform resistivity throughout the surface (resistive contour density: r₀). For the mentioned photoelectric conversion device of a photovoltatic type constituted of the first resistive layer 1, second resistive layer 2, and the depletion layer 3, there are provided electrodes 4, 5 attached to both ends of the first resistive layer 1 a distance L apart and electrodes 6, 7 attached to both end portions of the second resistive layer 2 corresponding to the electrodes 4, 5, respectively. In the present embodiment, the origin is taken at the position of the electrodes 4, 6 and the X axis is taken in the direction from the electrodes 4, 6 to the electrodes 5, 7. Further, in the present embodiment, the second resistive layer 2 is so arranged that it has resistivity dependent upon the distance from the electrode 6 at its one end, that is, the resistive contour density on the second resistive layer 2 is sufficiently close to 0 at the position of the electrode 6 (x = 0), the density is r₀ at the position of the electrode 7 (x = L), and the resistive contour density r linearly increases between these two positions, or r = (r₀ / L)·x (4) The electrodes 4, 5, 6, 7 are each connected with a current detector, not shown, and it is adapted such that, when the photoelectric currents are generated in the apparatus for detecting position/variance of input light according to the present embodiment, the currents to flow through the electrodes 4, 5, 6, 7 are detected as i₁, i₂, j₁, j₂, respectively. Incidentally, l, w, and h in Figs. 1 (a) and (b) represent external dimensions, i.e., length, width, and height, respectively, of the apparatus for detecting position/variance of input light of the present embodiment. Since the apparatus for detecting position/variance of input light according to the first embodiment of the present invention is structured as described above, the intensity (light energy), average position (center-of-gravity position), and variance (spread) of the beam of light incident on the first resistive layer 1 are obtained as described below. Suppose now that a beam of light having the intensity distribution ρ (x) of Gaussian distribution as shown in Fig. 2 is incident as indicated by the arrow A in Fig. 1(a). Here, referring to the Gaussian distribution, the average position is represented by x, variance by σ ², maximum intensity by I max , and the total intensity (the area indicated by hatching in Fig. 2) by It. An bit, or element, of a beam of light, i.e., a portion thereof between [x, x + dx] generates di of positive holes and dj of electrons by photoelectric conversion, so that di = K·ρ (x)dx = - dj (5) where K is efficiency of photoelectric conversion. The positive holes di flows along the first resistive layer 1 and the electrons dj (= - di) reaches the second resistive layer 2 by way of the depletion layer 3 and flows along the second resistive layer 2. Since the first resistive layer 1 has uniform resistive contour density r₀, the positive holes di is taken out from the electrodes 4 and 5 as di₁ and di₂, respectively, distributed in inverse proportion to the resistance from 0 to x and the resistance from x to L. Hence, di = di₁ + di₂ (6) The current values i₁, i₂ taken out from the electrodes 4, 5 are given, respectively, by i₁ = ∫ di₁ (9) i₂ = ∫ di₂ (10) What are actually measured are these current values i₁, i₂. From equations (10), (8), (5), i₂ is expressed as Thus, the average value of the coordinate x weighted by the intensity of the beam of light can be detected by the current i₂. But, the current value i₂ also depends on the intensity of the beam of light. And so, when the total current (i₁ + i₂) is obtained from equations (9), (10), (7), (8), (5), it is expressed as Thus, we can obtain the quantity relative to the total intensity It of the beam of light. Further, from equations (11), (12), we obtain Here, because it becomes possible to obtain a linear output proportional to the average x of the distances x from the position of the electrode 4 (one end of the photoelectric conversion device) to the positions of the beam of light. Thus, x /L as the data of center-of-gravity position of the beam of light can be obtained and K·It as the data of intensity (It) of the beam of light can be obtained from (i₁ + i₂). Then, since the second resistive layer 2 has the resistive contour density r as given by equation (4), the electron dj is distributed in inverse proportion to the resistance R₁(x) from O to x and the resistance R₂(x) from x to L and each thereof are taken out from the electrodes 6, 7 as dj₁, dj₂. Since R₁(x) = ∫₀ X rdx = r ₀·x²/(2L) (15) and the total resistance is R = ∫₀ L rdx = r ₀·L/2 (17) we obtain dj = dj₁ + dj₂ (18) The current values j₁, j₂ that are taken out from the electrodes 6, 7 are j₁ = ∫ dj₁ (21) j₂ = ∫ dj₂ (22) and what are actually measured are these current values j₁, j₂. From equations (22), (20), and (5), j₂ is expressed as Thus, the average of the squares of the coordinates x weighted by the intensity of the beam of light can