Ihor Pavlov

High-power high-repetition-rate single-mode Er-Yb-doped fiber laser system

We demonstrate an all-fiber-integrated, high-power chirped-pulse-amplification system operating at 1550 nm. The seed source is a soliton fiber laser with 156 MHz repetition rate. Two-stage single mode amplifier provides an amplification of more than 40 dB without significant spontaneous amplified emission. The power amplifier is based on cladding-pumped 10 µm-core Er-Yb co-doped fiber, the output of which was spliced into standard singlemode fiber. We obtain 10 W average power in a strictly singlemode operation. After dechirping with a grating compressor, near transform-limited, 450 fs-long pulses are obtained. The laser source exhibits excellent short and long-term intensity stability, with relative intensity noise measurements characterizing the short-term stability.

Diffraction-limited, 10-W, 5-ns, 100-kHz, all-fiber laser at 1.55 μm

This Letter reports on an all-fiber-integrated master-oscillator, power amplifier system at 1.55 μm producing 5-ns, 100-μJ pulses. These pulses are generated at a 100 kHz repetition rate, corresponding to 10 W of average power. The seed source is a low-power, current-modulated, single-frequency, distributed feedback semiconductor laser. System output is obtained from a standard single-mode fiber (Corning SMF-28). Consequently, the beam is truly diffraction limited, which was independently proven by M2 measurements. Further increase of peak power is limited by onset of significant spectral broadening due to nonlinear effects, primarily four-wave mixing. Numerical simulations based on six-level rate equations with full position- and time-dependence were developed to model propagation of pulses through the amplifier chain. This capability allows minimization of the amplified spontaneous emission, which can be directly measured using a fast acousto-optic modulator to gate the pulses.

Time-resolved imaging of ultrafast laser pulse interaction with transparent materials

A study of femtosecond laser interaction with a range of transparent solids, such as glass, sapphire, and fused silica in femtosecond-to-nanosecond time domain is reported. Time-resolved pump-probe microscopic imaging of femtosecond laser breakdown area in different transparent solids has been done. Both absorption and Femtosecond Time-resolved Optical Polarigraphy (FTOP) microscopy techniques were used. White continuum was used as a probe pulse. Strong filamented plasma absorption initially dominates, being replaced by refraction index variations in filament traces and blast wave at hundreds of picoseconds delays. Dynamics of transient absorption in K8 glass was for the first time precisely linked with the pump pulse passage observed by FTOP. Cylindrical blast wave generation was observed starting from 200 ps delays in K8 glass and silica and its velocity has been measured. Exponential decay time of laser-induced plasma in sapphire, both pure and Ti doped has been found.

In-chip microstructures and photonic devices fabricated by nonlinear laser lithography deep inside silicon

Silicon is an excellent material for microelectronics and integrated photonics1–3, with untapped potential for mid-infrared optics4. Despite broad recognition of the importance of the third dimension5,6, current lithography methods do not allow the fabrication of photonic devices and functional microelements directly inside silicon chips. Even relatively simple curved geometries cannot be realized with techniques like reactive ion etching. Embedded optical elements7, electronic devices and better electronic–photonic integration are lacking8. Here, we demonstrate laser-based fabrication of complex 3D structures deep inside silicon using 1-µm-sized dots and rod-like structures of adjustable length as basic building blocks. The laser-modified Si has an optical index different to that in unmodified parts, enabling the creation of numerous photonic devices. Optionally, these parts can be chemically etched to produce desired 3D shapes. We exemplify a plethora of subsurface—that is, ‘in-chip’—microstructures for microfluidic cooling of chips, vias, micro-electro-mechanical systems, photovoltaic applications and photonic devices that match or surpass corresponding state-of-the-art device performances.By exploiting dynamics arising from nonlinear laser–material interactions, functional microelements and arbitrarily complex 3D architectures deep inside silicon are fabricated with 1 μm resolution, without damaging the silicon above or below.

