JPS5816216A - talbot interferometer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention makes it possible to match the direction of shear with the direction of equally spaced parallel interference fringes obtained when the reference wavefront is a plane wave, and also to make it possible to match the direction of the shear with the direction of the equidistant parallel interference fringes obtained when the reference wavefront is a plane wave. The present invention relates to a Talbot interference needle that can also align the directions of equally spaced parallel interference fringes with respect to components.

A Talbot interferometer is an interference needle that is composed of collimated light and two gratings, and utilizes the Talbot effect and Moiré technology. This Talbot effect is caused by the superposition of the diffracted lights generated when collimated light illuminates the incident side diffraction grating, resulting in the exact same light intensity distribution at a position 1mdR/λ behind the grating as that immediately after the grating. and behind (2m+
1) At the position d”/λ, an image with the black and white of the grating inverted is obtained. Here, m is an integer, d is the grating pitch, and λ is the wavelength of the light. The resulting image is called a Fourier image, and when a phase object is inserted between the entrance side diffraction grating and the Fourier image at mdt/λ behind it, the Fourier image is deformed.The exit side diffraction grating is attached to this deformed Fourier image. The principle of the Talbot interference needle is to generate moiré fringes by superimposing them and to magnify and detect the deformation of the Fourier image.

This Talbot interference needle is known as a type of laterally shifted air ring interference needle. In general, in this type of interferometer, a useful method is to use equally spaced parallel fringes as the interference fringes corresponding to the paraxial component of a plane wave or a spherical wave, and to match the direction of the fringes with the direction of shear. ing. In the following description, equally spaced parallel interference fringes corresponding to the reference plane wave or the reference spherical wave will be referred to as reference interference fringes.

When the reference wavefront is a plane wave, the Talbot interference needle generally has a configuration as shown in FIG.

That is, a light source lamp 1, a condenser lens 2 (2a).

2b), the light emitted from the light source section 6 consisting of a filter 6, a diffuser plate 4, and a pinhole 5 enters a collimator lens 7 having a focal point at the pinhole 5, and becomes a bundle of light rays parallel to the optical axis (= parallel to the incident light beam). The sample 11 reaches the observation screen 10 via the side diffraction grating 8 and the exit side diffraction grating 9.The sample 11 is inserted between the entrance side diffraction grating 8 and the exit side diffraction grating 9; In some cases, the sample 11 is a lens, and its aberrations and striae can be observed.Also, when the reference wavefront is a spherical wave, the pinhole 5 is Placement at a position defocused from the focal point of the collimator lens 7 (this is done by two steps).

The entrance side diffraction grating 8 and the exit side diffraction grating 9 have a grating pitch of d, the reciprocal of 1/d is the fundamental frequency, and the grating 8.9
Comrades are placed a distance l, apart. As the coordinate axes, the y-axis is parallel to the grating direction of the incident-side diffraction grating 8, and the x-axis is perpendicular to the grating direction. In the actual operation of the interference needle, in order to make Moiré fringes appear clearly, the grating direction of the exit side diffraction grating 9 is rotated by a slight angle α clockwise with the optical axis C as the rotation axis with respect to the y-axis. Rotate and use. Sample 11
is placed at a distance of 12 from the exit side diffraction grating 9 in the direction of the light source section 6. Also, of the diffracted light generated by the incident side diffraction grating 8, the 0th order needle head passes through the sample 11 and is obtained by the observation screen 10, which is the phase distribution W(x, y).
shall be. In such a configuration, the interference pattern obtained when the reference wavefront is a plane wave is x(1-cosα) y sinα-(aw/a
x) In=m-d+constant, where m=Q, ±1, ±2, . . . It is known that the curves are represented by a group of curves.

This is a shearing interference pattern, but the reference interference fringe for the beam plane wave has an inclination of (cosα-1)Ainα
These are equally spaced parallel interference fringes. This shows that in a normal configuration, the direction of shear, that is, the direction of the X-axis, and the direction of the reference interference fringe for the reference plane wave cannot coincide.

Therefore, the mismatch in direction must be corrected by calculation or the range of use must be limited to an extent that can be ignored as a measurement error.

An object of the present invention is to improve the above-mentioned conventional device, and to provide a Talbot interference needle that matches the direction of shear with the reference plane wave (=corresponding standard interference fringe) and does not require correction of inclination. , the grating pitches of the entrance-side diffraction grating and the exit-side diffraction grating, which are arranged facing each other with a predetermined interval, are respectively d8 and dll (however, ds > ds), and the gratings are set at an angle α relative to the center of the optical axis. When tilted, c
It is characterized by having the following relationship: osα=d/dI.

The present invention will be explained in detail based on the embodiment shown in FIG. 3 and below.

The grating pitch of the entrance side diffraction grating 12 is dl, and the grating pip of the exit side diffraction grating 16 is dt (however, 't >'t)
and these fundamental frequencies are i, which is the reciprocal of the grating pitch.
/a+, 1/dffi. Diffraction grating 1
2.16 The spacing between the two is 18 as in the case of FIG. 2, and the distance from the diffraction grating 13 to the sample 11 is 12. As the coordinate axes, the y-axis is parallel to the grating direction of the entrance-side diffraction grating 12, and the X-axis is perpendicular to the grating direction, and the grating direction of the exit-side diffraction grating 16 is the optical axis C with respect to the y-axis. Assume that the rotation axis is rotated clockwise by an angle α.

