1. Field of the Invention
This invention relates to an optical type scanning microscope. This invention particularly relates to a scanning microscope, wherein an optical means, which irradiates a light beam to a sample, is moved with respect to a sample supporting member, on which the sample is supported, such that the light beam may scan the sample. This invention also relates to a device for detecting a scanning width, i.e., a width over which a light beam, or the like, scans a material, in an apparatus in which the material is scanned with the light beam, or the like. This invention additionally relates to a magnification indicating apparatus for a scanning microscope, such as an optical type scanning microscope or a scanning electron microscope, wherein an actual width of scanning with a probe is detected, and a magnification of the microscope is indicated in accordance with the detected scanning width.
2. Description of the Prior Art
Optical type scanning microscopes have heretofore been used. With the scanning microscope, a light beam is converged to a small light spot on a sample, and the sample is two-dimensionally scanned with the light spot. Light radiated out of the sample during the scanning (i.e., light which has passed through the sample, light which has been reflected from the sample, the fluorescence which is produced by the sample, or the like) is detected by a photodetector. An enlarged image of the sample is thereby obtained. An example of the scanning microscope is disclosed in Japanese Unexamined Patent Publication No. 62(1987)-217218.
In the conventional optical type scanning microscopes, a mechanism which two-dimensionally deflects a light beam by a light deflector is primarily employed as the scanning mechanism.
However, the scanning mechanism described above has the drawback in that a light deflector, such as a galvanometer mirror or an acousto-optic light deflector (hereinafter referred to as "AOD"), which is expensive must be used. Also, with the scanning mechanism described above, a light beam is deflected by a light deflector. As a result, the angle of incidence of the deflected light beam upon an objective lens of the light projecting optical means changes momentarily, and aberration is caused to occur. Therefore, the scanning mechanism described above also has the problem in that it is difficult for the objective lens to be designed such that aberration can be eliminated. Particularly, in cases where an AOD is utilized, astigmatism occurs in the light beam radiated out of the AOD. Therefore, in such cases, a special correction lens must be used, and the optical means cannot be kept simple.
In order to eliminate the aforesaid problems, a scanning mechanism has heretofore been proposed wherein a light beam is not deflected but a sample is scanned with the light spot of the light beam. For example, in U.S. Pat. No. 5,081,350, a novel mechanism has been proposed wherein a light projecting optical means is supported on a movable member, the movable member is moved reciprocally with respect to a sample supporting member, and a light spot of a light beam is thereby caused to scan a sample.
In U.S. Patent application Ser. No. 735,734, the applicant has proposed a movement mechanism for moving an optical means with respect to a sample supporting member. The proposed movement mechanism comprises a tuning fork having an end, on which an optical means or a sample supporting member is supported, and an excitation means composed of an electromagnet for applying a magnetic field, the intensity of which changes periodically, to the tuning fork, and thereby causing the tuning fork to vibrate. The proposed movement mechanism is advantageous over a movement mechanism utilizing, for example, a piezo-electric device or an ultrasonic vibrator, in that the width, over which the optical means moves with respect to the sample supporting member, i.e. the width, over which the light beam scans the sample, can be kept large. (The width, over which the light beam scans the sample, is determined by the amplitude of the tuning fork.) Therefore, when the proposed movement mechanism is employed in a scanning microscope, an image of a large area of the sample can be formed.
In most of conventional scanning microscopes, light radiated out of a sample (i.e., light which has passed through the sample, light which has been reflected from the sample, the fluorescence which is produced by the sample, or the like) is detected by a photodetector, and a serial output generated by the photodetector is fed into a signal processing means. The signal processing means samples and quantizes the output received from the photodetector. In this manner, image signal components of a digital image signal are obtained which correspond to respective positions lying along each main scanning line on the sample.
However, in such cases, if a light beam scanning mechanism, which is composed of a tuning fork and an electromagnet, is utilized, problems may occur in that a distortion occurs in an image which is reproduced from the digital image signal. This is because the displacement of the tuning fork does not change linearly with respect to time but changes in accordance with characteristics close to a sine function. Such problems also occur when a light beam scanning mechanism other than the light beam scanning mechanism composed of a tuning fork and an electromagnet is utilized.
