Laser-induced damage threshold of ZnGeP2 crystal for (sub)picosecond 1-µm laser pulse

The laser-induced damage threshold (LIDT) was measured for a Z n G e P ₂ crystal exposed to 0.3-9.5 ps 1030-nm laser pulses. Single-pulse LIDT fluence was ∼0.22J/c m ² for the laser pulse widths of 0.3-3.5 ps and increased until 0.76J/c m ² for 9.5-ps pulses. Multi-pulse LIDT fluence for 0.3-ps pulses at repetition frequencies in the range of 100 Hz-1 kHz was ∼0.053J/c m ² and decreased further at higher, multi-kHz, pulse repetition frequencies. The coating of the Z n G e P ₂ crystal surface with an anti-reflection multi-layer thin film increased the multi-pulse LIDT by one order of magnitude, up to 0.62J/c m ² (about 2T W/c m ²). The significant increase in LIDT coupled with a decrease in reflection losses provides a way to cardinally improve efficiency of frequency conversion of popular 1-µm ultrashort pulses into mid- and far-IR ranges with a thin AR-coated Z n G e P ₂ crystal sample.

Pulse-width-dependent critical power for self-focusing of ultrashort laser pulses in bulk dielectrics

Microscale filamentation of 0.25 NA-focused, linearly and circularly polarized 1030 nm and 515 nm ultrashort laser pulses of variable pulse widths in fused silica, fluorite, and natural and synthetic diamonds demonstrates the Raman-Kerr effect in the form of critical pulse power magnitudes, proportional to squared wavelength and inversely proportional to laser pulse width of 0.3-10 ps. The first trend represents the common spectral relationship between the quantities, while the second indicates its time-integrated inertial contribution of Raman-active lattice polarization, appearing in transmission spectra via ultrafast optical-phonon Raman scattering. The optical-phonon contribution to the nonlinear polarization could come from laser field-induced spontaneous/stimulated Raman scattering and coherent optical phonons generated by electron-hole plasma with its clamped density in the nonlinear focus. Almost constant product value of the (sub)picosecond laser pulse widths and corresponding critical pulse powers for self-focusing and filamentation in the dielectrics ("critical pulse energy") apparently implies constant magnitude of the nonlinear polarization and other "clamped" filamentation parameters at the given wavelength.

Controllable ablative machining of Al/Ti and Ti/Al nano-layers on a Si substrate by single-pulse femtosecond laser irradiation

Results concerning the controllable ablation of nano-layered thin films (NLTF) by femtosecond laser pulses are presented. Investigated samples were titanium-aluminum bilayers, deposited on a silicon substrate, with the top titanium or aluminum layer of variable thickness on the surface. Irradiation was done in ambient air with single femtosecond laser pulses under standard laboratory conditions. The samples were analyzed by complementary methods of optical and scanning electron microscopy and optical profilometry, exhibiting laser-fluence-dependent ablative removal either of the top layer or the entire bilayer or even partial ablation of the underlying silicon substrate. The removal (spallation) threshold fluences for the topmost layer are scalable versus its thickness almost irrespectively of its material, being rather selective for the Ti-coated samples and much less selective for the Al-coated samples. The removal of the entire bilayers was found to be strongly influenced by electronic properties of the underlying metallic layer, dictating the NLTF-Si adhesion, heat conduction, and capacity in the NLTFs toward the NLTF-Si interface and beyond, as well as by their thermophysical characteristics, e.g., almost twice higher melting temperature and enthalpy for Ti. As a result, precise fs-laser machining of the entire NLTFs is pronounced and selective for the samples with the fusible Al at the low-adhesion Al-Si interfaces, compared with the incomplete NLTF removal from the high-adhesion and refractory Ti-Si interfaces.

