Combined Pulsed Laser Research Articles

Dynamic characterization of plasma and combustion wave interactions during millisecond-nanosecond combined laser-induced enhanced damage on fused silica

Fused silica, which is widely used in optical systems, limits the load capacity of the optical system when it is damaged by laser irradiation. In this paper, a combined millisecond-nanosecond pulsed laser induced triple combustion wave dynamics model for fused silica generation is developed. The relationship between pulse delay and the dynamic propagation of plasma and combustion waves induced by combined laser-induced fused silica was studied from three aspects: theory, simulation, and experiment. The results show that the energy deposition of the nanosecond laser injects energy into the dilute plasma, which increases the speed of the double-burning wave to form a triple-burning wave. In addition, it was found that the combined effect of viscous shear between the plasma plume and the air exacerbates the degree of imbalance in the Knudsen layer instantaneously releasing pressure and increasing the complexity of plasma and combustion wave propagation, recoil pressure produces a more complex crack network on the fused silica surface. The results provide a better understanding of the propagation properties of plasma and triple-burning waves during combined millisecond-nanosecond induced fused silica damage.

Study on the influence of side-blown airflow velocities on plasma and combustion wave generated from fused silica induced by combined pulse laser

This study examines the impact of variations in side-blowing airflow velocity on plasma generation, combustion wave propagation mechanisms, and surface damage in fused silica induced by a combined millisecond-nanosecond pulsed laser. The airflow rate and pulse delay are the main experimental variables. The evolution of plasma motion was recorded using ultrafast time-resolved optical shadowing. The experimental results demonstrate that the expansion velocities of the plasma and combustion wave are influenced differently by the side-blowing airflow at different airflow rates (0.2 Ma, 0.4 Ma, and 0.6 Ma). As the flow rate of the side-blow air stream increases, the initial expansion velocities of the plasma and combustion wave gradually decrease, and the side-blow air stream increasingly suppresses the plasma. It is important to note that the target vapor is always formed and ionized into plasma during the combined pulse laser action. Therefore, the side-blown airflow alone cannot completely clear the plasma. Depending on the delay conditions, the pressure of the side-blowing airflow, the influence of inverse Bremsstrahlung radiation absorption and target surface absorption mechanisms can lead to a phenomenon known as the double combustion waves when using a nanosecond pulse laser. Both simulation and experimental results are consistent, indicating the potential for further exploration of fused silica targets in the laser field.

248 Functional and psychological outcomes of combined pulsed dye laser and fractional carbon dioxide laser treatment for scars in pediatric patients

Scars can manifest with cosmetic disfigurement, functional impairment, and discomfort which can be particularly impactful in children and adolescents. Laser therapy has been recently developed as a useful modality to improve both the appearance of scars and the functional status of patients. Our study aims to determine an association between ratings of blind evaluators and patient reported outcomes in pediatric scar patients pre- and post-treatment with combined pulsed dye laser (PDL) and fractional carbon dioxide (CO2) laser therapy.

The effectiveness of long Pulsed Nd:YAG Laser alone for treatment of keloids and hypertrophic scars versus its combination with bleomycin.

Pathological scars are benign hyper-proliferative growths of dermal collagen that causes severe psychological and physical problems. This study was performed to assess and compare safety and clinical efficiency of combined pulsed Nd-YAG laser and intralesional bleomycin versus pulsed Nd-YAG laser alone to treat the hypertrophic scars and keloids. Randomly, 40 patients with hypertrophic scars or keloids were divided into two groups A and B. Group A were handled by pulsed Nd:YAG laser and intralesional bleomycin while group B were handled by pulsed Nd:YAG laser only. Response was assessed subjectively by clinical imaging and modified Vancouver Scar Scale (mVSS). While for objective evaluation, skin biopsies were taken from volunteer patients before and after treatment, and were examined by Hematoxylin and eosin staining (H&E) and Masson trichrome staining. Our study demonstrated almost complete improvement in 4 (20%) patients, partial improvement in 16 (80%) patients and 0 patient with no improvement in group A. Furthermore, in group B, we demonstrated almost complete improvement in 2 (10%) patients, partial in 14 (70%) patients and no improvement in 4 (20%) patients. Modified Vancouver Scar Scale reduced from 10.15 to 3.5 in group A and from 11.05 to 4.95 in group B. Elastica Masson-Goldner staining and Hematoxylin and eosin staining showed that treatment in both groups structurally changed tissue collagen. Long-pulsed Nd-YAG laser combined with intralesional bleomycin could be a promising way for treatment of keloids or hypertrophic scars.

