Ps Duration Research Articles

Manipulation and applications of ultrafast all-optical switching based on transient absorption and dispersion in KTN crystals.

Potassium tantalate niobate (KTN) represents a noteworthy category of optical crystals known for their superior nonlinear optical properties. In this study, we conducted measurements of femtosecond time-resolved transient absorption (TA) spectra in KTa0.57Nb0.43O3 crystals. Notably, a rapid and pronounced "plateau" phase, ∼1.5 ps in duration, was detected at the onset of the TA kinetics and succeeded by two distinct decay components, exhibiting lifetimes of ∼140 ps and over 10 ns, respectively. We attribute these observations to a decay process involving two-photon absorption, dispersion characteristics, and excited state absorption. Based on this unique TA characteristic of KTN crystals, an all-optical switching strategy was proposed and utilized to measure the ultrafast lasing dynamics of single-crystal CH3NH3PbBr3 nanowires. This polarization-independent TA gate approach offers an adjustable gate width combining ps and ns time scales and introduces a versatile tool for advanced optical applications.

Transverse Inscription of Silicon Waveguides by Picosecond Laser Pulses

AbstractIn this work, picosecond laser inscription of segmented waveguides in crystalline silicon based on a deterministic single‐pulse modification process is demonstrated. Pulses of 43 ps duration at 1.55 wavelength are used to transversely inscribe periodic structures with a pulse‐to‐pulse pitch of ≈2 . Infrared shadowgraphy images and Raman spectroscopy measurements indicate that the modifications exhibit a spherical shape. Characterization of waveguide performance at 1.55 for various pulse energies and periods is carried out. Direct comparison with numerical simulations confirms the presence of graded index waveguides, encompassing a micrometer core size and a maximum refractive index change of . This short‐pulse inscription approach can pave the way for 3D integrated photonic devices in the bulk of silicon.

Bessel beam fabrication of graphitic micro electrodes in diamond using laser bursts

We present the fabrication of conductive graphitic microelectrodes in diamond by using pulsed Bessel beams in the burst mode laser writing regime. The graphitic wires are created in the bulk of a 500 μm thick monocrystalline HPHT diamond (with (100) orientation) perpendicular to the sample surface, without beam scanning or sample translation. In particular, the role of different burst features in the resistivity of such electrodes is investigated for two very different sub-pulse durations namely 200 fs and 10 ps, together with the role of thermal annealing. Micro-Raman spectroscopy is implemented to investigate the laser-induced crystalline modification, and the results obtained by using two different laser repetition rates, namely 20 Hz and 200 kHz, are compared. A comparison of the micro-Raman spectra and of the resistivity of the electrodes fabricated respectively with 10 ps single pulses and with bursts (of sub-pulses) of similar total duration has also been made, and we show that the burst mode writing regime allows to fabricate more conductive micro electrodes, thanks to the heat accumulation process leading to stronger graphitization. Moreover, the microfabrication of diamond by means of the longest available bursts (~ 46.7 ps duration) featured by 32 sub-pulses of 200 fs duration, with intra-burst time delay of 1.5 ps (sub-THz bursts), leads to graphitic wires with the lowest resistivity values obtained in this work, especially at low repetition rate such as 20 Hz. Indeed, micro electrodes with resistivity on the order of 0.01 Ω cm can be fabricated by Bessel beams in the burst mode regime even when the bursts are constituted by femtosecond laser sub-pulses, in contrast with the results of the standard writing regime with single fs pulses typically leading to less conductive micro electrodes.

Subnanosecond Electromagnetic Pulse Generated by a Long Spark Discharge: Lightning Implication

AbstractThe effects of generating pulsed radiation by a long spark discharge are important for the development of lightning models and applications related to lightning protection. In experiments with a Marx generator simulating a lightning discharge, we detected the radiation in the form of a single ultrawideband electromagnetic pulse (UWB EMP) about 200 ps in duration, and rising time about 100 ps. UWB EMP generation occurs during the breakdown of a “rod–rod” 4 m long gap. Pulses of almost unipolar shape are observed in more than half of all positive discharges. EMP emission occurs before the main stage, and corresponds to the start of the upward leader from a grounded electrode. In negative discharges, pulses are also observed, but less frequently and with a smaller amplitude. The UWB EMPs, given their large amplitude (more than 100 V/m at a distance of 90 m from the discharge), can be considered as possible new lightning damage factors.