In order to cope with the problems described above, it is considered to modulate the period of pixel clock pulses that determines the period, with which the output of a photodetector is sampled, so as to compensate for fluctuations in the speed, at which an optical means is moved reciprocally with respect to a sample supporting member. Such a method is effective, but it has the problem in that, if the relationship between the operation of the tuning fork (i.e., the movement of the optical means with respect to the sample supporting member) and the timing, with which the sampling process is begun, is not accurately kept at predetermined relationship, a distortion occurs in an image reproduced from the digital image signal.
The aforesaid scanning mechanism, wherein a light beam is not deflected but a sample is scanned with the light spot of the light beam, is broadly applicable to optical type scanning microscopes, scanning electron microscopes, scanning tunnel microscopes, light beam scanning read-out apparatuses, or the like. In such a scanning mechanism, a movement mechanism composed of a tuning fork and an electromagnet for resonating the tuning fork, a movement mechanism composed of a piezoelectric device, a movement mechanism composed of an ultrasonic vibrator, or the like, is often utilized in order to move a scanning means (e.g., a probe, on which a light projecting optical means, a stylus, or the like is supported, in cases where the scanning mechanism is employed in a scanning microscope) reciprocally and quickly with respect to a material which is to be scanned. In cases where such a movement mechanism is employed, the width, over which the scanning means moves reciprocally with respect to the material to be scanned, changes comparatively easily due to fluctuations in the drive voltage applied to the movement mechanism, or the like. If the width, over which the scanning means moves reciprocally with respect to the material to be scanned, changes, the width over which the light beam scans the material will change inevitably.
In cases where the scanning mechanism is employed in a scanning microscope, if the width over which the light beam scans the material changes, the magnification, with which a microscope image is formed, will deviate from a designed value. In cases where the scanning mechanism is employed in a light beam scanning read-out apparatus, if the width over which the light beam scans the material changes, the size of an image, which has been read out from the scanned material, will fluctuate. In order to eliminate such problems, it is necessary that the actual width, over which the light beam scans the material, is detected by a certain means. In accordance with the detected scanning width, the magnification of the microscope image should be indicated, or the operation of the scanning mechanism should be corrected such that the scanning width may be kept at a predetermined value.
As one of scanning width detecting devices for detecting the actual width, over which a light beam scans a material, there has heretofore been known a device comprising:
i) a grid pattern, which is combined with either one of a material to be scanned and a scanning means and which is constituted of a plurality of light reflecting members or light blocking members standing side by side with one another in a direction, along which the scanning means is moved reciprocally with respect to the material to be scanned, PA0 ii) a light projector, which is combined with the other of the material to be scanned and the scanning means and which irradiates a light beam to the grid pattern, PA0 iii) a light receiver for detecting the light beam, which has been reflected by the grid pattern, or the light beam, which has passed through the grid pattern, and PA0 iv) a means for counting the number of periodical fluctuations in a light beam detection signal, which has been generated by the light receiver. PA0 i) a sample supporting member on which a sample is supported, PA0 ii) an optical means which irradiates a light beam to said sample, PA0 iii) a movement mechanism which reciprocally moves said optical means with respect to said sample supporting member such that said light beam may scan said sample in main scanning directions and in sub-scanning directions, and PA0 iv) a photodetector for detecting light radiated out of the portion of said sample, which is exposed to said light beam, an image of said sample being thereby formed, PA0 a) a signal processing means for sampling a serial output of said photodetector and thereby generating image signal components of a digital image signal, which correspond to each main scanning line, PA0 b) a means for feeding pixel clock pulses into said signal processing means, the period of said pixel clock pulses being modulated so as to compensate for fluctuations in a speed, at which said optical means is moved reciprocally with respect to said sample supporting member, PA0 c) a means for generating a timing signal that determines the timing, with which the sampling process is begun, PA0 d) a grid pattern, which is secured to either one of said sample supporting member and said optical means and which is constituted of a plurality of light reflecting members or light blocking members standing side by side with one another in the direction, along which said optical means is moved reciprocally with respect to said sample supporting member, PA0 e) a light projector, which is associated with the other of said sample supporting member and said optical means and which irradiates a light beam to said grid pattern, PA0 f) a light receiver for detecting the light beam, which has been reflected by said grid pattern, or the