Evolution of compressive mechanical properties of early hypertrophic scar during laser treatment

Laser therapy has been widely used in the treatment of hypertrophic scars (HPS), but whether the mechanical properties of HPS tissue after laser treatment can be restored to those of normal skin remains unclear. In this paper, the relationship between the evolution of compressive mechanical properties and histological changes of HPS tissues following three successive combined pulsed dye laser (PDL) and fractional CO2 laser (CO2) treatments was investigated by compression tests and histological analysis. The early HPS model of rabbit ear was established by CO2 laser ablation. The loading–unloading tests and strain creep tests under the compression forces of 1 N, 2 N, and 3 N were carried out for normal skin, untreated HPS and HPS after different treatment times, respectively. The results showed that the compression ratio λ of all tissues revealed force dependence and rose with the increasing compression force, which was similar to the trend of most biological soft tissues. The histological changes of HPSs following laser treatment have a significant influence on the compressive mechanical response. Compared with the normal skin, the toughness and anti-deformation ability of HPS reduced due to the proliferation of collagen fibers and the destruction of elastic fibers, resulting in higher energy dissipation, compression ratio λ, and stable creep rate D, and lower elastic modulus. After three successive combined PDL/ CO2 laser treatments, the compressive mechanical properties and creep properties of HPS gradually approached that of the normal skin owing to the gradual restoration of the amount and distribution of collagen and elastic fibers in HPS. The results provide a new method for evaluating the clinical efficacy of laser therapy for treatment of HPS tissue.

Synthesis and Characterization of Cu2ZnSnS4 Thin Films Obtained by Combined Magnetron Sputtering and Pulsed Laser Deposition.

Cu2ZnSnS4 (CZTS) is a complex quaternary material, and obtaining a single-phase CZTS with no secondary phases is known to be challenging and dependent on the production technique. This work involves the synthesis and characterization of CZTS absorber layers for solar cells. Thin films were deposited on Si and glass substrates by a combined magnetron sputtering (MS) and pulsed laser deposition (PLD) hybrid system, followed by annealing without and with sulfur powder at 500 °C under argon (Ar) flow. Three different Cu2S, SnS2, and ZnS targets were used each time, employing a different target for PLD and the two others for MS. The effect of the different target arrangements and the role of annealing and/or sulfurization treatment were investigated. The characterization of the absorber films was performed by grazing incidence X-ray diffraction (GIXRD), X-ray reflectometry (XRR), Raman spectroscopy, scanning electron microscopy, and regular transmission spectroscopy. The film with ZnS deposited by PLD and SnS2 and Cu2S by MS was found to be the best for obtaining a single CZTS phase, with uniform surface morphology, a nearly stoichiometric composition, and an optimal band gap of 1.40 eV. These results show that a new method that combines the advantages of both MS and PLD techniques was successfully used to obtain single-phase Cu2ZnSnS4 films for solar cell applications.

Laser Speckle Contrast Imaging for the Objective Assessment of Blood Perfusion in Keloids Treated With Dual-Wavelength Laser Therapy.

Most of the widely used methods for the assessment of keloid treatment are subjective grading scales based on the opinion of an individual clinician or patient. There is a growing need for objective methods to evaluate keloid treatment. This study aimed to evaluate the value of laser speckle contrast imaging (LSCI) as an objective method for the assessment of dual-wavelength laser therapy for keloids. This prospective study included 21 patients with 54 keloids. All patients were treated with a combined 585-nm pulsed dye laser and 1,064 nm neodymium-doped yttrium aluminum garnet dual-wavelength laser at 4 weeks to 6 weeks intervals. Keloids were assessed using the Vancouver Scar Scale (VSS) and LSCI. The total VSS score significantly decreased after 4 sessions of treatment (p < .05). Blood perfusion in keloids as measured by LSCI was significantly reduced after treatment (p < .05). The improvement of chest keloids in terms of the total VSS score and blood perfusion was significantly greater than that of scapular keloids (p < .05). There was a positive correlation between decreased perfusion and reduced total VSS score (R2 = 0.84). Blood perfusion in keloids significantly decreased after dual-wavelength laser therapy. Laser speckle contrast imaging is a promising objective method for assessing the improvement of keloids treated with laser therapy.

