JPS60222702A - Fringe-scanning sharing interferometer - Google Patents

Abstract

PURPOSE:To obtain the titled interferometer, whose vibration resistance is improved, by providing two rectangular prisms in the vicinity of a beam splitter for splitting laser light, and commonly using optical elements. CONSTITUTION:Laser light from a laser light source 11 is split by a first beam splitter 13. The light beams are supplied to a curved surface to be measured 15 and a second beam splitter 16. Two rectangular prisms 17 and 18 are provided in the vicinity of the second beam splitter 16. The rectangular prism 17 is moved in the vertical direction by a pulse motor 19. The rectangular prism 18 is minutely moved in the incident direction of light by a piezoelectric element 20. Thus the shared part is formed. Therefore, the part, which commonly utilizes the light elements, are increased, vibration resistance is improved and the compact configuration can be attained.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a fringe scanning shearing interferometer, and more specifically, it is applicable to high precision measurement of flat, spherical and aspherical shapes, measurement of wavefront aberration and eccentricity of optical elements, This invention relates to a fringe scanning shearing interferometer that is applied to focal length measurements and the like.

(Prior Art) FIG. 1 shows the configuration of a conventional fringe scanning shearing interferometer.

In the figure, the symbol ■ is a laser light source, the symbol L1゜L2 is a collimator lens, the symbols 2 and 3 are half mirrors, the symbol L is
3 is an illumination lens, 4' is an engineering mirror, 5 is a piezoelectric element or magnetostrictive element, 6'r1 is a parallel plate, 7 is a half mirror, 1 is an imaging lens, 9 is a photoelectric detection device, and Reference numeral 10 indicates an object to be measured.

When measuring the shape of an object to be measured, the laser light emitted from the laser light source 1 is passed through collimator lenses L, L.

It becomes a parallel light, and)
The light passes through the illumination lens L3 and reaches the object to be measured 10.

The light reflected by the object to be defined 10 is passed through the illumination lens L3 to 1L.
11 reaches the half mirror 3, where this reflected light is 2
Be divided. One of the split lights is reflected from the half mirror 2 to the half mirror 7, and then enters the photoelectric detection device 9 from the half mirror 7 through the imaging lens L4. This is called the test wavefront. The other split light is also half mirror 3
From there, the optical path passes through a vibratory mirror 4 fixed to a piezoelectric element or magnetostrictive element 5 as a device for changing the optical path, passes through a parallel plate 6 that shifts the wavefront laterally with respect to the path of the light, and then... 7 and the imaging lens L4 to enter the photoelectric detection device 9. This is called a reference wavefront.

Therefore, the two waves l projected onto the photoelectric detection device 9
We carefully create interference fringes, measure the phase difference at each point of the interference fringes, calculate the wavefront to be measured from the measured values, and then locate the object to be measured.
This determines the surface shape of O.

゛ However, in this prior art, each wavefront after division is configured to propagate over a long distance between different optical elements, so it is susceptible to external influences such as vibrations, and therefore , there is a problem that measurement accuracy cannot be improved.

(Objective) Therefore, an object of the present invention is to provide an improved fringe scanning shearing interferometer that can improve vibration resistance and increase measurement N degree.

According to the above-mentioned object of the present invention, a fringe scanning shearing interferometer is provided which has a structure in which many optical elements are commonly used.

(Mizo Sei) The structure of the present invention will be explained below based on embodiments.

In FIG. 2, reference numeral 11 indicates a laser light source 17; reference numeral 12 indicates a collimator lens system; reference numeral 13 indicates a beam splitter as a splitting element for directing the course of the laser beam toward the object to be measured; Change the fixed wave surface on the side caused by light to a nearly parallel wave surface 11g! A converter lens is shown as a conversion element.

Further, reference numeral 16 indicates a beam splitter as an external cutting element that divides the traveling direction of the fracture-defined wavefront from the beam splitter vine 13 into two directions.

Two right-angled prisms 17 and 18 are arranged I6 at a position close to the beam splitter 16.

Among these single angle prisms, a right angle prism 17 (in particular, f#I means for varying the prism in a direction perpendicular to the direction of incidence of light is attached. As this variation means, for example, A pulse motor 19, a screw shaft [9a that is integral with the shaft of this pulse motor, and a frame 1:4=17a that is screwed to this screw shaft and is integrally attached to the Shimachi prism 17, etc. Can you name the configuration?

