JPS631221Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Fourier interference spectrophotometer. Fourier interference spectrophotometers usually use a Michelson-type interferometer, and while a moving mirror is moved, changes in the interference fringe are recorded as a function of the moving distance of the moving mirror, and this record is Fourier transformed to obtain the original light. This is a device that obtains spectroscopic data. An interferometer generally has a movable mirror to vary the optical path difference between two beams of light. Since a movable mirror does not cause sideways movement or changes in tilt when moving, the mirror sliding mechanism is required to have a mechanical precision of about a fraction of the measurement wavelength. In the case of a Fourier interferometry spectrophotometer, the movable mirror is moved at a high speed of about 10 mm/sec, so it is difficult to use the usual dovetail method for the sliding mechanism of the movable mirror; for example, a device such as an air bearing is used. It will be done. However, it is quite difficult to obtain the above-mentioned mechanical accuracy when moving the movable mirror at high speed with such a device, and conventionally, this type of spectrophotometer has been commercialized mainly for infrared light, and has not been commercialized for visible light. If one were to obtain such a device, the device would be extremely expensive due to the required accuracy.

The present invention aims to provide a Fourier interference spectrophotometer that does not require particularly high precision or a special mechanism for the moving mechanism of the movable mirror.

The present invention uses a corner cube mirror as a movable mirror, which is supported by an elastic diaphragm and driven electromagnetically, so that no frictional force acts on the movable support of the movable mirror, and there is no mechanical gap. ,
To provide a Fourier interferometry spectrophotometer in which the requirement for structural accuracy is significantly relaxed by utilizing the properties that the direction of reflected light does not change even if a corner cube is tilted, and the optical path length does not change. The present invention will be explained below with reference to Examples.

FIG. 1 shows an embodiment of the present invention. 1 is a semitransparent mirror, 2 is a fixed mirror, and 3 is a movable mirror. 4 is a light source, and the light travels as shown by the arrow in the figure and is emitted to the left. The fixed mirror 2 and the movable mirror 3 are both corner cube mirrors. The movable mirror 3 is fixed at the tip of a tube 5, and the tube 5 is held at the center of two elastic diaphragms 6, 6' with concentric waves, and the peripheral edges of both diaphragms are fixed. . A coil 7 is wound around the outer surface of the tube 5, and a current can be passed through this coil. 8 is a circular injection magnet, and the tube 5 is fitted on the outside of this magnet so that it can move freely in the axial direction. 9 is a cylindrical yoke that surrounds the outer periphery of the tube 5 and has a magnet 8 at its rear end.
is connected to. With this structure, the movable mirror 3 can be moved left and right by passing current through the coil 7. The amount of movement is measured by inputting a laser beam into an interferometer and counting the wave number of a change in brightness due to light interference at the wavelength of the laser beam on the output side. A laser beam that emits light in a wavelength range different from that used for spectroscopic analysis and light from a light source for spectroscopic analysis are superimposed and input into an interferometer, and on the output side, a filter is passed between the laser beam and the light in the wavelength range for spectroscopic analysis. If both are measured separately and recorded simultaneously, the changing waveform of the photometric value of the laser beam becomes a scale of the moving distance of the movable mirror.

Even if the angle of a corner cube mirror changes, the angle between the incident light and the outgoing light remains unchanged at 180°. Also, the corner cube mirror has lateral deviation d due to the location shown in Figure 2.
The optical path length does not change depending on This figure shows a cross section of a corner cube taken along a plane perpendicular to the plane that includes one ridgeline and faces the ridgeline.As is clear from the figure, a=a', b=b', and c is the lateral shift. Since it is equal to d and c'=d, c=c', and the optical path length from point S to W plane is a+b+c+l=
c′+a′+b′+l remains unchanged. Furthermore, even when the corner cube mirror is tilted, the optical path length does not change. Figure 3 is a cross-sectional view similar to Figure 2, showing the case where the corner cube is rotated around the 0 point, and the distance e from this ray is based on the round trip optical path length between S0 of the ray incident on the 0 point. Considering the round trip optical path length between the vertical plane W and the corner cube at point S of the ray shifted laterally, since the angle α' = α and the angle β' = β, a = b = c and ε = ε' Therefore, this optical path length is equal to the round trip optical path length between S0. Since the length of S0 is fixed regardless of the inclination of the corner cube, the optical path length does not change depending on the inclination of the corner cube.

