Single Picosecond Research Articles

Uncovering the binding nature of thiocyanate in contact ion pairs with lithium ions.

Ion pair formation is a fundamental molecular process that occurs in a wide variety of systems, including electrolytes, biological systems, and materials. In solution, the thiocyanate (SCN-) anion interacts with cations to form contact ion pairs (CIPs). Due to its ambidentate nature, thiocyanate can bind through either its sulfur or nitrogen atoms, depending on the solvent. This study focuses on the binding nature of thiocyanate with lithium ions as a function of the solvents using FTIR, 2D infrared spectroscopy (2DIR) spectroscopies, and theoretical calculations. The study reveals that the SCN- binding mode (S or N end) in CIPs can be identified through 2DIR spectroscopy but not by linear IR spectroscopy. Linear IR spectroscopy shows that the CN stretch frequencies are too close to one another to separate N- and S-bound CIPs. Moreover, the IR spectrum shows that the S-C stretch presents different frequencies for the salt in different solvents, but it is related to the anion speciation rather than to its binding mode. A similar trend is observed for the anion bend. 2DIR spectra show different dynamics for N-bound and S-bound thiocyanate. In particular, the frequency-frequency correlation function (FFCF) dynamics extracted from the 2DIR spectra have a single picosecond exponential decay for N-bound thiocyanate and a biexponential decay for S-bound thiocyanate, consistent with the binding mode of the anion. Finally, it is also observed that the binding mode also affects the line shape parameters, probably due to the different molecular mechanisms of the FFCF for N- and S-bound CIPs.

Femtosecond intramolecular rearrangement of the CH3NCS radical cation.

Strong-field ionization, involving tunnel ionization and electron rescattering, enables femtosecond time-resolved dynamics measurements of chemical reactions involving radical cations. Here, we compare the formation of CH3S+ following the strong-field ionization of the isomers CH3SCN and CH3NCS. The former involves the release of neutral CN, while the latter involves an intramolecular rearrangement. We find the intramolecular rearrangement takes place on a single picosecond timescale and exhibits vibrational coherence. Density functional theory and coupled-cluster calculations on the neutral and singly ionized species help us determine the driving force responsible for intramolecular rearrangement in CH3NCS. Our findings illustrate the complexity that accompanies radical cation chemistry following electron ionization and demonstrate a useful tool for understanding cation dynamics after ionization.

Ultraefficient resistance switching between charge ordered phases in 1T-TaS2 with a single picosecond electrical pulse

Progress in high-performance computing demands significant advances in memory technology. Among novel memory technologies that promise efficient device operation on a sub-ns timescale, resistance switching between charge ordered phases of 1T-TaS2 has shown to be potentially useful for development of high-speed, energy efficient nonvolatile memory devices. Measurement of the electrical operation of such devices in the picosecond regime is technically challenging and hitherto still largely unexplored. Here, we use an optoelectronic “laboratory-on-a-chip” experiment for measurement of ultrafast memory switching, enabling accurate measurement of electrical switching parameters with 100 fs temporal resolution. Photoexcitation and electro-optic sampling on a (Cd,Mn)Te substrate are used to generate and, subsequently, measure electrical pulse propagation with intra-band excitation and sub-gap probing, respectively. We demonstrate high contrast nonvolatile resistance switching from high to low resistance states of a 1T-TaS2 device using single sub-2 ps electrical pulses. Using detailed modeling, we find that the switching energy density per unit area is exceptionally small, EA= 9.4 fJ/μm2. The speed and energy efficiency of an electronic “write” process place the 1T-TaS2 devices into a category of their own among new generation nonvolatile memory devices.

