JPS59212727A - Double beam interferometer - Google Patents

Abstract

PURPOSE:To make the measurement with a double beam interferometer quick by intersecting two coherent parallel luminous fluxes on the light receiving plane of an optical detecter so that they interfere with each other while all of an incident collimater, beam splitter, plane mirror, image forming optical system, and optical detector are fixed. CONSTITUTION:A double beam interferometer is constituted in such a way that all of its incident collimater 2, beam splitter 3, plane mirrors 5 and 6, image forming optical system 7, and optical detector 8 are fixed. Two coherent parallel luminous fluxes are intersected with the other on the light receiving plane of the optical detector 8 so that they interfere with each other while all the sections 2, 3, 5, 6, 7, and 8 mentioned above are fixed. When such an arrangement is made, the interference fringes of the two parallel luminous fluxes can be resolved in accordance with their phases from the zero order to a higher order and quick photometric measurement can be performed by photoelectric scanning.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention has a beam splitter and two plane mirrors,
This is a three-beam interference δ beam in which each of the flat (a1) mirrors has an equal inclination angle with each optical axis of the light beam split into two by the beam splitter.

Fourier transform spectrophotometers have the feature of simultaneously measuring light of all wavelengths in the spectrum of the light to be measured, and are originally suitable for measuring constantly changing light or moving specimens.

However, the Michelson interferometer, which is often used in conventional Fourier transform spectrophotometers, scans the 12th order of interference fringes by precisely linearly displacing one of two plane mirrors to change the optical path difference of the interference light. It is carried out.

Therefore, the speed at which the plane mirror is mechanically moved is a constraint on rapid spectrophotometry, and when measuring light with short wavelengths such as UV light, the accuracy of the linear displacement of the V-plane mirror and the amount of displacement are limited. fl+! It has the difficult points of I-determined accuracy and detection of the zero-order interference position.

Therefore, in the present invention, the incident collimator, heam splinter, plane reflector, imaging optical system, and photodetector are all fixed, and two coherent parallel light beams are applied to the light-receiving surface of the photodetector. 1-1 The objective is to perform cross-interference at the top, resolve the interference fringes into phases from the zero order to higher orders, and perform rapid photometry by photoelectric sweep, and the photodetector. The object of the present invention is to provide a three-beam interferometer that can accurately and stably read out the phase of the interference fringes produced from the position of the fringe on the detector J2.

Thus, the uncontrived three-beam interferometer consists of an incident light collimator, a beam splinter, two plane reflectors having mutually equal inclination angles for each of the three light beams divided by the beam splitter, and An imaging optical system that images interference fringes ranging from ceros order to high orders of two optical widths reflected from a plane reflecting mirror on the light receiving surface of a photodetector, and interference fringes ranging from zero orders to high orders. Striped Jji
It consists of a photodetector that divides the physical distribution into parts according to the order of interference and performs photometry.

See the drawing below 1u? First, a preferred embodiment of the present invention will be described. First, the first embodiment shown in FIG. 1 is composed of the following parts.

In other words, a lens that converts the incident light from the light source 1 at Q into a parallel beam, or a concave mirror collimator 2, or a concave mirror collimator 2, converts the incident light into a parallel beam in the horizontal plane in the figure, HH plane in the vertical plane, or I ('w plane). An incident light collimator 2, such as an aspherical lens system that focuses the light, or an off-axis concave mirror that utilizes astigmatism;
A beam splitter 6 consisting of a rectangular prism with a dimension of jiJ - two plane reflecting mirrors 5 and 6 that reflect the luminous flux divided by the beam splitter 3, and a beam splitter 6 that intersects the three luminous fluxes reflected from the two plane mirrors 5.6. It is composed of an imaging optical system 7 consisting of a lens or a concave mirror that produces interference fringes on the light-receiving surface of the photodetector 8, or the imaging optical system 7 is not shown in the figure. ' is arranged so as to form an image on 1 m of light received by the photodetector 8.

Also, is photodetector 8 a diode array detector? This is a detector that identifies and photometers the fringe pattern of interference fringes, such as an image tesector, multichannel tron, and hijicon'+rr.

It is located on the optical axis of the concave mirror collimator 2. Light source 1 shown in
When the light that is emitted from the main body and becomes a parallel beam by the concave mirror collimator 2 is perpendicularly incident on the beam splitter 6Q, the incident parallel beam is partially split by the semi-transparent mirror 4;
and enters the plane reflecting mirror 5.

The other part is reflected by the semi-transparent mirror 4, travels perpendicular to the direction of incidence, and enters the mirror 6 on the opposite side.

Plane rfiJ perpendicular to orthogonal light i1#IIdL
Considering 'HH' and H'll', the plane reflecting mirrors 5 and 6 each have an I direction, an H'H' curve, and an inclination of θ.

