scholarly journals Multiphoton Absorption Simulation of Sapphire Substrate under the Action of Femtosecond Laser for Larger Density of Pattern-Related Process Windows

Micromachines ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1571
Author(s):  
Xintian Cai ◽  
Chaoyue Ji ◽  
Changkai Li ◽  
Zhiqiang Tian ◽  
Xuan Wang ◽  
...  
Keyword(s):  
Femtosecond Laser ◽  
Sapphire Substrate ◽  
Femtosecond Lasers ◽  
Substrate Surface ◽  
Planck Equation ◽  
Photon Absorption ◽  
Semiconductor Film ◽  
Multiphoton Absorption ◽  
Free Electron Density ◽  
Related Process

It is essential to develop pattern-related process windows on substrate surface for reducing the dislocation density of wide bandgap semiconductor film growth. For extremely high instantaneous intensity and excellent photon absorption rate, femtosecond lasers are currently being increasingly adopted. However, the mechanism of the femtosecond laser developing pattern-related process windows on the substrate remains to be further revealed. In this paper, a model is established based on the Fokker–Planck equation and the two-temperature model (TTM) equation to simulate the ablation of a sapphire substrate under the action of a femtosecond laser. The transient nonlinear evolutions such as free electron density, absorption coefficient, and electron–lattice temperature are obtained. This paper focuses on simulating the multiphoton absorption of sapphire under femtosecond lasers of different wavelengths. The results show that within the range of 400 to 1030 nm, when the wavelength is large, the number of multiphoton required for ionization is larger, and wider and shallower ablation pits can be obtained. When the wavelength is smaller, the number of multiphoton is smaller, narrower and deeper ablation pits can be obtained. Under the simulation conditions presented in this paper, the minimum ablation pit depth can reach 0.11 μm and the minimum radius can reach 0.6 μm. In the range of 400 to 1030 nm, selecting a laser with a shorter wavelength can achieve pattern-related process windows with a smaller diameter, which is beneficial to increase the density of pattern-related process windows on the substrate surface. The simulation is consistent with existing theories and experimental results, and further reveals the transient nonlinear mechanism of the femtosecond laser developing the pattern-related process windows on the sapphire substrate.

scholarly journals New buffer sublayers with crystal structure of cubic syngony for growing the heteroepitaxial films of nitride compounds of type AIIIBV on sapphire substrates

1999 ◽  
Vol 4 (1) ◽  
Author(s):  
M.J. Kotelyanskii ◽  
I.M. Kotelyanskii ◽  
V.B. Kravchenko
Keyword(s):  
Crystal Structure ◽  
Sapphire Substrate ◽  
Substrate Surface ◽  
Lattice Parameter ◽  
Semiconductor Film ◽  
Plane Rotation ◽  
Parameter Mismatch ◽  
Working Surface ◽  
Aln Film ◽  
Image Position

We propose the use of a buffer sublayer made of materials with crystal structure of cubic syngony to eliminate 30° in-plane rotation of (0001) heteroepitaxial wurtzite type AIIIBV nitride films with respect to the (0001) or (110) working surface of the sapphire substrate. In these cases, the lattice parameter mismatch between the sapphire substrate surface and the semiconductor film is much smaller, and the cleavage planes of the sapphire and the semiconductor films with wurtzite structure forming the active region of a heterolaser are parallel. It is shown experimentally that using, for instance, Nb on (0001) Al2O3 or NbN on (110) Al2O3, allows the elimination of the 30° in-plane rotation of the (0001)AlN film with respect to the (0001) or (110) working surface of the sapphire substrate.

INTRACELLULAR MANIPULATION BY FEMTOSECOND LASERS: REVIEW

2009 ◽  
Vol 02 (01) ◽  
pp. 1-8 ◽  
Author(s):  
WATARU WATANABE ◽  
SACHIHIIRO MATSUNAGA ◽  
KIICHI FUKUI ◽  
KAZUYOSHI ITOH
Keyword(s):  
Femtosecond Laser ◽  
Femtosecond Lasers ◽  
Numerical Aperture ◽  
Laser Pulses ◽  
Living Cells ◽  
Femtosecond Laser Pulses ◽  
Multiphoton Absorption ◽  
High Numerical Aperture ◽  
Recent Advances

Multiphoton absorption of femtosecond laser pulses focused through an objective with high numerical aperture (NA) can be used to image and manipulate cellular and intracellular objects. This review highlights recent advances in intracellular manipulation, including nanosurgery and labeling in living cells with femtosecond lasers.