Generation and regulation of electromagnetic pulses induced by hybrid laser pulses interacting with solid targets

In inertial confinement fusion, electromagnetic pulses (EMPs) can be produced during high-power laser interacting with solid targets, which are intimately related to laser intensity and laser energy. In this study, EMPs generated by hybrid laser pulses coupling with targets are recorded and analyzed. The results indicate that a single picosecond laser gives birth to the most intense EMPs, but they are remarkably suppressed when a nanosecond laser-shooting target is triggered before the picosecond and femtosecond laser. One possible hypothesis is proposed based on x-rays inducing pre-ablation that generates pre-plasma at the surfaces of the picosecond target and femtosecond target, leading to a sharp drop both in the energy and number of the emitting hot electrons and protons. The findings will deepen our understanding of the mechanism of EMPs’ generation and will also open a new avenue to regulate EMPs by hybrid laser pulses.

Noise reduction and 3D image restoration of single photon counting LiDAR using adaptive gating

Single photon LiDAR is considered as one of the most important tools in acquiring target information with high accuracy under extreme imaging conditions, as it offers single photon sensitivity and picosecond timing resolution. However, such technique sense the scene with the photons reflected by the target, thus resulting in severe degradation of image in presence of strong noise. Range gating with high-speed electronics is an effective way to suppress the noise, unfortunately, such technique suffers from manually selecting the parameters and limited gating width. This paper presents a target information extracting and image restoration method under large observation window, which first obtain the depth distribution of the target and extract the information within the range by analyzing the model of signal and noise, then further improve the image quality by adopting advanced image restoration algorithm and henceforth shows better results than those denoising method that purely relying on hardware. In the experiment, photon-per-pixel (PPP) was as low as 3.020 and signal-to-background ratio (SBR) was as low as 0.106, the proposed method is able to improve SBR with a factor of 19.330. Compared to classical algorithm named cross correlation, the reconstruction signal to noise ratio (RSNR) increased 33.520dB by further cooperating with advanced image restoration algorithm, thus improved the ability of sensing accurate target information under extreme cases.

Characteristics and formation mechanism of filamentary plasma string induced by single picosecond laser pulse in sapphire

Characteristics and formation mechanism of filamentary plasma string induced by single picosecond laser pulse in sapphire

Nanoparticle Fragmentation Below the Melting Point Under Single Picosecond Laser Pulse Stimulation.

Understanding the laser-nanomaterials interaction including nanomaterial fragmentation has important implications in nanoparticle manufacturing, energy, and biomedical sciences. So far, three mechanisms of laser-induced fragmentation have been recognized including non-thermal processes and thermomechanical force under femtosecond pulses, and the phase transitions under nanosecond pulses. Here we show that single picosecond (ps) laser pulse stimulation leads to anomalous fragmentation of gold nanoparticles that deviates from these three mechanisms. The ps laser fragmentation was weakly dependent on particle size, and it resulted in a bimodal size distribution. Importantly, ps laser stimulation fragmented particles below the whole particle melting point and below the threshold for non-thermal mechanism. We propose a framework based on near-field enhancement and nanoparticle surface melting to account for the ps laser-induced fragmentation observed here. This study reveals a new form of surface ablation that occurs under picosecond laser stimulation at low fluence.

Femtosecond dynamics and coherence of ionic retro-Diels–Alder reactions

Ultrafast tunnel ionization enables femtosecond time-resolved dynamic measurements of the retro-Diels-Alder reactions of positively charged cyclohexene, norbornene, and dicyclopentadiene. Unlike the reaction times of 500-600ps that are observed following UV excitation of neutral species, on the ionic potential energy surfaces, these reactions occur on a single picosecond timescale and, in some cases, exhibit vibrational coherence. In the case of norbornene, a 270cm-1 vibrational mode is found to modulate the retro-Diels-Alder reaction.

Damage Inside Borosilicate Glass by a Single Picosecond Laser Pulse.

