JPH0915049A - Optical path length varying mechanism - Google Patents

Abstract

PURPOSE: To control the variation of optical path length easily by disposing a rotary means at a position separated by a predetermined distance from the central axis of a corner cube prism formed to reflect an incident luminous flux back to an incident optical path and turning the rotary shaft of a rotary board while inclining a predetermined angle. CONSTITUTION: A corner cube prism 11 is fixed, at the bottom part thereof, to a board 12 coupled with the rotary shaft 14 of a motor 13. The corner cube prism 11 comprises three internal reflection prism faces making an angle of 90 deg. each other wherein the incoming face and outgoing face are set normal to the diagonal of cube so that the incident light is reflected on three faces and returned back to the incident optical path. The corner cube prism 11 is bonded with the central axis thereof being shifted by a distance (d) from the center of rotation of the board 12. Consequently, the optical path length can be varied by 4d.sinθ.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of an optical path length variable mechanism such as a Fourier near infrared spectroscope (FT-NIR).

[0002]

2. Description of the Related Art In Fourier near-infrared spectroscopes and similar spectroscopes, the method of varying the optical path length is, for example, a method in which a corner cube is linearly moved by a voice coil, and two mirrors are diagonally opposed to each other. There is a method of reciprocally rotating the attached disc.

FIG. 3 is a block diagram showing an example of a Michelson interferometer unit incorporated in a Fourier near infrared spectroscope having a variable optical path length according to the above method. In the figure, the light from the lamp light source 1 is collimated by the first lens 2 and is incident on the beam splitter 3. The incident light is split into two by the beam splitter 3, one of which is incident on the fixed corner cube 4 and the other of which is incident on the movable corner cube 5.

The movable corner cube 5 is a voice coil 7
The optical path length can be varied by moving the voice coil in the left-right direction by driving the voice coil. The light reflected by the fixed corner cube 4 passes through the beam splitter 3 and enters the second lens 6, and the light reflected by the movable corner cube 5 is also reflected by the beam splitter 3 and enters the lens 6. The light entering the lens 6 is interference light. The light focused by the lens 6 is guided to a sample (not shown), and the intensity of the light passing through the sample is measured by a photodetector (not shown).

In such a structure, the fixed corner cube 4 of the Michelson interferometer unit is fixed, only the movable corner cube 5 is moved in the left-right direction, and the change in the interference signal at that time is measured by the photodetector. The spectral characteristics of the sample can be obtained by Fourier transforming this measurement signal.

[0006]

However, the variable optical path length mechanism including the movable corner cube 5 and the voice coil 6 has a drawback in that it is vulnerable to external vibration.

On the other hand, the optical path length changing mechanism according to the above-mentioned method, as shown in FIG. 4, has two mirrors 9 and 10 on the disk 8.
Are obliquely opposed to the axis connecting the centers of the mirrors, and the optical path length is changed by rotating (reciprocating rotation) the disk 8. However, in the optical path length variable mechanism having such a structure, it is necessary to reciprocally rotate the disc, and therefore there is a drawback that a complicated mechanism is required.

In view of the above points, an object of the present invention is to realize an optical path length varying mechanism having a relatively simple structure, resistant to external vibration, and capable of easily controlling the amount of change in the optical path length. To do.

[0009]

In order to achieve such an object, according to the present invention, a corner cube prism and a rotating substrate on which the corner cube prism is mounted,
Rotating means for rotating the rotating substrate about a position separated from the central axis of the corner cube prism by a distance d is provided, and the rotating shaft of the rotating substrate with respect to the optical axis of the incident light to the corner cube prism. Is the predetermined angle θ
By rotating the rotating substrate while tilting only 4d ・ s
It is characterized in that it is configured so as to obtain a variation amount of the optical path length of inθ.

[0010]

[Function] Distance d from the central axis of the corner cube prism
The rotation axis is rotated at a position separated by only, and the rotation axis is tilted by θ with respect to the optical axis. Thereby, the variation amount of the optical path difference of 4d · sin θ can be obtained. The amount of change can be adjusted to the distance d and the angle θ.

[0011]

The present invention will be described in detail below with reference to the drawings.
FIG. 1 is a configuration diagram showing an embodiment of an optical path length varying mechanism according to the present invention. In the figure, 11 is a corner cube prism, 12 is a rotating substrate, and 13 is a motor. The bottom surface of the corner cube prism 11 is attached to a substrate 12, and the substrate 12 is connected to a rotating shaft (hereinafter simply referred to as shaft) 14 of a motor 13. The portion composed of the motor 13 and the shaft 14 is referred to as rotating means.

The corner cube prisms 11 are separated from each other by 9
It consists of three 0 ° internal reflecting prism surfaces (two reflecting prism surfaces are shown in the figure for the sake of simplicity), and the incident surface and the outgoing surface are perpendicular to the diagonal of the cube. The incident light is formed so that the incident light is reflected by the three surfaces and the incident light flux returns to the incident light path. The corner cube prism 11 is joined with its center axis decentered from the center of rotation of the substrate 12 (the rotation axis of rotation by the rotation means) by a distance d.

When the substrate 12 is rotated by arranging the rotation axis with an inclination of θ with respect to the optical axis as shown in the figure, the corner cube prism 11 also rotates, but it also moves in the optical axis direction, so the optical path difference changes. To do. Amount of change (variable amount of optical path difference)
Is 2 × 2d · sin θ = 4d · sin θ. The variable amount can be adjusted by the eccentric amount d and the angle θ.

When the return light is directed in the same direction as the incident light,
A fixed mirror 15 may be provided as shown in FIG. 2 to return the light. The variable amount of the optical path difference is 8d · sin θ.

The present invention is not limited to the structure of the above embodiment, but various modifications can be made.

[0016]

As described above, according to the present invention, the following effects can be obtained. (1) The optical path difference can be changed by rotating the disc in one direction, which does not require complicated operations such as lateral movement and reciprocating rotation as in the past, and a simple rotating mechanism is sufficient. . (2) The structure can be strong against external vibration. (3) By adjusting the eccentricity amount d and the angle θ, it is possible to obtain an arbitrary variation amount of the optical path difference.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an optical path difference varying mechanism according to the present invention.

FIG. 2 is a configuration diagram of another embodiment of the present invention.

FIG. 3 is a configuration diagram showing a conventional example of a Michelson interferometer unit incorporated in a Fourier near-infrared spectroscope.

FIG. 4 is a configuration diagram showing an example of another conventional optical path difference varying mechanism.

[Explanation of symbols]

 11 disk 12 corner cube prism 13 motor 14 axis 15 fixed mirror

Claims (3)

[Claims] 1. A corner cube prism formed so that an incident light beam is reflected in an incident light path, a rotating substrate on which the corner cube prism is mounted, and a central axis of the corner cube prism are separated by a predetermined distance d. The rotating substrate is provided with a rotating shaft at a position to rotate the rotating substrate, and the rotating substrate is rotated by inclining the rotating shaft of the rotating substrate by a predetermined angle θ with respect to the optical axis of the incident light to the corner cube prism. By letting
An optical path length variable mechanism characterized in that it is configured to obtain an amount of change in optical path length of 4d · sin θ. 2. The optical path length varying mechanism according to claim 1, wherein the variable amount of the optical path difference is adjusted by changing the settings of the distance d and the angle θ. 3. The variable optical path length mechanism according to claim 1, wherein a fixed mirror is arranged on the front surface of the corner cube prism to return the return light in the same direction as the incident light.