Absolute measurement approach for crystal growth height based on a polarization-synchronized phase-shifting interferometer.

The quality of the solid deuterium-deuterium (D-D) layer in the inertial confinement fusion (ICF) target plays a vital role in the success of fusion experiments. A good understanding of how the quality is affected by the unstable growth of D-D crystal is required. This article provides an approach of measuring D-D layer absolute height in real time by combining monitoring algorithms and a synchronous phase-shifting interferometer. In the approach taken, a real-time monitoring technology, in which an antivibration algorithm is added, is used to get an absolute height of monitoring zone, overcoming the inability to accurately detect the saltus step in the interferometric measurement. Meanwhile, the polarization-synchronized phase-shifting technology is propitious to retrieve the D-D height distribution in a whole interferogram. Consequently, the categorical altitude of the D-D layer in entire crystalline regions can be obtained. Simulation analysis together with experiments have proved that a non-contact, rapid, and high-precision measurement of the D-D crystal absolute height can be realized by using the interferometer and method proposed.

Phase unwrapping in ICF target interferometric measurement via deep learning.

This paper proposes an unwrapping algorithm based on deep learning for inertial confinement fusion (ICF) target interferograms. With a deep convolutional neural network (CNN), the task of phase unwrapping is transferred into a problem of semantic segmentation. A method for producing the data set for the ICF target measurement system is demonstrated. The noisy wrapped phase is preprocessed using a guided filter. Postprocessing is introduced to refine the final result, ensuring the proposed method can still accurately unwrap the phase even when the segmentation result of the CNN is not perfect. Simulations and actual interferograms show that our method has better accuracy and antinoise ability than some classical unwrapping approaches. In addition, the generalization capability of our method is verified by successfully applying it to an aspheric nonnull test system. By adjusting the data set, the proposed method may be transferred to other systems.

Detailed investigation of the iterative analysis for inertial confinement fusion target characterization.

The iterative algorithm based on optical path difference and ray deflection (IAORD) is investigated in detail, and an advanced version (AIAORD) is proposed to obtain the refractive indices of the shell and the ice layer of the inertial confinement fusion (ICF) target simultaneously. The concept of the fixed-point iteration is introduced in the advanced algorithm, and it is found that the right choice of the combination of the input values and the characteristic curves is the key to ensure convergence in the iteration. The test uncertainties of the index measurement are analyzed by simulations, and they show that the uncertainties of the refractive indices of the shell and ice layer are 9.94% and 1.20%, respectively. Characteristic curves of typical ICF targets are studied, from which we conclude that AIAORD is versatile and suitable for the applications with any two unknown target parameters to be solved.

Design of a high-spectral-resolution lidar for atmospheric temperature measurement down to the near ground.

In this paper, a high-spectral-resolution lidar (HSRL) for profiling atmospheric temperature from the ground to 10 km is proposed. A double Nd:YAG laser produces the transmitted laser at 532 nm. The backscattering lidar signal is passed through two different saturated iodine-vapor filters and thus obtains molecular scattering signals that can be employed to determine the temperature. A coaxial postposition transceiver is constructed with an off-axis aspheric reflective telescope (OART). The design of the transceiver and that of the OART are demonstrated. With this transceiver, the lidar blind zone where the overlap factor is zero can be reduced greatly, and accurate temperature measurement for full elevation can be achieved. The whole system is optimized with theoretical models based on geometrical optics and statistical error analyses. Monte Carlo simulations display the performance of the designed HSRL, showing that the all-day temperature retrieval error is better than 1.4 K from the ground to 10 km. The proposed HSRL is expected to provide more accurate atmospheric auxiliary parameters for the detection of aerosols' optical characteristics.

ICF target DT-layer refractive index and thickness from iterative analysis.

An iterative algorithm based on optical path difference (OPD) and ray deflection is proposed to obtain the DT (deuterium-tritium)-layer refractive index and thickness of the ICF (inertial confinement fusion) target simultaneously. Starting from an assumed initial value, the refractive index and thickness are solved back and forth until the iteration stopping criterion is reached. Simulations show that the relative retrieval error of the DT-layer refractive index is better than 0.05% after finite iterations, and that of the thickness is better than 0.1%. Experiments show that the target shell refractive index and thickness can be retrieved with a relative error below ±2%. The test uncertainties from experiments were also analyzed.

Effects of auxiliary atmospheric state parameters on the aerosol optical properties retrieval errors of high-spectral-resolution lidar.

A detailed assessment is carried out in relation to the influence of the uncertainties associated with the input auxiliary atmospheric state parameters on retrieving aerosol optical properties from high-spectral-resolution lidar (HSRL) observations. The study starts from a review of the main spectral structure of the Rayleigh backscattering followed by evaluating the temperature effects on a backscattering cross section of atmospheric molecules based on numerical simulation. It shows that the transmittance of the background interference filter should be taken into account, depending on the full width at half maximum, although overall temperature dependence is negligible. Based on the Taylor expansion of the Tenti S6 model, the systematic errors arising from input temperature and pressure profiles are analyzed. It is demonstrated that the atmospheric pressure profiles have limited effects on the inversion results of aerosol optical parameters, as the atmospheric pressure is usually quite stable. The relative errors of the aerosol backscatter coefficient mainly stem from temperature profile errors and highly depend on the aerosol concentration. Quantitatively, the aerosol backscatter coefficient error could be larger than 5% with a 3 K deviation of temperature when the backscatter ratio is larger than 1.1. The accuracy of aerosol extinction coefficient retrieval is affected not only by the error in temperature, but also by the error in temperature lapse rate; the retrieval accuracy is more sensitive to the latter than the former. Further analysis based on the sounding temperature data shows that the variation of the temperature inversion layer during the night could induce a bias larger than 0.04 km-1 on the aerosol extinction coefficient retrieval. Therefore, the time resolution of temperature measurement from sounding balloons twice per day is too low to obtain an accurate retrieval of the aerosol optical properties from the HSRL.