We investigate damage inside the bulk of borosilicate glass by a single shot of IR picosecond laser pulse both experimentally and numerically. In our experiments, bulk damage of borosilicate glass with aspect ratio of about 1:10 is generated. The shape and size of the damage site are shown to correspond to an electron cloud with density of about 10 cm. The underlying mechanism of electron generation by multiphoton ionization and avalanche ionization is numerically investigated. The multiphoton ionization rate and avalanche ionization rate are determined by fitting experimental results. The relative role of multiphoton ionization and avalanche ionization are numerically studied and the percentage of electron contribution from each ionization channel is determined.

Nanotwist of aluminum with irradiation of a single optical vortex pulse

A nanoscale twisting of aluminum (Al) is demonstrated by irradiation with a single picosecond optical vortex pulse with relatively low energy near the ablation threshold, due to the orbital angular momentum (OAM) transfer effects. The twisting needle is easily transformed into a microscale non-twisting needle by only the deposition of several overlaid optical vortex pulses. Irradiation with a picosecond/nanosecond optical vortex pulse with a millijoule level pulse energy also enabled the fabrication of a microscale non-twisting needle. Such nano/microstructuring of Al provides a new physical insight for the interaction between OAM and materials, and it also offers an entirely new nano/microfabrication technique towards ultraviolet plasmonic devices.

Sub-nanosecond pulse generation in a microchip Nd:La0.15Gd0.85VO4 laser

A sub-nanosecond microchip laser was constructed using a Nd:La0.15Gd0.85VO4 with Cr4+:YAG saturable absorber. A single 880 ps pulse was recorded under an incident pump power of 4.91 W, corresponding to a repetition rate of 35 kHz. When the incident pump power exceeded 5 W, the system transferred a single picosecond pulse train into 0.9/1.1 ns two pulse train forms. The average output power increased from 108 mW to 130 mW, corresponding to a peak power decrease from 3.5 kW to ~1.8 kW, which might be utilized for laser pulse self-calibrations in time-of-flight distance measurements.

Microneedle structuring of Si(111) by irradiation with picosecond optical vortex pulses

We report on comparative studies of the optical vortex-induced structures of both Si(100) and Si(111) by irradiation with a single optical vortex picosecond pulse. Furthermore, we address the effects of the total angular momentum (TAM) on the optical vortex-induced microneedle. Si(111) allows for the faster growth of the microneedle, although this impacts the monocrystallization of the needle. The TAM then forces the melted silicon to spin axially, thereby yielding an efficient accumulation of melted silicon on the substrate for microneedle formation. These results provide new fundamental insights into the interactions between optical vortex fields and irradiated materials.

Investigation on the effects of laser parameters on the plasma profile of copper using picosecond laser induced plasma spectroscopy

Laser induced plasma generation and characterization, affected by laser parameters and sample physical properties, represent important phenomena in many fields of applications. In this work, we present new studies on the effects of an appropriate combination of laser wavelengths and pulse energies on the generated plasma characterization using a single shot picosecond Nd:YAG laser. The plasma plume of a pure copper sample has been generated by laser induced plasma spectroscopy (LIPS) using a single shot 170 ps laser pulse with wavelengths (266, 355, 532 and 1064 nm) and varying laser fluence (10–41 J/cm2). The spectral intensities of Cu I 324.75, 327.39, 515.32 and 521.82 nm have been observed. The plasma electron temperature and density have been determined from the Boltzmann plots and Stark-broadening profiles of the plasma spectral lines, respectively, assuming the local thermodynamic equilibrium (LTE) condition. It has been found that the electron temperature and electron density values increase from around 10,000 to 20,000 K and around 2 × 1017 to 1.5 × 1018 cm−3, respectively, with the increase in the laser wavelength and pulse fluence gradually. These observations can be understood due to the variations of mass-ablation rates, inverse-Bremsstrahlung, and photo-ionization with the studied pulse wavelength and pulse energy. The obtained results explore the opportunity to control specific generated plasma parameters by applying proper picosecond pulse parameters which can be considered in many fields of material science spectroscopic analysis and control the plasma interaction dynamics.