be detected by the current value j₂. But the current value j₂ is also dependent on the intensity of the beam of light. Then, if the total current value (j₁ + j₂) is obtained by using equations (21), (22), (19), (20), and (5), it is expressed as from which the quantity relative to the intensity of the beam of light is obtained, and from equations (23) and (24), we obtain Here, since after all, it is made possible to take out a quadratic output /L² proportional to the average of the squares of the distances x between the position of the electrode 6 (one end of the photoelectric conversion device) and the positions of the beam of light from j₂/(j₁ + j₂) . Accordingly, the variance (spread) σ ² can be obtained, based on equations (13) and (25), from As a consequence of the foregoing, three characteristic quantities of the beam of light, x /L, σ ²/L², and K·It, are expressed as K·It = i₁ + i₂, or - (j₁ + j₂) (30) Thus, by the use of a computing element as shown in Fig. 3, the average position (point-of-gravity position) x , variance (spread) σ ², and intensity (light energy) It of the beam of light based on the above equations (28), (29), and (30) can be obtained from the current values i₁, i₂, j₁, and j₂ output from the electrodes 4 - 7. Referring to Fig. 3, reference numerals 8 and 9 denote adders, 10 and 11 denote dividers, 12 denotes a subtractor, and 13 denotes a multiplier. The second resistive layer 2 having a resistive contour density proportional to the distance can be materialized by changing the doped quantity of impurities and also by varying the film thickness of the second resistive layer 2 in inverse proportion to the distance (resistive contour density ∝ 1/film thickness ∝ distance). According to the first embodiment of the present invention, the linear output i₂/(i₁ + i₂) proportional to the average value x of the distances x and the quadratic output j₂/(j₁ + j₂) proportional to the average of the squares of the distances x of the beam of light incident on the first resistive layer can thus be obtained not using an imaging device or the like but using a device of a very simple structure, and the average position (center-of-gravity position) x and the variance σ ² can be detected from these outputs quite easily and economically. Besides, these values can be detected with high response and accuracy. Therefore, such advantages are also obtained that measurement of spread of a light spot, detection of defocusing in a measuring instrument using a beam of light, detection of flaws on or roughness of a surface, or shape of a surface as an object of inspection or the like can be executed with great ease. 2. Second Embodiment of the Present Invention: Fig. 4 is a perspective view showing an apparatus for detecting position/variance of input light as a second embodiment of the present invention. The second embodiment is based on the invention as defined in claim 3 for obtaining two-dimensional average position, intensity, and variance of a beam of light. In the apparatus for detecting position/variance of input light virtually of the same structure as the first embodiment, there are provided, as shown in Fig. 4, electrodes 14, 15 attached to both ends of the first resistive layer 1 suitably spaced apart and disposed in the direction of the y axis so as to cross the electrodes 4, 5 at right angles, and further, there are provided electrodes 16, 17 attached to the second resistive layer 2 opposing to the electrodes 14, 15, respectively. The second resistive layer 2 in the present embodiment is arranged so that it has appropriate resistive contour densities linearly increasing along both the x and y axes. Therefore, the present embodiment performs a function, as the extension of the one-dimensional detection performed by the first embodiment, of two-dimensional detection of intensity, average position, and variance of a beam of light. That is, the method for obtaining x from the electrodes 4, 5 and from the electrodes 6, 7 is the same as in the one-dimensional detection and the variance σ X ² in the direction of the x axis is similarly obtained from these data. And further, it is possible to obtain y from the electrodes 14, 15 and from the electrodes 16, 17, and from these data, the variance σ Y ² in the direction of the y axis. Thus, two-dimensional point-of-gravity position (x, y), variance (σ X ², σ Y ²), and intensity (It) of the beam of light can be obtained and similar effects to those attained in the first embodiment can be attained. In the above, however, the intensity It is obtained from the sum of the current values taken out from four electrodes of either the first resistive layer 1 or the second resistive layer 2 as shown in Fig. 4. 