scholarly journals Numerical Simulation of the Photobleaching Process in Laser-Induced Fluorescence Photobleaching Anemometer

Micromachines ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1592
Author(s):  
Yu Chen ◽  
Shuangshuang Meng ◽  
Kaige Wang ◽  
Jintao Bai ◽  
Wei Zhao
Keyword(s):  
Power Density ◽  
Laser Power ◽  
Diagnostic Technique ◽  
Laser Induced Fluorescence ◽  
Laser Power Density ◽  
Fluorescent Dye ◽  
Optical Diffraction ◽  
Diffusion Reaction ◽  
Actual Condition ◽  
Reaction Coefficient

At present, a novel flow diagnostic technique for micro/nanofluidics velocity measurement—laser-induced fluorescence photobleaching anemometer (LIFPA)—has been developed and successfully applied in broad areas, e.g., electrokinetic turbulence in micromixers and AC electroosmotic flow. Nevertheless, in previous investigations, to qualitatively reveal the dynamics of the photobleaching process of LIFPA, an approximation of uniform laser distribution was applied. This is different from the actual condition where the laser power density distribution is normally Gaussian. In this investigation, we numerically studied the photobleaching process of fluorescent dye in the laser focus region, according to the convection–diffusion reaction equation. The profiles of effective dye concentration and fluorescence were elucidated. The relationship between the commonly used photobleaching time constant obtained by experiments and the photochemical reaction coefficient is revealed. With the established model, we further discuss the effective spatial resolution of LIFPA and study the influence of the detection region of fluorescence on the performance of the LIFPA system. It is found that at sufficiently high excitation laser power density, LIFPA can even achieve a super-resolution that breaks the limit of optical diffraction. We hope the current investigation can reveal the photobleaching process of fluorescent dye under high laser power density illumination, to enhance our understanding of fluorescent dynamics and photochemistry and develop more powerful photobleaching-related flow diagnostic techniques.

scholarly journals Influence of Saturation Phenomena on Laser-Excited Atomic Fluorescence Flame Spectrometry

1973 ◽  
Vol 28 (2) ◽  
pp. 273-279
Author(s):  
J. Kühl ◽  
S. Neumann ◽  
M. Kriese
Keyword(s):  
Power Density ◽  
Laser Power ◽  
Atomic Emission ◽  
Equation Model ◽  
Laser Power Density ◽  
Atomic Level ◽  
Dye Laser ◽  
Atomic Fluorescence ◽  
Emission Flame ◽  
Flame Spectrometry

Using a simple rate equation model, the laser power density Ic necessary to reach 50% of the saturation limited population of the excited atomic level under typical flame conditions is calculated. For Na atoms aspirated into the flame a saturating power density for irradiation with a narrow dye laser line (bandwidth 0.033 Å) of Ic ~ 0.4 kW/cm2 was determined. With the aid of a dye laser with an appropriate laser power density, analytical curves for Na were measured yielding a detection limit of 0.2 ng/ml. This sensitivity is comparable with the best results obtained by atomic emission flame spectrometry.

Experimental Study on Testing Ni-Containing Stainless Steel Protective Coatings by Pulsed Laser Scratching

2010 ◽  
Vol 43 ◽  
pp. 651-656
Author(s):  
Ai Xin Feng ◽  
Yu Peng Cao ◽  
Chuan Chao Xu ◽  
Huai Yang Sun ◽  
Gui Fen Ni ◽  
...  
Keyword(s):  
Residual Stress ◽  
Stainless Steel ◽  
Power Density ◽  
Laser Power ◽  
Protective Coatings ◽  
Three Dimensional ◽  
Pulsed Laser ◽  
Laser Power Density ◽  
The Matrix ◽  
The Impact

In the experiment, we use pulsed laser to conduct discrete scratching on Ni-containing stainless steel protective coatings to test residual stress situation after the matrix is scratched; then to analyze the the impact of the impact stress wave on coating - substrate bonding strength according to the test results, finally to infer the laser power density range within which it occurs coating failure. The study shows that: after laser discrete scratching, the residual stress of the center of the laser-loaded point on matrix surface gradually reduces when the pulsed laser power density increases. The matrix produces a corresponding residual compressive stress under the laser power density reaches a certain value. The actual failure threshold values are 12.006 GW/cm2, 11.829GW/cm2 and 12.193GW/cm2 measured by the three-dimensional topography instrument testing the discrete scratch point of three groups of samples and verified by using a microscope

