Effect of optical diffraction on laser heating of a field emitter

1986 ◽  
Vol 64 (1) ◽  
pp. 111-117 ◽  
Author(s):  
E. S. Robins ◽  
M. J. G. Lee ◽  
P. Langlois
Keyword(s):  
Electromagnetic Field ◽  
Plane Wave ◽  
Laser Beam ◽  
Laser Heating ◽  
Focal Spot ◽  
Incident Beam ◽  
Optical Diffraction ◽  
Field Emitter ◽  
Complicated Geometry ◽  
Direction Of Polarization

The wavelength of the illuminating radiation used in studies of photofield emission is comparable to the diameter of the shank of the field emitter. Under these conditions, diffraction is expected to play an important role in determining the absorption of energy from the electromagnetic field. The complicated geometry of the field emitter has so far prevented an exact calculation of this effect. By considering the diffraction of a plane wave by an idealized model of a field emitter, we have calculated the absorption of energy from an incident focussed laser beam. Calculations based on the present results yield accurate predictions of the magnitude of the temperature rise and its dependence on the position of the focal spot and on the direction of polarization of the incident beam.

scholarly journals Generation of a poloidal magnetic field in a noncollisional plasma by an elliptically polarized Gaussian laser beam

1998 ◽  
Vol 16 (2) ◽  
pp. 277-283
Author(s):  
M.K. Srivastava ◽  
S.V. Lawande ◽  
D. Dutta ◽  
S. Sarkar ◽  
M. Khan ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Laser Beam ◽  
Density Profile ◽  
Focal Spot ◽  
Collisionless Plasma ◽  
Incident Beam ◽  
Gaussian Laser Beam ◽  
Poloidal Magnetic Field ◽  
Angular Correction ◽  
Elliptically Polarized

The generation of poloidal magnetic field in an inhomogeneous cold, collisionless plasma by an elliptically polarized Gaussian laser beam is discussed. A field in the range of megagauss is induced by the laser inhomogeneity effect even for a normal incident beam. This field scales as I0 λ, where I0 and λ are the intensity and wavelength of the laser beam, respectively, and is independent of the density profile structure. The small angular correction factor due to focal spot asymmetry scales as ∼I0λ3 and may be significant for a small-sized plasma with a steep density profile. The limitation of our model is discussed, with possible implications.

scholarly journals Asymmetric Diffraction in Plasmonic Meta-Gratings Using an IT-Shaped Nanoslit Array

Sensors ◽  
2021 ◽  
Vol 21 (12) ◽  
pp. 4097
Author(s):  
Hee-Dong Jeong ◽  
Seong-Won Moon ◽  
Seung-Yeol Lee
Keyword(s):  
Plane Wave ◽  
Periodic Structures ◽  
Single Layer ◽  
Optical Diffraction ◽  
Back Side ◽  
Infrared Band ◽  
Effective Period ◽  
Wave Nature ◽  
Control Light ◽  
Meta Atom

Diffraction is a fundamental phenomenon that reveals the wave nature of light. When a plane wave is transmitted or reflected from a grating or other periodic structures, diffracted light waves propagate at several angles that are specified by the period of the given structure. When the optical period is shorter than the wavelength, constructive interference of diffracted light rays from the subwavelength-scale grating forms a uniform plane wave. Many studies have shown that through the appropriate design of meta-atom geometry, metasurfaces can be used to control light properties. However, most semitransparent metasurfaces are designed to perform symmetric operation with regard to diffraction, meaning that light diffraction occurs identically for front- and back-side illumination. We propose a simple single-layer plasmonic metasurface that achieves asymmetric diffraction by optimizing the transmission phase from two types of nanoslits with I- and T-shaped structures. As the proposed structure is designed to have a different effective period for each observation side, it is either diffractive or nondiffractive depending on the direction of observation. The designed structure exhibits a diffraction angle of 54°, which can be further tuned by applying different period conditions. We expect the proposed asymmetric diffraction meta-grating to have great potential for the miniaturized optical diffraction control systems in the infrared band and compact optical diffraction filters for integrated optics.

scholarly journals 1178 J, 527 nm near diffraction limited laser based on a complete closed-loop adaptive optics controlled off-axis multi-pass amplification laser system

2021 ◽  
Vol 9 ◽  
Author(s):  
Deen Wang ◽  
Xin Zhang ◽  
Wanjun Dai ◽  
Ying Yang ◽  
Xuewei Deng ◽  
...  
Keyword(s):  
Laser Beam ◽  
Adaptive Optics ◽  
Closed Loop ◽  
Focal Spot ◽  
Beam Quality ◽  
Laser System ◽  
Diffraction Limit ◽  
Kdp Crystal ◽  
Main Amplifier

Abstract A 1178 J near diffraction limited 527 nm laser is realized in a complete closed-loop adaptive optics (AO) controlled off-axis multi-pass amplification laser system. Generated from a fiber laser and amplified by the pre-amplifier and the main amplifier, a 1053 nm laser beam with the energy of 1900 J is obtained and converted into a 527 nm laser beam by a KDP crystal with 62% conversion efficiency, 1178 J and beam quality of 7.93 times the diffraction limit (DL). By using a complete closed-loop AO configuration, the static and dynamic wavefront distortions of the laser system are measured and compensated. After correction, the diameter of the circle enclosing 80% energy is improved remarkably from 7.93DL to 1.29DL. The focal spot is highly concentrated and the 1178 J, 527 nm near diffraction limited laser is achieved.