Features of the immunological profile of blood and urine in patients with post-infectious glomerulonephritis

The timely diagnosis and treatment of post-infectious glomerulonephritis (PIGN) is currently limited by the erased and low-symptom nature of the disease, which leads to the search for informative biological markers of the disease, which can be used as immunological indicators of blood and urine. The study was carried out in order to establish the characteristic changes in the immunological parameters of blood and urine in patients with PIGN. The study included 60 patients with PIGN from among the patients, hospitalized in the nephrology department of the Republican Clinical Hospital of Health Care Ministry of the Chuvash Republic in 2015-2018. In addition to the generally accepted research methods, the patients underwent: 1) the determination of indicators of innate and acquired immune response in the blood (CD3+ -, CD3+ CD4+-, CD3+CD8+-, CD4+CD25+-, CD95+-, CD20+-, CD14+CD282+-, CD14+CD284+- cells; levels of IgG, IgA, IgM, circulating immune complexes, C3, C4) and urine (levels of IgG, IgA, IgM, C3, C4); 2) the determination of the levels of cytokines - IL-1β, Ra-IL-1β, IL-2, IL-4, IL-8, IL-10, IL-17A in blood serum and urine. The data obtained were compared with those of the group of healthy individuals. The changes in blood immunological parameters, identified in the group of patients with PIGN, indicate the activation of innate immunity (the increase in the number of CD14+TLR2+- cells) and the humoral component of adaptive immunity (the increase in the number of B-lymphocytes, hyperimmunoglobulinemia - the increase in IgM and IgA levels) against the background of the decrease in the number of T (CD3+) - lymphocytes and regulatory (CD4+CD25high) - cells, hypocomplementemia (decreased levels of C3, C4). The increase in the content of C3, IgG and IgA was found in the urine. The cytokine profile of blood in patients with PIGN was characterized by the increase in the levels of pro- and anti-inflammatory cytokines IL-1β, Ra-IL-1β, IL-2, IL-8, IL-10, IL-17A, with the exception of IL-4, which remained on the levels of healthy individuals. The cytokine profile of urine in patients was characterized by the increase in the levels of pro-inflammatory cytokines IL-1β, IL-2, IL-8, IL-17A and anti-inflammatory cytokine - IL-10, with no changes in the content of Ra-IL-1β and IL-4. The revealed features of the immunological profile of blood and urine in patients with PIGN reflect the immunopathogenetic mechanisms of this disease.

Elementary autonomous surface microfluidic devices based on laser-fabricated wetting gradient microtextures that drive directional water flows

Topography-dependent tuning of water wettability was achieved on a stainless steel surface textured by nanosecond-laser pulses at different laser fluences, with the minimal contribution of the surface chemical modification. Such differently-wet neighboring surface spots were demonstrated to drive an autonomous directional water flow. A series of elementary microfluidic devices based on the spatial wetting gradients were designed and tested as building blocks of "green", energy-saving autonomous microfluidic circuits.

Broadband and fine-structured luminescence in diamond facilitated by femtosecond laser driven electron impact and injection of "vacancy-interstitial" pairs

Ultrafast heating of photoionized free electrons by high-numerical-aperture (0.25-0.65) focused visible-range ultrashort laser pulses provides their resonant impact trapping into intra-gap electronic states of point defect centers in a natural IaA/B diamond with a high concentration of poorly aggregated nitrogen impurity atoms. This excites fine-structured, broadband (UV-near-infrared) polychromatic luminescence of the centers over the entire bandgap. The observed luminescence spectra revealed substitutional nitrogen interaction with non-equilibrium intrinsic carbon vacancies, produced simultaneously as Frenkel "vacancy-interstitial" pairs during the laser exposure.