Effects of combined Pulsed Dye Laser and Fractional CO2 Laser treatment of burn scars and correlation with plasma levels of collagen type I, MMP-2 and TIMP-1

Hypertrophic burn scars remain a significant burden for patients and a challenge for clinicians. The aimAssessement of the efficacy of combined Pulsed Dye Laser and Ablative Fractional CO2 Laser therapy on hyperthophic scars and correlation with plasma levels of MMP-2, TIMP-1 and alpha-1 type I collagen. Patients and methodsTwenty five pediatric subjects were enrolled into the study. Control group consisted of age-matched subjects admitted for surgical repair of inguinal hernia. For the assessment of the results of laser treatment we used the Vancouver scar scale (VSS), and Patient-Observer Scar Assessment Scale (POSAS). We also correlated clinical results with plasma levels of MMP-2, TIMP-1 and alpha-1 type I collagen. ResultsAll subjects reported the laser treatment resulted in improvement and were somewhat satisfied or very satisfied with their experience. No adverse events were reported. The levels of MMP-2, TIMP-1 and alpha-1 type I collagen in our patients with scars before laser threatment were higher in comparison to controls. We also found statistically significant decrease in the levels of MMP-2, TIMP-1 and alpha-1 type I collagen after laser treatment of burn scars ConclusionsOur study clearly shows that combined CO2-AFL treatment for burn scars improve texture, colour, function and alleviate pruritus. We believe that decrease in the levels of MMP-2, TIMP-1 and alpha-1 type I collagen after laser treatment of burn scars, reflects reduced dynamic of scar.

Stearic Acid/Layered Double Hydroxides Composite Thin Films Deposited by Combined Laser Techniques.

We report on the investigation of stearic acid-layered double hydroxide (LDH) composite films, with controlled wettability capabilities, deposited by a combined pulsed laser deposition (PLD)-matrix-assisted pulsed laser evaporation (MAPLE) system. Two pulsed lasers working in IR or UV were used for experiments, allowing the use of proper deposition parameters (wavelength, laser fluence, repetition rate) for each organic and inorganic component material. We have studied the time stability and wettability properties of the films and we have seen that the morphology of the surface has a low effect on the wettability of the surfaces. The obtained composite films consist in stearic acid aggregates in LDH structure, exhibiting a shift to hydrophobicity after 36 months of storage.

The Effectiveness of Early Combined CO2 Ablative Fractional Laser and 595-nm Pulsed Dye Laser Treatment After Scar Revision.

Scars are significant complications of wound healing and associated with negative physical, psychological, and cosmetic effects. Scar revision and laser treatment have been used over the past century to improve many different types of scars. Here, we evaluated the effectiveness of early combined carbon dioxide ablative fractional laser (AFL) and pulsed dye laser (PDL) treatment after scar revision. Fourteen patients who underwent scar revision were enrolled. All patients were treated with both a 10,600-nm AFL and a 595-nm PDL commencing 2 weeks after scar revision and continuing at 4-week intervals for a total of 4 treatments. Vancouver Scar Scale scores were evaluated before treatment and 5 months after the final treatment. All Vancouver Scar Scale scores improved significantly except that of scar height. We encountered no adverse complications (wound disruption, or hyper- or hypopigmentation) during follow-up. Early combined carbon dioxide AFL and PDL treatment after scar revision effectively and safely minimized scar formation.

