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卫星飞秒激光测距理论上可达到亚微米量级的测距精度,但飞秒激光脉冲在大气中传输时由色散导致的脉冲展宽显著,会使测距精度下降。为补偿飞秒激光脉冲在大气中的色散需对其色散量进行定量计算。推导了飞秒激光脉冲在大气中的群速度色散和脉冲展宽公式,表明脉冲展宽程度和群速度色散及传输距离有关;中心波长相同的飞秒激光脉冲脉宽越窄色散越严重,而当脉宽相同时,中心波长越短色散越严重。计算比较了大气和BK7玻璃的群延时、群速度色散和三阶色散。卫星激光测距系统应采用中心波长较长的1 550 nm的飞秒激光脉冲,脉宽应适当选取。由于飞秒激光色散严重,提出了采用单模光纤序列进行粗补偿和采用光栅对进行精密补偿的两种补偿相结合的方式对其色散进行补偿。
Satellite femtosecond laser ranging theory can reach the sub-micron ranging accuracy, but the femtosecond laser pulse transmission in the atmosphere caused by the pulse broadening significantly, will lead to the accuracy of the reduction. In order to compensate the dispersion of femtosecond laser pulses in the atmosphere, the amount of dispersion needs to be calculated quantitatively. The formulas of group velocity dispersion and pulse broadening of femtosecond laser pulses in the atmosphere are deduced. It shows that the degree of pulse broadening is related to the group velocity dispersion and transmission distance. The narrower the pulse width of the femtosecond laser pulses with the same center wavelength, the more serious the dispersion is. The same width, the shorter the center wavelength dispersion more serious. The group delay, group velocity dispersion, and third-order dispersion of the atmosphere and BK7 glass are compared. Satellite laser ranging system should use a longer center wavelength of 1 550 nm femtosecond laser pulse, the pulse width should be properly selected. Due to the serious dispersion of femtosecond laser, the dispersion compensation is proposed by combining the coarse compensation with the single-mode optical fiber and the grating with grating compensation.