Using such a grating 12.16, the interference pattern observed on the observation screen 10 when the reference wavefront is a plane is (1/d, -cosα/dhi')x-)-(sinα
/d*>Y-(1/dt)-aw/ax)! , = m + constant, where m = Q, ±1, ±2, etc., resulting in a group of curves. Here, the rotation angle α of the exit side diffraction grating 16 is adjusted so that the coefficient of the first term becomes 0.
α” dt/dt is obtained. This can be realized by setting the grating pitch as dl>d!. By doing this, the interference pattern becomes (sin α/da)y − ( 1/ds) - (aw/ax
)zs2m0 constant, the corresponding reference interference fringes are parallel interference fringes parallel to the X axis with equal intervals of 47 sin α, which coincide with the shear direction and provide the desired properties.

Moreover, since the configuration is as described above, it is also possible to match the equally spaced parallel interference fringes for the paraxial component of the spherical wave with the shear direction. The interference fringes obtained when using the paraxial component of a spherical wave as a reference wavefront are ((l+/d+)・(i/R)+ (1/d+) −(
cosα/dt))X+(aimα/d2)y−(1/
d+)-ew/Fx)zs=m+constant where m=Q, ±1, ±2,...R is the radius of curvature of the spherical wave when the exit side diffraction grating 13 is the apex, and the center of curvature is a negative value when it is closer to the light edge part 6 than the exit side diffraction grating 13, and a positive value when it is on the opposite side (two sides). Therefore, when cos α'q 4/dl,
The radius of curvature is R=(lI/di) ((cosα/dt)−(i/c
tυ) corresponding to the paraxial component of the spherical wave,
The direction of share can be matched. This property is useful when measuring the spherical aberration of a lens or the like under a finite distance imaging condition.

In the embodiment shown in FIG. 5, the collimator lens 7 and sample 11 are removed from the configuration diagram shown in FIG.
FIG. 2 is a configuration diagram for measuring spherical aberration when one of the conjugate imaging points of is located at infinity. The diffraction gratings 12 and 13 have the above-mentioned relationship cosα=d2/dI, and the lens 14 to be tested is placed on the optical axis C so that its focal position coincides with the pinhole 5. At this time, the reference wavefront is a plane wave and the shear direction is the same as that of the reference interference fringe; therefore, the deviation between the interference fringe passing through the optical axis C and the X-axis is an amount directly proportional to the amount of transverse aberration of spherical aberration. becomes. Regarding the amount of longitudinal aberration, the interference fringes are rotated about the optical axis C by moving the light source section 6 back and forth along the optical axis and defocusing the lens 14 to be tested. If the intersection of the interference fringes passing through the optical axis C and the X-axis is plotted against the amount of defocus at this time, this is the amount of longitudinal aberration of spherical aberration. As described above, according to this embodiment, it is possible to measure spherical aberration without correcting the inclination of the reference interference fringes.

The embodiment shown in FIG. 6 is a configuration diagram for measuring the spherical aberration of a lens under finite distance imaging conditions.

The lens to be tested 14 is placed on the optical axis C so that one of its conjugate imaging points coincides with the pinhole 5. In addition, the diffraction grating 12.16 is arranged as R= (lt/d+) ((coaα/da)−(i /
ds) )-' However, the arrangement is such that R is the distance of the imaging point P measured by the exit-side diffraction grating 16. At this time, the spherical wave corresponding to the imaging point P becomes the reference interference fringe and coincides with the shear direction, so that the spherical aberration of the lens can be measured in the same manner as in the case of FIG.

The Talbot interferometer according to the present invention can match the direction of the reference interference fringe corresponding to a plane wave with the direction of shear by adjusting the angle and pitch of the gratings to a predetermined relationship as described above. There is no need to correct the tilt,
By selecting the fundamental zero frequency and angle of the exit-side diffraction grating, a reference interference fringe with a desired pitch can be obtained. Further, reference interference fringes corresponding to spherical waves can also be obtained.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional Talbot interferometer, Fig. 2 is a perspective view of its diffraction grating, Fig. 3 and subsequent figures are examples of the Talbot interferometer according to the present invention, and Fig. 6 is a block diagram thereof. , FIG. 4 is a perspective view of the diffraction grating, and FIGS. 5 and 6 are configuration diagrams for measuring the spherical aberration of a lens. 6 is a light source, 7 is a collimator lens, 10 is an observation screen, 11 is a sample, 12 is an entrance side diffraction grating, 13 is an exit side diffraction grating, 14 is a test lens, d is a grating pitch of the entrance side diffraction grating , d is the grating pitch of the exit side diffraction grating, 11 is the distance between the entrance side diffraction grating and the exit side diffraction grating, l
t is the distance between the sample and the exit side diffraction grating, and P is the imaging point. 1

Claims (1)

[Claims] 1. Each of the grating pitches d of the entrance-side diffraction grating and the exit-side diffraction grating arranged oppositely at a predetermined interval,
and dt (where '+ >'t), and when the gratings are tilted at an angle α relative to the optical axis center, COIα=
A Talbot interference needle characterized by having a relationship of dt/'s. 2. The grating direction of the entrance side diffraction grating is in the vertical direction, and the grating direction of the exit side diffraction grating is tilted at an angle α from the vertical line so that the reference interference fringes appear in the horizontal direction. Talbot interferometer as described.