Highly efficient stimulated Raman scattering of sub-picosecond laser pulses in BaWO4 for 10.6 µm difference frequency generation

Transient stimulated Raman scattering (SRS) of 0.3 ps 515 nm laser pulses in ${\rm BaWO_4}$BaWO₄ crystal was experimentally demonstrated with efficiency up to ${\sim}{20}\% $∼20% for the Stokes component with a wavenumber of ${\sim}{925}\;{{\rm cm}^{ - 1}}$∼925cm^-1 in a simple single-pass geometry. This anomalous high efficiency was obtained due to the laser pulse self-phase modulation resulting in spectral broadening and seeding the SRS. The applicability of seed pulse production for a high-pressure sub-picosecond ${{\rm CO}_2}$CO₂ laser amplifier via difference frequency generation in ${{\rm LiGaS}_2}$LiGaS₂ crystal was numerically verified.

IR femtosecond laser micro-filaments in diamond visualized by inter-band UV photoluminescence

Single microscale filaments were produced in monocrystalline Ia-type diamond by 1030 nm, 300 fs laser pulses tightly focused at NA = 0.3 and different peak powers, visualized by transverse imaging and spectrally characterized by longitudinal micro-spectroscopy, using intrinsic UV A-band photoluminescence (PL) with its peak at about 430 nm. Power-dependent scaling relationships for the local PL yield and diameters of the accompanying luminous micro-channels of recombining electron-hole plasma indicate a transition from three-photon absorption to free-carrier plasma absorption, as the consequent energy deposition mechanisms at increasing peak laser power. Power-dependent elongation of the luminous micro-channels versus peak laser power fitted by a Marburger formula yields, on average a diffraction-based estimate of 0.6 MW critical power for self-focusing within the diamond at the pump laser wavelength of 1030 nm.

Refractive twisted microaxicons

Complex-shaped light fields with specially designed intensity, phase, and polarization distributions are highly demanded for various applications including optical tweezers, laser material processing, and lithography. Here, we propose a novel (to the best of our knowledge) optical element formed by the twisting of a conic surface, a twisted microaxicon, allowing us to controllably generate high-quality spiral-shaped intensity patterns. Performance of the proposed element was analyzed both analytically and numerically using ray approximation and the rigorous finite difference time domain (FDTD) solution of Maxwell's equation. The main geometric parameters, an apex cone angle and a degree of twisting, were considered to control and optimize the generated spiral-shaped intensity patterns. The three-dimensional structure of such a microaxicon cannot be described by an unambiguous height function; therefore, it has no diffraction analogue in the form of a thin optical element. Such an element can be produced via direct laser ablation of transparent targets with structured laser beams or direct laser writing via two-photon photopolymerization and can be used in various micro- and nano-optical applications.

Plasmonic Nanolenses Produced by Cylindrical Vector Beam Printing for Sensing Applications

Interaction of complex-shaped light fields with specially designed plasmonic nanostructures gives rise to various intriguing optical phenomena like nanofocusing of surface waves, enhanced nonlinear optical response and appearance of specific low-loss modes, which can not be excited with ordinary Gaussian-shaped beams. Related complex-shaped nanostructures are commonly fabricated using rather expensive and time-consuming electron- and ion-beam lithography techniques limiting real-life applicability of such an approach. In this respect, plasmonic nanostructures designed to benefit from their excitation with complex-shaped light fields, as well as high-performing techniques allowing inexpensive and flexible fabrication of such structures, are of great demand for various applications. Here, we demonstrate a simple direct maskless laser-based approach for fabrication of back-reflector-coupled plasmonic nanorings arrays. The approach is based on delicate ablation of an upper metal film of a metal-insulator-metal (MIM) sandwich with donut-shaped laser pulses followed by argon ion-beam polishing. After being excited with a radially polarized beam, the MIM configuration of the nanorings permitted to realize efficient nanofocusing of constructively interfering plasmonic waves excited in the gap area between the nanoring and back-reflector mirror. For optimized MIM geometry excited by radially polarized CVB, substantial enhancement of the electromagnetic near-fields at the center of the ring within a single focal spot with the size of 0.37λ2 can be achieved, which is confirmed by Finite Difference Time Domain calculations, as well as by detection of 100-fold enhanced photoluminescent signal from adsorbed organic dye molecules. Simple large-scale and cost-efficient fabrication procedure offering also a freedom in the choice of materials to design MIM structures, along with remarkable optical and plasmonic characteristics of the produced structures make them promising for realization of various nanophotonic and biosensing platforms that utilize cylindrical vector beam as a pump source.