3. Third Embodiment of the Present Invention: Fig. 5 is a perspective view showing an apparatus for detecting position/variance of input light as a third embodiment of the present invention. The third embodiment is for obtaining one-dimensional average position, intensity, and variance of a beam of light based on the invention as defined in claim 4. As shown in Fig. 5, the third embodiment is provided with a first resistive layer 1A formed of a P type semiconductor to receive a light input and a second resistive layer 2A formed of N type semiconductor connected with the first resistive layer 1A through a depletion layer 3, in which the second resistive layer 2A is connected to a bias electrode 18. The first resistive layer 1A is divided into a plurality of slip formed resistive layer segments 1a, 1b. The slip resistive layer segments 1a, 1b are disposed in an alternate manner, of which the slip formed resistive layer segments 1a located at odd numbered places (predetermined alternate places) are provided with uniform resistivity throughout the surfaces, whereas the slip formed resistive layer segments 1b located at even numbered places (other places than the above predetermined alternate places) are provided with the resistive contour density linearly increasing in the direction of the x axis. And, while each slip formed resistive layer 1a is attached to electrodes 4A, 5A at both end portions thereof, each slip formed resistive layer ib is attached to electrodes 6A, 7A at both end portions thereof, and it is adapted such that the linear output and quadratic output are, in the same manner as in the above first embodiment, obtained from current values i₁, i₂, j₁, and j₂ detected from the electrodes 4A, 5A, 6A, and 7a, whereby one-dimensional average position, intensity, and variance of the beam of light can be detected and the same effects as obtained from the first embodiment can be provided. Incidentally, if the second resistive layer 2A is arranged to cross the first resistive layer 1A at right angles and divided into slip formed resistive layer segments similar to the slip formed resistive layer segments 1a, 1b, so that the average position, intensity, and variance of the beam of light may be detected in the direction of the y axis in the same manner as the average position, intensity, and variance of the beam of light are detected in the direction of the x axis by the slip formed resistive layer segments 1a, 1b of the first resistive layer 1A, two-dimensional detection of the average position, intensity, and variance of the beam of light can be achieved even by the present embodiment based on the invention as defined in claim 4. Since semiconductors of amorphous silicon were used in the above described first to third embodiments, a depletion layer was provided between the first resistive layer and the second resistive layer, but if crystal silicon is used, the need for provision of the depletion layer can be eliminated because a depletion layer is formed on the interface even if the P layer and the N layer are connected directly,. 4. Fourth Embodiment of the Present Invention: Figs. 6 - 9 are for showing apparatus for detecting position/variance of input light as a fourth embodiment of the present invention, in which Fig. 6 is a side view for showing the same, Figs. 7(a) and (b) are plan views showing, respectively, forms of a first and a second shielding masks, Figs. 8(a) and (b) are graphs showing relationships between the detected current values by the photoelectric conversion devices masked by the first and the second masks and the positions on the photoelectric conversion devices, and Fig. 9 is a side view showing a variation of the apparatus of the present embodiment. The fourth embodiment is for obtaining one-dimensional average position, intensity, and variance of a beam of light based on the invention as defined in claim 5. As shown in Fig. 6, the fourth embodiment is provided with three photodiodes 19-1 to 19-3 as photoelectric conversion devices having translucency, each photodiode being constituted of a p layer 19a, i layer 19b, and an n layer 19c and adapted upon receipt of a light input to output a predetermined current by photoelectric conversion corresponding to the light intensity. Onto the top and bottom surfaces of each of the photodiodes 19-1 to 19-3 are attached transparent and electrically conductive films 20, through which it is adapted such that I₀, I₁, and I₂ from the photodiodes 19-1 to 19-3 are obtained. Each of the diodes 19-1 to 19-3 with the transparent conductive films attached to both the top and bottom surfaces thereof is mounted on a glass substrate. In the present invention, while the surface of the photodiode 19-2 on the input light side is covered by a first shielding mask 22a of the form as shown in Fig. 7(a) through an insulating protection film 23 having translucency, the surface of the photodiode 19-3 on the input light side is covered by a second shielding mask 22b of the form as shown in Fig. 7(b) through an insulating protection film 23 having translucency. Namely, the boundary line between the shielded portion by the first shielding mask 22a and photosensitive portion of the photodiode 19-2 becomes a linear line given by y = (w/L)·x when the origin is taken at the bottom left-hand corner of the photodiode 19-2, the x