CN109827523B - System error calibration device and method based on interference measurement system of point diffraction wave - Google Patents
System error calibration device and method based on interference measurement system of point diffraction wave Download PDFInfo
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- CN109827523B CN109827523B CN201910176201.XA CN201910176201A CN109827523B CN 109827523 B CN109827523 B CN 109827523B CN 201910176201 A CN201910176201 A CN 201910176201A CN 109827523 B CN109827523 B CN 109827523B
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Abstract
The invention relates to a system error calibration device and method of an interferometric system based on point diffraction waves. A beam of light reflected by a beam splitter in an interference system is coupled into an optical fiber through focusing, then the other end face of the optical fiber is placed at a position about a few microns near a rear focal point (cat eye) of a reference spherical mirror, divergent spherical waves diffracted by optical fiber points enter the interference system after being collimated by a standard spherical mirror to form interference with a wave surface reflected by a reference surface of the standard spherical mirror, a plurality of frames of phase-shift interference fringes are collected through a CCD, and then a phase result is recovered through a phase-shift algorithm and used as a system error to form a calibration file. The method provides a new solution for calibrating the high-precision interferometry system error, and calibrates the reference surface and the interferometry system error by using the high-precision wavefront generated by point diffraction, and has the advantages of convenient operation and high precision.
Description
Technical Field
The invention belongs to the field of advanced optical manufacturing and detection, relates to an optical system error calibration device, and particularly relates to a system error calibration device and method of a high-precision interferometric system.
Background
The rapid development of modern scientific technology enables the ancient optical technology to generate new vitality, and the demand of high-precision optical elements is urgent in national large-scale scientific engineering such as large-caliber astronomical telescope systems, inertial confinement nuclear fusion (ICF) devices, synchrotron radiation systems, gravitational wave detection systems, deep ultraviolet and Extreme Ultraviolet (EUV) projection exposure systems and the like. For example, 50 optical elements with the caliber of 340mm are required in the LIGO, and the surface shape quality is better than 0.3nm rms; the surface shape quality requirement of near thousand meter-level optical elements in the inertial confinement fusion device ICF reaches 0.5nm rms; the surface shape quality requirement of the deep ultraviolet and extreme ultraviolet photoetching objective lens is more up to 0.1nm rms. The optical elements generally require the optical surface shape detection precision to reach the ultra-high precision of sub-nanometer (rms), which undoubtedly brings great challenges to modern optical detection. The digital phase-shifting laser interferometer is the mainstream equipment for surface shape detection at present, and the conventional commercial interferometer is represented by a time-domain phase-shifting interferometer produced by Zygo company in America, the detection precision is generally only PV:1/10-1/20 wavelength, which is mainly limited by the processing precision of an interference measurement reference surface, so that a new detection method or a calibration technology must be developed for ultra-precise surface shape detection with sub-nanometer precision. The point diffraction interference technology and the absolute detection technology are two main methods for realizing ultra-precise surface detection. The point diffraction interferometer adopts a submicron pinhole or an optical fiber tip to generate ideal reference wavefront by diffraction to be used as a natural reference to detect the spherical mirror, and the absolute detection technology adopts virtual digital reference to be applied to a commercial interferometer, removes the reference surface error through numerical operation, and finally obtains the absolute surface shape result of the measured mirror through separation. The development cost of the pinhole type point diffraction interferometer is high, and the roundness of the pinhole directly determines the quality of the generated diffraction wave surface.