Nanostructuring Borosilicate Glass With Near-Field Enhanced Energy Using a Femtosecond Laser Pulse

2006 ◽  
Vol 129 (1) ◽  
pp. 53-59 ◽  
Author(s):  
Alex Heltzel ◽  
Arvind Battula ◽  
J. R. Howell ◽  
Shaochen Chen
Keyword(s):  
Laser Pulse ◽  
Femtosecond Laser ◽  
Borosilicate Glass ◽  
Substrate Surface ◽  
Near Field ◽  
Planck Equation ◽  
Laser Pulses ◽  
Femtosecond Laser Pulses ◽  
Avalanche Ionization ◽  
Avalanche Process

A model based on the evolution of electron density derived from the Fokker-Planck equation has been built to describe ablation of dielectrics during femtosecond laser pulses. The model is verified against an experimental investigation of borosilicate glass with a 200fs laser pulse centered at 780nm wavelength in a range of laser energies. The ablation mechanisms in dielectrics include multi-photon ionization (MPI) and avalanche ionization. MPI dominates the ionization process during the first stages of the laser pulse, contributing seed electrons which supply avalanche ionization. The avalanche process initiates and becomes responsible for the majority of free-electron generation. The overall material removal is shown to be highly dependent upon the optical response of the dielectric as plasma is formed. The ablation model is employed to predict the response of borosilicate glass to an enhanced electromagnetic field due to the presence of microspheres on the substrate surface. It is shown that the diffraction limit can be broken, creating nanoscale surface modification. An experimental study accompanies the model, with AFM and SEM characterizations that are consistent with the predicted surface modifications.

scholarly journals Electric Field Assisted Femtosecond Laser Preparation of Au@TiO2 Composites with Controlled Morphology and Crystallinity for Photocatalytic Degradation

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 3816
Author(s):  
Xiaojie Li ◽  
Xin Li ◽  
Pei Zuo ◽  
Xiaozhe Chen ◽  
Misheng Liang ◽  
...  
Keyword(s):  
Femtosecond Laser ◽  
Electric Field ◽  
Photocatalytic Degradation ◽  
Au Nanoparticles ◽  
High Efficiency ◽  
Free Electron Density ◽  
Pulse Delay ◽  
Dye Pollutants ◽  
Amorphous Tio2 ◽  
Laser Liquid

TiO2 is popular in photocatalytic degradation dye pollutants due to its abundance and its stability under photochemical conditions. Au loaded TiO2 can achieve efficient absorption of visible light and deal with the problem of low conversion efficiency for solar energy of TiO2. This work presents a new strategy to prepare Au nanoparticles-loaded TiO2 composites through electric−field−assisted temporally−shaped femtosecond laser liquid-phase ablation of Au3+ and amorphous TiO2. By adjusting the laser pulse delay and electric field parameters, gold nanoparticles with different structures can be obtained, such as nanospheres, nanoclusters, and nanostars (AuNSs). AuNSs can promote the local crystallization of amorphous TiO2 in the preparation process and higher free electron density can also be excited to work together with the mixed crystalline phase, hindering the recombination between carriers and holes to achieve efficient photocatalytic degradation. The methylene blue can be effectively degraded by 86% within 30 min, and much higher than the 10% of Au nanoparticles loaded amorphous TiO2. Moreover, the present study reveals the crystallization process and control methods for preparing nanoparticles by laser liquid ablation, providing a green and effective new method for the preparation of high-efficiency photocatalytic materials.

