偏硼酸钡晶体中彩色锥形辐射特性的研究

Investigation of Colored Conical Emission inβ-Barium Borate Crystal

彩色锥形辐射是超短脉冲激光在非线性介质中传输时产生的一种特殊的非线性现象。实验研究了飞秒脉冲激光诱导偏硼酸钡(BBO)晶体产生的彩色锥形辐射现象,建立了彩色锥形辐射产生的物理模型,模拟了辐射角与波长的变化,分析了彩色锥形辐射的光谱特性。实验获得清晰的彩色锥形辐射图样,观测了抽运光入射角、光强度对彩色锥形辐射的影响。减小抽运光强与增大入射角,均导致锥形辐射外环产生明显的红移。实验现象与理论模拟相吻合,进一步表明彩色锥形辐射源于二次谐波的自发参量转换。

Colored conical emission （CCE） is an attractive nonlinear phenomenon, which is induced during intense ultra-short pulses propagating in nonlinear medium. A detailed experimental study on the generation of CCE in type- I β-barium borate （BBO） crystal pumped by femtosecond pulses is reported. A physical model based on CCE is constructed, it numerically calculates the conical angle with different wavelengths and the spectral characteristics of CCE is analyzed. The influence of parametrics on the characteristics of CCE is discussed in details. With the pumped intensity decreasing and the pulse incident angle increasing, the central wavelength of the CCE spectrum has a red shift based on the numerically simulation. The observation shows that the CCE is originated from spontaneous parametric down conversion of second harmonic pulses.