Picosecond Laser Techniques Research Articles

Synergy of Nd:YAG Picosecond Pulsed Laser Irradiation and Electrochemical Anodization in the Formation of TiO2 Nanostructures for the Photocatalytic Degradation of Pesticide Carbofuran

This study proposes a simple and controlled method for producing TiO2 with phase junction, oxygen vacancies, and Ti3+ by combining picosecond pulsed laser irradiation and electrochemical anodization. Ti mesh was pretreated by irradiating with a picosecond pulsed laser technique using an Nd:YAG laser (1064 nm) at two fluencies, 15 J/cm2 and 30 J/cm2. The samples were then subjected to electrochemical anodization to form TiO2 nanotube arrays on the previously laser-treated surface. This study will investigate the possibility of forming TiO2 nanotube arrays on a pre-laser-treated Ti substrate and determine their physicochemical and photocatalytic properties. The samples were characterized by FESEM, XRD, Raman, XPS, and UV-Vis DRS. UV-Vis spectroscopy was used to observe the progress of photocatalytic degradation for all samples, and degradation products were determined using GC-MS. With the synergistic effects of phase junction, oxygen vacancies, and Ti3+, the laser-treated TiO2 with 30 J/cm2 showed a higher photocatalytic degradation rate (85.1%) of the pesticide carbofuran compared to non-laser-treated TiO2 (54.8%), remaining stable during successive degradation cycles, which has promising practical applications.

Micromachining of High-Quality PMN-PT/Epoxy 1-3 Composite for High-Frequency (>30 MHz) Ultrasonic Transducer Applications.

Fabricating PMN-PT composites, the core component of high-frequency (>30 MHz) transducers, remains challenging due to their poor machinability and ultra-small kerfs. This urgent problem is significantly impeding the development of PMN-PT ultrasonic transducers for use in clinical research, biomedical sciences, and nondestructive testing. In this study, high-quality PMN-0.3PT/epoxy 1-3 composites at 30 MHz and 50 MHz were manufactured using a modified picosecond (1.5 ps) laser technique. Their performance was thoroughly analyzed, which was comparable to that with low-stress dry plasma etching. There were fewer microcracks around PMN-PT pillars. The minimum kerf was less than 4.5 μm and the highest aspect ratio was larger than 7.5. The micro domain morphology and hysteresis loops of PMN-PT pillars further confirmed that composites still maintained excellent piezoelectric performance and suffered fewer damages during laser cutting. The characterization results exhibited a large electromechanical coupling (>0.77), a high dielectric constant (>1600), and a relatively low acoustic impedance (<17 Mrayls). The ultrasonic transducers with centre frequencies of 30 MHz and 50 MHz were designed and prototyped to validate the performance of composites. The transducers showed broad bandwidth (>80%), high two-way insertion loss (>-23 dB), and imaging resolution superior to 40 μm. Finally, the C-scan experiments of IC chips were also used to further illustrate the applicability of transducers. These encouraging results further demonstrated that ultrafast laser technology will bring more accessible and affordable methods for fabricating high-frequency PMN-PT composite transducers with excellent performance.

33527 What is the most effective picosecond laser protocol for tattoo removal? A comparative study by histopathologic review

Background: Picosecond lasers have become widely adapted as the mainstay of tattoo removal due to their faster heating of target chromophores and consequently more effective tattoo removal. Different protocols for tattoo removal using the picosecond laser are actively being studied. Our investigation focuses on the R20 method: repeated exposure to laser light at 20-minute intervals in a single session. Several preliminary studies have shown that R20 technique could be effective in reducing treatment time while maintaining efficacy. Objective: This study aims to compare different picosecond laser techniques in clearing tattoos. Methods and materials: Three patients with tattoos (1 on foot, 2 on arms) underwent skin biopsy followed by laser tattoo removal. The target site was divided into 4 areas, each of which received different protocols: picosecond laser alone, R20 method, picosecond MLA followed by picosecond toning, and picosecond laser after gel application. The protocols were all performed five times at 1-month intervals. After treatment completion, 1 patient underwent biopsy of all four treatment sites while the other 2 underwent biopsy only at the R20 treatment area. Results: Histopathologic evaluation showed that the R20 treatment site had the least remaining intradermal pigmentation. Picosecond MLA followed by picosecond toning laser was shown to have the following best outcome. Conclusion: Our report compares skin biopsy findings before and after laser treatment and clinical results for tattoo removal. Although the number of cases is small, our preliminary findings suggest that the Pico R20 is favorable for tattoo removal.

