scholarly journals Laser-induced jetting and controlled droplet formation

2016 ◽  
Vol 3 (1) ◽  
Author(s):  
Mihail Lucian Pascu ◽  
Ionut Relu Andrei ◽  
Jean-Pierre Delville
Keyword(s):  
Laser Pulse ◽  
Beam Energy ◽  
High Speed ◽  
Laser Excitation ◽  
Single Mother ◽  
General Context ◽  
Shape Evolution ◽  
Geometrical Symmetry ◽  
Jet Printing ◽  
532 Nm

AbstractThe article reports, in the general context of developing techniques to generate microjets, nanojets and even individual nanodroplets, a new method to obtain such formations by interaction of a single laser pulse at 532 nm with an individual/single mother droplet in pendant position in open air. The beam energy per pulse is varied between 0.25 and 1 mJ, the focus diameter is 90 μm, and the droplet’s volumes are either 3 μl or 3.5 μl. Droplet’s shape evolution and jet emission at impact with laser pulse was visualised with a high speed camera working at 10 kfps. Reproducible jets and/or separated microdroplets and nanodroplets are obtained which shows potential for applications in particular in jet printing. It is demonstrated that it becomes possible to play with the geometrical symmetry of both laser excitation and liquid in order to manage the number and the orientation of an induced microjet and consequently to actuate the orientation and the production of nanodroplets by light.

Nonlinear optical properties of colloidal carbon nanoparticles: nanodiamonds and carbon dots

RSC Advances ◽  
2014 ◽  
Vol 4 (76) ◽  
pp. 40152-40160 ◽  
Author(s):  
Irene Papagiannouli ◽  
Athanasios B. Bourlinos ◽  
Aristides Bakandritsos ◽  
Stelios Couris
Keyword(s):  
Optical Properties ◽  
Carbon Dots ◽  
Carbon Nanoparticles ◽  
Nonlinear Optical ◽  
Laser Excitation ◽  
Optical Limiting ◽  
Nonlinear Optical Properties ◽  
Nlo Response ◽  
Colloidal Carbon ◽  
532 Nm

Nanodiamonds (NDs) and carbon-dots (CDs) suspensions exhibit significant NLO response under both ps and ns laser excitation. NDs exhibit important optical limiting action under nanosecond visible (532 nm) and infrared (1064 nm) laser excitation.

Spectrochemical Analysis of Liquids Using Laser-Induced Plasma Emissions: Effects of Laser Wavelength

1997 ◽  
Vol 51 (1) ◽  
pp. 87-91 ◽  
Author(s):  
W. F. Ho ◽  
C. W. Ng ◽  
N. H. Cheung
Keyword(s):  
Laser Pulse ◽  
Signal To Noise Ratio ◽  
Laser Wavelength ◽  
Spectrochemical Analysis ◽  
Liquid Jets ◽  
Single Shot ◽  
Transient Nature ◽  
Vapor Plume ◽  
193 Nm ◽  
532 Nm

The plasma plume emissions produced by pulsed (∼ 10 ns) laser ablation of liquid jets were monitored for spectrochemical analysis. Laser wavelengths at 532 and 193 nm were used, and sodium was the test analyte. As expected, the 532-nm laser pulse produced very intense plasma continuum emissions that masked the sodium signal for the first hundred nanoseconds, especially near the bright core of the vapor plume. Neither time-gating nor spatial masking could significantly improve the single-shot signal-to-noise ratio, since the transient nature of the emissions placed stringent demands on timing precision while the small size of the plume required accurate mask positioning—both antithetical to the inherent instability of jet ablation. In sharp contrast, the 193-nm laser pulse produced relatively dim plasma flash but intense sodium emissions, rendering it ideal for analytical applications.

Experiment Research of Laser Induced Air Breakdown

2014 ◽  
Vol 599-601 ◽  
pp. 201-204
Author(s):  
Hai Dong Wu
Keyword(s):  
Energy Conversion ◽  
High Speed ◽  
Laser Excitation ◽  
Laser Energy ◽  
Ionization Process ◽  
High Speed Camera ◽  
Experiment Research ◽  
Sound Energy ◽  
Air Breakdown

The principle of laser induced air breakdown was introduced. The laser energy conversion in ionization process was studied. The phenomenon of laser induced air breakdown was observed by using high speed camera. It was found that a higher laser energy induced more laser energy to transfer into light and sound energy. The plasma reached maximum in shape in about 20 to 30 ns after laser excitation, and disappeared in about 16μs.

