剩余啁啾对自相关法测量超短脉冲脉宽的影响

为了研究待测超短脉冲存在剩余啁啾对2次谐波自相关法测量脉宽产生的影响,以2次谐波自相关法测量原理为出发点,采用2次耦合波方程数值模拟计算了中心波长800nm、脉宽100fs的超短激光脉冲存在不同啁啾量时,经过偏硼酸钡(β-BaB2O4,BBO)晶体Ⅰ类非共线相位匹配进行2次谐波自相关测量对测量结果的影响。分析发现,正啁啾使测量值比实际值偏大,负啁啾使测量值偏小;负啁啾比正啁啾对脉宽测量的影响更大,当脉冲的啁啾参量C=20时测量误差为23%,而C=-20时测量误差高达53%;且测量误差随啁啾量的增大而增大。模拟计算了非线性晶体厚度对脉宽测量的影响,结果表明,选取较薄的非线性晶体能够有效控制啁啾量引起的测量误差,使用非线性晶体的厚度L≤0.5Ld可将脉宽测量误差控制在理想的范围。

Effect of residual chirp on ultrashort pulse width measured with autocorrelation method

To study the effect of residual chirp on ultrashort pulse width measurement by means of the second harmonic autocorrelation,starting from its measurement principle,the effect was simulated for ultrashort laser pulses with different chirps at center wavelength of 800nm and pulse width of 100fs.The results show that the measured value would be larger than factual value with positive chirp,smaller with negative chirp.Moreover,the measurement error will be augmented with the chirp.The effect of the thickness of β-BaB2O4 (BBO) crystal on the pulse width measurement was also discussed numerically.It is found that choosing thin nonlinear crystal could control the measurement error effectively.Using the nonlinear crystal width of L≤0.5Ld, the measurement error caused by chirp can be controlled to an ideal range.