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Transient absorption (TA) spectroscopy is considered as a powerful technique that reflects the ultrafast dynamics of photogenerated carriers in photoelectric and photocatalysis materials. However, limited by its sensitivity, the photogenerated carrier density in TA measurements of solar energy materials is usually much higher than that in the real working condition. Here, we present a combination of kHz macro-pulse and MHz micro-pulse technique for an ultrahigh sensitive TA spectrometer, which improves the sensitivity to the 10−7 level of ΔOD. It enables us to study ultrafast carrier dynamics pumped by very low power, which can avoid the influence of many-body interactions and the nonlinear effect associated with high carrier density. This work provides a novel TA method with ultrahigh sensitivity, which will play an important role in investigating the carrier dynamics of semiconductors in the working condition.

We demonstrate a method to synthesize ultra-high repetition rate bursts of ultrashort laser pulses containing any number of pulses within a burst with identical pulse separation and adjustable amplitude. The key element to synthesize the GHz bursts of ultrashort laser pulses is an active fiber loop. The method was implemented in the fiber chirped pulse amplification system to obtain 72 nJ-energy bursts of 20 pulses with a 2.65 GHz intra-burst pulse repetition rate and a 500 kHz burst repetition rate. The dispersion compensation mechanism ensured a mean pulse duration of 570 fs within the bursts.

Rope-like structures are ubiquitous in Nature. They are supermolecular assemblies of macromolecules responsible for the structural and mechanical integrity of plant and animal tissues. Collagen fibrils with diameters between 50 and 500 nm and their helical supermolecular structure are good examples of such nanoscale biological ropes. Like man-made laid ropes, fibrils are typically loaded in tension, and due to their large aspect ratio, they are, in principle, prone to buckling and torsional instabilities. One way to study buckling of a rigid rod is to attach it to a stretched elastic substrate that is then returned to its original length. In the case of single collagen fibrils, the observed behavior depends on the degree of hydration. By going from buckling in ambient conditions to immersed in a buffer, fibrils go from the well-known sine wave response to a localized behavior reminiscent of the bird-caging of laid ropes. In addition, in ambient conditions, the sine wave response coexists with the formation of loops along the length of the fibrils, as observed for the torsional instability of a twisted filament when tension is decreased. This work provides direct evidence that single collagen fibrils are highly susceptible to axial compression because of their helical supermolecular structure. As a result, mammals that use collagen fibrils as their main load-bearing element in many tissues have evolved mitigating strategies that protect single fibrils from axial compression damage.

It is well known that dielectric breakdown in a liquid generates cavitation bubbles and shock waves. Here we demonstrate that when the liquid is bounded by two solid glass boundaries (10–20-μm separation), rings of microscopic bubbles can be nucleated around the laser-induced cavitation bubble. While generally acoustic nucleation is achieved with longitudinal waves of sufficient tension, this work demonstrates that acoustic cavitation can also be generated from transverse waves. Our experiments identify three waves originating at the boundaries: the fastest is the bulk wave in the solid, followed by a leaky Rayleigh wave at the liquid-solid contact, which is trailed by a Lamb-type wave. For the latter, the two solid boundaries act as a wave guide and generate intense and short-lived cavitation activity within the gap. Streak photography and high-speed photography reveal the microsecond-duration cavitation-bubble dynamics, and subpicosecond strobe photography visualizes the mechanism of bubble nucleation from the accelerated surface. Simulations coupling the solid mechanics with the acoustics support the experimentally observed mechanisms of transverse-wave-induced cavitation inception.

FemtoLux 3 laser was used as an illumination source in the wide-field second harmonic generation (SHG) microscope. Relatively high laser pulse energy at a medium pulse repetition frequency allowed for a faster single image acquisition compared to that using laser-scanning. It was also possible to acquire images of relatively large sample areas, which paved the way for the rapid imaging of macroscopic sample areas with microscopic resolution.

The study of topological phases of light underpins a promising paradigm for engineering disorder-immune compact photonic devices with unusual properties. Combined with an optical gain, topological photonic structures provide a novel platform for micro- and nanoscale lasers, which could benefit from nontrivial band topology and spatially localized gap states. Here, we propose and demonstrate experimentally active nanophotonic topological cavities incorporating III–V semiconductor quantum wells as a gain medium in the structure. We observe room-temperature lasing with a narrow spectrum, high coherence, and threshold behaviour. The emitted beam hosts a singularity encoded by a triade cavity mode that resides in the bandgap of two interfaced valley-Hall periodic photonic lattices with opposite parity breaking. Our findings make a step towards topologically controlled ultrasmall light sources with nontrivial radiation characteristics.

Bound states in the continuum (BICs) represent localized modes with energies embedded in the continuous spectrum of radiating waves. BICs were discovered initially as a mathematical curiosity in quantum mechanics, and more recently were employed in photonics. Pure mathematical bound states have infinitely-large quality factors (Q factors) and zero resonant linewidth. In optics, BICs are physically limited by a finite size, material absorption, structural disorder, and surface scattering, and they manifest themselves as the resonant states with large Q factors, also known as supercavity modes or quasi-BICs. Optical BIC resonances have been demonstrated only in extended 2D and 1D systems and have been employed for distinct applications including lasing and sensing. Optical quasi-BIC modes in individual nanoresonators have been discovered recently but they were never observed in experiment. Here, we demonstrate experimentally an isolated subwavelength nanoresonator hosting a quasi-BIC resonance. We fabricate the resonator from AlGaAs material on an engineered substrate, and couple to the quasi-BIC mode using structured light. We employ the resonator as a nonlinear nanoantenna and demonstrate record-high efficiency of second-harmonic generation. Our study brings a novel platform to resonant subwavelength photonics.

Photopolymerization by four-beam interference lithography on a preheated SZ2080 sample was explored at different initial temperatures of the sample: 20 °C, 50 °C, 75 °C, 100 °C, 125 °C, and 150 °C, and at exposure times ranging from 0.5 s to 5 s. The average laser power selected was ∼100 mW for the 300 ps duration pulses at a 1 kHz repetition rate. The experimental results demonstrate that the higher initial temperature of the sample positively influences the crosslinking of the patterns. These findings will improve polymerization protocols for multi-beam interference lithography.

In this paper the possibility to optimize the glass dicing process by controlling the axicon-generated Bessel beam ellipticity is presented. Single-shot intra-volume modifications in soda-lime glass followed by dicing experiments of 1 mm-thick samples are performed. The Bessel beam ellipticity is essential for glass dicing process. Such beam generates intra-volume modifications with transverse crack propagation in dominant direction. Orientation of these modifications parallel to the dicing direction gives significant advantages in terms of processing speed, glass breaking force and cutting quality.

Bio-inspired surfaces are able to decrease friction with fluids and gases. The most recognizable are shark-skin-like riblet surface structures. Such bio-inspired surfaces can be formed by the laser ablation technique. In this work, bio-inspired riblet surfaces with grooves were formed using picosecond ultraviolet laser ablation on pre-heated polytetrafluoroethylene (PTFE) at various sample temperatures. The ablation of hot PTFE was found to be 30% more efficient than the conventional laser structuring at the room temperature. The friction of structured PTFE surfaces with the flowing air was investigated by using drag a measurement setup. Results show the decrease of friction force by 6% with dimensionless riblet spacing around 14–20.