A fast and precise registration method for multi-image snapshot Fourier transform imaging spectroscopy is proposed. This method accomplishes registration of an image array using the positional relationship between homologous points in the subimages, which are obtained offline by preregistration. Through the preregistration process, the registration problem is converted to the problem of using a registration matrix to interpolate subimages. Therefore, the hardware interpolation of graphics processing unit (GPU) texture memory, which has speed advantages for its parallel computing, can be used to significantly enhance computational efficiency. Compared to a central processing unit, GPU performance showed ∼27 times acceleration in registration efficiency.
A grating encoder, which is composed of two equal periodic planar gratings, is proposed for measuring wide range three-axis displacements with nanometric resolution. In the optical reading system, one grating works as a reference planar grating, while another one is a scale planar grating. The grating encoder records the <i>x</i>- and <i>y</i>-axis displacement information in terms of the grating period, while it records the <i>z</i>-axis displacement information in terms of both the wavelength of the laser and the grating period. In this scheme, the gratings and other optical elements satisfy the Littrow configuration. The positions and the size of the detected interference zones are almost constant when the scale grating moves along the <i>z</i>-axis with respect to the optical reading system. Therefore, the measurement range is greatly enhanced in the z-axis direction. When the wavelength of the laser is 632.8 nm and the scale grating with period 8 μm is 100×100 mm<sup>2</sup>, the measured maximal <i>z</i>-axis displacement of the proposed encoder is 1263 mm theoretically.
Fourier-transform imaging spectrometers are rapidly developed due to their extensive use in industrial monitoring, target detection, and chemical identification. Static Fourier-transform imaging spectrometer (SFIS) containing a birefringent interferometer is one of the most popular directions due to its inherent robustness. However, the SFIS suffers from its low achievable signal-to-noise ratio (SNR) because of the restriction of incident angle. Meanwhile, in applications, the SNR is perhaps the most important factor to determine the usefulness of an instrument. In this paper, we report here a Static Fourier-transform imaging spectrometer based on differential structure (SFIS-DS) in the 400-800nm wavelength range with a high SNR. As in electronic system, the differential structure can double optical efficiency and strongly restrain common mode error in the SFIS-DS. And the differential structure described here is also available for any instruments containing a birefringent interferometer. However, the drawback of the SFIS-DS is that the two images obtained by the two differential channels need precise registration which can be overcome by a sub-pixel spatial registration algorithm. The experimental results indicate the SFIS-DS can increase the SNR by no less than 40%.
Through modulating the Bessel–Gaussian radially polarized vector beam by the cosine synthesized filter under a reflection paraboloid mirror system with maximum focusing semi-angle of π/2 , arbitrary-length super-Gaussian optical needles are created with consistent beam size of 0.36λ (full width at half maximum) and the electric field being pure longitudinally polarized (polarization conversion efficiency greater than 99%). Numerical calculations show that the on-axis intensity distributions are super-Gaussian, and the peak-valley intensity fluctuations are all within 1% for 4λ , 6λ , 8λ , and 10λ long light needles. The method remarkably improves the nondiffraction beam quality, compared with the subwavelength Gaussian light needle, which is generated by a narrow-width annular paraboloid mirror. Such a light beam may suit potential applications in particle acceleration, optical trapping, and microscopy.
Free volume theory and a model of polymerization kinetics are introduced to predict and analyze the curing shrinkage and kinetic parameters of an acrylate-based ultraviolet-embossing resist. Curing shrinkage tests have been designed and performed to verify the accuracy of the model. The experimental results are in good agreement with the simulated results of the conversion behavior. The reaction coefficients of polymerization predicted by this model are essentially correct when compared to the classical experimental values. Moreover, the dynamic shrinkage during polymerization determined experimentally matches the simulated result predicted by our model.
The effects of parameters of Bessel-Gaussian beam on the focusing characteristics are investigated in lens system with high numerical aperture. The maximal intensity shifts from focal spot in the case of larger value of parameters of BG beam. Meanwhile, the lateral resolution is increasing with the increase of value of parameters. The effect of parameters of Bessel-Gaussian beam on the achievement of optical needle is also explored. Obviously, the value of parameters is most important to obtain optical needle.
In order to study the validity of general focal length function in designing diffractive microlenses with long focal
depth, diffractive microlenses with different f-numbers are designed using general focal length function and their
focusing characteristics, such as real focal depth, real focal spot size, and diffractive efficiency, are investigated
using electromagnetic theory and boundary element method. Investigation results indicate that general focal
length function can be used to achieve long focal depth in designing diffractive microlenses, even twice over than
those of conventional diffractive microlenses with similar parameters.