The invention of the laser in 1960 created the possibility of using a source of coherent light as a transmitter for a laser radar (ladar). Coherent ladar shares many of the basic features of more common microwave radars. However, it is the extremely short operating wavelength of lasers that introduces new military applications, especially in the area of missile identification, space target tracking, remote rang finding, camouflage discrimination and toxic agent detection. Therefore, the most popular application field such as laser imaging and ranging were focused on CO2 laser in the last few decades. But during the development of solid state and fiber laser, some people said that the CO2 laser will be disappeared and will be replaced by the solid and fiber laser in the field of military and industry. The coherent CO2 laser radar will have the same destiny in the field of military affairs. However, to my opinion, the high power CO2 laser will be the most important laser source for laser radar and countermeasure in the future.
In order to lead the laser beam transmit in the atmosphere convergently, an experiment of laser focus at the distance of
450m and 300m has been operated in the outdoor place. The actual manipulations are as follows: Firstly, the laser was
collimated by a beam expander, then the near-parallel laser beam was transmitted with a Galileo telescope system, and
the distance between the concave lens and the convex lens can be tuned through a precise displacement platform, so the
focus of the system changed due to the tiny displacement of the concave lens. Secondly, the average power of the laser
spot can be measured using power meter, the power is 47.67mW and the standard deviation is 0.67mW while the focal
length is 450m. Thirdly, the energy distribution was found through the laser beam analyzer. The spot images were saved
using the beam analyzer, then the saved image can be processed with Matlab software afterwards. The function named
EDGE and Sobel operator was used in the pre-processing of the saved image, then method of median filter was used in
the course of image de-noising and 53H filter was adopted in the signal analysis. The diameter of laser spot was obtained
by the method above, the diameter is 5.56mm and the standard deviation is 0.24mm. The spot center excursion is
0.56mm, it is 10.43% of the total diameter of the laser spot. At last, the key factors of the energy dissipation in the
focusing system can be summarized as follows: restriction of the diffraction limit, attenuation in the atmosphere,
geometrical aberration of optical system, and the diffraction limit and the geometrical aberration are significant in the
three factors above, so we can reduce the impact of the both factors during the design of optical system. The reliable
referenced data of the system design can be acquired through the primary experiment research.
An improved algorithm of 2-D Empirical Mode Decomposition (EMD) in image processing has been presented. It
contains selecting extrema of the pixels and interpolation of them in the course of EMD, A variance phenomenon has
been discovered in the interpolation of boundary pixels. Delaunay Triangulation has been used to partition the selected
extrema, a pixel that not contained in the Delaunay polygon can be processed through symmetry principle, It can restrain
the variance phenomenon that appeared in the cubic spline interpolation. An image has been processed with the
improved algorithm, The calculation result of standard deviation between the original image and the reconstructed image
is 6.667×10-6 . A slight fluctuation can be seen from the calculation result. The reconstructed image is consistent with the
original image. It demonstrates that the improved algorithm been presented is accurate and feasible. The method of EMD
is used in image compression and de-noising more and more popular, therefore, the improved algorithm in the paper will
be useful in the course of calculation speed enhancement of image processing based on EMD.
Laser linewidth measurement has been realized in the paper through image processing and on non-air gap F-P . Firstly ,
The expression of linewidth measurement founded on non-air gap F-P has been obtained from the interference theory of
multi-beam of light. Secondly, The practical linewidth of pulse Nd:YAG laser has been measured with the method
above. An interference pattern produced by CCD was used for digital image processing. In the course of processing,
Canny operator was applied for the sake of picking-up the edge of interference circle, then the inner and external radius
of the interference circle can be acquired in the form of pixels. The actual physical size can be calculated through
relative transformation according to the radius of the interference circle. At last, Nd: YAG laser with 28ns pulsed-width
was used as the emission source, The experimental results based on the method above is 36.8 MHz. This data is in
agreement with 34.2 MHz through Discrete Fourier Transform(DFT), As we all know, the frequency resolving power of
DFT is depend on the effective acquisition points, So the cubic spline interpolation was introduced after the course of
DFT, and the better result has been achieved.
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