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Full-field heterodyne white light interferometry
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Abstract
In order to solve the problem that the displacement accuracy of linear displacement mechanism is too high in traditional white light interferometry, this paper proposes a full-field heterodyne white light interferometry. The technology mainly uses the white light interference signal with difference frequency as the light source to realize the high-precision detection of the coherent peak position under the conditions of large push step and low push precision. In this paper, the mathematical model of white light heterodyne interference is established firstly, and then the overall system design scheme is proposed according to the light intensity signal characteristics provided by the mathematical model. Then the feasibility of the measurement scheme is verified by experiments. At the end, theoretical analysis and data comparison are carried out for the influence of various errors on the calculation accuracy of the algorithm. The results of error analysis show that the white-light heterodyne interferometry technology provides higher measurement accuracy and better anti-interference performance, effectively reducing the strict dependence of traditional white light interferometry on the accuracy of linear displacement mechanism, and is an optical free-form surface detection technology. More solutions are available. -
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References
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Overview
Overview: In this paper, a measurement technique for full-field heterodyne white light interference is proposed. This technology uses white light interference signals with difference frequency to detect signal, aiming at reducing the high precision requirement of traditional white light interferometry for linear displacement mechanism. High-precision detection of coherent peak position under conditions of step size and low push-pull accuracy. Reducing the high precision requirements of the push-pull mechanism is of great significance for the development of white light interferometry. Firstly, the heterodyne signal is introduced on the basis of white light interferometry, and the mathematical model of white light heterodyne interference signal is established. According to the characteristics of light intensity signal and measurement target, a set of schemes for realizing white light heterodyne interference are proposed. The mathematical model of the difference interference signal has developed a special signal acquisition method, and the corresponding signal processing algorithm is proposed according to the signal acquisition method. The feasibility of the algorithm is verified by the simulation step measurement. Then the feasibility of the measurement scheme is verified by experiments. The experimental data analysis verifies that the system and algorithm principles are feasible. Finally, the effects of different scanning steps, scanning step precision and white noise of detector on the calculation accuracy of the algorithm are analyzed. The analysis results show that the full field white light heterodyne interferometry algorithm is more abundant than the traditional white light interferometry algorithm, and has higher measurement accuracy and stronger anti-interference. The step size is 50 nm and the step error is absolute. When the value is less than 5 nm, the calculation error in the case where the absolute value of the detector error is less than 1% of the amplitude can be stably maintained less than 0.1 nm, which can effectively reduce the dependence of the conventional white light interferometry on the high-precision linear displacement mechanism. Experiments have verified that this technique can achieve planar, spherical and aspherical surface measurements. This measurement technique can be used as an alternative to optical freeform measurement.
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Figure 1.
Signals of white optical heterodyne interferometry
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Figure 2.
Schematic diagram of coherent peak addressing
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Figure 3.
White light heterodyne interferometry schematic diagram
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Figure 4.
Simulation data fitting curve. (a) Envelop curve at low position; (b) Envelop curve at high position
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Figure 5.
Simulation results of white optical heterodyne interferometry. (a) Simulation model; (b) Recovery model
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Figure 6.
Effect of step size on calculation accuracy
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Figure 7.
Effect of step accuracy on calculation accuracy
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Figure 8.
Effect of detector noise on calculation accuracy
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Figure 9.
Experimental apparatus
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Figure 10.
Time domain intensity signal.
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Figure 11.
Experimental data fitting curve.