It is assumed that straight lines intersecting the HH plane and the H'H' plane of the l-m reflecting mirrors 5 and 6 stand at Mr and Mt points in the figure, and the mirrors are arranged so that the distances between AMr and AMt are equal.

A ray of light emitted from the light source 1 and passing through point A, indicated by Q, is divided by the semi-transparent mirror 4, a part is reflected by Mt of the flat reflecting mirror 5, and then reflected by the semi-transparent mirror 4 and sent to the imaging optics. The light passes through the system 7 and reaches a point PA on the light receiving surface of the photodetector 8.

The other part of the light rays is reflected by the point Mr of the mirror 6, passes through the semi-transparent mirror 4, passes through the imaging optical system 7, and reaches the point PA.

That is, the PA point is a real image of the Mr point and the Mt point created by the imaging optical system 7.

When the distance plane and the positive are equal and the Mr and Mt points are arranged 6 so that they each become the 7f image point with respect to the semitransparent mirror 4, the ray Mr PA and the positive positive at the PA point have equal optical path lengths. The interference optical path difference between the two beams at the point PA is zero.

Therefore, a zero-order interference fringe is located at the point PA, and after an arbitrary ray emitted from the light source 1 indicated by Q is divided by the semi-transparent mirror 4, one part is at Mt' of the plane reflecting mirror 5. The other one is reflected by the Mr' point of the plane reflecting mirror 6.

Each reflected light beam passes through an imaging optical system 7 to a photodetector 8.
P on the light receiving surface of , intersects at one point, and these 28 points correspond to the real image created by the imaging optical system 7 at the point Q1 where the extension line of the reflected light ray from Mr' intersects the HH plane.

Therefore, when the interval of PAPll is expressed as W, the optical path difference γ8 between the two beams BMt'P n and BM r'P n that intersect at 26 points becomes the value of the following equation.

When monochromatic light of wavelength A is emitted from the light source 1 indicated by Q, the pinch interval △ is expressed by the following formula on the light receiving surface of the photodetector 8.
An interference fringe with maximum intensity is created for each W.

As can be seen from the above equation (2), the peak intervals of the interference fringes created by monochromatic light are equal intervals, and the interval ΔW is proportional to the wavelength λ of the light.

Therefore, if monochromatic light with a known small bandpass wavelength, such as a laser beam, is incident and its interference fringes are measured, the value of W can be easily converted to the optical path difference, that is, the interference phase, according to formula ( ). can.

In addition, unless the arrangement of the imaging optical system 7 is changed, the phase conversion value of W measured once can be stably used.
In the case of a diode array detector with 2048 elements, △w
When the inclination angle θ is set to −5d, interference fringes up to the /1.00th order are measured.

That is, spectrum measurement with a resolution of 400 can be performed.

In the first embodiment shown in FIG. 1, the three mutually interfering beams reflected from the plane reflecting mirrors 5 and 6 enter the beam splitter 6 at an inclination angle of ±20 symmetrically with respect to the optical axis. Dispersion due to the refractive index of the splitter 6 does not affect interference fringes.

In the first embodiment shown in FIG. 1, the two flat reflectors 5 and 6 are arranged at right angles to each other, and even if the value of θ is changed, the angles formed by the two flat reflectors 5 and 6 are always right angles.

Therefore, by rotating the support base on which the two plane reflectors 5 and 6 are set at right angles around the vertical axis, it is possible to set an arbitrary value of θ, that is, it is possible to change the phase interval of the interference fringes. .

Furthermore, when the biplane reflecting mirror support is slightly displaced in parallel to the light 1i+I+L, the zero-order interference point PA is displaced to either the left or right on the light receiving surface, that is, the entire interference pattern is moved.

Therefore, by adjusting the position of the biplane mirror support base, interference fringes of any interference order range can be created on the light receiving surface of the photodetector 8.

Next, Embodiment 2 of the present invention shown in FIG. 2 and FIG. 13, which is a sectional view taken in the 1-1 direction of FIG. The support stand is vertical i
1 schematically represents an example of a support structure that is rotatable around Ii+I+ and whose heel of rotation is translatable in the direction of one optical axis;

X and y represent the input and output optical axes of interference 1.1,
Z is a vertical line that passes through the intersection of both corners and lies within the semi-transparent mirror surface of the beam splitter 11.

The frame 12 that holds the beat splitter 11 can be tilted with respect to the support 17 and rotated around the Z support so that the translucent mirror surface of the beam splitter 11 correctly aligns with the y-axis, and the y-axis and the y-axis It can be adjusted to divide the 90° angle between the two into three equal parts.

The mounting frames 14.16 of the two plane reflecting mirrors 13.15 are respectively mounted to the support base 18 so that the inclination and rotation around the vertical line can be adjusted.