scholarly journals Droplet Impact on Suspended Metallic Meshes: Effects of Wettability, Reynolds and Weber Numbers

Fluids ◽  
2020 ◽  
Vol 5 (2) ◽  
pp. 81 ◽  
Author(s):  
Konstantinos Vontas ◽  
Cristina Boscariol ◽  
Manolia Andredaki ◽  
Anastasios Georgoulas ◽  
Cyril Crua ◽  
...  
Keyword(s):  
General Context ◽  
Liquid Penetration ◽  
Droplet Impingement ◽  
Textile Design ◽  
Lower Viscosity ◽  
Wide Range ◽  
Jet Printing ◽  
Break Up ◽  
Metallic Meshes ◽  
The Impact

Liquid penetration analysis in porous media is of great importance in a wide range of applications such as ink jet printing technology, painting and textile design. This article presents an investigation of droplet impingement onto metallic meshes, aiming to provide insights by identifying and quantifying impact characteristics that are difficult to measure experimentally. For this purpose, an enhanced Volume-Of-Fluid (VOF) numerical simulation framework is utilised, previously developed in the general context of the OpenFOAM CFD Toolbox. Droplet impacts on metallic meshes are performed both experimentally and numerically with satisfactory degree of agreement. From the experimental investigation three main outcomes are observed—deposition, partial imbibition, and penetration. The penetration into suspended meshes leads to spectacular multiple jetting below the mesh. A higher amount of liquid penetration is linked to higher impact velocity, lower viscosity and larger pore size dimension. An estimation of the liquid penetration is given in order to evaluate the impregnation properties of the meshes. From the parametric analysis it is shown that liquid viscosity affects the adhesion characteristics of the drops significantly, whereas droplet break-up after the impact is mostly controlled by surface tension. Additionally, wettability characteristics are found to play an important role in both liquid penetration and droplet break-up below the mesh.

Effects of Liquid Viscosity on Laser-Induced Shock Dynamics

2019 ◽  
Author(s):  
Hiroki Kurahara ◽  
Keita Ando
Keyword(s):  
Pulse Laser ◽  
High Speed ◽  
Water Solution ◽  
Plasma Pressure ◽  
Rapid Expansion ◽  
Glycerol Concentration ◽  
Glycerol Water ◽  
Initial Plasma ◽  
Front Position ◽  
532 Nm

Abstract We experimentally study the effects of viscosity on laser-induced shockwave in glycerol-water solution. A shockwave is generated through rapid expansion of plasma, which is induced by focusing a 6 ns pulse laser (532 nm) of energy fixed at 1.66 ± 0.22 mJ into 80, 90, 100 wt% glycerol-water solution. The shockwave propagation is recorded by an ultra-high-speed camera taken at 100 Mfps together with a pulse laser stroboscope. The photographs are used to determine the shock front position as a function of time, which allows for calculating the shock pressure according to the stiffened-gas type Rankine-Hugoniot relation. It turns out that the initial plasma pressure is reduced by having higher glycerol concentration (i.e., higher viscosity); therefore, wave steepening effect is deemphasized, resulting in a smaller decay rate.

scholarly journals Multiphoton Ionization Mass Spectrometric (MPIMS) Study of Phenol: Mechanism of Ionic Fragment Formation

1983 ◽  
Vol 3 (1-6) ◽  
pp. 29-47 ◽  
Author(s):  
R. S. Pandolfi ◽  
D. A. Gobeli ◽  
Jonathan Lurie ◽  
M. A. El-Sayed
Keyword(s):  
Laser Pulse ◽  
Energy Levels ◽  
Multiphoton Ionization ◽  
Pulsed Laser ◽  
Ionic Species ◽  
Low Energy ◽  
Ionization Mass ◽  
Fragmentation Pattern ◽  
Dissociation Channel ◽  
532 Nm

Time of flight (TOF) mass spectrometry is used in conjunction with a variable repelling voltage technique to elucidate the mechanism by which phenol ionizes and dissociates under 266 nm pulsed laser irradiation in combination with a 532 nm or 355 nm pulsed laser. The results suggest that, like benzene, the molecular ion is the predominant precursor of all ionic species generated in the process. Predominance of C5Hx+ species at relatively low powers confirms the presence of a low energy dissociation channel involving the elimination of CO. The use of a second laser at 532 nm is found to selectively destroy the C5Hx+ (as compared to the parent ion) species. The parent ion is found to be protected from the radiation of the second laser pulse at 532 nm but not at 355 nm if the second laser pulse is delayed by 50 ns. This is explained in terms of relaxation within the parent ion energy levels, the location of a low energy dissociation channel and the wavelengths of the lasers used. The main aspects of the fragmentation pattern are discussed in terms of the statistical theory of Rebentrost and Ben-Shaul.