Numerical Simulation and Applications of a Method for Attenuating Laser Power Density

2013 ◽  
Vol 50 (2) ◽  
pp. 022201
Author(s):  
王振宝 Wang Zhenbao ◽  
冯国斌 Feng Guobin ◽  
杨鹏翎 Yang Pengling ◽  
冯刚 Feng Gang ◽  
闫燕 Yan Yan
Keyword(s):  
Numerical Simulation ◽  
Power Density ◽  
Laser Power ◽  
Laser Power Density

scholarly journals Investigation on Residual Stress Loss during Laser Peen Texturing of 316L Stainless Steel

2019 ◽  
Vol 9 (17) ◽  
pp. 3511 ◽  
Author(s):  
Kangmei Li ◽  
Yifei Wang ◽  
Yu Cai ◽  
Jun Hu
Keyword(s):  
Residual Stress ◽  
Compressive Stress ◽  
Power Density ◽  
Laser Power ◽  
Surface Deformation ◽  
Laser Power Density ◽  
Residual Compressive Stress ◽  
Laser Spot ◽  
Residual Tensile Stress ◽  
Spot Radius

Laser peen texturing (LPT) is a novelty way of surface texturing based on laser shock processing. One of the most important benefits of LPT is that it can not only fabricate surface textures but also induce residual compressive stress for the target material. However, the residual stress loss leads to partial loss of residual compressive stress and even causes residual tensile stress at the laser spot center. This phenomenon is not conducive to improving the mechanical properties of materials. In this study, a numerical simulation model of LPT was developed and validated by comparison of surface deformation with experiments. In order to investigate the phenomenon of residual stress loss quantitatively, an evaluation method of residual stress field was proposed. The effects of laser power density and laser spot radius on the residual stress, especially the residual stress loss, were systematically investigated. It is found that with the increase of laser power density or laser spot radius, the thickness of residual compressive layer in depth direction becomes larger. However, both the magnitude and the affecting zone size of residual stress loss will be increased, which implies a more severe residual stress loss phenomenon.

Tuning the Defects in AgO Nanoparticles/Graphene Bilayers System by Laser Power Density

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
H. Ferreira ◽  
M. Briones2, M. Camilo ◽  
G. Poma ◽  
Maria Quintana ◽  
A. Champi
Keyword(s):  
Power Density ◽  
Laser Power ◽  
Laser Power Density

Characterizing the Effect of Laser Power Density on Microstructure, Microhardness, and Surface Finish of Laser Deposited Titanium Alloy

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Rasheedat M. Mahamood ◽  
Esther T. Akinlabi ◽  
Mukul Shukla ◽  
Sisa Pityana
Keyword(s):  
Surface Roughness ◽  
Titanium Alloy ◽  
Power Density ◽  
Surface Finish ◽  
Laser Power ◽  
Optical Microscope ◽  
Laser Power Density ◽  
Grain Structure ◽  
Selection Of

This paper reports the effect of laser power density on the evolving properties of laser metal deposited titanium alloy. A total of sixteen experiments were performed, and the microstructure, microhardness and surface roughness of the samples were studied using the optical microscope (OP), microhardness indenter and stylus surface analyzer, respectively. The microstructure changed from finer martensitic alpha grain to coarser Widmastätten alpha grain structure as the laser power density was increased. The results show that the higher the laser power density employed, the smoother the obtained surface. The microhardness initially increased as the laser power density was increased and then decreased as the power density was further increased. The result obtained in this study is important for the selection of proper laser power density for the desired microstructure, microhardness and surface finish of part made from Ti6Al4V.

Preparation and Microstructure Control of Protein Thin Films Deposited by Pulsed Laser Deposition and Via Colloid Chemical Routes

2003 ◽  
Vol 788 ◽  
Author(s):  
Sayuri Nakayama ◽  
Ichiro Taketani ◽  
Sanshiro Nagare ◽  
Mamoru Senna
Keyword(s):  
Thin Film ◽  
Secondary Structure ◽  
Pulsed Laser Deposition ◽  
Power Density ◽  
Laser Power ◽  
Pulsed Laser ◽  
Laser Power Density ◽  
Laser Deposition ◽  
Random Coil ◽  
Β Sheet

