JPS61228414A - Optical device - Google Patents

Abstract

PURPOSE:To remove flare light completely by cutting off reflected light at the plane part of a plane optical member by a light shield member. CONSTITUTION:Light is reflected by a half-mirror 1 and its flare light which is reflected by the plane part 51a of a parallel plane plate 51 as shown by broken lines passes through the half-mirror 1 again and is then converged by a positive lens 61 on a spatial filter on its focal plane. Then, its position of convergence is at distance l from the optical axis of the positive lens 61 on the spatial filter 7 and the distance l is larger than the radius lO of the internal diameter part of the light shield part 72, so the flare light reflected by the plane part 51a shown by the broken lines is but off by the light shield part 72 of the spatial filter 7. Reflected light from a mirror 2 and reflected light from a mirror 3 from interference fringes 4 on a formation surface 4a. At this time, the reflected light from the plane part 51a is cut off the light shield part 72 of the filter 7, so the reflected light generates no noise in the interference fringes 4.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an optical device in which a flat optical member is arranged in a parallel light beam of an optical system.

(Background of the Invention) Conventionally, in an optical device, a planar optical member such as a prism or a plane-parallel plate is arranged in a parallel light beam of an optical system.

There is a problem in that the reflected light from the flat portion of the flat optical member becomes flare light, which adversely affects the performance of the optical system.

Conventional optical devices that take these problems into consideration include 1.
For example, there is a Twyman Green type interferometer as shown in FIG.

As shown in Fig. 7, in this interferometer, part of the parallel light beam incident on the half mirror 1 from the left side is reflected upward, and part of it is transmitted to the right side, and these reflected and transmitted lights are After being reflected by mirrors 2 and 3: Return to the half mirror 1 again, and form the forming surface 4a arranged below the half mirror 1.
Interference fringes 4 are formed thereon. A plane optical member 5 such as a phase plate or a polarizing plate is disposed in the parallel light beam between the half mirror 1 and the mirror 2. The plane portion 5a of the plane optical member 5 is provided at an angle with respect to the parallel light beam. As a result, the reflected light from the flat portion 5a reaches a different position within the plane on which the interference fringes 4 are formed than the reflected light from the mirror 2, and no noise is imparted to the interference fringes 4.

However, in such a conventional optical device, in order to prevent the reflected light from the flat portion 5a from flaring and causing noise to the interference fringes 4, the flat optical member 5 must be tilted considerably. It becomes necessary to increase the size of the planar optical member 5, which increases the size of the entire optical system, and because the planar optical member 5 is tilted considerably, the deviation of the optical axis becomes large, making it difficult to manufacture and adjust the optical system. There was a problem with this.

(Objective of the Invention) The present invention has been made by focusing on such conventional problems, and it is possible to avoid tilting the flat part of a flat optical member placed in a parallel light beam to a large extent with respect to the parallel light beam. It is an object of the present invention to provide an optical device that can completely eliminate reflected light on the flat surface, that is, flare light, which adversely affects the performance of the optical system.

(Summary of the Invention) The gist of the present invention for achieving the above object is to provide an optical device in which a plane optical member is disposed in a parallel light beam of an optical system with its plane portion inclined with respect to the parallel light beam. A positive lens is provided in the parallel light beam, and a light shielding member for blocking light reflected by the flat surface is provided at the focal position of the positive lens.

In the optical device having the above configuration, the light reflected from the flat portion is blocked by the light shielding member, and the reflected light is prevented from turning into flare light and having an adverse effect on the properties of the optical system.

(Example) Each example of the present invention will be described below based on one drawing. Note that the same parts as in the conventional example are given the same reference numerals.

A first embodiment of the present invention will be described based on FIGS. 1 and 2. In this embodiment, the present invention is applied to a Twyman Green type interferometer.

As shown in Figure 1, the Twyman-Green interferometer is
A half mirror 1 that reflects part of the parallel light flux a entering from the left side upward and transmits part of it to the right side, and mirrors 2 and 3 arranged perpendicular to the optical axis of the reflected light and transmitted light. , a parallel plane plate 51 as a plane optical member 5 disposed in a parallel beam C between the half mirror 1 and the mirror 2, and a parallel beam C between the half mirror 1 and the surface 4a on which interference fringes 4 are formed. It consists of a Keplerian-type afocal system 6 provided in the area and a spatial filter 7 as a light shielding member.