Deformation of a liquid surface by laser heating: laser-beam self-focusing and generation of capillary waves

1986 ◽  
Vol 64 (9) ◽  
pp. 1341-1344 ◽  
Author(s):  
J. Hartikainen ◽  
J. Jaarinen ◽  
M. Luukkala
Keyword(s):  
Laser Beam ◽  
Laser Heating ◽  
Surface Deformation ◽  
Liquid Surface ◽  
Capillary Waves ◽  
The Self ◽  
Self Focusing

The surface deformation of oil by laser heating is presented. The self-focusing of the reflected beam and the generation of capillary waves are observed.

Improved degassing in laser beam welding of aluminum die casting by an electromagnetic field

2018 ◽  
Vol 253 ◽  
pp. 51-56 ◽  
Author(s):  
André Fritzsche ◽  
Kai Hilgenberg ◽  
Fabian Teichmann ◽  
Helge Pries ◽  
Klaus Dilger ◽  
...  
Keyword(s):  
Electromagnetic Field ◽  
Laser Beam ◽  
Die Casting ◽  
Laser Beam Welding

scholarly journals Self-Focusing of Hermite-Cosh-Gaussian Laser Beams in Plasma under Density Transition

2014 ◽  
Vol 2014 ◽  
pp. 1-5 ◽  
Author(s):  
Manzoor Ahmad Wani ◽  
Niti Kant
Keyword(s):  
Laser Beam ◽  
Plasma Density ◽  
Focal Spot ◽  
Beam Width ◽  
Spot Size ◽  
Laser Beams ◽  
Equation Approach ◽  
Focal Spot Size ◽  
Self Focusing ◽  
Small Spot

Self-focusing of Hermite-Cosh-Gaussian (HChG) laser beam in plasma under density transition has been discussed here. The field distribution in the medium is expressed in terms of beam-width parameters and decentered parameter. The differential equations for the beam-width parameters are established by a parabolic wave equation approach under paraxial approximation. To overcome the defocusing, localized upward plasma density ramp is considered, so that the laser beam is focused on a small spot size. Plasma density ramp plays an important role in reducing the defocusing effect and maintaining the focal spot size up to several Rayleigh lengths. To discuss the nature of self-focusing, the behaviour of beam-width parameters with dimensionless distance of propagation for various values of decentered parameters is examined by numerical estimates. The results are presented graphically and the effect of plasma density ramp and decentered parameter on self-focusing of the beams has been discussed.

scholarly journals Simulation of laser heating distribution for a thermoplastic composite: effects of AFP head parameters

2020 ◽  
Vol 110 (7-8) ◽  
pp. 2105-2117
Author(s):  
Omar Baho ◽  
Gilles Ausias ◽  
Yves Grohens ◽  
Julien Férec
Keyword(s):  
Laser Beam ◽  
Laser Heating ◽  
Thermal Model ◽  
Laser Energy ◽  
Thermoplastic Composite ◽  
Thermoplastic Composites ◽  
Efficient Production ◽  
Fiber Placement ◽  
Aerospace Applications ◽  
Automated Fiber Placement

Abstract Laser-assisted automated fiber placement (AFP) is highly suitable for an efficient production of thermoplastic-matrix composite parts, especially for aeronautic/aerospace applications. Heat input by laser heating provides many advantages such as better temperature controls and uniform heating projections. However, this laser beam distribution can be affected by the AFP head system, mainly at the roller level. In this paper, a new optico-thermal model is established to evaluate the laser energy quantity absorbed by a poly(ether ether ketone) reinforced with carbon fibers (APC-2). During the simulation process, the illuminated radiative material properties are characterized and evaluated in terms of the roller deformation, the tilt of the robot head, and the reflection phenomenon between the substrate and the incoming tape. After computing the radiative source term using a ray-tracing method, these data are used to predict the temperature distribution on both heated surfaces of the composite during the process. The results show that both the roller deformation and the tilt of head make it possible to focus the laser beam on a small area, which considerably affects the quality of the finished part. These findings demonstrate that this optico-thermal model can be used to predict numerically the insufficient heating area and thermoplastic composites heating law.

Force Analysis, Mechanical Energy and Laser Heating Evaluation of Scratch Tests on Silicon Carbide (4H-SiC) in Micro-Laser Assisted Machining (µ-LAM) Process

2009 ◽  
Author(s):  
Amir R. Shayan ◽  
Huseyin Bogac Poyraz ◽  
Deepak Ravindra ◽  
Muralidhar Ghantasala ◽  
John A. Patten
Keyword(s):  
Laser Beam ◽  
Cutting Forces ◽  
Laser Heating ◽  
Cutting Tool ◽  
Work Piece ◽  
Force Analysis ◽  
Diamond Cutting ◽  
Laser Assisted Machining ◽  
Scratch Tests ◽  
Diamond Cutting Tool

The purpose of applying a laser beam in the micro-laser assisted machining (μ-LAM) process is to preferentially heat and thermally soften the surface layer of the work piece material (4H-SiC) at the interface with a diamond cutting tool. In the μ-LAM process the laser beam (1480 nm and 400 mW) is delivered to the work piece material through a transparent diamond cutting tool. Thus the cutting tool and the laser system are integrated and coupled; in contrast with other LAM processes where the cutting tool and laser are separate and distinct systems. Scratches were made on a 4H-SiC substrate using the μ-LAM process. The characteristics of the scratches, such as depth and width, are principally a function of the cutting tool geometry, applied forces, cutting speed, and laser heating. White light interferometer microscopy and Atomic Force Microscopy (AFM) techniques were used to measure the geometry (depth and width) of the scratches. Force analysis was carried out to evaluate the laser heating effect on the cutting forces and the measured depth of cut. The force analysis included an evaluation of the mechanical work, specific energy, and understanding the effect of laser heating on the cutting process. The scratch tests performed on 4H-SiC with the laser heating showed that there is a greater than 50% reduction in relative calculated hardness values of work piece material, resulting in a significant reduction in cutting forces.

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