By this adjustment, the plane reflecting mirrors 13, 15 are set so that their mirror surfaces are correctly parallel to the vertical line and at right angles to each other.

The support base 18 of the two plane reflectors 13 and 15 is the sliding base 1
It can be rotated around the rotating shaft 25 of 9 by a screw feeder 22 and fixed by a tightening screw 26.

The sliding table 19 is fixed to the head 20 by the feed screw 21.
It moves in parallel along the axis.

In front of the flat reflecting mirror 15, an opening/closing shutter 24 is attached to the support base 18 of the flat reflecting mirror 13.15, substantially parallel to the mirror surface.

This opening/closing shutter 24 can be opened and closed manually or electrically as desired.

By having the above structure, two plane reflecting mirrors 13
．． 15 with respect to the optical axis can be easily changed, thereby easily changing the interference fringe pinch interval on the light receiving surface of the photodetector 8 shown in FIG.

Further, by displacing the sliding table 19, the position of the zero-order interference fringes formed on the light receiving surface of the photodetector 8 can be changed, and the position of the zero-order interference fringe formed on the light receiving surface of the photodetector 8 can be changed to any number of steps. A range of high-order interference fringes can be created.

Each interference order of this arbitrary high-order interference fringe is determined by inputting a small monochromatic light with a known wavelength (D bandpass), first creating a zero-order interference fringe on the photodetector 8, and reading out its position.

Then, by counting the two interference fringe peaks that appear at the position where the zeoa interference fringe was and other specified positions while moving the sliding table 19, the finally set interference fringe can be calculated. It is possible to check and measure the order of interference.

If there is an error in parallelism with respect to y ifζF while moving the slide table 19, it will appear as a change in the pitch interval of the interference fringes, but this can be detected by photometrically measuring the entire interference fringe with the photodetector 8.

This parallelism error is ultimately caused by the two plane reflecting mirrors 1 and 15.
can be corrected by rotating the support stand 18.

The purpose of providing the opening/closing shutter 24 described above is as follows.

That is, the interference fringe pattern created by the two parallel light beams on the light receiving surface of the photodetector 8 uses the light intensity distribution of each light beam as a baseline, and takes the interference fringe intensity distribution of the baseline.

Generally, this baseline is not flat, but exhibits a curved distribution and sometimes exhibits irregularities.

Further, non-uniformity of photometric sensitivity on the light receiving surface of the photodetector 8, that is, when there is locality, causes an error in interference fringe intensity distribution measurement.

One or more photometric error and baseline effects are not included in the intensity distribution of the spectrum of light to be measured.

Therefore, if the interference fringe intensity distribution measurement containing this error is Fourier transformed, an incorrect spectrum will be obtained.

It is desirable to correct the curvature of the baseline and the non-uniformity of sensitivity of the photodetector 8 and perform Fourier transformation on the interference fringe intensity distribution value that lies on a flat baseline.

In a correctly optically adjusted three-beam interferometer, the two beams interfering with 7r have approximately equal intensities and equal intensity distributions.

One of the light beams is blocked, and only the other light beam is detected by a photodetector 8.
The luminous flux intensity distribution of the light to be measured can be measured by making the light incident on the light beam.

This photometric value also includes sensitivity non-uniformity of the photodetector 8 itself.

Using the photometered single beam light intensity distribution value, the photometered value of the interference fringe light intensity 1 mark distribution photometered by opening the opening/closing shank 24 is baseline corrected.

This baseline-corrected interference fringe value is subjected to Fourier transformation.

Although it is easy for a computer to perform baseline correction of interference fringe photometric values using baseline values that have been measured in advance or repeatedly and alternately, the opening/closing shunter 24 is provided for the purpose of performing the above operation. be.

Practical Example 3 of the present invention shown in FIG. 4 is suitable for a somewhat limited spectrophotometry in which there is no need to change the monochromatic light interference fringe peak interval, and it is not necessary to change the position where the zero-order interference fringe appears. This is a three-beam interferometer with a simple structure and high stability.

The optical axis of the incident light flux is x + T + 1i, and the optical axis of the output light is y
The translucent m-plane 34 of the beam printer 66 is y
The angle formed by X and y, including the y-axis (not shown) perpendicular to the axis and the y-axis, is divided into three equal parts.

The angle φ between the 64th surface of the semi-transparent mirror and the 6th plane of the flat reflecting mirror (Mr, Mr. f is (45
゜10θ).

Therefore, the two plane reflecting mirrors 5 and 6 are! It is orthogonal to f.

The light emitted from the light source 61 located at Q of the focal point of the concave mirror collimator 62 above the incident optical axis is converted into a parallel beam of 1μ by the lens and the concave mirror collimator 2 and then sent to the beam splitter.
66 is perpendicularly incident.