axis is taken to the right, and the y axis is taken upwardly. Thus, the photodiode 19-2 is adapted to be exposed to the light at its portion whose width at a position x is proportional to x, (w/L)·x , by means of the shielding mask 22a. Likewise, the boundary line between the shielded portion by the second shielding mask 22b and the photosensitive portion of the photodiode 19-3 becomes a parabola given by y = (w/L²)·x² when the same coordinate system as above is taken. And thus, the photodiode 19-3 is adapted to be exposed to the light at its portion whose width at a position x is proportional to the square of x, (w/L²)·x² by means of the shielding mask 22b. The photodiodes 19-2 and 19-3 whose top surfaces are covered by the shielding masks 22a and 22b as described above and the photodiode 19-1 are piled up in the order of 19-1, 19-2, and 19-3 from above through transparent adhesive layers 24. With the above described construction, the total intensity, average position x , and the variance σ ² of a beam of light are obtained in the following manner. Supposing now that a beam of light having the same intensity distribution ρ (x) as shown in Fig. 2 is incident as indicated by the arrow A in Fig. 6, the current value I₀ detected by the photodiode 19-1 whose photosensitive surface is not shielded at all becomes I₀ = K₀·∫₀ L ρ (x)dx = K ₀·It (31) and from this current value I₀ is obtained the quantity relative to the intensity It of the beam of light. The current value I₁ detected by the photodiode 19-2 covered by the shielding mask 22a has a relationship with the incident position x of the beam of light as shown in Fig. 8(a) and therefore expressed as I₁ = K₁·a₁·∫₀ L x·ρ (x)dx (32) and it leads to that the average value of the coordinate x weighted by the intensity of the beam of light can be detected by the current value I₁. Likewise, the current value I₂ detected by the photodiode 19-3 covered by the shielding mask 22b has a relationship with the input position x of the beam of light as shown in Fig. 8(b) and therefore expressed as I₂ = K₂·a₂·∫₀ L x ²·ρ (x)dx (33) and it leads to that the average of the squares of the coordinates x weighted by the intensity of the beam of light can be detested by the current value I₂. In the above, K₀, K₁, and K₂ are efficiency of photoelectric conversion of each of the photodiodes 19-1 to 19-3. Hence, from (14), (31), (32), we obtain I₁/I₀ = (K₁/K₀)·a₁· x (34) and, from this I₁/I₀, a linear output proportional to the average x of the distances x between one end of the photodiode 19-2 and the positions of the beam of light can be taken out. And, from (26), (31), (33), we obtain and from this I₂/I₀ can be obtained a quadratic output proportional to the average of the squares of the distances x between one end of the photodiode 19-3 and the positions of the beam of light. In reality, the light quantity of the beam of light is gradually attenuated as it is transmitted through the photodiodes 19-1 to 19-3 in succession, and therefore, it is required to obtain the attenuation factor in advance and take it into consideration in making calculations according to the above equations (32) - (35). However, for simplicity's sake, the present embodiment is described on the assumption that there is produced no such attenuation in the beam of light. In the present embodiment, according to the above results, the intensity It of the beam of light is obtained from equation (31) and the average position x of the beam of light from equation (34), and further, the variance σ ² is obtained, based on equations (34) and (35), from the following equation (36). In the present embodiment, if, for example, slit light whose width is negligible is incident on the apparatus in two different positions x₁ and x₂ as shown in Figs. 7 and 8 (here, it is assumed that K₀ = K₁ = K₂ = 1 , for simplicity's sake), then the detected current values I₁, I₂ will be I₁ = a₁·(x₁ + x₂) (37) I₂ = a₂·(x₁² + x₂²) (38) From these equations (37), (38), we obtain (x₁ - x₂)² = 2I₂/a₂ - (I₁/a₁)² (39) and from equation (39), the distance | x₁ - x₂ | between the two bundles of rays can be detected. Thus, also by the apparatus of the present embodiment, the linear output can be obtained based on equation (34) and the quadratic output can be obtained from equation (35), and thereby, the one-dimensional average position, intensity, and variance of a beam of light can be detected and the same effect as in the first embodiment can be obtained, and further, when two bundles of rays are incident, the distance therebetween can also be detected from equation (39). Although the apparatus shown in Fig. 6 is constructed such that the photodiodes 19-1 to 19-3 are each mounted on a glass substrate 21 and then piled up through an adhesive layer 24, the apparatus may also be arranged such that the photodiodes 19-1 to 19-3 are directly piled up through a protective insulating film 23 and the whole is mounted on a single glass substrate 21A as shown in Fig. 9. By so doing, such effects will be obtained that the apparatus can be made thinner, and further, stray light due to reflection by the glass substrates 21 within the apparatus can be reduced. 