Combined pulsed laser drilling of metal by continuous wave laser and nanosecond pulse train

In this paper, a new form of combined pulsed laser (CPL) consisting of continuous wave (CW) laser and nanosecond (ns) pulse train was proposed for drilling Q235B steel without high-pressure gas jet. The average power of CW laser ranged from 100 to 700 W, while the average power of the ns laser was fixed at 12 W. The experiments were carried out to study the influence of the average CW laser power on the drilling efficiency and quality of CPL. The results show that there were two completely different matching mechanisms between the CW laser and ns pulse train. Firstly, during the CPL drilling with the 100-200 W CW laser, the ns pulse train could be used to timely and periodically eject the central part of the molten metal, leaving a recast layer with a thickness of up to 200 μm. In addition, for the CPL drilling with the 550 W CW laser, a little part of molten metal was continuously ejected by the ns pulse train, and all of the remaining molten metal could be removed by the boiling of molten metal, thus leaving a recast layer with thickness less than 10 μm. The new CPL presented in this paper has an important guiding significance for improving the quality and making full use of the high efficiency of CW laser drilling.

Hybrid CdS nanowires/Si heterostructure photodetector fabricated by intense pulsed light assisted - laser ablation in liquid

Synthesis of CdS nanowires NWs by combined intense pulsed light (IPL) and pulsed laser ablation in liquid is demonstrated for the first time. An IPL source providing 3 ms duration pulses was used to assist the synthesis of CdS nanowires by 7 ns pulsed laser ablation of cadmium target in thiourea and CTAB solution. The results showed a small increase in optical energy band gap of CdS NWs and a decrease of the nanowires diameter from 50 to 40 nm after combining the IPL. The intensity of the photoluminescence emission peak located at 458 nm was doubled when the IPL combined laser ablation process. In addition the synthesized CdS nanowires showed single crystalline pure hexagonal wurtzite phase with decreased particles agglomeration and smaller particle size. Raman spectra were improved too by revealing sharp and shifted peaks at 293 and 585 cm−1. The figures of merit of hybrid n-CdSNWs/p-Si heterojunction photodetector namely responsivity and minority carrier lifetime were found to be improved remarkably after using IPL assisted laser ablation.

Thin WBx and WyTi1−yBx films deposited by combined magnetron sputtering and pulsed laser deposition technique

The coatings of tungsten borides (WBx) and tungsten borides doped with titanium (WyTi1−yBx) were deposited by using combined magnetron sputtering - pulsed laser deposition technique. In the case of WBx coatings, pure tungsten target was evaporated by a laser pulse at 1064 nm wavelength and pure boron target was sputtered by a magnetron. In the case of WyTi1−yBx coatings, the W2B5 target was sputtered by the magnetron and titanium target was evaporated by the laser pulse at 1064 nm wavelength. The content of titanium dopant changed from 1.1 to 5.5 at.%. The microstructure, chemical and phase composition of deposited coatings were investigated by means of Scanning Electron Microscopy, Energy Dispersive X-Ray Spectroscopy, X-Ray Photoelectron Spectroscopy and X-Ray Diffractometry, respectively. The Vickers hardness and Young's modulus were determined by using the nanoindentation test. Nanocrystalline WB coatings with dominant WB2 phase were obtained at a substrate temperature of 520 °C. The coatings were superhard with a hardness of 47–50 GPa and the mean value of surface roughness was <6 nm. The WBx coatings doped with 5.5 at.% Ti had hardness similar to the coatings sputtered by magnetron from W2B5 target.

Acoustic emission during the millisecond laser-optical glass interaction assisted by the nanosecond laser

A hydrophone is used to detect the acoustic emission for the combined pulsed laser (CPL)-BK7 glass interaction. The CPL is composed of a nanosecond (ns) laser and a millisecond (ms) laser, which are separated with a certain period of time. Owing to the material defects affected mechanism, fluctuations are observed for the transmission time and the intensity of the acoustic emission during the ns laser interaction period. A weak and a strong acoustic emissions with spectrums dominated in the ranges of 10kHz∼60kHz and less than 8kHz, respectively, are detected during the remaining millisecond laser irradiation period. The two different behaviors of the acoustic emission are analyzed together with the evolution of the plume emission captured by the high speed camera during the laser irradiation and the ablated morphology on the sample. Results show that the high-frequency acoustic signal arises from a weak interaction process that a short lifetime plume emission and a shallow pit at the sample surface are observed. While the low-frequency acoustic signal is associated with a strong interaction process that an intense plume emission and a conical shaped cavity are detected. The consistent behaviors for the acoustic emission, the plume emission and the ablated size in dependence on the delay make the acoustic signal detection a reliable method in monitoring the CPL-BK7 glass interaction process and estimating the ablation results.