The light beam passing through point A of this light flux is divided into two by a semi-transparent mirror 64,
A portion passes through the semi-transparent mirror 64 and hits the Mt point on the 5th plane of the plane reflecting mirror, and the other part is reflected on the 34th plane of the semi-transparent mirror and travels in the y-axis direction to reach the Mr point on the 6th plane of the plane reflecting mirror. It is assumed that the distance between the corresponding i revision and AMr is equal, that is, Mr is the semi-transparent mirror 6 of Mt.
Suppose that it is a mapping point for four planes.

The light rays reflected by Mt and Mr pass through the compensator 65 with an inclination of ±20 with respect to the optical axis y,
A point P on the light receiving surface of the photodetector 67 is focused by the imaging optical system 66 . interfering with each other.

The Po point corresponds to the real image of the Mt and Mr points created by the imaging optical system.

2, the optical path difference is zero when the condition of AMt = AMr is satisfied.

In other words, the interference fringes created at Po are zero-order interference fringes,
A ray passing through any point B other than point A is divided by a semi-transparent mirror 64, and then divided into points 1M7 and M7 of a plane reflecting mirror 5.6, respectively.
It is reflected at point r'.

These two reflected light beams pass through the compensator 65 with an inclination of ±20 relative to the y-axis, and intersect and interfere by the imaging optical system 66 at a point Pw on the light receiving surface of the photodetector 67.

Passing through points Mt and Mr, which are equidistant from point A, the optical axis y
Considering the planes HH and H'H' that are perpendicular to the planes HH and
When expressed as B, the point Pw on the light-receiving surface "-" is nothing but the real image of the intersection point QB imaged by the imaging optical system 66.

Therefore, if the distance of POPW is W, and the refractive index of both the beam splitter 6 and the compensator 65 is n (λ), then the two beams BMt'Pw and B which cross interfere at the point PW
The optical path difference γP' between M-BiPw is expressed by the following equation.

Ti of wavelength λ with small bandpass from light source 61 shown as Q
When t color 9 is incident, the light received by the photodetector 67 is 1m-[-
Interference fringes with peaks of maximum intensity are created at equal intervals.

When the peak interval is expressed as ΔW, its magnitude is expressed by the following equation.

As can be seen from the above equation (4), ΔW is proportional to the wavelength λ of the light and at the same time changes depending on the dispersion of the beam splitter 66 and compensator 65.

Therefore, when obtaining the spectrum of the measured light by Fourier transforming the measured value of the intensity distribution of this interference fringe, it is necessary to prepare the measured value of the interference fringe intensity distribution with a known value of refractive index n(λ) and dispersion over the measurement wavelength range. It is necessary to perform value correction. In the two-beam interferometer of Example 3 in Fig. 4, once monochromatic light is incident and the intensity distribution of interference fringes formed on the light receiving surface of the photodetector 8 is measured, Po position and P. The interference phase conversion value of the distance W from the distance W is determined as a device constant.

The photodetector 8 is a detector such as a diode array detector, an image desector, a multichannel tron, or a vidicon tube, which can photometer the intensity distribution of interference fringes by decomposing them into interference orders.

Therefore, in the three-beam interferometer of the present invention, two coherent parallel light beams are produced while all of the constituent parts, such as the incident collimator, the beam splitter-1 plane reflecting mirror, the imaging optical system, and the photodetector, are fixed. It is possible to perform cross-interference on the light-receiving surface of a photodetector, resolve the interference fringes by phase from zero order to higher order, and perform rapid photometry by charging sweep. This method has the advantage that the phase of the interference fringes can be accurately and stably read out from the position of the detected fringes.

[Brief explanation of the drawing]

FIG. 1 shows a schematic diagram of the optical system of a three-beam interferometer in Embodiment 1 of the present invention, FIG. 2 shows a schematic diagram of the support structure in Embodiment 2 of the present invention, and FIG. 171 of
FIG. 4 shows a schematic diagram of the optical system of a three-beam interferometer in Embodiment 3 of the present invention. 1.61...Light source, 12.32...Concave mirror collimator,
3.11. '33...beam splitter-15,6,1
3゜15 ・Plane reflecting mirror, 7, 66 ・・Imaging optical system, 8
．． 37'...Photodetector.

Claims (1)

[Claims] Incident light collimator, beam splitter 1 Each of the three beams of light divided into two by the beam splitter 1
! The two plane reflecting mirrors have the same inclination angle with respect to qI+, and the three interfering beams reflected from the plane reflecting mirror range from the zeroth order to the higher order - [two interference fringes are detected by the photodetector. A 29-bundle system characterized by comprising an imaging optical system that forms an image on a plane 2, and a photodetector that quickly generates light by decomposing the intensity distribution of interference fringes ranging from zero order to high order into interference orders. Juwata nnn (.