JPS61264314A - Scanning type optical microscope - Google Patents

Abstract

PURPOSE:To obtain a microscope which uses an acousto-optic deflecting element and has a fast scanning speed and excellent resolving power by letting a pupil projection lens system satisfy specific condition. CONSTITUTION:This microscope is equipped with a light source, an objective optical system which converges illumination luminous flux from the light source on a body 22 to be observed, acousto-optic deflecting elements 12 and 19 which are arranged between the light source and objective optical system and vary the angle of incidence of the illumination luminous flux upon the objective optical system to make a scan, an afocal relay optical system 41 which projects the illumination luminous flux upon the acousto-optic deflecting elements, and the pupil projection lens system which projects the image of the acousto-optic deflecting elements on the exit pupil 14 of the objective optical system. In this case, the pupil projection system satisfies the condition shown by f (epsilon/P)EP. In the equation, (f) is the focal length of the pupil projection lens system, epsilonthe size of effective aperture of the acousto-optic deflecting elements, (p) the size of the exit pupil of the objective optical system viewed from the side of the pupil projection lens 20, and EP the distance from the image position of the objective optical system to the exit pupil.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a scanning optical microscope.

[Conventional technology]

Traditionally, scanning optical microscopes use rotating polygon mirrors.

Although it is known that an object to be observed is scanned two-dimensionally using a galvanometer mirror, such a scanning optical microscope has a drawback of slow scanning speed. For this reason, the patent application filed by the inventor of the present application in 1986-62
No. 262 proposes a scanning optical microscope that uses a so-called acousto-optic optical deflector (hereinafter referred to as AOD) instead of a reflecting mirror such as a rotating polygon mirror or a galvano mirror. To explain this with reference to FIG. 2, a light beam 10 from a laser light source, which can be equivalently considered as a point light source, passes through a heam splitter 11 and enters a first light deflection element 22. This light deflection element 12 is arranged at a position conjugate with the exit pupil 14 of the objective lens 13. If no deflection is performed, light beam 1
0 travels along the optical axis 15. When performing deflection, that is, when scanning the light beam 10, since the light deflection element 12 is provided at the pupil position, the direction of the light beam 10 is the off-axis principal ray 16.
The center of the light beam 10 also coincides with the off-axis principal ray 16. These light beams then pass through pupil transmission lenses 17 and 1
8 and enters a second optical deflection element 19 located at the pupil position. This optical deflection element 19
When performing scanning in the Y direction, the previous optical deflection element 12 is
Directional scanning will be performed. If an optical deflection element capable of deflecting in both the X and Y directions is used, only one optical deflection element is required. The image lens 21 causes the light to enter the pupil 14 of the objective lens 13 . Since the direction and center of the off-axis light beam formed by the optical deflection elements 12 and 19 coincide with the off-axis principal ray 16, the off-axis light beam also passes through the pupil 14 of the objective lens 13.
be accurately incident on . These light beams then produce point-like light that is diffraction-limited on the object 22 by the objective lens 13. By scanning the object 22 two-dimensionally in the X-Y direction using the light deflecting elements 12 and 19, the point light scans the object 22 two-dimensionally.

When observing the light transmitted through the object 22, the light is collected by the condenser lens 23 and detected by the detector 24. still,
A detector 24 is also installed at the pupil position.

Therefore, since off-axis light also always occurs at the same position, the detector 2
Detector 2 can prevent the effects of sensitivity unevenness, etc.
In order to carry out differential detection in which the area of 4 is also small, the detector 24 is composed of two detectors 25 and 26,
These are installed symmetrically with respect to the optical axis 15. in this case,
Since the beam center and the off-axis principal ray are set to coincide even with off-axis light, the detectors 25 and 26 are arranged symmetrically with respect to the off-axis principal ray, allowing accurate differential detection. I can do it.