[Determining of cytokine levels in the urine in clinical practice.]

The paper presents data on the study of the content of cytokines (IL-1β, RAIL-1β, IL-2, IL-4, IL-10, IL-17A, TNF-, IFN-γ) in the morning urine using enzyme immunoassay in healthy individuals (n = 20) and in patients with acute glomerulonephritis (n = 93). The determination of cytokine levels in patients was carried out in the debut of the disease and 12 months after the onset of the disease. The obtained indicators of cytokine content in the urine are presented as absolute values in pg/ml and creatinine-normalized values calculated by the formula: cytokine level (pg/ml) / urine creatinine (µmol/ml). The study was made of changes in the content of cytokines in the urine of patients with glomerulonephritis with respect to a group of healthy individuals, as well as the dynamics of the content of cytokines in the urine during the 12-month observation period. The results of the study showed that the absolute values of cytokines in urine can distort the true picture of the cytokine profile of urine in renal pathology. Normalized values of the predominant number of pro- and anti-inflammatory cytokines (IL-1β, IL-2, IL-8, IL-10, IL-17A and TNF-α) in patients with glomerulonephritis were significantly higher than the corresponding indicators of healthy individuals. The normalized values of cytokines were shown to be as more sensitive indicators than absolute values in the course of analyzing differences in the cytokine profile in patients with glomerulonephritis, depending on chronic and acute course of the disease. These indicators influenced the outcome of glomerulonephritis, assessed, as a rule, 12 months after the onset of the disease. Thus, the low levels of IL-1β, IL-8 and IL-17А detected in the debut of the disease in combination with the high level of RAIL-1β determined the chronization of glomerulonephritis. So, the creatinine-normalized cytokine levels in the urine expand the possibilities of using the evaluation of the cytokine profile of urine to establish changes in the cytokine content in the urine in renal pathology and predict the chronization of glomerulonephritis.

Symmetry-wise nanopatterning and plasmonic excitation of ring-like gold nanoholes by structured femtosecond laser pulses with different polarizations

Low- and ultralow-energy tightly focused 200 fs, 515 nm donut-shaped laser pulses at 0.25 and 0.65 NA focusing were used for single-shot ablative pulse-energy scalable nanopatterning of 50 nm thick gold film and the following plasmonic excitation of dye monolayer photoluminescence (PL) in the fabricated nanostructures, respectively. The same pulses at much lower, non-ablative nanojoule energies, and the same focusing and linear, azimuthal, or radial polarizations provided efficient spectrally and symmetry-matched excitation of both localized and delocalized surface electromagnetic modes in the separate, ring-like through holes and their arrays in the film envisioned by our modeling, thus resulting in a polarization-sensitive yield of rhodamine 6G dye PL. The demonstrated consistency between the symmetries of the donut-shaped low-energy photo-exciting laser beam, its polarization state, and the donut-shaped gold nanostructures, produced by the same beam at high, ablative pulse energies, paves the way to smart, self-consistent nanofabrication and plasmonic sensing, when the structured light interacts with the consistently structured matter.

10-million-elements-per-second printing of infrared-resonant plasmonic arrays by multiplexed laser pulses

We report on high-quality infrared (IR)-resonant plasmonic nanoantenna arrays fabricated on a thin gold film by tightly focused femtosecond (fs) laser pulses coming at submegahertz repetition rates at a printing rate of 10 million elements per second. To achieve this, the laser pulses were spatially multiplexed by fused silica diffractive optical elements into 51 identical submicrometer-sized laser spots arranged into a linear array at periodicity down to 1 μm. The demonstrated high-throughput nanopatterning modality indicates fs laser maskless microablation as an emerging robust, flexible, and competitive lithographic tool for advanced fabrication of IR-range plasmonic sensors for environmental sensing, chemosensing, and biosensing.

