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Abstract This study examines burst laser-induced pitting (BLIP), an understudied surface modification phenomenon driven by ultrafast laser bursts with sub-picosecond to picosecond inter-pulse delays. Through SEM and AFM analysis, we characterize BLIP as sub-micron pits with polarizationdependent oval shapes, alongside high-fluence melting zones and localized ripple-like structures. Unlike conventional LIPSS, BLIP demonstrates exceptional energy coupling efficiency, evidenced by 10× greater damage areas and a steeper fluence-scaling expansion rate than LIPSS, attributed to transient carrier-mediated processes. Pit density decays exponentially with delay (τ ≈ 6.6-8.9 ps), matching the timescale of self-trapped exciton (STE) relaxation, while spatial statistics reveal a delay-driven transition from field-guided ordering (1-5 ps) to randomized distributions (>10 ps). The resonant-like angular distributions and delay-dependent ellipticity reduction indicate competing mechanisms: optical field enhancement dominates at short delays, while energy dissipation and structure disordering prevail at longer delays. Simulation of nanoplasma excitation reveals near-field optical field enhancements responsible for the ellipticity and ripple-like structures. Beyond their fundamental significance, these BLIP nanostructures offer practical functionalities, including use as anti-reflection coatings and hydrophobic surfaces. These findings establish BLIP as a new paradigm in ultrafast laser-material interactions, where burst parameters selectively activate defect-mediated or field-driven modification pathways in dielectrics. 

We demonstrate, for the first time, the direct writing of curved optical waveguides in monocrystalline silicon with curve radii from 2 mm to 6 cm. The bending loss of the curved waveguides is measured and a good agreement with theoretical values is found. Raman spectroscopy measurements suggest the formation of inhomogeneous amorphous and polycrystalline phases in the laser-modified region. This direct laser-writing method may advance fabrication capabilities for integrated 3D silicon photonic devices. 

Optical isolators, reliably integrated on-chip, are crucial components for a wide range of optical systems and applications. We introduce a new class of wideband nonmagnetic and linear optical isolators based on nonlinear frequency conversion and spectral filtering among the pump, signal, and idler wavelengths. The scheme is experimentally demonstrated using difference-frequency generation in periodically poled thin-film lithium niobate integrated devices and short- and long-pass optical filters. We demonstrate a wide bandwidth of more than 150 nm, limited only by the measurement setup, and an optical isolation ratio of up to 18 dB for the involved idler and signal waves. The difference of transmittance at the signal wavelength between forward and backward propagation is 40 dB. We also discuss pathways for substantial isolation improvement using appropriate anti-reflection coatings. The integrable isolator, operating in the telecommunication band, is characterized by a perfectly linear output versus input power dependence and can be incorporated into high-speed telecom and datacom systems as well as a variety of other applications.