Enhanced flow boiling of HFE-7100 in picosecond laser fabricated copper microchannel heat sink

The enhanced flow boiling heat transfer of HFE-7100 in wavy copper microchannel heat sink was experimentally studied, which was fabricated with the picosecond laser technique. The micro porous structures were naturally formed on the sidewall and bottom of microchannel during the laser fabrication process, which increase the wall surface roughness. In single-phase flow region, the evaluation of performance evaluation criteria (PEC) proves the heat transfer enhancement overcomes the pressure-drop penalty in present wavy microchannel. In two-phase flow region, the flow patterns including bubbly flow, slug flow and annular flow were captured with the visualization technique, three heat transfer modes including heat convection, nucleate boiling and thin film evaporation were analyzed in detail. In wavy microchannel, the nucleate bubble on concave channel sidewall has a different apparent shape with a larger growth rate compared to that on convex one. In the thin film evaporation stage, the thickness of liquid film varies and it depends on the difference in curvatures between bubbles and sinusoidal channel sidewall. Compared to the straight channel, an increase of 28.89% for CHF can be achieved in wavy one, and the heat transfer coefficient enhancements of 60.76% and 52.71% are obtained in wavy one at the nucleate boiling stage and thin film evaporation stage, respectively.

Phonons induced by laser pulses for Brillouin scattering measurements

To overcome the problem of low intensity of Brillouin scattered light from thermal phonons, we stimulated the Brillouin scattering by inducing coherent phonons in a glass sample. To develop a completely noncontact measurement method, we induced phonons at 500–800 MHz by a picosecond pulse laser technique and studied how these affect the scattered light. Results show an increase in the intensity of scattered light if the stimulation with the pulse laser is performed. At a distance of 0.75 mm between the pulse laser and the probe laser, we were able to observe an increase of 34 times in the intensity of scattered light. By using a much smaller pulse length of the laser, we can expect stimulation in the GHz range in the future.

Phase Change Behavior of Sn20Sb80/Si Nano-Composite Multilayer Thin Films

Nano-composite multilayer Sn20Sb80/Si thin films were studied by thermal, electrical and optical methods. Compared with Sn20Sb80, Sn20Sb80/Si film was proved to be a more promising candidate for phase change memory device applications because of its higher crystallization temperature (246°C) and larger crystallization activation energy (2.6 eV). The bandgap was broadened with the increase of Si layer thickness. The crystallization of Sn20Sb80 was restrained after the adding of more Si film layers confirmed by X-ray diffraction patterns. A smoother surface was obtained with the root-mean-square surface roughness of 0.753 nm for [Sn20Sb80(3nm)/Si(7nm)]5 thin film. The measurement using the picosecond laser technique showed that [Sn20Sb80(3nm)/Si(7nm)]5 thin film could achieve the crystalline-to-amorphous phase transform within 2.8 ns irradiated by the laser pulse.

Acne Scar Successfully Treated with a Picosecond Laser and Subdermal Minimal Surgery Technique

Acne Scar Successfully Treated with a Picosecond Laser and Subdermal Minimal Surgery Technique

Investigating the effect of picosecond laser texturing on microstructure and biofunctionalization of titanium alloy

Laser processing technique has been an effective method to enhance the medical implant’s biocompatibility through forming specific textures on titanium alloy implant surface. In this paper, a 1064nm pulsed picosecond laser on TC4 titanium alloy implant samples was conducted to obtain optimal parameters for well-structured textures, controllable micro-grooves and improved osteoblast adhesion and proliferation. Picosecond laser technique is generally characterized by the high flexibility and advanced properties, which could make structural features including topography quality and detailed dimensions expediently improved and changed by adjusting laser processing parameters. To obtain the optimal laser processing parameters for desired microstructures, orthogonal experiments and related SEM, EDS and SPM analysis were conducted under various laser powers, repetition frequencies, scan speeds and scan numbers. Thus, the correlation between picosecond laser processing parameters and its corresponding microstructure feature of the micro-grooves was established. In addition, the immunofluorescence detection of cell actin cytoskeleton shows that structured textures can promote cell adhesion and play an important role in cell contact guidance.

Patterning of multilayer graphene on glass substrate by using ultraviolet picosecond laser pulses

This paper presents an approach that involves directly patterning multilayer graphene on a glass substrate by using ultraviolet picosecond (PS) laser irradiation. The PS laser is ultrafast, with a pulse duration of 15ps, and can be operated at a wavelength of 355nm. In this study, the multiple pulse ablation threshold fluence for patterning multilayer graphene was 5.2J/cm2, with a pulse repetition rate of 200kHz and at a fixed scanning speed of 250mm/s. The effect of laser parameters on the width, depth, and quality of patterning was explored. To investigate laser-nonablated and laser-ablated multilayer graphene, the characteristics of graphene thin film were measured using Raman, transmittance, and electrical analyses. The experimental results revealed that the PS laser is a promising and competitive tool for ablating multiple layers to several layers of graphene thin films and even for completely removing graphene thin-film layers. The PS laser technique can be useful in developing graphene-based devices. Moreover, this approach has the potential for industrial applications.