ABSTRACTProtein thin film (mainly silk fibroin) was prepared by pulsed laser deposition (PLD) with 1064nm IR-beam and via colloid chemical routes. Thickness, surface roughness, and microstructures of the deposited film were examined by quartz crystal microbalance sensor, field emission scanning electron microscope (FE-SEM), and atomic force microscope (AFM). The laser power density was varied systematically for PLD to control the microstructures of the film and the secondary structure (β-sheet, α-helix, or random coil) of the protein. Secondary structure of the target and film was examined by FT-IR. Films prepared by PLD comprise by agglomerated particles with their primary particle size around 30nm. The size of the primary particles was uniform, especially for the film prepared at low laser power density. At low laser power density, proportion of β-sheet increased and that of random coil decreased. Proportion of random coil was also increased by the wet colloidal process. PLD with low power density is most suitable to preserve the secondary structure in the protein thin film.

scholarly journals Optimization of X-ray emission from a laser-produced plasma in a narrow wavelength band

1992 ◽  
Vol 10 (4) ◽  
pp. 759-765 ◽  
Author(s):  
G. E. Van Dorssen ◽  
E. Louis ◽  
F. Bijkerk
Keyword(s):  
Power Density ◽  
Laser Power ◽  
Multilayer Coating ◽  
Target Surface ◽  
Laser Power Density ◽  
Strong Increase ◽  
Wavelength Band ◽  
Line Radiation ◽  
X Ray ◽  
Photoconductive Detector

The X-ray emission from laser-produced plasmas at an X-ray wavelength of approximately 10.4 nm was measured for Al and Gd target materials. The laser power density on the target surface was varied between 1.5 × 1010 and 3 × 1012 W/cm2 to obtain different electron temperatures. The output from the plasma was measured using an X-ray reflecting Pd-C multilayer coating as a wavelength-selective element and a diamond photoconductive detector. The emission at 10.4 nm is strongest at the low end of the power density range investigated. A strong increase is found for Al targets due to a contribution of line radiation, which is not present in the Gd plasmas. The measured conversion efficiency for Al plasmas was (4.5 ± 1)% in a 3% bandwidth at an X-ray wavelength of 10.4 nm.

Synthesis and control of micro to noanscale porous structures of diamond like carbon films

2006 ◽  
Vol 954 ◽  
Author(s):  
Peter Feng ◽  
Ben Yang ◽  
H. X. Zhang ◽  
X. P. Wang ◽  
Noel Upia ◽  
...  
Keyword(s):  
Power Density ◽  
Laser Power ◽  
Carbon Films ◽  
Laser Power Density ◽  
Diamond Like Carbon ◽  
Excimer Laser Ablation ◽  
Target Yield ◽  
Krf Excimer Laser ◽  
And Control ◽  
The Relationship

ABSTRACTDiamond like carbon (DLC) films are synthesized on various substrates using a pulsed KrF excimer laser ablation deposition technique. Variations of laser power density, substrate temperature, angle and distance between the substrate and target yield different sizes of porous surfaces of DLC films. Microscope is used to examine the surfaces. Raman scattering is used to characterize the samples, and the typical G and D bands have been identified. Intensities and profiles of the G and D bands closely depend on laser power density. The relationship between the deposition rate and the power density is also studied.

scholarly journals Nanosecond laser pulses for aluminum and copper drilling

2018 ◽  
Vol 16 (36) ◽  
pp. 47-52
Author(s):  
Walid K. Hamoudi
Keyword(s):  
Thermal Conductivity ◽  
Melting Point ◽  
Laser Pulse ◽  
Power Density ◽  
Laser Power ◽  
Laser Pulses ◽  
Laser Power Density ◽  
Nanosecond Laser ◽  
Operating Wavelength ◽  
Nanosecond Laser Pulses

Nd:YAG laser pulses of 9 nanosecond pulse duration and operating wavelength at 1.06 μm, were utilized to drill high thermal conductivity and high reflectivity aluminum and copper foils. The results showed a dependence of drilled holes characteristics on laser power density and the number of laser pulses used. Drilled depth of 74 ϻm was obtained in aluminum at 11.036×108 W/cm2 of laser power density. Due to its higher melting point, copper required higher laser power density and/or larger number of laser pulses to melt, and a maximum depth of 25 μm was reached at 13.46×108 W/cm2 using single laser pulse.

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