Nanochannel structures with a feature size deeply under the diffraction limit and a high aspect ratio hold huge biomedical significance, which is especially challenging to be realized on hard and brittle materials, such as silica, diamond, and sapphire. By simultaneously depositing the pulse energy on the surface and inside the sample, nanochannels with the smallest feature size of 18 nm (∼1 / 30λ) and more than 200 aspect ratios are achieved inside silica, the mechanism of which can be concluded as the surface assisting material ejection effect. Both the experimental and theoretical results prove that the coaction of the superficial “hot domain” and internal hot domain dominates the generation of the nanochannels, which gives new insights into the laser-material interacting mechanisms and potentially promotes the corresponding application fields.

For Brillouin optical time-domain analysis (BOTDA) based on distributed Brillouin amplification (DBA), constant Brillouin response achieved by the exponentially variable bandwidth/intensity pump modulation suffers from the much lower pumping efficiency for long-range sensing, which counterbalances the merit of DBA. In this Letter, pump modulation by multiple constant bandwidths was proposed and demonstrated. The ～98.9 km sensing with ～5 m spatial resolution and no use of optical pulse coding (OPC) was achieved by ～8 dBm Brillouin pump, which is lower by ～9 dB in theory by comparison with exponentially increased bandwidth modulation. Compared with traditional DBA-BOTDA, signal-to-noise ratio (SNR) enhancement with >4.6 dB was obtained. The flattened standard deviation (STD) of Brillouin frequency shift (BFS) (less than ～2 MHz) along the whole fiber was demonstrated.

The impacts of Brillouin pump depletion and nonlinear amplification in coded long-range Brillouin optical time-domain analysis (BOTDA) based on distributed Brillouin amplification (DBA) were studied. The error of Brillouin frequency shift (BFS) due to Brillouin pump depletion was compared for DBA-BOTDA using non-cyclic and cyclic coding. For non-cyclic coding, significant over- and under-shoots of BFS were found in the range with larger BFS variation, such as hot spot. The impact of Brillouin pump depletion can be reduced considerably by cyclic coding. Furthermore, to compensate the BFS error due to nonlinear amplification, a simple and effective log linearization was proposed and demonstrated.