Rich complex behaviour of self-assembled nanoparticles far from equilibrium

A profoundly fundamental question at the interface between physics and biology remains open: what are the minimum requirements for emergence of complex behaviour from nonliving systems? Here, we address this question and report complex behaviour of tens to thousands of colloidal nanoparticles in a system designed to be as plain as possible: the system is driven far from equilibrium by ultrafast laser pulses that create spatiotemporal temperature gradients, inducing Marangoni flow that drags particles towards aggregation; strong Brownian motion, used as source of fluctuations, opposes aggregation. Nonlinear feedback mechanisms naturally arise between flow, aggregate and Brownian motion, allowing fast external control with minimal intervention. Consequently, complex behaviour, analogous to those seen in living organisms, emerges, whereby aggregates can self-sustain, self-regulate, self-replicate, self-heal and can be transferred from one location to another, all within seconds. Aggregates can comprise only one pattern or bifurcated patterns can coexist, compete, endure or perish.

Direct observation of the space-time transformation of a femtosecond laser pulse in fused quartz

The transformation of a femtosecond laser pulse propagating in fused quartz before and after its transition to a filamentation regime has been investigated by femtosecond time-resolved optical polarigraphy. The spatial periodicity of a light field along and across the propagation axis has been detected and its nature has been attributed to the interference of the conical and plane components of the wave packet of the filament. The “supraluminal” motions of the observed filament intensity maximum are due to the longitudinal transformation of the pulse profile.

The alignment of nematic liquid crystal by the Ti layer processed by nonlinear laser lithography

ABSTRACT It is well known that the alignment of liquid crystals (LCs) can be realised by rubbing or photoalignment technologies. Recently, nonlinear laser lithography (NLL) was introduced as a fast, relatively low-cost method for large area nano-grating fabrication based on laser-induced periodic surface structuring. In this letter for the first time, the usage of the NLL as a perspective method of the alignment of nematics was presented. By NLL, nanogrooves with about 0.92 μm period were formed on Ti layer. The nanostructured Ti layer (NSTL) was coated with oxidianiline-polyimide film with annealing of the polymer followed without any further processing. Aligning properties of NSTLs were examined with combined twist LC cell. The dependencies of the twist angle of LC cells and azimuthal anchoring energy (AE) of layers on scanning speed and power of laser beam during processing of the Ti layer were the focus of our studies as well. The maximum azimuthal AE, obtained for pure NSTL, is comparable with photoalignment technology. It was found that the deposition of polyimide film on NSTL leads to the gain effect of the azimuthal AE. Also, atomic force microscopy (AFM) study of aligning surfaces was carried out. GRAPHICAL ABSTRACT

Balancing gain narrowing with self phase modulation: 100-fs, 800-nJ from an all-fiber-integrated Yb amplifier

This paper presents a novel scheme for multi-stage fiber amplification of ultrashort pulses, where each stage is designed to mimic pulse amplification and shaping as closely as possible a scaled-version of intra-cavity pulse amplification and scaling, thereby balancing gain narrowing with self-phase modulation (SPM). While additional work is necessary for full optimisation, as a first experimental demonstration of this approach, a highly integrated Yb-doped oscillator-amplifier system, which generates 1.15-μJ, 20-ps pulses at 1030 nm, which are dechirped in a grating compressor, yielding 0.8-μJ, 100-fs pulses at 1-MHz repetition rate, was constructed.

Nonlinear laser lithography for enhanced tribological properties

This paper investigates a new field for application of femtosecond laser-induced periodic surface structures (LIPSS). We designed an innovative solution to reduce coefficient of friction of mechanical parts by using the nonlinear laser lithography technique (NLL).

Interaction of femtosecond filaments in sapphire

The interaction of two femtosecond filaments has been studied in single-crystal sapphire at small crossing angles 1.2° ÷5°. Regular multifilament pattern (MFP) can be formed in the overlapping area of two beams, which depends on the pulse energy, crossing angle, and phase difference. As a special realization of MFP, formation of a single filament from two different pump beams was for the first time observed. The number of filaments in the MFP depends on the number of the interference maxima in overlapping area, whose power exceeds critical power for self-focusing. We demonstrate control of multifilament pattern, changing the phase shift between the interacting beams. Attraction and repulsion of the filaments is observed in vicinity of the overlapping region for both in- and counter-phase beams depending on the position Z along the propagation axis. Transformation of near- and far-field images of the single filament, formed by two pump beams, and spectra of its axial emission have been studied depending on the filament length. It has been shown that four-wave mixing plays a major role in forming the axial emission spectrum.