The parallel plane plate 51 is arranged so as to be inclined by a small angle θl with respect to the plane portion 51a which is a parallel beam of light.

Keplerian type 7 focal system 6 is a positive lens 61.62
It consists of

The spatial filter 7 is provided at the focal point of the positive lens 61 and is formed into a disk shape. This spatial filter 7 includes a transmission section 71 that allows the reflected light (interference light) from the mirror 2.3 to pass through, and a reflected light (flare light) from the flat section 51a.
It is composed of a ring-shaped light shielding part 72 that blocks light.

The size of this light shielding portion 72 is determined as follows.

The reflected light from the flat portion 51a is focused by a positive lens 61 on its focal plane at a position shifted by a distance si from the optical axis of the positive lens 61. This distance 81 is calculated by dividing the focal length of the positive lens 61 by f.

J1=fetan2θl It is indicated by.

Therefore, assuming that the radius of the inner diameter portion of the light shielding portion 72 is 0, the light shielding portion 72 is formed so that no<l.

In the interferometer having the above configuration, half mirror 1 is
A part of the parallel light beam a incident on is reflected upward, and a part thereof is transmitted to the right.

Of the light reflected by the half mirror 1, the flare light reflected by the flat part 51a of the parallel plane plate 51 as shown by the broken line in the figure returns to the half mirror 1 again.

The light passes through the half mirror 1 and is focused by the positive lens 61 onto the spatial filter 7 located on its focal plane. The light condensing position is located on the spatial filter 7 at a distance of 1lllfL from the optical axis of the positive lens 61, and since this distance is larger than the radius or O of the inner diameter of the light shielding part 72, the plane shown by the broken line The flare light reflected by the portion 51a is blocked by the light blocking portion 72 of the spatial filter 7.

In addition, among the light reflected by the half mirror 1, the parallel plane plate 5
1 and reflected by the mirror 2 passes through the parallel plane plate 51 and the half mirror 1, is condensed by the positive lens 61, passes through the transmission part 71 of the spatial filter 7,
The light is made into parallel light by the positive lens 62 and reaches the forming surface 4a.

On the other hand, the parallel light beam a that has passed through the half mirror 1 is reflected by the mirror 3 and returns to the half mirror 1 again.

It is reflected by the half mirror 1. This reflected light.

Similar to the reflected light from the mirror 2, the light is focused by the positive lens 61 and passes through the transmission part 71 of the spatial filter 7,
The light is made into parallel light by the positive lens 62 and reaches the forming surface 4a.

Therefore, interference fringes 4 are formed on the formation surface 4a by the reflected light from the mirror 2 and the reflected light from the mirror 3.

At this time, the reflected light from the flat part 51a is filtered through the spatial filter 7.
Since the light is blocked by the light blocking portion 72, the reflected light does not add noise to the interference fringes 4.

In the first embodiment, the light shielding part 72 of the spatial filter 7 is formed in a ring shape, but the light shielding part 72 of the spatial filter 7 may be formed as shown in FIG. 3(a), (b) or (C). It's okay.

That is, in FIG. 3a, the light shielding part 7 of the spatial filter 7
2 is formed by a circular spot.

The center of the light shielding portion 72 is located at the position l=f·tan 2θ1.

In FIG. 3, the light shielding portion 72 of the spatial filter 7 is formed in an annular shape. The center of the light shielding part 72 is l=f・t
an 2θl position.

In FIG. 3C, the light blocking portion 72 of the spatial filter 7 is formed by a rectangular spot. The center of the light shielding portion 72 is located at the position l=f@tan2θ1.

Further, in the first embodiment, the plane portion 5 of the parallel plane plate 51 is
1a, that is, the light reflected from the surface of the plane-parallel plate 51, was configured to be blocked by the light-shielding portion 72, but the light-shielding portion 72 was configured to block the light reflected from the back surface 51b of the plane-parallel plate 51. Needless to say, it is configurable.

Next, a second embodiment of the present invention will be described based on FIG.

In this embodiment, the parallel plane plate 5 is used as the plane optical member 5.
A prism 52 is used instead of 1.

The other configurations are the same as those of the first embodiment.

This prism 52 has a plane portion 52a while collimating the beam.
It is arranged at an angle of θ2 with respect to the parallel light beam.

The wedge angle formed by the flat portion 52a and the flat portion 52b of the prism 52 is α.

In order to block the light reflected by the plane portion 52b of the prism 52 by the light blocking portion 72 of the spatial filter 7, the light blocking portion 72
The size of 2 is determined as follows.