Multi-beam pulsed-laser patterning of plasmonic films using broadband diffractive optical elements

Multi-sector broadband diffractive optical elements (DOEs) were designed and fabricated from fused silica for high-efficiency multiplexing of femtosecond and nanosecond Gaussian laser beams into multiple (up to one 100) optically tunable microbeams with increased high-numerical aperture (NA) focal depths. Various DOE-related issues, such as high-NA laser focusing, laser pulsewidth, and DOE symmetry-dependent heat conduction effects, as well as the corresponding spatial resolution, were discussed in the context of high-throughput laser patterning. The increased focal depths provided by such DOEs, their high multiplexing efficiency and damage threshold, as well as easy-to-implement optical shaping of output microbeams provide advanced opportunities for direct, mask-free, and vacuum-free high-throughput subtractive (ablative) and displacive pulsed-laser patterning of various nanoplasmonic films for surface-enhanced spectroscopy, sensing, and light control.

The role of circulating cytokines and thyroid hormones in the development of the nephrotic variant of glomerulonephritis

The purpose of the research - studying the features of the production of pro- and anti-inflammatory cytokines, as well as indicators of thyroid status in patients with nephrotic variant of glomerulonephritis (GN). Research methods.

METHODS

The examination involved 78 patients with primary GN, including 30 patients with nephrotic syndrome (NS) and 48 GN patients who had no NS symptoms. Laboratory researches included the determination of the concentration of the main cytokines circulating in the blood - IL-1b, IL-2, IL-4, IL-10, IFN-g and the receptor antagonist of IL-1b - Rа-IL-1b by the method of solid-phase enzyme linked immunosorbent assay enzyme immunoassay (ELISA) in the system of the bideterminant definition of antigen with the use of peroxidase as indicator enzyme using standard sets (“Cytokine”, St.-Petersburg) according to the technique attached to a set. The investigation of the basic indicators of thyroid status - free thyroxine (FT4), free triiodothyronine (FT3), thyroid-stimulating hormone (TSH), anti-thyroid peroxydase antibodies (TPOAb) is carried out by the ELISA using standard sets and NGO techniques «Diagnostic systems» (N-Novgorod). The researches were conducted twice - before the hospitalization (1-2 days) and after the end of a stationary stage of treatment (12-14 days).

RESULTS

In 90% of patients with nephrotic option of GN there have been identified laboratory signs of hypothyroidism of different degrees of severity accompanied by increasing of production levels of proinflammatory cytokine IL-1b and IL-4, related to the activity of a humoral link of adaptive immunity. The reduction of glomerular, erythropoietic, concentration kidney functions, as well as proteinuria in patients with nephrotic option GN are associated with the decrease of T4 levels in the blood and increased levels of the cytokines circulating in the blood - IL-1b and IL-4.

CONCLUSION

The obtained data demonstrate that the high level of production of IL-1b and IL-4 in GN patients causes hypothyroidism resulting in the formation of NS.

Dynamic polarization flip in nanoripples on photoexcited Ti surface near its surface plasmon resonance

Both normal and abnormal sub-100-nanometer ripples (wavenumber ∼10  μm(-1)) were separately observed on Ti surfaces excited by linearly polarized IR femtosecond laser pulses at lower and higher fluences. Numerical modeling of dispersion curves for surface plasmon-polaritons on the photoexcited Ti surfaces demonstrates its surface plasmon resonance with the peak wavenumber ∼8  μm(-1) spectrally tuned by prompt surface optical response, prompt surface charging, and pre-oxidation, with normal/abnormal nanoripples appearing at its red/blue shoulders, respectively.