Controlling ultrafast laser writing in silica glass by pulse temporal contrast.

We demonstrate that the temporal contrast of femtosecond light pulses is a critical parameter in laser writing inside transparent dielectrics, allowing different material modifications. In particular, anisotropic nanopores in silica glass are produced by high-contrast of 107 femtosecond Yb:KGW laser pulses rather than low-contrast of 103 Yb fiber laser pulses. The difference originates in the fiber laser storing a third of its energy in a post-pulse of up to 200 ps duration. The absorption of this low-intensity fraction of the pulse by laser-induced transient defects with relatively long lifetime and low excitation energy, such as self-trapped holes, drastically changes the kinetics of energy deposition and the type of material modification. We also demonstrate that low-contrast pulses are effective in creating lamellar birefringent structures, possibly driven by a quadrupole nonlinear current.

Picosecond laser filament-guided electrical discharges in air at 1 kHz repetition rate

Laser-induced filaments have been shown to reduce the voltage necessary to initiate electrical discharges in atmospheric air and guide their propagation over long distances. Here we demonstrate the stable generation of laser filament-guided electrical discharge columns in air initiated by high energy (up to 250 mJ) 1030 nm wavelength laser pulses of 7 ps duration at repetition rates up to 1 kHz and we discuss the processes leading to breakdown. A current proportional to the laser pulse energy is observed to arise as soon as the laser pulse arrives, initiating a high impedance phase of the discharge. Full breakdown, characterized by impedance collapse, occurs 100 ns to several µs later. A record 4.7-fold reduction in breakdown voltage for dc-biased discharges, which remains practically independent of the repetition rate up to 1 kHz, is observed to be primarily caused by a single laser pulse that produces a large (∼80%) density depression. The radial gaps between the filamentary plasma channel and the hollowed electrodes employed are shown to play a significant role in the breakdown dynamics. A rapid increase of 3-4 orders of magnitude in current is observed to follow the formation of localized radial current channels linking the filament to the electrodes. The increased understanding and control of kHz repetition rate filament-guided discharges can aid their use in applications.

Theoretical Analysis of Integrated Nanophotonic Q‐Switched Laser Based on Gain and Saturable Absorption by Two‐Dimensional Materials

A nanophotonic passively Q‐switched lasing element in the near infrared is proposed and theoretically investigated. It consists of a silicon‐rich nitride disk resonator enhanced with the contemporary hetero‐bilayer and a graphene monolayer to provide gain and saturable absorption, respectively. The two‐dimensional materials are placed on top of the disk resonator and are separated by a spacer of hexagonal boron nitride. emits at 1128 nm due to the radiative recombination of interlayer excitons after being optically pumped at 740 nm. Optical pumping is conducted in a guided‐wave manner aiming at achieving a high overall efficiency by critically coupling to a cavity mode near the pump transition. The response of the proposed pulsed laser is assessed by utilizing a coupled‐mode theory framework fed with linear finite‐element method simulations, rigorously derived from the Maxwell–Bloch equations. Following a meticulous design process and exploiting the guided pumping scheme, an ultralow lasing threshold of just μW is obtained. Overall, the Q‐switched laser delivers pulsed light inside an integrated bus waveguide with mW peak power, ps duration, and GHz repetition rates requiring sub‐mW continuous wave pumping. These properties are highly promising for communication applications and highlight the potential of two‐dimensional materials for nanophotonic light sources.

Efficient Assessment of 'Instantaneous pK' Values from Molecular Dynamics Simulations.

We present a molecular simulation approach to studying the role of local and momentary molecular environment for potential acid-base reactions. For this, we combine thermodynamic considerations on the pK of ionic species with rapid sampling of energy changes related to (de)protonation. Using dispersed carbonate ions in water as a reference, our approach aims at the fast assessment of the momentary protonation energy, and thus the 'instantaneous pK', of calcium-carbonate ion aggregates. The latter include transient complexes that are elusive to long sampling runs. This motivated the elaboration of approximate, yet particularly fast assessable sampling strategies. Along this line, we were able to characterize instantaneous pK values at a statistical accuracy of 0.4 pK units within sampling runs of only 10 ps duration, whereas statistical errors reduce to 0.1 pK units in 75 ps sampling runs, respectively. This readily enabled the required time resolution for the characterization of [Cax (CO3 )y ]2(x-y) aggregates with x=1,2 and y=1,2,3, respectively. In turn, the analysis of the pH-dependent nature of calcite-water interfaces and dynamically ordered liquid-like oxyanion polymers (dollop) domains is outlined at 10 ps resolution.

