JPH0536723B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a measuring device for precisely measuring the shape of a flat, spherical or aspherical surface of a lens, mirror, etc.

BACKGROUND ART FIG. 5 shows the specific configuration of a fringe scanning type common path shearing interferometer as a highly accurate and highly stable shape measuring device that does not require a prototype to create a reference wavefront. In the figure, a beam 52 reflected from an object to be measured 51 becomes two beams that are laterally shifted by a shearing device 56 in which a beam splitter 53 and a reflecting surface 54 are installed parallel to each other. The resulting interference fringes are input from the imaging device 58 to the computer 60 via the frame memory 59. At this time, the reflecting surface 54 is moved by the piezo drive device 55.
The wavefront is moved by a small amount at , giving phase modulation to one side of the laterally shifted wavefront. This interference fringe data is transferred to an electronic computer 6.
The shape can be measured by analyzing with 0.

Problems to be Solved by the Invention However, in the above configuration, the multilayer coating of the beam splitter 53 in the shearing device 56 cannot completely remove high-order reflected light higher than the secondary reflected light. This has the problem that it mixes into interference fringes as noise, making it impossible to improve measurement accuracy.

In view of the above problems, the present invention aims to improve measurement accuracy by removing high-order reflected light generated by the shearing device.

Means for Solving the Problems In order to solve the above problems, the shape measuring device of the present invention has a beam splitter and a reflecting surface installed at an angle to each other, and a light shielding plate near the focal point of the light flux conversion lens. It is.

Effect The present invention has the above-described configuration, and by slightly tilting the total reflection mirror with respect to the beam splitter, the output angle of the laterally shifted wavefront is changed, and various shifted wavefronts are placed near the focal position of the light flux conversion lens. Spots appear discretely. The knife edge blocks the spot of the horizontally shifted wavefront caused by the second-order or higher-order reflected light.

As a result, high-order reflected light that is a noise component of shearing interference fringes can be removed, and shape measurement accuracy can be improved.

Embodiment A shape measuring device according to an embodiment of the present invention will be described below with reference to the drawings.

In Fig. 1, 1 is a He-Ne laser light source, the emitted laser beam is expanded into a beam of sufficient diameter by a beam expander 2, transmitted through a first beam splitter 3, and transmitted through a transmission spherical lens. 4 creates a spherical wavefront. The object to be measured 5 is set at the position of the optimum spherical wavefront. The light beam reflected from the object to be measured 5 passes through the transmission spherical lens 4, is reflected by the first beam splitter 3, and enters the second beam splitter 6. In FIG. 2, the incident light beam is separated into a reflected light beam 21 and a transmitted light beam 22 at the vapor deposition surface 20. The transmitted light beam 22 is transmitted through a reflecting surface 7 installed at a slight angle with respect to the second beam splitter 6.
The beam is reflected by the beam, enters the second beam splitter 6 again, and exits at a slight angle with respect to the reflected beam 21. Further, the transmitted light beam 22 is partially 2
Next, it is reflected, reflected by the reflecting surface 5, transmitted through the second beam splitter 6, and outputted at a slight angle with respect to the reflected light 21. Similarly, third-order or higher-order emitted light is emitted at slightly different angles. These light fluxes are focused by a light flux conversion lens 8 into discrete spots near the focal position. Among these spots, spots corresponding to higher-order reflected light beams are shielded by a light shielding plate 9. The two light beams that are not blocked generate interference fringes on the imaging device 10. Above 2
Since the light flux passes through almost the same optical path, it is extremely stable against changes in the environment. These interference fringes are input to the electronic computer 12 via the frame memory 11.

As shown in Fig. 3, the interference fringes are the amount of deviation from the set spherical wavefront of the object to be measured 5 (hereinafter referred to as aspherical amount).
It appears in response to the difference 32 between the wavefront 30 showing , and the wavefront 31 obtained by laterally shifting the wavefront 30 by a lateral shift amount 33 . Since the density of interference fringes changes depending on the size of the aspherical surface, by changing the distance between the second beam splitter 6 and the reflecting surface 7, the amount of lateral shift 3 can be adjusted.
3 to set the interference fringe density suitable for analysis. Further, when the reflecting surface 7 is moved by a small amount by the piezo drive device 13 and one of the laterally shifted beams is phase-modulated by one wavelength of the light source wavelength, the interference fringes change. The amount of light at each observation point on the imaging device 10 changes sinusoidally in accordance with the phase modulation. Using this waveform, the phase at each observation point can be measured with high precision. Since these phase data are differential information of the shape data, by integrating them with the electronic computer 12,
The amount of aspherical surface can be determined. At this time, the influence of the inclination of the reflecting surface 7 and the tilt and defocus at the time of setting the object to be measured 5 can be removed by the computer 31 using the least squares method. Furthermore, by changing the amount of defocus and determining the amount of change in the coefficient of defocus in the least square method at this time, the radius of curvature of the optimum spherical wavefront of the object to be measured 5 can be determined with high accuracy.

Although FIG. 1 shows an example of measuring a concave surface, it goes without saying that when measuring a convex surface, the object to be measured 40 should be placed closer to the transmitting spherical lens 42 than the focal point 42 of the transmitting spherical lens 41 as shown in FIG. stomach. In the case of measuring a planar shape, the transmission spherical lens 41 may be removed. Further, although the first beam splitter 3 is described as a prism type, it may be a flat plate type. Furthermore, in this embodiment, the reflecting surface 7 is moved to provide phase modulation, but it is clear that the second beam splitter 6 may also be moved. In addition, although the reflecting surface 7 provides the inclination of the laterally shifted light beam, the second beam splitter 6 may also provide the inclination.

Effects of the Invention As described above, the present invention removes high-order reflected light by installing the reflective surface or the second beam splitter at an angle and by providing a light shielding plate near the focal point of the light flux conversion lens. Noise components are removed and shape measurement accuracy can be improved.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a shape measuring device according to an embodiment of the present invention, Fig. 2 is an explanatory diagram of a method for removing high-order reflected light, and Fig. 3 is an explanatory diagram of the principle of shearing interferometry.
FIG. 4 is an explanatory diagram of the installation of a convex surface to be inspected, and FIG. 5 is a configuration diagram of a conventional shape measuring device. DESCRIPTION OF SYMBOLS 1... He-Ne laser light source, 2... Beam expander, 5... Measured object, 6... Second beam splitter, 7... Reflection surface, 8... Light flux conversion lens, 9... Light shielding Board, 10... Imaging device, 11...
Frame memory, 12...Electronic computer, 13...
Piezo drive device, 14...processing device.

Claims (1)

[Claims] 1. A light source, a lens system including at least an afocal lens group for irradiating the light beam from the light source onto the measured object, and generating laterally shifted light beams emitted at different angles from the reflected light from the measured object. a beam splitter and a reflecting surface installed at an angle with respect to each other for the purpose of changing the beam, a moving device for at least one of the beam splitter or the reflecting surface for phase modulating the laterally shifted beam, and a lens for converting the diameter of the beam. . A shape measuring device comprising: a light shielding plate installed near the focal point of the lens; and a processing device that calculates a shape from interference fringes generated by the two laterally shifted light beams.