The actual displacement of the corner cube is not centered on the 0 point, but can be regarded as a rotation fixed to an arm with a radius R centered on point C, as shown in FIG.
In this case, the corner cube has a lateral shift of only Rsinθ and an inclination of θ, as well as a retreat of δ, and the change in optical path length due to this retreat is 2δ. In order for this 2δ to be 1/8 wavelength, S needs to be approximately 0.03μ or less, assuming a wavelength of 0.5μ. δ is δ=R(1-cosθ)... (1) If θ is small, cosθ=1-1/2θ ² can be set, so equation (1) is δ=R/2θ ² ... (2) becomes. Point C can be considered to be approximately on the middle side of the two diaphragms in the embodiment shown in FIG.
The allowable tilt angle θ from the formula is 0.03=10 ⁴ /2・θ ² (μ) θ=0.00245 radian ≒ 0.147°, which is a sufficiently large angle, and therefore the optical path due to the tilt due to the swinging of the corner cube. The effect on the difference is negligible with sufficient precision.

This calculation example assumes unfavorable design specifications.The above point C is the center of gravity of the integral structure of the corner cube, cylinder 5, and coil 7, and it is not designed to locate this near the apex of the corner cube. It is easy to set the midpoint between the two diaphragms near the apex of the corner cube, and the swinging of the corner cube can be limited to tilting around the apex. Since the influence of this tilting does not appear at all due to the nature of the Yub, a highly accurate movable mirror moving mechanism can be realized very easily.

One side is 30mm x 30mm as a corner cube, 3
The diaphragm is a phosphor bronze plate with a thickness of 0.125 mm and a diameter of 200 mm.The configuration is as shown in Figure 1, with the direction of movement perpendicular, and the electromagnetic force of the coil 7 By holding the cube in the pushed-up position and reducing the current, the corner cube can be moved downward by its own weight, resulting in a movement distance of approximately 10 mm. Note that the reason for using two diaphragms is to control the swinging of the corner cube, so it is not necessary, and one diaphragm is sufficient, especially when moving in the vertical direction.

The Fourier interference spectrophotometer of the present invention has the above-mentioned configuration and can largely tolerate lateral wobbling, tilting, etc. caused by the movement of the movable mirror. In other words, movement can be performed with sufficiently high precision. In this way, according to the present invention, it is possible to provide not only Fourier interference spectrophotometers in the infrared region but also Fourier interference spectrometers in the visible and ultraviolet regions, which require higher precision, at low cost. become.

[Brief explanation of the drawing]

Fig. 1 is a plan view of an embodiment of the device of the present invention;
The figure is a diagram explaining the change in optical path length due to the lateral movement of the corner cube mirror, Figure 3 is a diagram explaining the change in optical path length due to the tilt of the corner cube mirror, and Figure 4 is a diagram explaining the change in optical path length due to the tilt of the corner cube mirror. It is a figure which shows the retreat of a corner cube when it occurs centering on the back of a corner cube. 1... Semi-transparent mirror, 2... Fixed mirror, 3... Movable mirror, 4... Light source, 5... Tube, 6, 6'... Diaphragm, 7... Coil, 8... Magnet, 9...
…yoke.

Claims (1)

[Scope of utility model registration request] At least the movable mirror is a corner cube mirror, held at the center of a diaphragm whose periphery is fixed, a cylindrical coil concentric with and perpendicular to the diaphragm is attached to the diaphragm, and this coil is attached in a radial direction concentric with the coil. A Fourier interferometry spectrophotometer that is placed in a magnetic field to allow electrical current to pass through it.