Prognostic factors associated with non-remission and low disease activity status af ter one year of psoriatic arthritis patients treatment in real practice

Background. Remission/low disease activity (LDA) are acceptable goal of psoriatic arthritis (PsA) treatment. Prognostic factors for non-remission/LDA hasn’t been fully studied yet and data is limited. The aim – to determine the prognostic factors associated with non-remission/LDA status within 1 year of treatment in PsA pts in real practice. Methods. 292 pts (M/F=122/170) with active PsA fulfilling the CASPAR criteria were included. Mean age 46.1±12.5 years (yrs), PsA duration 10.4±7.1 months (mos), psoriasis (Ps) duration 19.32±12.08 mos, body mass index (BMI) 27.7±5.6 kg/m2 , median (Me) of DAPSA – 23.8 [14.7; 37.4]. 182 pts was given therapy with synthetic (s) DMARDs predominantly methotrexate (MTX), 110 pts – bDMARDs as monotherapy or with combination with MTX or other sDMARDs. At baseline (BL) and at 1 year of therapy PsA activity by tender/swelling joint count (TJC)/68, (SJC)/66, pain (VAS), Patient global assessment disease activity (PtGA, VAS), CRP (mg/l), dactylitis, enthesitis by LEI and plantar fascia, BSA (%), HAQ, DAPSA were evaluated. DAPSA>28 indicate high disease activity (HDA), DAPSA=15–28 – moderate activity (MoDA), DAPSA=5–14 – LDA, DAPSA≤4 – remission. By 1 year of therapy the proportion of pts who had not reached remission or LDA were calculated. The one-factor model of logistic regression was used to identify a group of features that are associated with remission or LDA nonachievement. M±SD, Me [Q25; Q75], Min–Max, %, t-test, Peаrson χ2 , Mann – Whitney tests, ORs with 95% CI were performed. All p<0.05, were considered to indicate statistical significance. Results. At 1 year of therapy 116 pts of 292 (40%) have HDA/MoDA by DAPSA. Remission/LDA was reached in 176 (60%) pts, 110 of them (62.5%) were treated with bDMARDs. Comparative analysis in both groups and one-factor model of logistic regression showed the following features at BL were associated with non-remission/LDA status: TJC>5 (p<0.001), SJC>3 (p<0.001), CRP>10 mg/l (p<0.001), HAQ>0.5 (p<0.001), presence of enthesitis (p<0.001), dactylitis (p<0.001), BMI>30 (p<0.002) and had to be treated with sDMARDs. PsA pts with combination of these clinical features at first visit have a higher risk of not achieving remission/LDA status in comparison to PsA pts without them, OR with 95% CI. Conclusion. In real practice remission/LDA cannot achieve 40% PsA pts despite going through therapy. It is a combination of clinical fea tures at BL – TJC>3, SJC>5, CRP>10 mg/l, HAQ>0.5, presence of enthesitis, dactylitis, BMI>30 kg/m2 and sDMARDs monotherapy – that constitutesa prognostic factor with negative impact on achievement remission/LDA after 1 year of treatment.

Long distance laser filamentation using Yb:YAG kHz laser

In the framework of the Laser Lightning Rod project, whose aim is to show that laser-induced filaments can guide lightning discharges over considerable distances, we study over a distance of 140 m the filaments created by a laser system with J-range pulses of 1 ps duration at 1 kHz repetition rate. We investigate the spatial evolution of the multiple filamentation regime using the fundamental beam at 1030 nm or using combination with the second and third harmonics. The measurements were made using both a collimated beam and a loosely focused beam.

