Mitrofanov A V, Sidorov-Biryukov D A, Glek P B, Rozhko M V, Stepanov E A, Shutov A D, Ryabchuk S V, Voronin A A, Fedotov A B, Zheltikov A M
Opt Lett. 2020 Feb 1;45(3):750-753. doi: 10.1364/OL.45.000750.
Coherent-wake plasma emission induced by ultrashort mid-infrared laser pulses on a solid target is shown to give rise to high-brightness, high-order harmonic radiation, offering a promising source of attosecond pulses and a probe for ultrafast subrelativistic plasma dynamics. With 80-fs, 0.2-TW pulses of 3.9-μm radiation used as a driver, optical harmonics up to the 34th order are detected, with their spectra stretching from the mid-infrared region to the extreme ultraviolet region. The harmonic spectrum is found to be highly sensitive to the chirp of the driver. Particle-in-cell analysis of this effect suggests, in agreement with the generic scenario of coherent-wake emission, that optical harmonics are radiated as trains of extremely short, attosecond ultraviolet pulses with a pulse-to-pulse interval varying over the pulse train. A positive chirp of the driver pulse can partially compensate for this variation in the interpulse separation, allowing harmonics of the highest orders to be generated in the plasma emission spectrum.
研究表明，超短中红外激光脉冲在固体靶上诱导产生的相干尾流等离子体发射会产生高亮度的高阶谐波辐射，这为阿秒脉冲提供了一个有前景的光源，并可用于超快亚相对论等离子体动力学的探测。以80飞秒、0.2太瓦的3.9微米辐射脉冲作为驱动源，检测到了高达34阶的光学谐波，其光谱从中红外区域延伸到极紫外区域。发现谐波光谱对驱动源的啁啾非常敏感。对此效应的粒子模拟分析表明，与相干尾流发射的一般情况一致，光学谐波是以一系列极短的阿秒紫外脉冲的形式辐射出来的，脉冲间的间隔在脉冲序列中会发生变化。驱动脉冲的正啁啾可以部分补偿脉冲间间隔的这种变化，从而使得在等离子体发射光谱中能够产生最高阶的谐波。
