RESUMEN

A method of the three-hole optical observation is presented that can measure the chromatic dispersion angle with the advantage of overcoming the influence of out-of-focus images on the measurement results, especially those that are out-of-focus due to the ambient temperature change. This paper uses the refractive index model and the actual meteorological data to calculate the chromatic dispersion angles during the observation period for comparison and analysis to demonstrate the reliability of the optical observation. The optical observation results are generally consistent with the calculated results, but the local distribution is relatively discrete. Additionally, the optics method applies to the observation targets under arbitrary paths in the dynamic atmosphere, and the observed results can better reflect the real atmosphere condition of the chromatic dispersion angle, providing more accurate data for research in related fields.

RESUMEN

In order to solve the problem of atmospheric influence on the far-field measurement of the quality of a laser beam, we proposed a direct wavefront measurement system based on the Hartmann detection principle, which can measure large apertures and high-power laser beams. The measuring system was composed of a lens array and a detector. The wavefront detection of a large aperture laser beam could be realized by controlling the distance between the lenses and the size of the lens. The influence of different duty cycle factors on the accuracy of the wavefront reconstruction under the same arrangement and different arrangement conditions was simulated and analyzed. The simulation results showed that when the sub-lenses of the system were not in close contact, the reconstruction accuracy of the duty factor of 0.8 was close to that of the case of the duty factor of 1. Within a certain detection range, the hexagonal arrangement of 19 lenses and the arrangement of 8 × 8 lens arrays had a high wavefront restoration accuracy; both were lower than 0.10 λ. The system proposed in this paper was suitable for measuring a large aperture laser beam, providing a new idea for measuring and analyzing the quality of large aperture laser beams. It also has an important significance for improving the measurement accuracy of the beam quality.

Asunto(s)

Lentes , Simulación por Computador , Luz , Diseño de Equipo , Rayos Láser

RESUMEN

This paper proposes a new laser parameter measuring method based on cone-arranged fibers to further improve the measurable spot size, allowable incident angle range, and spatial sampling resolution. This method takes a conical array composed of flexible fibers to sample and shrink the cross-section spot of the laser beam, facilitating low-distortion shooting with a charge-coupled diode (CCD) camera, and adopts homogenized processing and algorithm analysis to correct the spot. This method is experimentally proven to achieve high-accuracy measurements with a decimeter-level spot-receiving surface, millimeter-level resolution, and high tolerance in order to incite skew angle. Comparing the measured spot under normal incidence with the real one, the root mean square error (RMSE) of their power in the bucket (PIB) curves is less than 1%. When the incident angle change is between -8° and 8°, the RMSE is less than 2% and the measurement error of total power is less than 5% based on the premise that the fiber's numerical aperture (NA) is 0.22. The possibility of further optimizing the measurement method by changing the fiber parameters and array design is also reported.

RESUMEN

By using the differential scintillation method suggested and described in this work, vibrations of unmanned aircraft vehicle platforms can be eliminated. Therefore, airborne beacons have great potential applications in turbulence measurements along an arbitrary atmospheric path. The experiment with a constant beacon shows that the retrieved results of the differential scintillation method have good consistency with the scintillation index inversion method. Additionally, a similar verification was carried out between a simulative airborne beacon and a constant beacon; the differential scintillation method indicated more consistent results than the scintillation index inversion method, and its retrieved results of different beacons were in good agreement with a correlation coefficient close to 1, reaching 0.994. In verification experiments over a slant path, the retrieved results of the differential scintillation method showed good statistical properties when an airborne beacon was measured under various weather conditions. The results indicated that the new, to the best of our knowledge, proposed differential scintillation method is a reliable and feasible technique for eliminating stability issues in the measurements of airborne beacons.

RESUMEN

In this paper, a new prototypical Scheimpflug lidar capable of detecting the aerosol extinction coefficient and vertical atmospheric transmittance at 1 km above the ground is described. The lidar system operates at 532 nm and can be used to detect aerosol extinction coefficients throughout an entire day. Then, the vertical atmospheric transmittance can be determined from the extinction coefficients with the equation of numerical integration in this area. CCD flat fielding of the image data is used to mitigate the effects of pixel sensitivity variation. An efficient method of two-dimensional wavelet transform according to a local threshold value has been proposed to reduce the Gaussian white noise in the lidar signal. Furthermore, a new iteration method of backscattering ratio based on genetic algorithm is presented to calculate the aerosol extinction coefficient and vertical atmospheric transmittance. Some simulations are performed to reduce the different levels of noise in the simulated signal in order to test the precision of the de-noising method and inversion algorithm. The simulation result shows that the root-mean-square errors of extinction coefficients are all less than 0.02 km-1, and that the relative errors of the atmospheric transmittance between the model and inversion data are below 0.56% for all cases. The feasibility of the instrument and the inversion algorithm have also been verified by an optical experiment. The average relative errors of aerosol extinction coefficients between the Scheimpflug lidar and the conventional backscattering elastic lidar are 3.54% and 2.79% in the full overlap heights of two time points, respectively. This work opens up new possibilities of using a small-scale Scheimpflug lidar system for the remote sensing of atmospheric aerosols.

RESUMEN

Previous studies have shown that the isoplanatic angle (θ0) can be measured by using plane-wave scintillation. The problem of measuring the isoplanatic angle in a finite distance using spherical-wave scintillation is considered in this Letter. Based on theoretical analysis and numerical evaluation, we found that by selecting suitable aperture size and aperture separations, the isoplanatic angle can be estimated through spherical-wave scintillation and covariance of irradiance in three received apertures using a point source. The error of θ0 measured by this method is less than 6% in typical turbulence models.

RESUMEN

We have developed a differential column image motion (DCIM) lidar for measuring real-time vertical profiles of Fried's transverse coherence length (r0) and testing it against a differential image motion (DIM) lidar and a DIM monitor by observing stars throughout a range of turbulent conditions. With the DCIM lidar system parameters elaborately designed and the detector installed with an angle corresponding to the receiving telescope axis, the focal position of the laser guide star from a range of altitudes that coincide with the CCD's receiving area, r0 of different altitudes can be obtained simultaneously. The experiment results support the DCIM lidar and confirm that a high temporal and spatial resolution r0 profile can be measured with this method.