A high-precision point diffraction interferometer prototype is developed only by Nikon abroad and is successfully used for detecting the sub-nanometer precision of an EUV lens, and the development condition of a pinhole type point diffraction interferometer engineering prototype is reported in 2016 of Changchun optical machines in China; compared with a pinhole type point diffraction interferometer, the optical fiber point diffraction interferometer has two remarkable advantages: (1) system setup and fiber alignment are relatively simple; (2) the fringe contrast is adjustable for the measured surfaces of different reflectivities. However, one inherent disadvantage of the point diffraction interferometer is that the system is bulky and has very strict environmental requirements. The history of absolute measurement technology can be traced back to 1893, that a liquid level is adopted to replace a reference surface of an interferometer and is used as a plane reference for interference detection, a double-sphere method is firstly proposed in 1973 by A.E. Jesen aiming at the spherical absolute measurement technology, errors of the reference surface can be effectively calibrated by a random sphere method and a rotational translation method developed later, but the absolute measurement technology generally needs to carry out repeated experiments at a plurality of different positions in a high-stability environment, the absolute surface shapes of the reference surface and the lateral surface are recovered through complex data processing according to experimental results, and in addition, different experimenters can bring great uncertainty to the calibration results. Aiming at the existing problems of high-precision interferometry, the invention provides a method for calibrating the system error (mainly the reference surface error) of a common interferometer by using an ideal wave surface generated by point diffraction, can realize sub-nanometer ultra-precise optical surface shape detection, and has the advantages of simple structure and high calibration precision.
Disclosure of Invention
The invention aims to provide a system error calibration device and a method of an interferometry system.
The technical scheme adopted by the invention is as follows: a systematic error calibration apparatus for an interferometric system based on point-diffracted waves, the apparatus comprising:
a laser 1 for generating a frequency-stabilized uniform laser beam;
the beam expanding and collimating system 2 is used for expanding and collimating the cone-shaped light beam emitted by the laser 1 into parallel light;
a beam splitter prism 3 for reflecting a part of the parallel light to a focusing lens 4; the beam splitter prism 3 is also used for reflecting the reference wave surface reflected by the standard spherical mirror 6 and the wave surface of the fiber point diffraction wave collimated by the standard spherical mirror 6 to the focusing imaging system;
the focusing lens 4 is used for focusing the parallel light beams reflected by the beam splitter prism 3 and then coupling the light beams into the optical fiber 5 or a pinhole;
an optical fiber 5 or a pinhole for generating a high-precision point diffraction wave surface;
the standard spherical mirror 6 is used for generating a reference wave surface in the interference system and simultaneously collimating the measured mirror 7 and the point diffraction wave surface into the interference system;
the measured mirror 7 is a measured surface in an experiment and interferes with the wave front reflected by the reference surface;
an imaging lens 8 for imaging the interference fringes onto the detector;
a detector 9 for recording the interference fringes.
The fiber core diameter or the pinhole diameter of the optical fiber 5 or the pinhole for generating the high-precision point diffraction wave surface is in submicron or micron order, and the numerical aperture NA of the optical fiber is larger than that of a standard spherical lens.
A method for systematic error calibration of an interferometric measurement system based on point-diffracted waves, the method comprising:
step S1, coupling a beam of light reflected by the beam splitter prism 3 in the interference system into the optical fiber 5 or the pinhole through the focusing lens 4;
step S2, placing the other end face or pinhole of the optical fiber 5 at the focus of the standard spherical mirror 6, namely, at the position about a few microns near the cat eye, so that the point diffraction wave surface can illuminate the whole reference spherical surface and be collimated by the standard spherical mirror 6 to enter the interference system, and simultaneously ensuring that a beam of light transmitted by the beam splitter prism 3 is focused by the standard lens and is not reflected back to the interference system by the end face of the optical fiber;
step S3, pushing the standard spherical mirror 6 through a phase shifter (PZT) to realize phase shifting, collecting a multi-frame interference pattern by using a detector 9, recovering phase information through a phase shifting algorithm by using the detector 9 as a CCD camera, and storing the phase information as a calibration file;
and S4, removing the optical fiber 5 or the pinhole, directly measuring the measured mirror 7, and subtracting the calibration file in the step S3 from the obtained result to remove the system error and complete the absolute detection of the measured mirror surface shape.
The principle of the invention is as follows: a system error calibration device of an interference measurement system based on point diffraction waves comprises a laser, a beam expanding and collimating system, a beam splitting prism, a focusing lens, an optical fiber or a pinhole, a standard spherical mirror, an imaging lens and a CCD camera. The detection device is calibrated aiming at the concave standard spherical mirror.