5. Fifth Embodiment of the Present Invention: Fig. 10 is a side view of an apparatus for detecting position/variance of input light as a fifth embodiment of the present invention. The present fifth embodiment, like the above described fourth embodiment, is based on the invention as defined in claim 5. What is different in the fifth embodiment from the above described fourth embodiment is that the photodiodes 19-2 and 19-3 are changed from the piled up structure to a structure such that a beam of light incident thereon is split and directed to two surfaces by means of a beam splitter 25, and thereby, one-dimensional average position, intensity, and variance of the beam of light are made obtainable. That is, as shown in Fig. 10, a beam of light is once introduced to the beam splitter 25 and split by the beam splitter 25 into two directions at right angles with each other to reach the photodiode 19-2 covered by the first shielding mask 22 [refer to Fig. 7 (a)] and to the photodiode 19-3 covered by the second shielding mask 22b [refer to Fig. 7(b)], so that the current values I₁, I₂ corresponding to equations (32), (33) are obtained from those photodiodes 19-2, 19-3. Although, there is not shown in Fig. 10 a photoelectric conversion device for detecting the intensity of the beam of light corresponding to the photodiode 19-1 in the fourth embodiment, it is in reality arranged by means of another beam splitter, a half mirror, or the like, such that the incident beam of light is introduced to the photoelectric conversion device, not shown, for detecting the light intensity, and thereby, the detected current corresponding to the current value I₀ in the fourth embodiment can be obtained. Thus, also by the apparatus of the present embodiment, the intensity of the beam of light It can be obtained from equation (31), the average position x of the beam of light can be obtained from equation (34), and the variance σ ² can be obtained from equation (36), and the same effect as obtained in the fourth embodiment can be obtained. Besides, according to the present embodiment, since the beam of light is directly introduced to the photodiodes 19-2 and 19-3, there are produced no such things that occur in the fourth embodiment as attenuation of the beam of light, stray light resulting from the glass substrate, and interference with the detection by the shielding mask 22a on the upper side, and therefore accuracy in the measurement can be improved. 6. Sixth Embodiment of the Present Invention: Figs. 11 and 12 are for showing an apparatus for detecting position/variance of input light as a sixth embodiment of the present invention, of which Fig. 11(a) is a plan view and Fig. 11(b) is a front view of the same and Fig. 12 is a side view showing an example of arrangement of the same. The present sixth embodiment, like the above described fourth and fifth embodiments, is also based on the invention as defined in claim 5. The apparatus of the present embodiment is formed of a plurality of the devices S structured the same as the fourth embodiment (refer to Fig. 6), which are arranged side by side on a plane as shown in Figs. 11(a) and (b). By detecting current values I₀, I₁, I₂ for each device S with the described arrangement, the light intensity at each position of the device S can be obtained according to equation (31), and besides, the average position and variance of the input light at each position of the device S in the longitudinal direction [the vertical direction on Fig. 11(a)] con be obtained according to equations (34), (36), respectively. Therefore, according to the present embodiment, even if, for example, a beam of light having a considerable area of circular spread is incident on the apparatus, the input light can be detected as a collection of strip-formed beams divided by each of the devices S. Hence, the input light can be detected not only for intensity but also for vertical position and variance as described above regardless of the position of the incidence of the input light. Further, by preparing two devices as shown in Figs. 11(a) and (b) and arranging them as shown in Fig. 12 so that an incident beam of light may be split into two directions at right angles with each other by means of a beam splitter 26 and received by the two apparatus, it becomes possible not only to detect vertical position and variance but also to detect horizontal position and variance of the input light. Thus, it is enabled to detect two-dimensional position and variance of input light very accurately. 