The reflected light from the flat portion 52b is focused by the positive lens 61 on its focal plane at a position shifted by a distance from the optical axis of the positive lens 61. This distance reading is dan=fφjan
It is represented by (θ2+β).

Here, β is the exit angle from the plane of the flat portion 52a, sinβ=nsin(2α+020) It is.

Here, 020 is the refraction angle on the plane of the flat part 52a, and n
It is expressed as sin θ20=sin 02.

Therefore, when a spatial filter 7 as shown in FIG. 2 is used as a light shielding member, the radius fLO is no<
If the light shielding part 72 is formed so that the prism 52 can be seen clearly, the light reflected by the flat part 52b of the prism 52 will be blocked by the light shielding part 72, and the reflected light will not add noise to the interference fringes 4.

Next, a third embodiment of the present invention will be described based on a WIJS diagram.

In this embodiment, a half prism 5 is used as the planar optical member 5.
3 is provided at the position of the half mirror 1 in place of the half mirror 1, and the other configurations are the same as in each of the above embodiments.

This half prism 53 has a parallelogram-shaped cross section in a plane including the optical axis. Therefore, for the light beam that passes through the half prism, it functions as a parallel plane plate,
Parallelism is maintained before and after the half prism 53, making it easy to adjust the optical axis.

In this embodiment as well, the light reflected by the flat parts 53b and 53c of the half prism 53 is blocked by the light blocking part 72 of the spatial filter 7, as in the above embodiments.

Furthermore, when the angles α and β which the entrance surface and the exit surface of the half prism 53 make with respect to the plane perpendicular to the incident light beam and the exit light beam, respectively, are equal (α−β), the half prism 53
Regarding the light reflected by the semi-transparent surface 53a of No. 3, since this prism 53 functions as a parallel plane plate, it is advantageous in that less aberration occurs.

Furthermore, if the half prism 53 is made into a rectangular parallelepiped shape in which right triangles are joined as shown in FIG. In addition, since a configuration can be adopted in which the incident light beam a and the reflected light beam a to the half prism 53 are perpendicular to each other, an advantageous state in terms of thin film characteristics can be maintained, and adjustment of the suspension optical system can also be made advantageous.

It goes without saying that each of the positive lenses 61
．． The lens 62 may be a single lens, a compound lens, or a laminated lens.

Furthermore, the optical device according to the present invention is not limited to the interferometer described above, and depending on the size of the light shielding part, the position of the light shielding member may not necessarily coincide with the focal position of the positive lens, but may cause a flare. It is possible to remove light.

(Effects of the Invention) According to the optical device according to the present invention, a positive lens is provided in the parallel light beam, and a light shielding member provided at the focal point of the positive lens blocks reflected light on the flat surface of the flat optical member. Therefore, the plane part of the plane optical member disposed in the parallel light beam is not tilted too much with respect to the parallel light flux, and the reflected light at the plane part, that is, the flare light, which adversely affects the properties of the optical system, can be prevented. Since it can be completely removed and the flat part does not need to be tilted too much with respect to the parallel light beam, the flat optical member can be made smaller, making it possible to downsize the entire optical system. Easier to manufacture and adjust.

[Brief explanation of the drawing]

1 and 2 show a first embodiment of the present invention, FIG. 1 is a schematic diagram showing the main parts of the optical device, FIG. 2 is a plan view of the main parts, and FIG. 3 (a) , (b), and (C) are respectively plan views of modified examples of the main parts shown in FIG. 2, FIG. 4 is a schematic diagram showing the main parts of the optical device according to the second embodiment of the present invention, and FIG. 6 is a schematic diagram showing the main parts of an optical device according to a third embodiment of the present invention, FIG. 6 is an explanatory diagram of an optical path of another embodiment of the half prism shown in FIG. 5, and FIG. 7 is a diagram showing a conventional optical device. FIG. 2 is a schematic diagram showing the main parts. 5...Parallel plane member 6...Positive lens 7...
Spatial filter (light shielding member) 51 a, 52 b, 53 b, "r 3
c ---Plane section Fig. 1 Fig. 3

Claims (1)

[Claims] In an optical device in which a plane optical member is arranged in a parallel light beam of an optical system with its plane part tilted with respect to the parallel light beam,
An optical device characterized in that a positive lens is provided in the parallel light beam, and a light shielding member for blocking light reflected by the flat portion is provided at a focal position of the positive lens.