Investigation of Multimode Self-Similar Pulse Compression in Tapered Photonic Crystal Fibers

In this paper, we theoretically investigate the multimode self-similar pulse compression (MM-SSPC) in tapered photonic crystal fibers. To expand the self-similar theory beyond single-mode scenarios, we have discovered through analytical analysis that the width of the input pulse has a significant impact on perturbing the MM-SSPC process. We proceed to solve the multimode generalized nonlinear Schrödinger equation using numerical methods for various input pulse widths, which leads to the observation of three distinct types of multimode pulse compression. MM-SSPC only takes place when the input pulse width is comparatively longer. Our numerical results are consistent with the predictions of analytical calculations. Our results demonstrate that by using input pulses of 2.5 ps in duration, three modes can be compressed in a self-similar manner to 200 fs, which corresponds to a compression factor of 12.5. Finally, We establish the minimum input pulse width required to enable the MM-SSPC to function for the three specific modes of interest. Our findings provide an effective guidance to design pulse compressor for the generation of pedestal-free, high-energy femtosecond pulses.

Noise-like pulses generation and its beam self-cleaning effect in an all-fiber multimode cavity with a figure-8 scheme

The beam profiles of multimode mode-locked fiber lasers are highly multimode, the speckled beam profiles limit their potential application. To improve the beam profiles of multimode mode-locked fiber lasers, we proposed an all-fiber figure-8 multimode cavity and experimentally demonstrated the generation of noise-like pulses (NLPs) and beam self-cleaning of NLPs in the cavity at 1.5 µm. The laser was mode locked by a nonlinear amplifying loop mirror, an Er/Yb co-doped fiber provided gain, and 50 m OM4 fiber introduced enough nonlinear phase shift difference. The scheme generated NLPs with 159 mW average power, 2.78 MHz repetition rate and 57.19 nJ pulse energy. The packet duration of the NLPs increased from 0.61 ns to 2.99 ns when the pump power was increased from 2 W to 9 W. Nonlinear beam self-cleaning with a near Gaussian beam profile output was achieved in the multimode fiber laser. The M2 was measured to be 2.41 at the pulse energy of 6.83 nJ. We also obtained spatiotemporal mode-locked pulses with 1.03 ps duration and speckled beam profiles. This is the first experimental demonstration of NLPs in multimode fiber lasers, and beam self-cleaning of NLPs was observed for the first time. The results enriched nonlinear dynamics in multimode fiber lasers.

Sub-GHz resolution line-by-line pulse shaper for driving superconducting circuits

We demonstrate a sub-GHz resolution, fully programmable Fourier-domain pulse shaper capable of generating arbitrary optical pulse patterns for superconducting circuit platforms. This high resolution allows line-by-line pulse shaping of a 1 GHz-spaced comb, and the pulse shaper can accommodate an optical bandwidth as large as 1 THz, which represents the highest resolution programmable line-by-line pulse shaping to our knowledge. Linear optical sampling with a dual-comb system confirms independent control of 1 GHz-spaced optical lines, and the low phase noise of the pulse shaper is characterized. We apply the pulse shaper as an optical drive for an array of Josephson junctions operating at a temperature of 4 K, where cryogenic photodetection of pulse doublets with user-defined separation characterizes the Josephson junction response. Furthermore, we demonstrate a pulse-density modulation pattern of 4 ps duration optical pulses that can serve as the high bandwidth drive of a quantum-based Josephson arbitrary waveform synthesizer. By leveraging the exquisite control, large bandwidth, and low noise of photonics, this represents an important advance toward the realization of high power and high spectral purity AC voltage standards at gigahertz frequencies without requiring 100 GHz bandwidth driving electronics.

