For the first time, we studied the change in a short-wavelength cutoff of a mid-IR pulse spectrum with an increase in a nonlinear optical interaction length in calcium fluoride. We investigate a transformation of an anti-Stokes wing in a pulse spectrum during light bullet formation under anomalous group velocity dispersion. An experimental scheme allowing a variation of a pulse propagation length in dielectric sample was employed. We compare results of numerical simulations provided by both, slowly-evolving-wave approximation method and unidirectional pulse propagating equation, under experimental conditions. It was found that a short-wavelength cutoff of an isolated anti-Stokes wing in light bullet’s spectrum shifts towards short-wave region by several hundred nanometers during light bullet formation. Moreover, the shift of a short-wavelength cutoff is 100 nm per 100 μm of a pulse propagation length in a sample at the initial stage of light bullet appearance. The short-wavelength cutoff of already formed propagating light bullet changes slightly. With an increase in pulse energy, the short-wavelength cutoff decreases. The observed shift of the cutoff wavelength during the light bullet formation exhibits a general behaviour for all considered pulse energies.

首次，我们研究了中红外脉冲光谱的短波长截止随着氟化钙中非线性光学相互作用长度的增加而发生的变化。我们研究反常斯托克斯机翼在异常子群速度色散下的轻子弹形成过程中的脉冲光谱中的转变。采用允许改变电介质样品中脉冲传播长度的实验方案。我们在实验条件下比较了慢波近似法和单向脉冲传播方程提供的数值模拟结果。研究发现，在子弹形成过程中，孤立的反斯托克斯机翼在子弹光谱中的短波截止点向短波区域偏移了数百纳米。而且，在子弹出现的初始阶段，样品中短波长截止的位移为每100μm脉冲传播长度100 nm。已经形成的传播光子弹的短波截止频率略有变化。随着脉冲能量的增加，短波截止频率降低。对于所有考虑的脉冲能量，在子弹形成期间观察到的截止波长的偏移表现出一般的行为。