Effect of single pulsed picosecond and 100 nanosecond laser cleaning on surface morphology and welding quality of aluminium alloy

Removing the oxide film and dirt on the surface of the aluminium alloy can improve the welding quality of the aluminium alloy. In this paper, the characteristics of picosecond and 100 nanosecond pulsed laser cleaning aluminium alloys are explored by changing the average laser power, spot overlap ratio and scanning trajectory overlap rate. The results show that the oxide laser removal depth and diameter are related to the average power. As the average laser power increases, the depth and diameter of the ablation pit increase. At the same average power, the nanosecond laser ablation depth is greater than the picosecond laser. To achieve good surface quality, the nanosecond laser requires a higher overlap rate than the picosecond laser. The high overlap rate results in a nanosecond laser cleaning efficiency that is much lower than that of a picosecond laser. More importantly, the surface quality obtained by picosecond laser cleaning is much better than nanosecond laser cleaning. In addition, the welding experiment shows that the laser cleaning pre-treatment can effectively improve the welding quality.

Demonstration of a 2 ps, 5 TW peak power, long-wave infrared laser based on chirped-pulse amplification with mixed-isotope CO2 amplifiers

We report generation of 5 TW peak power in a 2 ps pulse at 9.2 µm via chirped-pulse amplification (CPA) in mixed-isotope high-pressure CO2 laser amplifiers. This represents the highest peak power in a single picosecond pulse format and the shortest pulse at terawatt peak power ever achieved in the long-wave infrared (LWIR) spectral range. Maximum demonstrated energy of the compressed pulse is 14 J and minimum period between shots is 20 s. The successful implementation of the chirped pulse amplification technique in a short-pulse gas laser opens a route to development of LWIR laser facilities with tens of terawatts of peak power, thus approaching the number of photons per optical cycle of current near-infrared laser systems based on solid-state active media.

Picosecond Pulse Generation by Second-Order Distributed Feedback Dye Laser

A Configuration of a second-order distributed feedback dye laser pumped by a nanosecond Nd:YAG laser is setup. The tuning range is narrower than that in the case of the first-order DFDL but lower noise and more stable is obtained. Single picoseconds pulse tunable in range of 543 to 596 nm can be observed by using different laser dyes. The tuning range is extended to the shorter wavelengths, which is closed to pumping wavelength.

Effect of laser wavelength on the thermal behavior of amorphous GST films irradiated by a single frequency-tripled picosecond laser

In this paper, the effect of laser wavelength on the thermal behavior of amorphous Ge2Sb2Te5 (a-GST) films induced by a frequency-tripled picosecond laser was carried out using 3D surface profile, SEM, TEM and Raman measurement. Melting thresholds of a-GST films with different wavelengths of 355 nm (3.5 mJ/cm2), 532 nm (28 mJ/cm2) and 1064 nm (22.3 mJ/cm2) were obtained, respectively. It showed that with the increase of wavelength from 355 to 532 and 1064 nm, pit morphologies and crystallization degree didn’t follow a monotonous relation, which were mainly affected by melting threshold, optical penetration depth as well as photon energy. TEM images demonstrated that 532 nm laser-treated samples got more complete crystallization than those 355 nm laser treated. Besides, for the remarkable discrepancy in optical penetration depth among the three laser wavelengths, the crystallization process of a-GST at 355 and 532 nm wavelengths performed with a surficial heating mode, different from that at 1064 nm wavelength with a body heating mode. The present study paves the way to achieve the big-data storage using different wavelengths.

