The concept of coherence is of fundamental importance for describing the physical characteristics of light and for evaluating the suitability for experimental application. In the case of pulsed laser sources, the pulse-to-pulse coherence is usually considered for a judgment of the compressibility of the pulse train. This type of coherence is often lost during propagation through a highly nonlinear medium, and pulses prove incompressible despite multioctave spectral coverage. Notwithstanding the apparent loss of interpulse coherence, however, supercontinua enable applications in precision frequency metrology that rely on coherence between different spectral components within a laser pulse. To judge the suitability of a light source for the latter application, we define an alternative criterion, which we term intrapulse coherence. This definition plays a limiting role in the carrier-envelope phase measurement and stabilization of ultrashort pulses. It is shown by numerical simulation and further corroborated by experimental data that filamentation-based supercontinuum generation may lead to a loss of intrapulse coherence despite near-perfect compressibility of the pulse train. This loss of coherence may severely limit active and passive carrier-envelope phase stabilization schemes and applications in optical high-field physics.

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脉冲内相干在载波包络相位稳定中的作用

相干的概念对于描述光的物理特性和评估实验应用的适用性至关重要。对于脉冲激光源，通常考虑脉冲间相干性，以判断脉冲序列的可压缩性。通过高非线性介质传播时，通常会丢失这种相干性，并且尽管具有多倍频程频谱覆盖，脉冲仍被证明是不可压缩的。尽管存在明显的脉冲间相干性损失，但是，超连续谱仍然可以应用在依赖于激光脉冲内不同光谱分量之间相干性的精确频率计量中。为了判断光源对后一种应用的适合性，我们定义了一个替代标准，我们将其称为脉冲内相干。该定义在载波包络相位测量和超短脉冲的稳定中起着限制作用。通过数值模拟显示，并通过实验数据进一步证实，尽管脉冲序列具有近乎完美的可压缩性，但基于细丝化的超连续谱的产生可能会导致脉冲内相干性的损失。这种相干性损失可能会严重限制有源和无源载流子-信封相位稳定方案及其在光学高场物理学中的应用。