Dynamic white-light interferometry via multiwavelength tilt iteration and sliding local least squares.

The growing interest in microprofile measurements for advanced semiconductor manufacturing and electronic glass screens has stimulated the demand for in situ dynamic white-light interferometry (DWLI). However, it is challenging to perform vibration-insensitive measurements because of the broad-spectrum interference. In this Letter, we report a vertical scanning DWLI using multiwavelength tilt iteration and sliding local least squares. Numerical simulations and comparative experiments were conducted to verify the principle and performance of the proposed method. To the best of our knowledge, this is the first time such a DWLI has been proposed to achieve excellent vibration-resistant performance without using complex photoelectric compensation systems.

Surface defect measurement of ICF capsules under a limited depth of field.

A surface defect detection device based on null interferometric microscopy (NIM) enables the measurement of surface defects in inertial confinement fusion (ICF) capsules. However, the microscope objective with a large numerical aperture in NIM causes the depth of field (DOF) of the system to be shallow, limiting the field of view (FOV) of the measurement. To expand the measurement FOV, a reconstruction method for the defocused surface defects in the FOV is presented, the angular spectrum diffraction model from the surface to the tilted plane is established, and the phase recovery method of the defocused surface defects is proposed by the theory of angular spectrum diffraction. Both the simulated and experimental results show that the proposed method can achieve the phase recovery of the surface defects in the defocused state and expand the measurement FOV, which improves the measurement accuracy and efficiency of the surface defects of the ICF capsules.

Dynamic wavefront measurement with a point diffraction interferometer based on birefringence polarization beam splitting.

In this study, we proposed a point diffraction interferometer based on birefringence polarization beam splitting (BPBS-PDI) for transmission wavefront measurements. Using the polarization beam splitting property of birefringent crystals and a specially designed calcite crystal as a polarization beam splitter, two beams of linearly polarized light with orthogonal polarization directions and a small angular separation can be obtained to produce the reference and test beams with perpendicular polarization directions through a pinhole point diffraction plate. By introducing spatial synchronization phase-shifting technology, influencing factors such as environmental vibrations on the measurement results, are reduced. Subsequently, the birefringent crystal and system error calibration methods were studied. Finally, a BPBS-PDI experimental device was set up to obtain the wavefront distribution of the lens to be tested. The experimental results are consistent with those of the ZYGO interferometer, indicating that the BPBS-PDI wavefront measurement method can be used to measure a lens transmission wavefront with high accuracy.

Least-squares calibration method for double-grating interferometers used in measurement of long-focal-length lenses.

In this paper, we propose a new calibration method for long-focal-length measurement using a double-grating interferometer. A numerical analysis of the relative error in measurement proves that the main factor affecting accuracy is the angle of inclination between grating grids. Hence, we present a least-squares calibration method using a series of lenses to correct this error. Experiments conducted to demonstrate high precision in wide-range focal length measurement (5-85 m) exhibited an error lower than 0.1% and a repeatability better than 0.03%.

Optical homogeneity measurement of parallel plates by wavelength-tuning interferometry using nonuniform fast Fourier transform.

Wavelength-tuning interferometry is commonly employed to measure the optical homogeneity of parallel plates. However, the nonlinearity of phase shifts caused by wavelength tuning errors and environmental vibration leads to a spatially uniform error in the calculated phase distribution. Herein, a wavelength-tuning interferometry method based on nonuniform fast Fourier transform (WTI-NUFFT) was developed, which solves the spectral aliasing resulting from the spatially uniform error. The characteristics of the WTI-NUFFT method were estimated through comparison with the FFT method. Both the simulated and experimental results showed that the WTI-NUFFT method can improve the accuracy of the optical homogeneity measurement of parallel plates.

Null interferometric microscope for ICF-capsule surface-defect detection.

Isolated defects on the surface of the inertial confinement fusion (ICF) capsule reduce the probability of ignition. Here, to the best of our knowledge, we present the first null interferometric microscope (NIM) for direct and large-field surface defects detection on ICF capsules. The planar reference mirror in conventional interferometric microscopes is replaced by a spherical reference mirror to achieve null interference in the full field of view. Further, via the use of a short-coherence light source system, parasitic fringes are avoided. The feasibility of the NIM is verified via experiments on a 0.7 mm diameter capsule. A 1 mm diameter ICF capsule is also tested by the NIM to prove that the NIM has the ability to measure capsules with different diameters.

Dynamic wavefront measurement with a pinhole linear polarizer point-diffraction interferometer.

We propose a pinhole linear polarizer point-diffraction interferometer (PLP-PDI) for dynamic wavefront measurements. The proposed interferometer uses a metallic wire grid linear polarizer that acts as a point-diffraction plate to generate an ideal spherical wave, from which we can obtain orthogonally polarized reference and test beams. The special polarization phase-shifting configuration allows four phase-shifted interferograms to be captured in a single shot with high precision and stability. The wavefront can then be reconstructed using a phase-unwrapping algorithm. In this paper, we describe the theory of the PLP-PDI and analyze the possible errors introduced by the device. The feasibility of the proposed PLP-PDI was verified by direct measurements of a wavefront. The experimental results show that the proposed PLP-PDI is an effective and efficient tool for the dynamic measurement of wavefronts.