Treatment of recalcitrant port-wine stains (PWS) using a combined pulsed dye laser (PDL) and radiofrequency (RF) energy device

Pulsed dye laser (PDL) is the treatment of choice for port-wine stains (PWS). Some PWS are recalcitrant to this modality. A number of reasons for PDL treatment resistance have been described, including inadequate heat generation. We evaluated PDL combined with radiofrequency (RF) energy into a single device to target larger and deeper blood vessels and overcome PDL resistance. This was an open-label, prospective, single-center investigation of a novel device combining RF energy with PDL conducted to treat recalcitrant PWS. Ten patients with 11 recalcitrant PWS were enrolled. Each PWS was divided into 5 treatment areas: PDL alone, RF alone, PDL+RF, RF+PDL, and untreated control. Patients underwent a maximum of 6 treatments, scheduled 4 to 6weeks apart with follow-up evaluation at 4 and 12weeks after the final treatment. Colorimetry and standardized digital photography were performed at all visits. Lesional biopsy specimens were collected for selected patients. Areas treated with RF followed by PDL and PDL followed by RF showed the greatest improvement based on blinded review of digital photographs, reaching statistical significance (P value<.05) at the 12-week follow-up evaluation when compared with baseline. Adverse events, including purpura, erythema, edema, scabbing, crusting, and blistering, resolved without sequelae; a small residual scar was noted in 1 patient. Small sample size and short follow-up period are limitations. Combined RF/PDL technology is promising for the treatment of recalcitrant PWS.

Microscopic charge carrier lifetime in silicon from a transient approach

We present an experimental approach to determine the charge carrier lifetime in silicon based on the measured transient decay of the emitted photoluminescence intensity, requiring only a crystal volume of 50 μm in diameter. This becomes feasible by a combination of the time correlated single photon counting technique and confocal microscopy. Using combined pulsed and pulse train laser excitation, we obtain a self-consistent charge carrier lifetime in a high dynamic range from 100 ns to ms and an injection range from 1010 cm−3 to high injection densities. An iterative data evaluation routine incorporates all effects induced by the spatially non-homogeneous charge carrier generation.

Temperature dependent exchange bias training effect in single-crystalline BiFeO3/Co bilayers

Single-crystalline BiFeO3 (BFO)/Co bilayers were prepared by combined pulsed laser deposition and magnetron sputtering on (001) SrTiO3 substrates. Exchange bias (EB) and accompanying training effect have been studied as a function of temperature (T) between 5 K and 300 K. A non-monotonic exchange field variation with sharp increase below 100 K has been observed. In the meanwhile, strong training effect was recorded when T &amp;lt; 100 K and it weakens monotonically with increasing T up to 300 K. These temperature dependent EB and training effect may be caused by the uncompensated spins in both the interfacial spin-glass (SG) phase at low temperature and the antiferromagnetic BFO layer at higher temperature. The low temperature EB training results can be well fitted by a modified Binek's model considering asymmetric changes of the pinning SG spins at the descending and the ascending branches.

Plaque-Type Glomuvenous Malformations Successfully Treated Using Combined Pulsed Dye Laser and Neodymium-Doped Yttrium Aluminum Garnet Laser

Plaque-Type Glomuvenous Malformations Successfully Treated Using Combined Pulsed Dye Laser and Neodymium-Doped Yttrium Aluminum Garnet Laser

Keloid scars in type VI skin successfully treated with combined surgery and pulsed dye laser therapy

Keloid scars in type VI skin successfully treated with combined surgery and pulsed dye laser therapy

Active coherent beam combining of a five-element, 800 W nanosecond fiber amplifier array

Coherent beam combining of an 800 W nanosecond single-frequency fiber amplifier array has been demonstrated. Five high-power all-fiberized Yb-fiber amplifiers were tiled into a crisscross array, and the laser beams were actively phase-locked by using the stochastic parallel gradient descent algorithm. The contrast of the far-field intensity pattern of the combined beam was more than 91.6%. The combined pulsed laser has a pulse width of ~3.5 ns and a peak power of 21.5 kW.