Flash-imprinting of intense femtosecond surface plasmons for advanced nanoantenna fabrication

In this work, we demonstrate an all-laser method of fabrication of optical nanoantennas (ONAs) with an additional coupling/focusing diffractive element. This method is based on double-shot femtosecond laser nanoablation of a thin supported metallic film, inducing a sequence of electrodynamic (surface plasmon-polariton [SPP] excitation and interference), thermal (melting, ablation and ultrafast cooling), and hydrodynamic processes. In particular, the thermal and hydrodynamic processes are important for ONA formation after the first laser shot, while second spatially shifted laser shot via an induced SPP wave results in a radial surface grating near the nanoantenna. Such gratings provide efficient coupling between incident laser radiation and SPP waves, thus significantly improving the ONA efficiency.

Formation of crownlike and related nanostructures on thin supported gold films irradiated by single diffraction-limited nanosecond laser pulses

A type of laser-induced surface relief nanostructure-the nanocrown-on thin metallic films was studied both experimentally and theoretically. The nanocrowns, representing a thin corrugated rim of resolidified melt and resembling well-known impact-induced water-crown splashes, were produced by single diffraction-limited nanosecond laser pulses on thin gold films of variable thickness on low-melting copper and high-melting tungsten substrates, providing different transient melting and adhesion conditions for these films. The proposed model of the nanocrown formation, based on a hydrodynamical (thermocapillary Marangoni) surface instability and described by a Kuramoto-Sivashinsky equation, envisions key steps of the nanocrown appearance and gives qualitative predictions of the acquired nanocrown parameters.

Through nanohole formation in thin metallic film by single nanosecond laser pulses using optical dielectric apertureless probe

Separate nanoholes with the minimum size down to 35 nm (~λ/15) and nanohole arrays with the hole size about 100 nm (~λ/5) were fabricated in a 50 nm optically "thick" Au/Pd film, using single 532 nm pump nanosecond laser pulses focused to diffraction-limited spots by a specially designed apertureless dielectric fiber probe. Nanohole fabrication in the metallic film was found to result from lateral heat diffusion and center-symmetrical lateral expulsion of the melt by its vapor recoil pressure. The optimized apertureless dielectric microprobe was demonstrated to enable laser fabrication of deep through nanoholes.

Near-critical phase explosion promoting breakdown plasma ignition during laser ablation of graphite

Removal rate, air shock, and ablative recoil pressure parameters were measured as a function of laser intensity I(peak) during nanosecond laser ablation of graphite. Surface vaporization of molten graphite at low intensities I(peak)<0.15 GW/cm(2) was observed to transform into its near-critical phase explosion (intense homogeneous boiling) at the threshold intensity I(PE)≈0.15 GW/cm(2) in the form of a drastic, correlated rise of removal rate, air shock, and ablative recoil pressure magnitudes. Just above this threshold (I(peak)≥0.25 GW/cm(2)), the explosive mass removal ended up with saturation of the removal rate, much slower increase of the air and recoil pressure magnitudes, and appearance of a visible surface plasma spark. In this regime, the measured far-field air shock pressure amplitude exhibits a sublinear dependence on laser intensity (∝I(peak)(4/9)), while the source plasma shock pressure demonstrates a sublinear trend (∝I(peak)(3/4)), both indicating the subcritical character of the plasma. Against expectations, in this regime the plasma recoil pressure increases versus I(peak) superlinearly (∝I(peak)(1.1)), rather than sublinearly (∝I(peak)(3/4)), with the mentioned difference related to the intensity-dependent initial spatial plasma dimensions within the laser waist on the graphite surface and to the plasma formation time during the heating laser pulse (overall, the pressure source effect). The strict coincidence of the phase explosion, providing high (kbar) hydrodynamic pressures of ablation products, and the ignition of ablative laser plasma in the carbon plume may indicate the ablative pressure-dependent character of the underlying optical breakdown at the high plume pressures, initiating the plasma formation. The experimental data evidence that the spatiotemporal extension of the plasma in the laser plume and ambient air during the heating laser pulse is supported by fast lateral electron and radiative heat conduction (laser-supported combustion wave regime), rather than by propagation of a strong shock wave (laser-supported detonation wave regime).