Chongfan Technology
News
31
2024
-
07
Shanghai Opto-Machine Institute has made progress in the study of the self-focusing threshold of femtosecond laser air filamentary
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Recently, the research team of the State Key Laboratory of Strong Field Laser Physics, Shanghai Institute of Optics and Mechanics, Chinese Academy of Sciences, has made progress in the study of the self-focusing threshold of heavy frequency-dependent femtosecond laser air filamentary. The results were published in Optics Express under the title "Pulse repetition-rate effect on the critical power for self-focusing of femtosecond laser in air.
Femtosecond laser filamenting is produced from the dynamic balance of Kerr self-focusing effect and plasma defocusing effect, and shows great application potential in ultra-short pulse compression, terahertz radiation, atmospheric remote sensing, weather control and other fields. The development of high-frequency femtosecond laser technology has brought new opportunities for optical filaments in the fields of cloud penetration, artificial lightning, and laser processing. In recent research work, the team focused on the atmospheric filamentous process of high repetition frequency femtosecond laser and found the characteristics and laws of high repetition frequency femtosecond laser filamentous (Adv. Photon. Res.4, 2200338 (2023)) clarified the influence mechanism of pulse accumulation effect on light intensity (High Power Laser 11, e46 (2023)), plasma density and temperature (Chin. Opt. Lett. 22, 013201 (2024)), and solved the bottleneck problem of optical filament automation caused by pulse accumulation effect (Light: Sci. & Appl. 13, 42 (2024)). However, the self-focusing threshold is a key parameter to evaluate whether the filamentous process occurs, and the influence of the pulse accumulation effect of high repetition frequency dependence on the self-focusing threshold of femtosecond laser filament is not clear.
In this work, the researchers used the dual effects of geometric focusing and Kerr self-focusing in the process of femtosecond laser air filamentation to propose a new method for determining the self-focusing threshold based on double-peak fitting. Through in-depth analysis of residuals, mean square root error, fitting determination coefficient, etc., it is proved that the proposed method is superior to the traditional Gaussian fitting method, and can determine the self-focusing threshold more accurately. The research team measured the self-focusing thresholds of femtosecond laser filamentation at 1kHz,500Hz,100Hz and 50Hz repetition frequencies in the air, and found a new rule that the self-focusing threshold is lower and easier to filamentation than femtosecond laser pulses with lower repetition frequency and high repetition frequency in the air. Numerical simulation results confirm the accuracy of the experimental rule. This work provides a new idea for the study of self-focusing, and is of great significance in understanding the characteristics of high-repetition-frequency femtosecond laser filaments.
Figure 1. On-axis fluorescence signal induced by a filament at incident energies of (a) 240 µJ, (B) 280 µJ, (c) 300 µJ, and (d) 325 µJ at a repetition rate of 1 kHz. (e) Residual plot of traditional Gaussian fit and bimodal fit.
Figure 2. The peak position of the filament-induced fluorescence signal (double-peak fit) as a function of pulse energy at repetition rates of (a) 1 kHz, (B) 500Hz, (c) 100Hz, and (d) 50Hz. The intersection between the red fit lines represents the self-focus threshold. (e) Self-focusing threshold as a function of repetition frequency using conventional Gaussian fit (blue) and bimodal fit (red).
This work has been supported by the National Natural Science Foundation of China, the key international cooperation project of the Chinese Academy of Sciences, and the Shanghai Science and Technology Project.
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