The specific steps of system error calibration of the interferometry system based on point diffraction waves are as follows:
1) a beam of light reflected by a beam splitting prism in the interference system is focused by a focusing lens and then coupled into an optical fiber or a pinhole, and the other end face of the optical fiber or the pinhole is clamped by a high-precision five-dimensional adjusting frame and is placed at the focus position of a standard spherical mirror of the interference system.
2) The adjusting frame is adjusted to enable the point diffraction wave surface to illuminate the whole standard spherical mirror, and the convergent light emitted by the interference system through the standard spherical mirror is ensured not to be reflected by the end face of the optical fiber.
3) And collecting a multi-frame phase-shift interference fringe pattern by a detector through a phase shifter on a standard spherical mirror, recovering phase information by using a phase-shift algorithm to serve as a system error of the interference measurement system, and storing the system error as a calibration file.
4) And removing the optical fiber or the pinhole, directly measuring the measured mirror by using an interferometer, and subtracting the calibration file from the obtained result to obtain the absolute surface shape result of the measured mirror.
Compared with the prior art, the invention has the advantages that:
(1) compared with a point diffraction interferometer, the method has the advantages of simple structure and small volume, and can be directly applied to commercial interferometers. In addition, the point diffraction interferometer can only be used for detecting the concave measured mirror surface, and the device can realize the ultra-precise detection of the convex mirror surface.
(2) Compared with a point diffraction interferometer, the method can utilize the whole wave surface of the point diffraction wave, and the requirement on the numerical aperture of the point diffraction wave is relatively low.
(3) Compared with the absolute measurement technology, the method does not need repeated experiments at different positions, avoids errors introduced by operators, reduces the uncertainty of the measurement result, and has higher precision. The method has the characteristics of ideal spherical waves of a point diffraction interferometer and has a natural standard of ultra-precise interferometry.
Drawings
FIG. 1 is a schematic diagram of error calibration and measurement of an interferometric system based on fiber point diffraction waves according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of system error calibration of an interferometric system based on pinhole point diffraction according to the present invention;
FIG. 3 is a schematic diagram of the generation of diffracted waves at an end surface of an optical fiber according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of pinhole diffraction wave generation according to the present invention;
FIG. 5 is a schematic diagram of interference fringes obtained by calibrating an interference system by using a fiber point diffracted wave according to the present invention.
Detailed Description
The invention will be described in detail with reference to the accompanying drawing and the specific embodiments by taking the diffracted wave of the optical fiber point as an example.
As shown in fig. 1, an interferometric system error calibration apparatus based on fiber point diffraction waves of this embodiment includes:
a laser 1 for generating a frequency-stabilized laser beam;
the collimation and beam expansion system 2 is used for collimating the light beam emitted by the laser 1 into parallel light;
a beam splitter prism 3 for reflecting a part of the parallel light to a focusing lens 4; the beam splitter prism 3 is also used for transmitting a part of parallel light to a standard spherical mirror 6; the beam splitter prism 3 is also used for reflecting the reference wavefront reflected by the reference surface of the standard spherical mirror 6 and the measured wavefront reflected by the measured mirror 7 to the detector 9;
the focusing lens 4 is used for focusing the parallel light beams reflected by the beam splitter prism 3 and is coupled to the end face of the optical fiber 5;
the other end face of the optical fiber 5 is used for generating a point diffraction spherical wavefront to calibrate the error of the whole interference measurement system.
The standard spherical mirror 6 is used for obtaining a reference wavefront of spherical interference detection by the interference measurement system; the standard spherical mirror 6 is also used to collimate the optical fiber point diffraction spherical waves into the interference system.
The measured mirror 7 is a measured mirror in actual measurement;
the imaging lens 8 is used for imaging the interference images of the reference wave surface and the measured wave surface onto the detector 9;
a detector 9 for recording interferograms; the detector 9 is a CCD camera;
the measuring process and the detection steps of the device are as follows:
the first step is as follows: the end face of the optical fiber for emitting point diffraction waves is placed at the focus position of the standard spherical mirror, the optical fiber is finely adjusted through the high-precision five-dimensional adjusting frame, the optical fiber deviates from the focus position, light focused by the focusing lens 4 is guaranteed not to be reflected by the end face of the optical fiber, and meanwhile point diffraction wave energy is guaranteed to illuminate the whole standard spherical mirror.