Thermochemical writing with high spatial resolution on Ti films utilising picosecond laser

In this paper, we investigate the local oxidation of titanium thin films under the action of picosecond laser pulses. Periodical structures were recorded by the multi-beam interference scheme utilizing various numbers of laser beams, and the relationship between spatial resolution and the contrast of the structures was studied. The Raman spectra of the laser processing regions confirmed the oxidation even under the action of a single picosecond pulse. An analytical simulation of titanium film oxidation in the interference field was provided, and obtained results are correlated with the experimental data. The results of theoretical modeling show that the thermochemical effects of picosecond laser pulses allow recording periodic structures with a period of 0.65 lines per μm. The demonstrated results are important in the adaptation of technological laser systems for the manufacture of diffractive optical elements.

Pattern analysis of 532- and 1,064-nm picosecond-domain laser-induced immediate tissue reactions in ex vivo pigmented micropig skin

Optical pulses from picosecond lasers can be delivered to the skin as single, flat-top beams or fractionated beams using a beam splitter or microlens array (MLA). In this study, picosecond neodymium:yttrium aluminum garnet laser treatment using a single flat-top beam and an MLA-type beam at the wavelengths of 532 nm and 1,064 nm were delivered on ex vivo genotype-regulated, pigmented micropig skin. Skin specimens were obtained immediately after treatment and microscopically analyzed. Single flat-top beam treatment at a wavelength of 532 nm and a fluence of 0.05-J/cm2 reduced melanin pigments in epidermal keratinocytes and melanocytes, compared to untreated controls. Additionally, 0.1 J/cm2- and 1.3 J/cm2-fluenced laser treatment at 532 nm elicited noticeable vacuolation of keratinocytes and melanocytes within all epidermal layers. Single flat-top beam picosecond laser treatment at a wavelength of 1,064 nm and a fluence of 0.18 J/cm2 also reduced melanin pigments in keratinocytes and melanocytes. Treatment at 1,064-nm and fluences of 1.4 J/cm2 and 2.8 J/cm2 generated increasing degrees of vacuolated keratinocytes and melanocytes. Meanwhile, 532- and 1,064-nm MLA-type, picosecond laser treatment elicited fractionated zones of laser-induced micro-vacuolization in the epidermis and dermis. Therein, the sizes and degrees of tissue reactions differed according to wavelength, fluence, and distance between the microlens and skin.

Surface characteristics of alkaline earth boro-aluminosilicate glass following single picosecond laser pulse exposure at different focal positions

We investigated the surface characteristics of alkaline earth boro-aluminosilicate glass (EAGLE XG, Coring), which is used in display applications, irradiated by a high power picosecond (ps, 10−12 s) pulsed laser beam while varying the position of focal position in and out of the top and bottom surfaces of the glass and the irradiation fluence of laser beam. Upon the single shot exposure of a 10 ps pulsed laser at the wavelength of 1064 nm, we found that laser processing of this type of glass is possible only near the surfaces above the certain threshold fluence high enough to cause enough multiphoton absorption. The processing threshold values were found to be 11 ± 2 and 7.1 ± 1.4 J/cm2 for 3.0 and 5.0 μJ excitation pulse energies corresponding to the intensities of 3.3 × 1012 and 5.5 × 1012 W/cm2, respectively. The morphological changes on the surfaces due to a single shot laser processing occurred until the focal position moved away from the surfaces about 10 μm outside of the glass at 3.0 μJ of pulse energy, which is longer than Rayleigh length. The distance that focal position moved inside of the glass to provide enough nonlinear absorption for laser processing on the surface increased several times compared to the cases of focal position moved outside. The distance also increased with increasing the pulse energy to 5.0 μJ. It was also found that the top surface was processed mainly by ablation with no significant melting at this fluence range and the bottom surfaces suffered considerable thermal damage such as melting and resolidification while no processing occurred deep inside of the glass further away from both the top and the bottom surfaces as the focal position moved from the top to the bottom surfaces. We expect that most of absorption occurs near the surface when the focal position is near the top surface while more absorption occurs inside of glass before the laser beam reaches the bottom surface when the focal position is near the bottom surface. Our single shot exposure results inspire some important insights on application of laser processing by ps pulses on glass type materials.