2. When detecting with reflected light from the object 22, the object 22
The light beam reflected from the objective lens 13 and its pupil 1
4 and further passes through the imaging lens 21 to form an image. This imaging plane is the plane on which images are observed with a normal optical microscope.

Furthermore, the light beam is passed through the optical deflection element 19 by the pupil projection lens 20.
Come back to the top.

In this way, the reflected beam returns to the beam splitter 11 through exactly the same path as when it entered the object, and is extracted by the beam splitter 11 to become the detection beam 27. Since the reflected beam passes through the optical deflection element 19.12 and returns, the detection beam 27 does not move even when scanning off-axis. By providing a pinhole 29 at a narrowed position and detecting it with a detector 30 behind the pinhole, it is possible to obtain a flare-free image with a higher resolution than that of an ordinary microscope, as in the conventional example described above. It goes without saying that a normal image can be obtained without providing the pinhole 29, and if a sunspot-shaped light shield is provided at the position where the light beam is focused, a dark-field image can be easily observed. . Further, if the detector 30 is composed of two detectors 31 and 32 and installed symmetrically with respect to the optical axis at a position where the light beam spreads, differential observation can be performed. In this case, since the AOD is used as the scanning member, the scanning speed is sufficiently high, so that it is possible to display the object image in real time on the screen of a TV monitor (not shown) using signals from the detector.

[Problem that the invention seeks to solve]

In a scanning optical microscope with such a configuration, the light deflection element is disposed at a position conjugate with the exit pupil of the objective lens, or preferably in the vicinity of the exit pupil. In order to prevent exit pupil vignetting, the size of the aperture of the light deflection element must be larger than or equal to the size of the exit pupil. However, since it is impossible to increase the effective aperture of an AOD, if the above-mentioned vignetting is prevented, the scanning beam will not be able to sufficiently fill the exit pupil of the objective lens. There was a problem that only a part of the scanning optical system could be utilized and the resolving power of the scanning optical system was not very good.

In view of the above points, it is an object of the present invention to provide a scanning optical microscope that uses an AOD and has a high scanning speed and good resolution.

[Means and actions for solving the problem] The above purpose is:
According to the present invention, a light source, an objective optical system that focuses the illumination light beam emitted from the light source onto an object to be observed, and an objective optical system that is disposed between the light source and the objective optical system; an acousto-optic light deflection element that performs scanning by changing the incident angle of the illumination light flux entering the acousto-optic light deflection element; an afocal relay optical system that projects the illumination light flux onto the acousto-optic light deflection element;
and a pupil projection lens system for projecting the acousto-optic light deflection element onto the exit pupil of the objective optical system, and the pupil projection lens system is f-, -E.

Here, f: focal length of the pupil projection lens system, ε: size of the effective aperture of the acousto-optic light deflection element, p: size of the exit pupil of the objective optical system as seen from the pupil projection lens side, E2: objective optics This problem is solved by a scanning optical microscope characterized by satisfying the condition of the distance from the image position of the system to the exit pupil.

According to this invention, since the pupil projection lens system satisfies the above conditions, the effective aperture of the acousto-optic light deflection element matches the exit pupil of the objective optical system, and thus the large NA of the objective optical system is sufficient. Therefore, a scanning optical system having a resolving power equivalent to that of a microscope optical system can be obtained. In other words, even with an acousto-optic light deflection element having a small effective aperture, it is possible to match the effective aperture to the exit pupil size of the objective optical system, and therefore a scanning optical microscope that effectively utilizes the resolving power of the microscope optical system can be obtained. It will be done.

〔Example〕

The present invention will be described below with reference to an embodiment shown in FIG. 1. The basic configuration is the same as the conventional example shown in FIG. and have focal lengths f and f2, respectively, and the pupil projection lens 20 has a focal length f. Further, the objective lens 13 and the imaging lens (in this case, a barrel lens) 21 constitute an objective optical system 42 . These optical elements are then connected to the objective optical system 4.
The exit pupil 14 of No. 2 is projected by the pupil projection lens 20 to the back focal position A of the pupil transmission lens 18 and further to the front focal position B of the pupil transmission lens 17 by the afocal relay optical system 41. Note that each pupil transmission lens 17 and 18 of the afocal relay optical system 41 is set to f,=f2 for simplicity in design and implementation.