The second step is that: observing interference fringes on the CCD camera, and finely adjusting the posture of the optical fiber until the number of the fringes is less than 3.
The third step: and (3) moving the standard spherical mirror by using a phase shifter, and recording a plurality of frames of phase-shifting interferograms by using a CCD camera.
The fourth step: and recovering phase information by using a phase shift algorithm to serve as a system error and form a calibration file.
The fifth step: and removing the optical fiber, and carrying out experimental measurement by using the calibration file to obtain the absolute surface shape result of the measured mirror by subtracting the calibration file from the surface shape result.
The device has simple structure and higher calibration precision, and provides a new absolute calibration way for the interferometric measurement of the ultra-precise optical surface shape.
The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should cover the scope of the present invention by partial modification or replacement within the technical scope of the present invention.
Claims (3)
1. A system error calibration device for an interferometric measurement system based on point diffraction waves, the device comprising:
a laser (1) for generating a frequency-stabilized uniform laser beam;
the beam expanding and collimating system (2) is used for expanding and collimating the cone-shaped light beam emitted by the laser (1) into parallel light;
a beam splitter prism (3) for reflecting a part of the parallel light to a focusing lens (4); the beam splitter prism (3) is also used for reflecting a reference wave surface reflected by the standard spherical mirror (6) and a wave surface obtained after the fiber point diffraction waves are collimated by the standard spherical mirror (6) to the imaging lens (8);
the focusing lens (4) is used for focusing the parallel light beams reflected by the beam splitter prism (3) and then coupling the parallel light beams into the optical fiber (5) or a pinhole;
an optical fiber (5) or a pinhole for generating a high-precision point diffraction wave surface;
the standard spherical mirror (6) is used for obtaining a reference wavefront of spherical interference detection by the interference measurement system; the standard spherical mirror (6) is also used for collimating optical fiber point diffraction spherical waves into the interference system;
the measured mirror (7) is a measured surface in an experiment and interferes with the wave front reflected by the reference surface; the imaging lens (8) is used for imaging wave surface interference fringes obtained by collimating a reference wave surface reflected by the standard spherical mirror (6) and diffracted waves of optical fiber points by the standard spherical mirror (6) onto the detector (9);
a detector (9) for recording the interference fringes.
2. The system error calibration device of an interferometric system based on point diffracted waves of claim 1, wherein: the fiber core diameter or the pinhole diameter of the optical fiber (5) or the pinhole for generating the high-precision point diffraction wave surface is in submicron or micron order, and the numerical aperture NA of the optical fiber or the pinhole is larger than that of a standard spherical lens.
3. A system error calibration method of an interferometry system based on point diffraction waves is characterized by comprising the following steps:
step S1, coupling a beam of light reflected by a beam splitter prism (3) in the interference system into an optical fiber (5) or a pinhole through a focusing lens (4);
s2, placing the other end face or pinhole of the optical fiber (5) at the focus of the standard spherical mirror (6), namely a position of a cat eye, which is a few microns, so that the point diffraction wave surface can illuminate the whole reference spherical surface and is collimated by the standard spherical mirror (6) to enter the interference system, and simultaneously ensuring that a beam of light transmitted by the beam splitter prism (3) is focused by the focusing lens and is not reflected back to the interference system by the end face of the optical fiber;
s3, pushing a standard spherical mirror (6) to realize phase shifting through a phase shifter PZT, collecting a multi-frame interferogram by using a detector (9), recovering phase information through a phase shifting algorithm by using the detector (9) as a CCD camera, and storing the phase information as a calibration file;
and S4, removing the optical fiber (5) or the pinhole, directly measuring the measured mirror (7), and subtracting the calibration file in the step S3 from the obtained result to remove the system error and complete the absolute detection of the measured mirror surface shape.
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| US6876456B2 (en) * | 2002-09-27 | 2005-04-05 | The Regents Of The University Of California | Absolute calibration of optical flats |
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