In addition to the above, a piezo element may also be used as the variation means.

On the other hand, with respect to the right-angle prism 18, a means is provided for causing the prism to change by a minute amount in the same direction as the direction of incidence of light so as to share the prism.

As a means for this sharing, a piezo element 2o provided integrally with the right angle prism 18 can be mentioned.

Next, code 21'L'! , the two right angle prisms 17
18 and the beam splitter 16 are reflected onto the photoelectric detection device 22 to cause interference fringes to appear.

In determining the curved surface to be measured J5, the following operation is carried out.

The light emitted from the laser light source 11 passes through the collimator lens system 12, becomes parallel light, is turned left by the beam splitter □ 13, is converted into a spherical wave of the reference spherical surface by the converter lens □4, and is incident on the defined curved surface 15. be done.

However, the reference spherical surface here is a spherical surface whose radius ratio is the distance from the focal point of the comparator lens 14 to the apex on the optical axis of the curved surface 15 to be measured. If the deviation from the reference spherical surface at any point on the curved surface 15 to be measured is d/2, then
The wavefront reflected from the curved surface 15 to be measured becomes a wavefront having a wavefront aberration of d. By measuring this d, the shape of the curved surface 15 to be measured can be known.

Now, the reflected light beam from the constant curved surface 15 to be measured becomes light containing information about the shape of the curved surface 150 to be measured (after 1 step, it is called a wavefront), and the converter 1/lens 14 and beam splinter 3 are again activated. Pass through beam splitter 16
Head to. By the way, this wavefront is a wavefront slightly shifted from a plane wave, and the shift angle t corresponds to exactly twice the shift fii between the curved surface to be measured and the reference spherical surface.

The beam splinter 16 splits the traveling direction of the wavefront 1 into two directions, and each wavefront 1 travels straight to the right angle prism 18.
The beam is reflected twice at the beam splitter 16 and then once more at the beam splitter 16 to reach the imaging lens 21. This wavefront will be referred to as wavefront A for convenience.

The other wavefront is reflected by the beam splinter 16 and enters the right-angle prism 17, is reflected twice, enters the beam splitter 16, and travels straight to the imaging lens 21. For convenience, this wavefront will be referred to as wavefront B.

This is done by driving the variable means taro pulse motor 19 to shift the C surface BOX by 1/2 S from the horizontal displacement by S by the rectangular prism 17.

As a result, interference fringes are generated on the photoelectric detection device 22 between wavefront A and wavefront B, which corresponds to a wavefront that is laterally shifted by S. In this sense, this interferometry is a shearing interferometry. It is.

At the same time, the right angle prism 18 is modulated by the piezoelectric element 2
It is possible to modulate the phase of wavefront A by making a minute change at 0. In this sense, the present interferometry is a fringe scanning method.

Therefore, this interference optical system constitutes a fringe scanning air ring interferometer.

(Effects) The fringe scanning shearing interferometer according to the present invention has a configuration in which two right-angled prisms are provided close to the dividing element,
There are many common optical elements that are interesting.

Therefore, vibration resistance is improved, and as a secondary effect, the device can be made smaller.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a fringe scanning shearing interferometer according to jjjf technology, and Fig. 2 is a diagram of a fringe scanning shearing interferometer according to the jjjf US technology.
FIG. 2 is a configuration diagram of an air ring interferometer. 15... Wavefront to be measured, 16... Beam splitter as splitting element, 17.18... Right angle prism, 19... Nockles motor, 19a... Screw, 17a... Frame body 1. 20... Piezo element as a modulation means, 21... Quadrature lens, 2
2... Photoelectric detection device.

Claims (1)

[Claims] A conversion element that converts a wavefront to be measured generated by projecting light onto a constant curved surface into a parallel (near) wavefront, and a dividing element that divides the traveling direction of the constant wavefront to be measured into two directions. And Goji 1 is located at the same distance and close to the above conversion element!
two wide-angle prisms, the uppers of these two right-angle prisms, a means for changing one right-angle prism in a direction perpendicular to the direction of incidence of light, and a means for changing the other right-angle prism in a direction perpendicular to the direction of incidence of light. The present invention is characterized by a means for causing air to fluctuate by a minute amount in the same direction, and a condensing lens that images the wavefronts that have passed through the two right-angle prisms on a photoelectric detection device to cause interference fringes to appear. Fringe scanning shearing interferometer.