Here, acousto-optic light deflection elements 1 arranged at pupil positions A and B
2.19, the effective aperture size is ε, and the exit pupil size of the objective optical system 42 as seen from the pupil projection lens 20 side is p.
Then, in order to make full use of the performance of the optical system of the microscope, it is necessary to fully utilize the numerical aperture of the objective optical system, and the pupil projection lens 20 has a pupil of ε P, =−・−・−(1) The pupil must be projected with magnification. by the way,
If the distance from the image position C of the objective optical system 42 to its exit pupil 14 is E9, the focal length of the pupil projection lens 20 is f=P, ・E, −・−1−−−・−(2)
Therefore, the exit pupil 14 is projected by the pupil projection lens 20 onto the acousto-optic deflection elements 12 and 19 at a magnification of P. At this time, the distance β from the image position C of the objective optical system 42 to the pupil position A is ff=f (P, +2)
It is automatically given by −1・−−−−−−+31. Further, the angle at which the acousto-optic light deflection elements 12 and 19 deflect the off-axis light is φ.

Then, φ, ε=φ21) −−−−−−・−・(4
) holds true, and the image height at image position C is φ
It is given by 2Ee.

Thus, from equations (1) and (2), the focal length “ga r #−
・E.

By using a pupil projection lens 20 given by p,
The exit pupil of the objective optical system and the effective aperture of the acousto-optic light deflection element substantially match, making it possible to scan an object with a resolving power equivalent to that of the optical system of a microscope.

〔Effect of the invention〕

As described above, according to the present invention, the effective aperture of the acousto-optic light deflection element and the exit of the objective optical system are Since the pupil substantially coincides with the pupil, the large NA of the objective optical system can be fully utilized, thus scanning can be performed with a resolution equivalent to that of a microscope optical system, and an acousto-optic optical deflection element is used as the scanning member. Because of this, the scanning speed is sufficiently high, and therefore an object image with good resolution and observable in real time can be displayed on the screen of the TV monitor, and an extremely effective scanning optical microscope can be provided.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an optical system of an embodiment of a scanning optical microscope according to the present invention, and FIG. 2 is a diagram showing an optical system of an example of a conventional scanning optical microscope. 10... Light beam, 11... Beam splitter, 12.19... Acousto-optic light deflection element, 13...
・Objective lens, 14... Exit pupil, 15... Optical axis, 16... Off-axis principal ray, 17.18... Pupil transmission lens, 20... Pupil projection lens. , 21...imaging lens, 22...object, 23...condenser lens, 24°25.26,30,31.32...
-Detector, 27...detection beam, 28...condensing lens, 29...pinhole, 41...afocal relay optical system, 42...objective optical system.

Claims (1)

[Scope of Claims] A light source, an objective optical system that focuses an illumination beam emitted from the light source onto an object to be observed, and an objective optical system disposed between the light source and the objective optical system. an acousto-optic light deflection element that performs scanning by changing the incident angle of the illumination light flux entering the acousto-optic light deflection element; an afocal relay optical system that projects the illumination light flux onto the acousto-optic light deflection element; A scanning type, comprising: a pupil projection lens system that projects onto the exit pupil of the objective optical system, and the pupil projection lens system satisfies the condition f≠(ε/p)E_p. Optical microscope. Here, f: focal length of the pupil projection lens system, ε: size of the effective aperture of the acousto-optic light deflection element, p: size of the exit pupil of the objective optical system as seen from the pupil projection lens side, E_p: objective optics Distance from system image position to exit pupil