A new integral enthesial-comorbididity index of psoriatic arthritis activity

To develop an integral index of psoriatic arthritis (PsA) activity. 117 patients with PsA (M/F - 63/54) were included. Patients' age 44±11 years, psoriasis (Ps) duration - 213±153 months, PsA duration - 73.4±78.5 months. Patients underwent standard clinical examination of PsA activity: tender (out of 68) and swollen (out of 66) joint counts (TJC, SJC), LEI, tenderness of the plantar fascia (PF), skin lesion severity (BSA), presence of nail Ps, body mass index (BMI), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), DAPSA, FACIT-F. Parametric and nonparametric statistic methods, correlation and ROC analysis were used. Mean DAPSA was 38±21, TJC - 14.2±10.6, SJC - 10.6±8.3, ESR - 30.5±29.5 mm/h, CRP - 23.3±29 mg/l, LEI - 1.2±1.5, FACIT-F - 32±11, BMI - 27.4±6.2 kg/m2. The following significant positive correlations were revealed: between DAPSA and BMI, patients' age, ESR, PsA and Ps duration, TJC, SJC, LEI, presence of PF enthesitis, skin lesion severity, presence of nail Ps. A negative correlation between FACIT-F and male sex was found. Based on the predictive model of parameters, the Entesial-Comorbid Index of PsA (ECIPsA) was created: 3.81×LEI+13.72×PF+0.54×Age-0.25×FACIT-F+7.36×BSA+7.94×PsA duration+5.5×Nail Ps+0.32×BMI-3.52, namely LEI - Leeds Enthesial Index; PF - pain in the PF; patient's age; FACIT-F - fatigue scale; BSA<3%=0, ≥3%=1; PsA duration≤2 years=0, >2 years=1; presence of nail Ps=1, absence=0; ECIPsA≥28 corresponds with high PsA activity according to DAPSA≥28. ROC analysis of sensitivity and specificity of the prognostic model demonstrated high correctness of the index: the area under the ROC curve was 0.768, 95% confidence interval (0.624-0.913). The new PsA activity index corresponds to the existing ones and takes into consideration the clinical heterogeneity and comorbidity of the disease.

Temporally probing the thermal phonon and charge transfer induced out-of-plane acoustical displacement of monolayer and bi-layer MoS2/GaN heterojunction

Acoustical behavior of semiconducting transition metal dichalcogenides determines the heat transfer pathway, and thus plays a crucial role in the electronics and optoelectronics design. In this research, van der Waals heterojunctions (vdWHs) consisting of transferred monolayer and bi-layer MoS2 on GaN substrate were studied. We observed an asymmetric bipolar acoustic strain wave with ∼5 ps duration, which describes the surface of substrate undergoing strong compressive deformation after weak tensile deformation in the out-of-plane direction. We developed a theory to explain the mechanisms responsible for the observed strain waveform in the vdWHs elastic system, and obtained the critical parameters of the carrier dynamics by temporal fitting. Our results not only report a coherent acoustic phonon generated in the vdWHs, which will complement our understanding of the thermal transfer at the 2D/substrate interface, but also provide information about the intrinsic properties in the vdWHs, which would benefit the design of the 2D-based devices in the future.

Microlesion healing dynamics in in vivo porcine skin after treatment with 1064 nm picosecond-domain Nd:YAG laser.

The fractionated picosecond laser produces microscopic lesions in the epidermis and dermis due to laser-induced optical breakdown (LIOB). There have been multiple histological reports, but the present literature lacks detailed in vivo studies after treatment with high-power laser systems. Our study aimed to characterize the healing patterns of microlesions induced with 150 ps duration 1064 nm MLA-type picosecond laser. The induced picosecond laser-tissue reactions with pulse energy of 50-250 mJ and different treatment modes were observed in in vivo porcine skin model over 10 days after the laser procedure. A macroscopic evaluation was combined with microscopic histological analysis to observe the healing dynamics of laser-induced microlesions. Superficial, intraepidermal cavitation bubbles were induced using microbeam fluence of 4-20 J/cm2 . Skin irritation scores positively correlated with pulse energy and dose. Our findings demonstrate that dose and pulse energy had a direct impact on epidermal thickness and lesions healing dynamics.

Boron carbon oxynitride coated arc-shaped fiber as an optical modulator for passively mode-locked fiber lasers at 1.5 and 2 μm wavelength

Two-dimensional (2D) materials have recently been explored as potential saturable absorbers (SAs) due to their remarkable optoelectronic and nonlinear optical properties. In this work, we have experimentally reported 2D boron carbon oxynitride (BCNO) as a potential mode-locker in erbium-(EDFL) and thulium-doped fiber lasers (TDFL) for the first time. The BCNO-coated arc-shaped fiber was explored as a novel optical loss modulator and exhibited a modulation depth of 8.2% and 5% at 1.5 μm and 2 μm, respectively. Mode-locking was achieved by the BCNO-coated arc-shaped fiber in EDFL having a pulse width, repetition rate, and center wavelength of 1.56 ps, 19.14 MHz, and 1562.2 nm, respectively. Mode-locked pulses of 1.456 ps duration were achieved by incorporating BCNO-coated arc-shaped fiber in TDFL, operated at center wavelength, repetition rate, and signal-to-noise ratio (SNR) of 1944 nm, 13 MHz, and 70.3 dB, respectively. These results prove BCNO to be a promising low-cost 2D material to be further explored for laser-related applications.

