Ultrafast dynamics of femtosecond laser-induced high spatial frequency periodic structures on silicon surfaces

Femtosecond laser-induced periodic surface structures(LIPSS)have been extensively studied over the past few decades.In particular,the period and groove width of high-spatial-frequency LIPSS(HSFL)is much smaller than the diffraction limit,making it a useful method for efficient nanomanufacturing.However,compared with the low-spatial-frequency LIPSS(LSFL),the structure size of the HSFL is smaller,and it is more easily submerged.Therefore,the formation mechanism of HSFL is complex and has always been a research hotspot in this field.In this study,regular LSFL with a period of 760 nm was fabricated in advance on a silicon surface with two-beam interference using an 800 nm,50 fs femtosecond laser.The ultrafast dynamics of HSFL formation on the silicon surface of prefabricated LSFL under single femtosecond laser pulse irradiation were observed and analyzed for the first time using collinear pump-probe imaging method.In general,the evolution of the surface structure undergoes five sequential stages:the LSFL begins to split,becomes uniform HSFL,degenerates into an irregular LSFL,undergoes secondary splitting into a weakly uniform HSFL,and evolves into an irregular LSFL or is submerged.The results indicate that the local enhancement of the submerged nanocavity,or the nanoplasma,in the prefabricated LSFL ridge led to the splitting of the LSFL,and the thermodynamic effect drove the homogenization of the splitting LSFL,which evolved into HSFL.

Periodic transparent nanowires in ITO film fabricated via femtosecond laser direct writing

This paper reports the fabrication of regular large-area laser-induced periodic surface structures(LIPSSs)in indium tin oxide(ITO)films via femtosecond laser direct writing focused by a cylindrical lens.The regular LIPSSs exhibited good properties as nanowires,with a resistivity almost equal to that of the initial ITO film.By changing the laser fluence,the nanowire resistances could be tuned from 15 to 73 kΩ/mm with a consistency of±10%.Furthermore,the average transmittance of the ITO films with regular LIPSSs in the range of 1200-2000 nm was improved from 21%to 60%.The regular LIPSS is promising for transparent electrodes of nano-optoelectronic devices-particularly in the near-infrared band.

Femtosecond laser-induced periodic structures:mechanisms, techniques, and applications

Over the past two decades,femtosecond laser-induced periodic structures(femtosecond-LIPSs)have become ubiquitous in a variety of materials,including metals,semiconductors,dielectrics,and polymers.Femtosecond-LIPSs have become a useful laser processing method,with broad prospects in adjusting material properties such as structural color,data storage,light absorption,and luminescence.This review discusses the formation mechanism of LIPSs,specifically the LIPS formation processes based on the pump-probe imaging method.The pulse shaping of a femtosecond laser in terms of the time/frequency,polarization,and spatial distribution is an efficient method for fabricating high-quality LIPSs.Various LIPS applications are also briefly introduced.The last part of this paper discusses the LIPS formation mechanism,as well as the high-efficiency and high-quality processing of LIPSs using shaped ultrafast lasers and their applications.

Extremely regular periodic surface structures in a large area efficiently induced on silicon by temporally shaped femtosecond laser

Femtosecond laser-induced periodic surface structures(LIPSS) have several applications in surface structuring and functionalization. Three major challenges exist in the fabrication of regular and uniform LIPSS: enhancing the periodic energy deposition, reducing the residual heat, and avoiding the deposited debris. Herein, we fabricate an extremely regular low-spatial-frequency LIPSS(LSFL) on a silicon surface by a temporally shaped femtosecond laser. Based on a 4 f configuration zero-dispersion pulse shaping system, a Fourier transform limit(FTL) pulse is shaped into a pulse train with varying intervals in the range of 0.25–16.2 ps using periodic π-phase step modulation. Under the irradiation of the shaped pulse with an interval of 16.2 ps, extremely regular LSFLs are efficiently fabricated on silicon. The scan velocity for fabricating regular LSFL is 2.3 times faster, while the LSFL depth is 2 times deeper, and the diffraction efficiency is 3 times higher than those of LSFL using the FTL pulse.The formation mechanisms of regular LSFL have been studied experimentally and theoretically. The results show that the temporally shaped pulse enhances the excitation of surface plasmon polaritons and the periodic energy deposition while reducing the residual thermal effects and avoiding the deposition of the ejected debris, eventually resulting in regular and deeper LSFL on the silicon surface.

Different genes involved in the amelioration of chronic neuropathic pain and comorbid anxiety by electroacupuncture with different intensities

Background:With its complex and prevalent symptoms,chronic neuropathic pain(CNP)is frequently combined with negative emotions.Electroacupuncture(EA)is a widely-used and effective treatment for CNP and pain-induced comorbid anxiety-like behaviors(PABs).Although different effects may result from EA with different intensities,the underlying mechanisms remain unclear.Objective:The study aimed to investigate the effects of EA with different intensities on CNP and PABs and the underlying mechanisms,by exploring the different genes through RNASeq in the spinal cord dorsal horn(SCDH)and periaqueductal gray(PAG).Methods:A spared nerve injury(SNI)model was established using male C57BL/6 J mice,and treated with EA of different intensities(0.1 mA or 0.3 mA,both at 100 Hz).The von-Frey tests,open field tests and elevated plus maze tests were used to measure the mechanical paw withdrawal threshold(PWT)and PABs of the mice.The tissues of SCDH and PAG regions were extracted to identify the changes in gene expression,and biofunctional analysis of differentially expressed genes(DEGs)was further performed by RNA-seq analysis.The expression of key DEGs and corresponding proteins was assessed using quantitative real-time PCR(qPCR)and protein immunofluorescence detection,respectively.Results:Both 0.1 mA and 0.3 mA EA at 100 Hz alleviated PABs compared with the SNI group.Furthermore,0.3 mA EA was effective in increasing PWT in SNI mice,whereas 0.1 mA EA was not.A total of 108 DEGs was identified in the SCDH,and 254 DEGs were identified in the PAG.Specifically,the expression of Tnr in SNI mice decreased after the treatment with 0.3 mA EA at 100 Hz,and the expression of Ptprb,Net1,Abcb1a and Adgrf5 in SNI mice decreased in the PAG after the treatment with 0.1 mA EA at 100 Hz.Conclusion:The effect of 0.3 mA EA on chronic pain may be related to the decrease of Tnr expression in SCDH,and the effect of 0.1 mA EA on PABs may be achieved by decreased expression of Ptprb and Net1 in PAG.