7. Seventh Embodiment of the Present Invention: Figs. 13(a), (b) are for showing an apparatus for detecting position/variance of input light as a seventh embodiment of the present invention, of which Fig. 13(a) is a plan view and Fig. 13(b) is a side view of the same. This seventh embodiment is based on the invention as defined in claim 6 for obtaining one-dimensional average position, intensity, and variance of a beam of light. The apparatus is constructed such that a photodiode 27 as a photoelectric conversion device is mounted on a glass substrate 30 and the surface of the photodiode 27 on the side of the input light is covered by a first shielding mask 28 of the same form as that shown in Fig. 7(a) and a second shielding mask 29 of the same form as that shown in Fig. 7(b). Both the shielding masks 28 and 29 are structured as liquid crystal shutters. That is, in the apparatus of the present embodiment, when both the shielding masks 28, 29 are in an off (open) state, the input light is introduced into the photodiode 27 not shielded at all, and therefrom, the current value I₀ corresponding to equation (31) is detected. When the shielding mask 28 is brought into an ON (closed) state by application of a driving voltage, the current value I₁ corresponding to equation (32) is detected, and further, when the shielding mask 29 is brought into an ON (closed) state by application of a driving voltage, the current value I₂ corresponding to equation (33) is detected. Accordingly, in the present embodiment, by controlling the application of driving voltages so that operations for turning OFF both the shielding masks 28 and 29, for turning ON only the shielding mask 28, and for turning ON the shielding mask 29 are repeated at predetermined intervals, the current values I₀, I₁, and I₂ can be detected on a time-division basis, and by combining these values, the intensity of the beam of light It can be obtained from equation (31), the average position x of the beam of light can be obtained from equation (34), and the variance σ ² can be obtained from equation (36). Thus, the effects as obtained from the fourth embodiment can be obtained, and what is more, such a thing is achieved only by having one set of photodiode 27 provided, not having plural sets of photodiodes piled up. Therefore the effect to make the apparatus itself thinner can also be obtained. Although a liquid crystal is used as the shutter in the present embodiment, electrooptic crystals of PLZT (lead lanthanum zirconate titanate), KDP (potassium dihydrogen-phosphate), or the like may be used, instead. 8. Eighth Embodiment of the Present Invention: Figs. 14(a), (b) are for showing an apparatus for detecting position/variance of input light as an eighth embodiment of the present invention, of which Fig. 14(a) is a plan view and Fig. 14(b) is a side view of the same. This eighth embodiment is based on the invention as defined in claim 8 for obtaining one-dimensional average position, intensity, and variance of a beam of light, and as shown in Figs. 14(a) and (b), provided with a photodiode 31 as a photoelectric conversion device constituted of a p layer 32, an i layer 33, and an n layer 34, in which the p layer 32 is divided in an insulated manner into three divisions 32a, 32b, and 32c through a linear line represented by y = (w/L)·x and a parabola represented by y = (w/L²)·x² , and it is adapted such that current values I P1 , I P2 , and I P3 are detected from the corresponding divisions 32a, 32b, and 32c. In the above, the coordinate system, (x, y), is set up the same as in the fourth embodiment. With the above described structure, when a beam of slit light having the distribution of light intensity ρ (x) in the x direction as shown in Fig. 2 and uniform distribution of light intensity in the y direction impinges on the hatched portion in Fig. 14(a), the total intensity It, average position x , and the variance of the beam of light are obtained in the following way. Also in the present embodiment, there is a relationship as shown in Fig. 8(a) between the position x and the detected current values I P1 + I P2 (= I₁) , and there is a relationship as shown in Fig. 8(b) between the position x and the detected current value I P1 (= I₂) . Then, representing the efficiency of photoelectric conversion by K and setting a₁ = w/L and a₂ = w/L² for simplicity's sake, the detected current values I P1 , I P2 , and I P3 are expressed as I P1 = K·∫₀ L ρ (x)·a ₂x²dx (40) I P2 = K·∫₀L ρ (x)·(a ₁x - a₂x²)dx (41) I P3 = K·∫₀ L ρ (x)·a ₁(L - x)dx (42) From these equations (40) - (42), we obtain I P1 + I P2 = K·∫₀ L ρ (x)·a₁xdx (44) Here, equations (43), (44), and (40) correspond to equations (31), (32), and (33) in the fourth embodiment, respectively. Therefore, the quantity relative to the total intensity of the beam of light is obtained from equation (43). And from equations (14), (43), and (44), we obtain and by this (I P1 + I P2 )/(I P1 + I P2 + I P3 ) is taken out the linear output proportional to the average x of the distances x between one end of the photodiode 31 and the positions of the beam of light. Further, from equations (26), (43), and (40), we obtain and by this I P1 /(I P1 + I P2 + I P3 ) is taken out the quadratic output proportional to the average of the squares of the distances x between one end of the photodiode 31 and the positions of the beam of light. As the result of the foregoing, the total intensity It of the beam of light is obtained from equation (43) and the average position x of the beam of light is obtained from equation (45), and based on equations (45) and (46), the variance σ ² is obtained from the following equation (47) Thus, also from the present embodiment, the same effect as obtained from the seventh embodiment can be obtained. 