Effects of mask-alignment error on point spread function for multi-level Fresnel diffractive lenses

The full aperture complex amplitude transmittance function of a multi-level diffraction lens with mask- alignment errors was derived based on scalar diffraction theory. The point spread function （PSF） was calculated by the Kirchhoff diffraction integral. It is found that the radius of the Airy disk increases with the increase of the error in the direction of misalignment, and the image center shifts along the direction of misalignment. A fourlevel diffractive lens with a diameter of 80 mm was fabricated, and its PSF and diffraction efficiency of ＋1st order were calculated and measured. The distribution of PSF is consistent with the calculated results, and the tested diffraction efficiency is slightly smaller than the calculated value; the relative error is 5.71%.

Boundary evaluation and error correction on pseudorandom spread spectrum photon counting system

The Cramer–Rao lower bound on range error is modeled for pseudo-random ranging systems using Geiger-mode avalanche photodiodes. The theoretical results are shown to agree with the Monte Carlo simulation, satisfying boundary evaluations. Experimental tests prove that range errors caused by the fluctuation of the number of photon counts in the laser echo pulse leads to the range drift of the time point spread function. The function relationship between the range error and the photon counting ratio is determined by using numerical fitting.Range errors due to a different echo energy is calibrated so that the corrected range root mean square error is improved to 1 cm.

Effect of refractive correction on ocular optical quality measurement using double-pass system

Background Optical Quality Analysis System II （OQAS, Visiometrics, Terrassa, Spain） that uses double-pass （DP） technique is the only commercially available device that allows objective measurement of ocular retinal image quality. This study aimed to evaluate the impact of spectacle lenses on the ocular optical quality parameters and the validity of the optometer within OQAS. Methods Seventy eyes of healthy volunteers were enrolled. Optical quality measurements were performed using OQAS with an artificial pupil diameter of 4.0 mm. Three consecutive measurements were obtained from spectacle correction corresponding to subjective refraction and from the OQAS built-in optometer separately. The modulation transfer function cutoff frequency, the Strehl ratio, the width of the point spread function （PSF） at 10% of its maximal height （PSF10）, and the width of the PSF at 50% of its maximal height （PSF50） were analyzed. Results There was no significant difference in any of the parameters between the spectacle correction and the optometer correction （all P 〉0.05, paired t-test）. A good agreement was found between both the methods and a good intraobserver repeatability in both the correction methods. Difference in best focus between two methods was the only parameter associated significantly with optical quality parameter differences. Best focus difference, built-in optometer correction with or without external cylindrical lens, and age were associated significantly with PSF10 difference. No linear correlation between refractive status and optical quality measurement difference was observed. A hyperopic bias （best focus difference of （0.50±0.44） D） and a relatively better optical quality using spectacle correction in high myopia group were found. Conclusions OQAS based on DP system is a clinically reliable instrument. In patients with high myopia, measurements using built-in optometer correction should be considered and interpreted with caution.

Algorithm based on local breeding of growing modes for convection-allowing ensemble forecasting

We propose a method based on the local breeding of growing modes(LBGM) considering strong local weather characteristics for convection-allowing ensemble forecasting. The impact radius was introduced in the breeding of growing modes to develop the LBGM method. In the local breeding process, the ratio between the root mean square error(RMSE) of local space forecast at each grid point and that of the initial full-field forecast is computed to rescale perturbations. Preliminary evaluations of the method based on a nature run were performed in terms of three aspects: perturbation structure, spread,and the RMSE of the forecast. The experimental results confirm that the local adaptability of perturbation schemes improves after rescaling by the LBGM method. For perturbation physical variables and some near-surface meteorological elements, the LBGM method could increase the spread and reduce the RMSE of forecast,improving the performance of the ensemble forecast system.In addition, different from those existing methods of global orthogonalization approach, this new initial-condition perturbation method takes into full consideration the local characteristics of the convective-scale weather system, thus making convectionallowing ensemble forecast more accurate.