Improved phase change behavior of Sb2Se material by Si addition for phase change memory

Compared with Sb2Se, Si–Sb–Se material is proved to be a promising candidate for phase change memory (PCM) use because of its higher crystallization temperature (~230°C), larger crystallization activation energy (3.25eV), and better data retention ability (168°C for 10years). Furthermore, the fast crystallization time 3.30ns is obtained for Si0.20(Sb2Se)0.80 material by the picosecond laser technique. The set switching is realized with low threshold current 6.9μA and voltage 1.80V, respectively. The reverse resistance transition can be achieved by an electric pulse as short as 8ns for Si0.20(Sb2Se)0.80-based PCM cell.

Al19Sb54Se27 material for high stability and high-speed phase-change memory applications

In comparison to Sb2Se, Al19Sb54Se27 has a higher crystallization temperature, larger crystallization activation energy, better data retention and a wider energy band gap. X-ray diffractometry and X-ray photoelectron spectroscopy were employed to study the crystalline structure and chemical bonding state, respectively, of the elements in Al19Sb54Se27. The picosecond laser technique was used to measure the phase-change time of Al19Sb54Se27. Phase-change memory devices based on Al19Sb54Se27 thin films were fabricated to test and evaluate their electrical properties.

Organic photochemistry

More than one thousand photochemistry papers were published in the most cited twenty-four scientific journals in 2007. With nanosecond, picosecond, and femtosecond laser techniques widely applied, detection of reactive intermediates, products of chemical bond dissociation, isomerizations, rearrangements, as well as the initial results of intramolecular energy or electron transfer, become facile. Complex photoluminescence, DNA sequence-directed structure and dynamics studies, photopolymerization, and photocatalysis remain important topics. Because optical single-molecule detection, photoprobes, and photosensors have been increasingly applied in the chemical and biological sciences, these have received specific attention. The photochemistry of nanoparticles and nanostructures has also attracted much attention. Optical devices, photoswitches, and two-photon/multiphoton chemistry have been widely investigated. In this review, we briefly summarize major progress in the photochemical sciences and selected applications are discussed.

Transmission and reflection times of phonon packets propagating through superlattices.

We study theoretically the asymptotic phase times of phonon packets scattered off the single- and double-superlattice structures which act as opaque barriers for phonons analogous to potential barriers for electrons. The analytical expressions for the transmission and reflection times are derived. For the systems consisting of semiconductor superlattices of the size of 1000 \AA{} we find that the time advance or delay of the transmitted and reflected packets range from 10 ps for a single-superlattice structure to 1 ns at resonances for a double-superlattice structure. These effects should be observable in the phonon generation and detection experiments utilizing a picosecond laser technique.

Nonradiative relaxation and ionization of the F center in NaBr studied with picosecond optical pulses.

With a picosecond pump-probe laser technique the recovery of the ground-state population after optical excitation of the F center in NaBr is studied. Two decay components are observed, the fastest one dominating at low temperatures. Its time constant is interpreted as the lifetime of the relaxed excited state and is established to be 61 ns at 10 K. This value is perfectly consistent with the experimental emission efficiency and the expected radiative lifetime, provided that the nonradiative transition to the ground state is assumed to occur after the relaxed excited state is reached. Within the same assumptions a nonradiative lifetime of 27 ns at zero temperature is predicted for the F center in NaI. A theoretical expression for vibronic tunneling to the ground state from a thermalized excited state is applied to the F center in alkali halides and is shown to agree equally well with the experimental emission efficiencies as the Dexter-Klick-Russell criterion. The same expression also accounts for the strong temperature dependence of the nonradiative relaxation process observed in NaBr below 100 K. At higher temperatures an accurate analysis of the radiationless transition rate is encumbered by the influence of ionization on the lifetime of the excited state. The relative contribution of the second, much slower decay component increases rapidly above 70 K and is related to retrapping of electrons released by ionization of F and F centers. © 1992 The American Physical Society.