9. Ninth Embodiment of the Present Invention: Fig. 15 is a plan view showing an apparatus for detecting position/variance of input light as a ninth embodiment of the present invention. Although this ninth embodiment is based on the invention as defined in claim 8 like the eighth embodiment, the apparatus of the present embodiment is provided with n pieces photodiodes, of a width of Δ w, structured as that in the eighth embodiment and these photodiodes are arranged as shown in Fig. 15 on one plane in the y direction in the order from 31-1 to 31-n. With the described structure, when a spot beam, not a slit beam as in the eighth embodiment, impinges on the apparatus where it is arranged such that Δ w « D (D: diameter of the spat beam), the distribution of light intensity in the y direction on each of the diodes 31-1 to 31-n is considered virtually uniform. By detecting the current values I P1 , I P2 , and I P3 for each photodiode 31-1 - 31-n, the intensity of the spot beam at the position of each photodiode 31-1 - 31-n can be obtained according to equation (43), and the average position and variance of the spot beam at each position can be obtained according to equations (45) and (47), respectively, and thus the same effect as obtained from the sixth embodiment can be obtained. 10. Tenth Embodiment of the Present Invention: Figs. 16 and 17 are for showing an apparatus for detecting position/variance of input light as a tenth embodiment of the present invention, of which Fig. 16 is a side view of the same and Figs. 17 (a), (b) are graphs showing transmittance properties of a linear characteristic ND filter and a quadratic characteristic ND filter, respectively. The tenth embodiment is based on the invention defined in claim 9 for obtaining one-dimensional average position, intensity, and variance of a beam of light, and as shown in Fig. 16, the tenth embodiment is provided with three sets of photomultipliers 35 - 37 as the photoelectric conversion devices each having a length of L. Here, the photomultiplier is an electron multiplier in which electrons emitted as a result of the photoelectric effect are increased in geometrical progression to provide an output corresponding to the intensity of the input light and is used specifically for photoelectric conversion of a weak beam of light. The surface of the photomultiplier 36 on the input light side is covered by the linear characteristic ND filter 38, whereas the surface of the photomultiplier 37 on the input light side is covered by the quadratic characteristic ND filter 39. Here, the linear characteristic ND filter 38 has, as shown in Fig. 17(a), the transmittance b₁x proportional to the distance x from one end of the photomultiplier 36, whereas the quadratic characteristic ND filter 39 has, as shown in Fig. 17(b), the transmittance b₂x² proportional to the square of the distance x from one end of the photomultiplier 37. Incidentally, the ND filter is a shortened form of the Neutral Density Filter whose transmittance is independent of the wavelength (color), i.e., whose spectral transmittance is flat. And, the incoming beam of light is adapted to be split by half mirrors 40, 41 so as to be incident on each of the photosensitive surfaces of the photomultipliers 35 - 37 perpendicularly thereto. With the described construction, when a beam of light having the light intensity distribution ρ (x) the same as in Fig. 2 is incident thereon, the output obtained from the photomultiplier 35 which has no filter and allows the beam of light to enter therein directly becomes and from this equation (48), the quantity relative to the total intensity of the beam of light can be obtained. The output V₁ from the photomultiplier 36 covered by the linear characteristic ND filter 38 becomes V₁ = K·∫₀ L ρ (x)·b₁·x dx (49) and it becomes possible to obtain from the output V₁ the average value of the coordinates x weighted by the intensity of the beam of light. Similarly, the output V₂ from the photomultiplier 37 covered by the quadratic characteristic ND filter 39 becomes V₂ = K·∫₀ L ρ (x)·b₂·x² dx (50) and it becomes possible to obtain from the output V₂ the average of the squares of the coordinates x weighted by the intensity of the beam of light. Here, K is efficiency of photoelectric conversion. Thus, from equations (14), (48), (49), we obtain V₁/V₀ = b₁· x (51) and from this V₁/V₀, the linear output proportional to the average x of the distances x between one end of the photomultiplier 36 and the positions of the beam of light can be taken out. And, from equations (14), (48), (50), we obtain and from this V₂/V₀, the quadratic