Flat crystal self-calibrating common optical path interferometer based on acousto-optic heterodyne phase shifting

Abstract

The invention discloses a flat-crystal self-calibrating common optical path interferometer based on acousto-optic heterodyne phase shifting. By adopting an acousto-optic frequency shifter for heterodyne interference phase-shifting, the presence of moving parts in the interferometer is effectively avoided, and the measurement accuracy is further improved. The interference is good, and the development difficulty and cost can be reduced, especially for the measurement of large-caliber surface shape, compared with the same advantage of mechanical drive; at the same time, using low-frequency difference heterodyne interference and continuous acquisition of high-speed area array detectors, the obtained The amount of information is richer, which is more conducive to accurately calculating the phase, and is more conducive to overcoming the influence of noise and other factors; in addition, adding point diffraction self-calibration beams, and using point diffraction light to pre-calibrate the reference mirror during measurement can reduce the accuracy of the reference mirror Requirements, and improve the accuracy of measurement, but also reduce the difficulty and cost of interferometer development.

Description

technical field [0001] The invention relates to the field of optical technology, in particular to a flat crystal self-calibrating common optical path interferometer based on acousto-optic heterodyne phase shifting. Background technique [0002] The high-end optical equipment represented by the projection exposure system of the deep ultraviolet lithography machine poses great challenges to the processing of optical components and the integration of optical systems. Interferometer is an indispensable core detection equipment for high-precision optical component processing and optical system integration, and the detection accuracy requirements are constantly improving. [0003] The optical surface shape detection methods used in traditional optical processing include Hartmann sensor method, knife edge method and contour method. These methods have different disadvantages such as non-digital subjective interpretation or contact damage to the test piece, and it is difficult to ac...

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Problems solved by technology

However, in fact, the wavelength tuning in the wavelength tuning laser is also to change the cavity length of the resonant cavity through piezoelectric machinery or changing the temperature, or to change the laser wavelength by mechanically rotating the grating, although the components that need to be driven are in the laser cavity. The weight is smaller than the reference mirror, but it is still unavoidable to reduce the precision caused by mechanical movement or temperature change, and the development of tunable lasers is difficult and costly; in addition, the number of steps that can be shifted is limited, and the information obtained is less and accurate. The degree still cannot meet the high-precision measurement requirements

[0009] In addition, some existing common optical path heterodyne interferometers require a reference mirror with extremely high surface shape accuracy as a scale, and the accuracy of the reference mirror directly determines the final measurement accuracy, and the manufacturing difficulty and cost of the reference mirror are extremely high. High, especially for large-aperture interferometers, the reference mirror directly restricts the caliber and precision of the interferometer

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