The transportation of lidar’s laser beam in seawater is simulated by Monte Carlo method, which combined with statistic, estimate method and weigh method. It should be hypothesized that the incidence laser beam is vertical down and the beam is infinitude thin and vertical. The edge of atmosphere and seawater is located as cone. The axial line of the cone is same to the axial line of the laser impulse spread. It shows that the FOV (fields of view) of lidar’s detector have some influence to the waveform of echo signals. The influence is quite clear when the fields of view is quite small. The larger of the fields of view is, the slower the attenuation speed is. The trend goes to saturation when the fields of view add to a certainty. The conclusion is that the best receiving FOV is between 50mrad ~ 70mrad to the on-board lidar system which located in height at about 500 meters.
In this paper, it is described that two common methods to determine the thermal lens focal length (both assistant lens and double beams) with the analysis of their theoretical error, and proposed a new method to measure thermal lens focal length (M2) based on the relative beam propagation of Gaussian single and multi modes beam. The calculated equations of thermal lens focal length using proposed M2 method were reckoned, and its effectiveness has been testified by both the theoretical analysis and the experimental research.