Characterization of Laser Cleaning of Copper for Soldering Processes

2000 ◽  
Vol 123 (3) ◽  
pp. 521-527 ◽  
Author(s):  
J. M. Lee ◽  
K. G. Watkins ◽  
W. M. Steen
Keyword(s):  
Laser Pulse ◽  
Printed Circuit Boards ◽  
Acoustic Monitoring ◽  
Mechanical Effect ◽  
Laser Cleaning ◽  
Process Window ◽  
Circuit Boards ◽  
Copper Surfaces ◽  
532 Nm

The laser cleaning of copper surfaces with a Nd:YAG Q-switched laser pulse for the improvement of solder quality on printed circuit boards (PCBs) has been monitored and characterized by sensing the acoustic emission during the process and one-dimensional mathematical model analysis. It was found that selective removal of copper oxides from the surface was achieved by the laser operation, which was described theoretically by the model and was confirmed experimentally by the acoustic monitoring. The acoustic monitoring provided not only threshold laser fluence and optimal process window for the cleaning of copper but also the clear possibility for real-time surface monitoring of the process. Different features at the two laser wavelengths used (1064 nm and 532 nm) were observed in the surface morphology, i.e., the laser pulse with 532 nm wavelength produced a lightly sputtered wide area around the laser crater. From the theoretical and experimental investigation of laser cleaning mechanisms at different wavelengths, it was found that the mechanical effect induced by the intense shock waves was much more dominant at 532 nm wavelength than at 1064 nm.

Investigation of Fuel Spray Propagation, Combustion and Soot Formation/Oxidation in a Single Cylinder Medium Speed Diesel Engine

2012 ◽  
Author(s):  
Fridolin Unfug ◽  
Uwe Wagner ◽  
Kai W. Beck ◽  
Juergen Pfeil ◽  
Ulf Waldenmaier ◽  
...  
Keyword(s):  
Diesel Engine ◽  
Diesel Engines ◽  
High Speed ◽  
Liquid Fuel ◽  
Combustion Process ◽  
Fuel Spray ◽  
Soot Concentration ◽  
Single Cylinder ◽  
Medium Speed ◽  
532 Nm

To fulfil strict emission regulations and the need for higher efficiency of future Diesel engines require an optimized combustion process. Optical investigations represent a powerful tool for getting a better understanding of the ongoing processes. For medium speed Diesel engines, optical investigations are relatively rare or not available. The “Institut für Kolbenmaschinen” (IFKM) and MAN Diesel & Turbo SE performed extensive optical in-situ investigations of the injection and combustion process of a MAN 32/44 CR single cylinder medium speed Diesel engine that provide previously unavailable insights into the ongoing processes. The optical investigations aimed on fuel spray visualization, high-speed soot luminescence measurement and two colour pyrometry applied for five combustion chamber regions. To apply the optical measurement techniques, two optical accesses were designed. Access no. 1 is placed near the cylinder liner. Access no. 2 is located close to the injector in a 46° angle to the cylinder vertical axis. An insert was used which consists of an illumination port and a visualization endoscope. Additionally some special nozzle designs were used beside the standard nozzle, which have one separated nozzle hole. This enables a simultaneous view from both optical accesses on the same flame cone. For Mie-Scattering investigation a pulsed Nd:YAG-Laser with 532 nm wavelength was used for illumination and a CCD-camera with an upstream 532 nm optical filter was used for visualization. This combination allows observing the liquid fuel distribution even after start of combustion. Penetration depth of liquid fuel spray was analysed for different swirl numbers, intake manifold pressures, injection timings and injection pressures. High-speed flame visualization was done by two CMOS cameras which were mounted at two different optical accesses with view on the same flame cone. Due to this application a simultaneous measurement of the flame distribution of two different views was possible. This enables a 3-dimensional investigation of the flame propagation process. In addition, the advanced two colour pyrometry was applied for five different regions of the same flame cone. Due to a calibration after each measurement the absolute radiant flux can be calculated and thus the absolute temperature and soot concentration. With this procedure it was possible to give a real temperature and soot concentration distribution of the flame cone. To provide more detailed information about the combustion process, selected engine operation points were simulated with a modified version of the CFD code KIVA3v-Release2 at the IFKM. The simulated results were compared to the measured data.

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