Вынужденное комбинационное рассеяние 0.3-ps лазерных импульсов с длиной волны 515 nm в кристаллах Ca-=SUB=-3-=/SUB=-(VO-=SUB=-4-=/SUB=-)-=SUB=-2-=/SUB=- и Ca-=SUB=-0.27-=/SUB=-Sr-=SUB=-0.3-=/SUB=-(VO-=SUB=-4-=/SUB=-)-=SUB=-2-=/SUB=-

The prospects of SRS-active calcium/strontium orthovanadate crystals, Ca3(VO4)2 and Ca2.7Sr0.3(VO4)2, for spectral conversion of ultrashort visible-range laser pulses evaluated in a single-pass scheme with pump focusing into the samples. For the ~3 J incident laser pulses of 0.3 ps duration at wavelength of 515 nm the energy conversion efficiency of up to ~3.5% to the Stokes component shifted in frequency by ~850 cm–1 obtained in a 1.3 cm long sample of Ca2.7Sr0.3(VO4)2 crystal. Simultaneously, in the transmitted radiation spectrum the amplitude of Stokes component reached 1/3 of the amplitude at the pump wavelength. Under the same conditions, SRS in a Ca3(VO4)2 crystal was not detected at all. It was shown that the observed differences can be explained by the attenuation of pump pulse due to difference in two-photon absorption in these crystals.

Vibrational response and temperature of shock-compressed Pt: In situ extended x-ray absorption fine structure measurements to 325 GPa

Single-pulse ($\ensuremath{\sim}100$-ps duration) extended x-ray absorption fine structure (EXAFS) measurements were obtained in laser-shocked Pt to examine atomic vibrational properties and to determine temperatures for shock pressures from 72 to 325 GPa. Pt x-ray absorption spectra were recorded while a planar shock wave was propagating through the Pt sample. The absorption spectrum corresponding to the shocked Pt was obtained by subtracting the ambient Pt contribution from the measured absorption spectrum. Fits to the shocked-state EXAFS data provided Pt lattice parameters consistent with the known Pt Hugoniot and the mean-squared relative displacements (MSRDs) for nearest-neighbor Pt atoms. Pt temperatures in the shocked state, estimated from the MSRDs using the correlated Debye model and correlated Einstein models, were consistent with both the Hugoniot temperatures calculated by integration along the Hugoniot and with the Hugoniot temperatures from published first-principles calculations. However, the agreement between the Hugoniot temperatures from EXAFS measurements and the calculated Hugoniot temperatures is not as good above 200 GPa, likely due to anharmonic effects. The present results demonstrate that single-pulse synchrotron EXAFS measurements in laser-shocked solids are useful for quantitative temperature determination and for examination of vibrational properties, including anharmonicity, at extreme pressure-temperature conditions.

Ultrashort pulse thulium-doped fiber laser with molybdenum trioxide on tapered fiber

This paper demonstrates ultrashort pulse generation using molybdenum trioxide (MoO3) saturable absorber (SA) integrated into a thulium-doped fiber laser. The average particle size of the MoO3 material was 9.54 µm. The MoO3/polydimethylsiloxane composite was prepared and spin-coated on a tapered fiber to fabricate the SA device. It had a modulation depth of 2.89% and demonstrated a high damage threshold, extending beyond 19.34 GW/cm2. From the evanescent light-matter interaction, stable self-starting mode-locked soliton pulses of 1.22 ps duration at 1941.4 nm central wavelength were obtained. The pulse repetition rate was 10.84 MHz with 3.3 nm spectral bandwidth. At 1.15 W pump power, the soliton pulse energy was 0.68 nJ corresponding to a peak power of 492 W. The work exhibited comparable pulse performances in the 2 µm wavelength range while utilizing simple SA fabrication procedures of micro-sized MoO3 materials.