Quantitative Analysis of the Hemoglobin Oxygenation State of Rat Brain In Vivo by Picosecond Time-Resolved Spectrophotometry

Through the use of a picosecond laser pulse of near-infrared light at 1,064 nm, the temporal profile of the transmitted light through the anesthetized rat head has been investigated. The light intensity at a certain time after the input pulse was exponentially attenuated by the hemoglobin concentration with hematocrit values from 1.5 to 50%, although the transmitted pulse broadened markedly due to scattering by the cerebral tissue. The optical pathlength, which is required for quantitation of the absolute absorbance change, was directly determined, by the time of flight measurement of the light pulses, as the product of the velocity of light in tissue and time. The mean concentration of hemoglobin in the brain could be determined quantitatively by the use of this pathlength. The oxygen saturation of venous blood determined by our time of flight measurement was very close to that in the internal jugular vein determined directly with a gas analyzer. Thus, the picosecond laser technique is useful for quantifying the blood oxygenation in tissues.

Time-resolved relaxation of one- and two-vibron states in the rubidium perchlorate crystal

The vibrational relaxation times of the ν 2 fundamental mode and the {2ν 2 + ν 1} = [Ω − + Ω +] Fermi doublet of the ClO the rubidium perchlorate crystal are investigated as a function of temperature between 7 and 300 K using high repetition-rate time-resolved picosecond laser techniques. The results show that the neighboring Ω − and Ω + transitions relax predominantly by up-conversion to the higher ν 3 level via scattering of a single lattice phonon, whereas the ν 2 state mainly decays to the relatively more distance upper ν 4 level by scattering of two lattice phonons.

Investigation of the pulse characteristics of fast-response photodetecting apparatus by using continuous laser with mode synchronization

At the present time only semiconductor lasers [i] are utilized extensively for the metrological certification of broadband photodetection apparatus (PDA) in pulse and energetic photometry. Among their disadvantages should be generation in a narrow spectrum band in the near IR of the spectrum range and dependence of the radiation spectrum on the temperature, low peak power and complexity of formation of pulses of picosecond duration, inhomogeneity of the directivity pattern, and subjectivity to degradation of the semiconducting radiation structures during exploitation. The development of new broadband PDA requires the production of highly stable sources of 6-pulses of picosecond duration, generating in broad spectrum and dynamic bands. This problem can be solved successfully on the basis of continuous lasers (ionic, YAG:Nd ~§ organic dyes, coloring centers) operating in the mode synchronization (MS) regime with frequency regulatable selection of single pulses [2]. Nevertheless, despite the significant progress in the domain of picosecond laser technique, the utilization of continuous lasers with MS for pulse photometry has still not been utilized extensively.

Picosecond dynamics of barrier crossing in solution: A study of the conformational change of excited state 1,1′-binaphthyl

The rates of optically induced conformational changes of excited state 1,1′-binaphthyl in a series of alcohol solvents were measured by a picosecond laser technique. Excellent agreement with experiment is found for the Kramers model for both the intermediate and high friction regimes using a frequency independent friction coefficient evaluated from classical hydrodynamics. This is the first observation of Kramers behavior in the intermediate friction regime and indicates that deviations from Kramers behavior is not a universal phenomenon in the conformational dynamics of flexible molecules in solution. It also emphasizes the possibility that the observed deviations from the Kramers model can be due to effects other than non-Markovian friction.

Radiationless decay of the second excited singlet states of aromatic thiones: Experimental verification of the energy gap law

Abstract S2 → S0 fluorescence quantum yields and S2 lifetimes of eight aromatic thiones in inert perfluoroalkane solutions at room temperature have been measured using picosecond laser techniques. Photostable, structurally rigid thiones undergo S2 → S1 internal conversion at rates consistent with the energy gap law of radiationless transitions. An average electronic coupling matrix element of 1.9 × 102 cm−1 is found.

Picosecond laser spectroscopy of chromium(III) complexes. Probing the photophysics of 4T 2 excited states of Cr(bpy) 33+ and Cr(4,7-Me 2phen) 33+ ions in aqueous solution

Picosecond laser techniques have been used to probe the photophysics of the short-lived 4T 2 excited states of Cr(bpy) 3 3+ and Cr(4,7-Me 2phen) 3 3+ complexes (bpy is 2,2′-bipyridine and 4,7-Me 2phen is 4,7- dimethylphenanthroline). Contrary to the previously reported value of the lifetime of ( 4T 2)Cr(bpy) 3 3+ (≈10 ps) obtained from resonance Ramans studies(3.2 ns laser pulse), luminescence and time-resolved absorption spectroscopy using mode-locked Nd : YAG laser pulses of 30 ps (fwhm) indicate that the lifetime of these quartet states is ≈10–20 ns.