2023 Vol. 3, No. 2

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Research Article
Femtosecond-Laser-Induced All-Silicon Dielectric Metasurfaces Assisted by Wet Chemical Etching
Ioanna Sakellari, Sotiris Droulias, Andreas Lemonis and Emmanuel I. Stratakis
2023, 2023(2) doi: 10.34133/ultrafastscience.0019

All-dielectric metasurfaces offer low material loss and strong field localization and are, therefore, well suited for ultrathin and compact optical devices for electomagnetic wave manipulation at the nanoscale. All-silicon dielectric metasurfaces, in particular,may additionally offer the desired compatibility with complementary metal-oxide semiconductor technology and, hence, are ideal candidates for large-scale monolithic integration on a photonic chip. However, in conventional silicon microfabrication approaches,the combination of mask photolithography with reactive ion etching usually involves expensive masks and multiple preprocessing stages leading to increased cost and fabrication times. In this work, a single-step lithographical approach is proposed for the realization of all-silicon dielectric resonant metasurfaces that involves femtosecond laser processing of silicon below ablation threshold in combination with subsequent wet chemical etching. The method exploits the different etching rate between laser-modified and untreated regions, enabling large-area fabrication of patterned silicon surfaces in a facile and cost-efficient manufacturing approach. It is presented how two-dimensional silicon micro/nanostructures with controllable features, such as nanocones, can be effectively generated and, as a proof of concept, an all-silicon dielectric metasurface device supporting antiferromagnetic order is experimentally demonstrated.

Identification of the Decay Pathway of Photoexcited Nucleobases
Xiangxu Mu, Ming Zhang, Jiechao Feng, Hanwei Yang, Nikita Medvedev, Xinyang,Liu, Leyi Yang, Zhenxiang Wu, Haitan Xu and Zheng Li
2023, 2023(2) doi: 10.34133/ultrafastscience.0015

The identification of the decay pathway of the nucleobase uracil after being photoexcited by ultraviolet light has been a long-standing problem. Various theoretical models have been proposed but yet to be verified. Here, we propose an experimental scheme to test the theoretical models of gas phase uracil decay mechanism by a combination of ultrafast x-ray spectroscopy, x-ray diffraction,and electron diffraction methods. Incorporating the signatures of multiple probing methods, we demonstrate an approach that can identify the dominant mechanism of the geometric and electronic relaxation of the photoexcited uracil molecule among several candidate models.

All-PM Fiber Mamyshev Oscillator Delivers Hundred-Nanojoule and Multi-Watt Sub-100 fs Pulses
Tao Wang, Can Li, Bo Ren, Kun Guo and Pu Zhou
2023, 2023(2) doi: 10.34133/ultrafastscience.0016

An all-fiber Mamyshev oscillator with a single amplification arm is experimentally demonstrated to achieve high-energy and high-average-power ultrafast pulse output, with the initiating of an external seed pulse. In the high-energy operation, a maximum single-pulse energy of 153 nJ is achieved at a repetition rate of 9.77 MHz. After compression with a pair of diffraction gratings, a measured pulse width of 73 fs with a record energy of 122.1 nJ and a peak power of 1.7 MW is obtained. In the high-average-power operation, up to 5th harmonic mode locking of the oscillator is realized via slightly adjusting the output coupling ratio and the cavity length. The achieved maximum output power is 3.4 W at a repetition rate of 44.08 MHz, while the corresponding pulse width is compressed to around ~100 fs. Meanwhile, the system is verified to be operated reliability in both high-energy and -average-power operation regimes through assessing its short- and long-term stabilities. To the best of our knowledge,these are the highest records in pulse energy and average power delivered from a single all-fiber ultrafast laser oscillator with picosecond/femtosecond pulse duration. It is believed that even higher-energy and -average-power ultrafast laser can be realized with the proposed laser scheme through further increasing the core diameter of the allfiber cavity, providing promising sources for advanced fabrication, biomedical imaging, laser micromachining, and other practical applications, as well as an unprecedented platform for exploring undiscovered nonlinear dynamics.

Breakdown Spectroscopy Induced by Nonlinear Interactions of Femtosecond Laser Filaments and Multidimensional Plasma Gratings
Mengyun Hu, Shupeng Xu, Shuai Yuan and Heping Zeng
2023, 2023(2) doi: 10.34133/ultrafastscience.0013

Breakdown spectroscopy is a valuable tool for determining elements in solids, liquids,and gases. All materials in the breakdown region can be ionized and dissociated into highly excited fragments and emit characteristic fluorescence spectra. In this sense, the elemental composition of materials can be evaluated by detecting the fluorescence spectrum. This paper reviews the recent developments in laser-induced breakdown spectroscopy. The traditional laser-induced breakdown spectroscopy,filament-induced breakdown spectroscopy, plasma grating, and multidimensional plasma grating-induced breakdown spectroscopy are introduced. There are also some proposals for applications of plasma gratings, such as laser ablation, laser deposition, and laser catalysis of chemical reactions in conjunction with research on the properties of plasma gratings