Fabrication of Three-Dimensional Micro-Structures with Two-Photon Absorption by Femtosecond Laser

2006 ◽  
Vol 532-533 ◽  
pp. 568-571
Author(s):  
Ming Zhou ◽  
Hai Feng Yang ◽  
Li Peng Liu ◽  
Lan Cai
Keyword(s):  
Photonic Crystal ◽  
Femtosecond Laser ◽  
Detection System ◽  
Three Dimensional ◽  
Photon Absorption ◽  
Micro Fabrication ◽  
Two Photon Absorption ◽  
Two Photon ◽  
Photo Polymerization ◽  
System A

The photo-polymerization induced by Two-Photon Absorption (TPA) is tightly confined in the focus because the efficiency of TPA is proportional to the square of intensity. Three-dimensional (3D) micro-fabrication can be achieved by controlling the movement of the focus. Based on this theory, a system for 3D-micro-fabrication with femtosecond laser is proposed. The system consists of a laser system, a microscope system, a real-time detection system and a 3D-movement system, etc. The precision of micro-machining reaches a level down to 700nm linewidth. The line width was inversely proportional to the fabrication speed, but proportional to laser power and NA. The experiment results were simulated, beam waist of 0.413μm and TPA cross section of 2×10-54cm4s was obtained. While we tried to optimize parameters, we also did some research about its applications. With TPA photo-polymerization by means of our experimental system, 3D photonic crystal of wood-pile structure twelve layers and photonic crystal fiber are manufactured. These results proved that the micro-fabrication system of TPA can not only obtain the resolution down to sub-micron level, but also realize real 3D micro-fabrication.

scholarly journals The study of spray impact on the heated sapphire plate

2021 ◽  
Vol 2119 (1) ◽  
pp. 012172
Author(s):  
T G Gigola ◽  
V V Cheverda
Keyword(s):  
Heat Transfer ◽  
Sapphire Substrate ◽  
Substrate Surface ◽  
Heated Surface ◽  
Local Heat ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Liquid Spray ◽  
Sapphire Plate

Abstract The process of the liquid spray impact on the heated surface is studied experimentally using the IR-transparent sapphire plate method. The spatiotemporal distribution of the temperature field on the sapphire substrate surface during impacting spray is received. The obtained experimental data are an important step in a study of the local characteristics of heat transfer in the areas of the contact lines during liquid spray impact on the heated surface. Further, the local heat fluxes and heat transfer coefficients will be determined by solving the problem of thermal conductivity in the sapphire substrate.

scholarly journals Titanium surface modification using femtosecond laser with 1013–1015 W/cm2 intensity in vacuum

2012 ◽  
Vol 31 (1) ◽  
pp. 29-36 ◽  
Author(s):  
M. Trtica ◽  
D. Batani ◽  
R. Redaelli ◽  
J. Limpouch ◽  
V. Kmetik ◽  
...  
Keyword(s):  
Surface Modification ◽  
Femtosecond Laser ◽  
Titanium Surface ◽  
Femtosecond Lasers ◽  
Single Pulse ◽  
Surface Structures ◽  
Pulse Regime ◽  
Periodic Surface ◽  
Reduced Intensity ◽  
Surface Changes

AbstractThe response of titanium surface irradiated with high intensity (1013 – 1015 W/cm2) Ti:sapphire laser was studied in vacuum. Most of the reported investigations were conducted with nano- to femtosecond lasers in gas atmospheres while the studies of titanium surface interacting with femtosecond laser in vacuum are scarce. The laser employed in our experiment was operating at 800 nm wavelength and pulse duration of 60 fs in single pulse regime. The observed surface changes and phenomena are (1) creation of craters, (2) formation of periodic surface structures at the reduced intensity, and (3) occurrence of plasma in front the target. Since microstructuring of titanium is very interesting in many areas (industry, medicine), it can be concluded from this study that the reported laser intensities can effectively be applied for micromachining of the titanium surface (increasing the roughness, formation of parallel periodic surface structures etc.).

Effective π-electron number and Symmetry Perturbation Effect on the Two-photon Absorption of Oligofluorenes

2021 ◽  
Author(s):  
Luis M.G. Abegão ◽  
Leandro Cocca ◽  
Jean-Christophe Mulatier ◽  
Delphine Pitrat ◽  
Chantal Andraud ◽  
...  
Keyword(s):  
Fluorescence Quantum Yield ◽  
Photon Absorption ◽  
Multiphoton Absorption ◽  
Electron Number ◽  
Two Photon Absorption ◽  
Two Photon ◽  
Optical Responses ◽  
High Fluorescence ◽  
Perturbation Effect ◽  
High Fluorescence Quantum Yield

Fluorene-based molecules present significant nonlinear optical responses, multiphoton absorption in the visible, which, combined with the high fluorescence quantum yield in organic solvents, could make this class of materials potentially...

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