Publication database

A subpicosecond laser system featuring a fiber chirped pulse amplification-based seed laser and a double-pass end-pumped Yb:YAG crystal power amplifier was investigated. The key novelty of the system was the application of depolarization compensation using a specially designed spatially variable wave plate. To the best of our knowledge, this method was applied for the first time. The presented laser system produced pulses of 441 fs duration, 116 µJ pulse energy at 116 W average power with a beam quality of M²∼2.1, featured optical-to-optical efficiency of 32% at room temperature (T=20°C), and had residual depolarization level of 2.7%.

FemtoLux 30 is a new 30 W femtosecond industrial grade laser build to work 24/7/365 without any interruptions. Other lasers of similar optical power use water for cooling, which means additional bulky and heavy water chiller is needed which require periodical maintenance (cooling system draining and rinsing, water and particle filter replacement). Moreover, in the unfortunate event of water leakage, not only laser head but also more expensive equipment could be damaged. FemtoLux 30 uses innovative direct refrigerant cooling method that do not contain any water inside the laser head and has much higher cooling efficiency. Laser cooling equipment is integrated together with the power supply unit into a single 4U rack mounted housing with a total weight of just < 15 kg. To tailor laser for specific applications, FemtoLux 30 laser has a tunable pulse duration from < 350 fs to 1 ps and can operate in very broad AOM controlled range of pulse repetition rate from a single shot to 4 MHz. While max energy of >250 µJ, that could be achieved while operating in a burst mode, could ensure higher ablation rates for different materials. FemtoLux 30 is designed as perfect tool for display and microelectronics manufacturing, as well as for micro processing and marking of brittle materials, such as glass, sapphire or ceramics, as well as for highest quality micro processing of different metals and polymers. Innovative laser control electronics ensures easy control of FemtoLux30, thus reducing time and resources required for integrating this laser into different equipment.

In the present work we performed research of supercontinuum generation in several commonly used and new supercontinuum generation crystals for subsequent nonlinear amplification, using 1–3 µJ energy pulses of 300 fs duration at 1 MHz repetition rate. Obtained supercontinuum spectra spanning over 480–1950 nm wavelength range at pump pulse energies as low as 200 nJ in KGW and YVO₄ crystals. We present simple experimental setups of stimulated Raman amplification and optical parametric amplification using supercontinuum seeds obtained from several selected crystals. We achieved total energy conversion efficiencies up to 9% both for optical parametric amplification setup and for stimulated Raman amplification setups. The optical parametric amplifier was tunable in the 680–980 nm spectral range and produced ultrashort pulses of 23–44 fs duration. Raman amplifier produced more than 130 mW average power at 1194 nm wavelength and featured broadened spectrum corresponding to Fourier transform limited ~ 100 fs pulse duration. We demonstrated that low power and low energy femtosecond lasers could be efficiently employed for the nonlinear wavelength conversion.

The paper shows visualization of cavitation inside a micro-Venturi channel. While the initial aim of the study was to establish supercavitating conditions inside a micro-Venturi, yet we found that this regime is suppressed due to the formation of a Kelvin-Helmholtz instability, which triggers a semi periodical attached cavity collapse. In depth observations using high speed imaging with visible light and X-rays revealed that this is, besides the re-entrant jet and the shock wave, a third mechanism leading to the shedding of cloud cavitation. In addition, a simple model was proposed which explains the formation of the Kelvin-Helmholtz instability in cavitating micro-Venturi and also offers explanation on why this is the dominant mechanism of cavitation cloud shedding at small scales.

Topological states of light represent counterintuitive optical modes localized at boundaries of finite-size optical structures that originate from the properties of the bulk. Being defined by bulk properties, such boundary states are insensitive to certain types of perturbations, thus naturally enhancing robustness of photonic circuitries. Conventionally, the N-dimensional bulk modes correspond to (N – 1)-dimensional boundary states. The higher-order bulk-boundary correspondence relates N-dimensional bulk to boundary states with dimensionality reduced by more than 1. A special interest lies in miniaturization of such higher-order topological states to the nanoscale. Here, we realize nanoscale topological corner states in metasurfaces with C6-symmetric honeycomb lattices. We directly observe nanoscale topology-empowered edge and corner localizations of light and enhancement of light–matter interactions via a nonlinear imaging technique. Control of light at the nanoscale empowered by topology may facilitate miniaturization and on-chip integration of classical and quantum photonic devices.

In this work, a double-pass end-pumped Yb:YAG amplifier system was investigated experimentally and numerically. The amplifier was seeded by a fibre-CPA based seed laser FemtoLux 30 (Ekspla). The presented laser system produced 129 W average power and 129 μJ energy pulses at 1 MHz pulse repetition rate, with optical-to-optical efficiency of 32% at room temperature (T = 20°C). The resulting beam quality was M² ∼ 2.1 and the measured depolarization losses were to 17.9%. After the compression, 441 fs pulse duration was achieved. During the work, comprehensive amplifier modelling was performed using the code written in Matlab. The modelling results matched well the experimental data, providing the tool to predict the performance of laser systems based on ytterbium-doped isotropic crystalline, ceramic and glass laser materials prior to designing and manufacturing.

We demonstrate the temporally and spatially controlled nucleation of bulk nanobubbles in water through pulsed laser irradiation with a collimated beam. Transient bubbles appear within the light exposed region once a tension wave passes through. The correlation between illumination and cavitation nucleation provides evidence that gaseous nanobubbles are nucleated in the liquid by a laser pulse with an intensity above 58  MW/cm². We estimate the radius of the nanobubbles through microscopic high-speed imaging and by solving the diffusion equation to be below 420 nm for ∼80% of the bubble population. This technique may provide a novel approach to test theories on existence of stable bulk nanobubbles.

Surface sensitivity of lanthanide-doped nanocrystals has a great utility in controlling their optical properties. Surface sensitivity can be principally promoted by energy migration. Herein, we demonstrate that cross-relaxation between lanthanides makes nanocrystals less sensitive to environmental changes. We show that by codoping ytterbium ions (Yb³⁺) and neodymium ions (Nd³⁺) in hexagonal-phase sodium yttrium fluorides, surface sensitivity can be manipulated by energy transfer from Yb³⁺ to Nd³⁺. These findings enhance our understanding of surface quenching of nanocrystals and offer new opportunities in developing highly luminous nanoprobes for molecular sensing and biomedical applications.

Collapsing cavitation bubbles produce intense microscopic flows. Here, in an aqueous environment, we seed single laser-induced bubbles (diameter about one millimeter) in proximity to a solid surface, in a regime that has not been well explored before in order to generate a “needle jet.” The needle jet propagates at supersonic speed through the gas phase toward the solid. It reaches average velocities of more than 850 ms−1 and thus is an order of magnitude faster than the regular jets that have frequently been observed in cavitation bubbles. The dynamics leading to the needle jet formation are studied with high speed imaging at five million frames per second with femtosecond illumination. This highly repeatable, localized flow phenomenon may be exploited for injection purposes or material processing, and it is expected to generate significantly larger water hammer pressures and may also play a role in cavitation erosion and peening.

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.