light beam, which has passed through said grid pattern, PA0 g) a means for sampling a light beam detection signal, which has been generated by said light receiver, in accordance with said pixel clock pulses and thereby generating a digital displacement signal, and PA0 h) a means for approximating the relationship between the order x, where x=1, 2, 3, . . . , in which signal components of said digital displacement signal representing specific points appearing at equal pitches on said grid pattern occur, and the order y, in which said signal components of said digital displacement signal are sampled, with a quadratic equation y=ax.sup.2 +bx+c, PA0 i) a material, which is to be scanned, PA0 ii) a scanning means, and PA0 iii) a movement mechanism which reciprocally moves said scanning means with respect to said material such that said scanning means may linearly scan said material, PA0 a) a grid pattern, which is combined with either one of said material and said scanning means and which is constituted of a plurality of light reflecting members or light blocking members standing side by side with one another at predetermined pitches in a direction, along which said scanning means is moved reciprocally with respect to said material, PA0 b) a light projector, which is combined with the other of said material and said scanning means and which irradiates a light beam to said grid pattern, PA0 c) a light receiver for detecting the light beam, which has been reflected by said grid pattern, or the light beam, which has passed through said grid pattern, PA0 d) a means for sampling a light beam detection signal, which has been generated by said light receiver, in accordance with predetermined sampling clock pulses and thereby generating a digital displacement signal, and PA0 e) a calculation means for approximating the relationship between the order x, where x=1, 2, 3, . . . , in which signal components of said digital displacement signal representing specific points appearing at equal pitches on said grid pattern occur, and the order y, in which said signal components of said digital displacement signal are sampled, with a simple equation y=ax+b, PA0 i) a sample, PA0 ii) a probe, and PA0 iii) a movement mechanism which reciprocally moves said probe with respect to said sample such that said probe may linearly scan said sample, PA0 a) the aforesaid scanning width detecting device in accordance with the present invention, PA0 b) a means for calculating a magnification of an image reproduction width in a microscope image reproducing means, which image reproduction width is taken in the direction of said scanning, with respect to the scanning width, which has been found by said scanning width detecting device, and PA0 c) an indicating means for indicating the magnification, which has thus been calculated.
In the scanning width detecting device
fluctuations in described above, the number of periodical the light beam detection signal represents the number of the light reflecting members or the light blocking members, across which the light beam irradiated from the light projector to the grid pattern has moved. Therefore, the width, over which the light beam scans the material, can be detected by counting the number of periodical fluctuations in the light beam detection signal. For example, in cases where the grid pattern is constituted of a plurality of the light reflecting members, and the light receiver detects the light beam, which has been reflected by the light reflecting members, the light beam detection signal generated by the light receiver periodically rises pulse-wise. Therefore, the actual width, over which the light beam scans the material, can be detected by counting the number, N, of the pulse-wise rising points in the light beam detection signal and multiplying the pitch, p, at which the light reflecting members of the grid pattern stand side by side with one another, by the number, N.
However, with the scanning width detecting device described above, errors easily occur in detecting the width, over which the light beam scans the material. Therefore, the scanning width detecting device described above cannot always be employed when the width, over which the light beam scans the material, is to be detected very accurately. How such errors occur will be described hereinbelow. By way of example, the number, N, is counted as being 100 in cases where the light beam irradiated from the light projector to the grid pattern has moved across 100 light reflecting members or 100 light blocking members (i.e., m'th through m+99'th members). Actually, in some cases, the light beam may begin scanning immediately before it is irradiated to the m'th member, and the scanning may be finished immediately after the light beam has moved across the m+99'th member. In other cases, the light beam may begin scanning when it is irradiated to a position in the vicinity of an m-1'th member, and the scanning may be finished at a position in the vicinity of an m+100'th member. In both cases, the width, over which the light beam scans the material, is detected as being equal to 100p. However, in the former cases, the actual width, over which the light beam scans the material, is close to 99p. In the latter cases, the actual width, over which the light beam scans the material, is close to 101p.
In order to eliminate the problems described above, it is considered to set the initial position, at which the scanning begins, at a predetermined position. However, in cases where a piezo-electric device, or the like, is employed as the reciprocal movement mechanism, it is very difficult to set the initial position, at which the scanning begins, at a predetermined position.