output proportional to the average of the squares of the distances x between one end of the photomultiplier 37 and the positions of the beam of light can be taken out. As a result of the foregoing, in the present embodiment, the total intensity It of the beam of light is obtained from equation (48), the average position x of the beam of light is obtained from equation (51), and the variance σ ² is obtained based on equations (51) and (52) from the following equation (53) Thus, also from the apparatus of the present embodiment, the same effect as obtained from the fifth embodiment can be obtained. Although, in the above description of the first to tenth embodiments, embodiments for and obtainable effects in detecting average position, intensity, and variance of slit light or spot light input have been disclosed, corpuscular rays such as electron rays and α rays can be equally detected for the average position, intensity, and variance by using semiconductor materials suited for treatment thereof. As described so far, with any of the first to sixth apparatus for detecting position/variance of input light of the present invention, the linear output proportional to the average value of the distances between one end of the photoelectric conversion device and the positions of the light input and the quadratic output proportional to the average of the squares of the above distances can be easily detected. Thus, by the method for detecting position/variance of input light of the present invention, without using expensive imaging devices and signal processing circuits used in the prior art, the position and variance of the input light can be obtained based on the above linear output and quadratic output quite easily and economically and with high response and accuracy. While the apparatus for detecting position/variance of input light of the present invention is applicable to various instruments, an example of such applications is a sensor for a surface roughness tester of a non-contact type as shown in Fig. 27, which functions on the principle that the intensity distribution of the scattered light depends on the roughness of the reflecting surface.

Claims: A photoelectric conversion apparatus comprising a photoelectric conversion device receiving a beam of input light constituted of a first resistive layer (1) formed of a first photoelectric conversion material and a second resistive layer (2) formed of a second photoelectric conversion material connected with said first resistive layer through a depletion layer (3) or directly, said first resistive layer being provided with uniform resistivity throughout its surface so that a linear output proportional to the average distance between one end of said photoelectric conversion device and the average position of said beam of input light is detected, characterized in that said second resistive layer is provided with resistivity dependent upon the distance from one end thereof so that a quadratic output proportional to the average of the squares of the distances between one end of said photoelectric conversion device and the positions illuminated by said beam and the variance of said beam of input light are derived from the current values taken out from the ends of said second resistive layer of the input light. A photoelectric conversion according to claim 1 characterized in that said first resistive layer is divided into a plurality of slip formed resistive layer segments, out of which those resistive layer segments located in the places numbered from one end thereof by predetermined numbers are provided with uniformal resistivity throughout their surfaces so that a linear output proportional to the average distance between one end of said photoelectric conversion device and the average position of the input light is detected, whereas those resistive layer segments located in the other places than the above mentioned places numbered from one end thereof by predetermined numbers are provided with resistivity dependent upon the distance from one end so that a quadratic output proportional to the average of the squares of the distances between one end of said photoelectric conversion device and the positions illuminated by the beam of input light and the variance of said beam of input light are derived from the currents values taken out from the ends of said resistive layer segments.

Inventors: IMAOKA SHINICHI, INOUE TAKAYOSHI, KAJIKAWA HIROSHI, KUSAKA TAKUYA, NAKAI YASUHIDE, NAKAUE AKIMITSU, NISHIMOTO YOSHIRO, NISHIMURA KOZO, ONISHI YOSHIHIKO, TACHIBANA HIROYUKI, TAKAMATSU HIROYUKI, TOJYO SHIGEKI, YONEDA YASUJI, IMAOKA, SHINICHI, INOUE, TAKAYOSHI, KAJIKAWA, HIROSHI, KUSAKA, TAKUYA, NAKAI, YASUHIDE, NAKAUE, AKIMITSU, NISHIMOTO, YOSHIRO, NISHIMURA, KOZO, ONISHI, YOSHIHIKO, TACHIBANA, HIROYUKI, TAKAMATSU, HIROYUKI, TOJYO, SHIGEKI, YONEDA, YASUJI
Applicants: KOBE STEEL LTD, KABUSHIKI KAISHA KOBE SEIKO SHO ALSO KNOWN AS KOBE STEEL LTD.
Application year: 1987
Main classification: G01S3
IPC codes: H01L31, H01L25, G01B11, G01S3