scholarly journals EXPERIMENTAL TECHNIQUE USING AN INTERFERENCE PATTERN FOR MEASURING DIRECTIONAL FLUCTUATIONS OF A LASER BEAM CREATED BY A STRONG THERMAL TURBULENCE

2008 ◽  
Vol 84 ◽  
pp. 289-306 ◽  
Author(s):  
Jacques Hona ◽  
Elisabeth Ngo Nyobe ◽  
Elkana Pemha
Keyword(s):  
Laser Beam ◽  
Interference Pattern ◽  
Experimental Technique ◽  
Thermal Turbulence

EXPERIMENTAL VERIFICATION OF THE TURBULENT EFFECTS ON LASER BEAM PROPAGATION IN SPACE

Atmósfera ◽  
2015 ◽  
Vol 27 (4) ◽  
pp. 385-401
Author(s):  
SHIVAN M. AUGUSTINE ◽  
NAVEN CHETTY
Keyword(s):  
Laser Beam ◽  
Turbulence Model ◽  
Thermal Effects ◽  
Fourier Transforms ◽  
Scintillation Index ◽  
Weak Turbulence ◽  
Laser Beam Propagation ◽  
Thermal Turbulence ◽  
Turbulence Effects ◽  
Path Lengths

In this work, we have modified an existing experimental setup to fully classify the thermal effects on a laser beam propagating in air. Improvements made to the setup include a new, more powerful laser, a precision designed turbulence delivery system, an imbedded pressure sensor, and a platform for height adjustability between the laser beam and the turbulence model. The setup was not only able to reproduce previous results exactly but also allowed new data for the turbulence strength C2n, the Rytov variance (scintillation) and the coherence diameter (Fried’s parameter) to be successfully measured. Analysis of the produced interferograms has been discussed using fast Fourier transforms. The results confirm, within the Kolmogorov regime, that phase and intensity fluctuations increase relative to temperature. The turbulent region exhibited very strong disturbances, in the range of 1.1 × 10–12 m–2/3 to 2.7 × 10–12 m–2/3. In spite of the strong turbulence strength, scintillation proved otherwise, since the condition for a weak turbulence environment was determined in the laboratory and a low scintillation index was to be expected. This is as a result of the relatively short propagation distances achieved in the laboratory. In the open atmosphere, path lengths extend over vast distances and in order for turbulent effects to be realized, the turbulence model must generate stronger turbulence. The model was, therefore, able to demonstrate its ability to fully quantify and determine the thermal turbulence effects on a propagating laser beam.

Approach to diameter measurement of optical fibres: Forward near-axis far-field interference

2001 ◽  
Vol 215 (4) ◽  
pp. 385-388 ◽  
Author(s):  
J Wu
Keyword(s):  
Laser Beam ◽  
Interference Pattern ◽  
Optical Fibre ◽  
Optical Fibres ◽  
Far Field ◽  
Diameter Measurement ◽  
Non Destructive

A new, simple, fast, accurate and non-destructive method is presented for determining the diameter of optical fibres. The technique is based on the analysis of the forward near-axis far-field interference pattern from an optical fibre illuminated by a laser beam perpendicular to its axis.

scholarly journals Influence of Thermal Turbulence in a Convective Ascending Stream on Phase Fluctuations of a Laser Beam

1969 ◽  
Vol 8 (6) ◽  
pp. 1111 ◽  
Author(s):  
M. Bertolotti ◽  
M. Carnevale ◽  
B. Crosignani ◽  
P. Di Porto
Keyword(s):  
Laser Beam ◽  
Phase Fluctuations ◽  
Thermal Turbulence

Analysis of the fluctuations of a laser beam due to thermal turbulence

Open Physics ◽  
2014 ◽  
Vol 12 (7) ◽  
Author(s):  
Sphumelele Ndlovu ◽  
Naven Chetty
Keyword(s):  
Refractive Index ◽  
Laser Beam ◽  
Thermal Fluctuations ◽  
Phase Shifts ◽  
Outer Scale ◽  
Thermal Turbulence ◽  
Close Proximity ◽  
Inner Scale

AbstractA laser beam propagating in air and passing through a point diffraction interferometer (PDI) produces stable interferograms that can be used to extract wavefront data such as major atmospheric characteristics: turbulence strength, inner scale and outer scale of the refractive index. These parameters need to be taken into consideration when developing defense laser weapons since they can be affected by thermal fluctuations that are due to the changes in temperature in close proximity to the propagating beam and results in phase shifts that can be used to calculate the temperature which causes wavefront perturbations on a propagating beam.

Surface quality inspection using a laser beam with a regular dynamic interference pattern

1993 ◽  
Author(s):  
Vladimir P. Ryabukho ◽  
Yuri A. Avetisyan ◽  
Andrey E. Grinevich ◽  
Dmitry A. Zimnyakov ◽  
Boris V. Feduleev ◽  
...  
Keyword(s):  
Laser Beam ◽  
Surface Quality ◽  
Interference Pattern ◽  
Quality Inspection ◽  
Dynamic Interference

scholarly journals Experimental determination of thermal turbulence effects on a propagating laser beam

Open Physics ◽  
2015 ◽  
Vol 13 (1) ◽  
Author(s):  
Sphumelele C. Ndlovu ◽  
Naven Chetty
Keyword(s):  
Laser Beam ◽  
Atmospheric Turbulence ◽  
Laser Beams ◽  
Reliable Technique ◽  
Thermal Turbulence ◽  
Turbulence Effects ◽  
The Military ◽  
Atmospheric Systems ◽  
Turbulence Parameters

AbstractThe effect of turbulence on propagating laser beams has been a subject of interest since the evolution of lasers back in 1959. In this work, an inexpensive and reliable technique for producing interferograms using a point diffraction interferometer (PDI) was considered to experimentally study the turbulence effects on a laser beam propagating through air. The formed interferograms from a propagating beamwere observed and digitally processed to study the strength of atmospheric turbulence. This technique was found to be sensitive enough to detect changes in applied temperature with distance between the simulated turbulence and laser path. These preliminary findings indicated that we can use a PDI method to detect and localise atmospheric turbulence parameters. Such parameters are very important for use in the military (defence laser weapons) and this is vital for South Africa (SA) since it has natural resources, is involved in peace keeping and mediation for other countries, and hence must have a strong defence system that will be able to locate, detect and destroy incoming missiles and other threatening atmospheric systems in order to protect its environment and avoid the initiation of countermeasures on its land.

Computer analysis of side-band holography in STEM

1991 ◽  
Vol 49 ◽  
pp. 684-685
Author(s):  
M.A. Gribelyuk ◽  
J.M. Cowley
Keyword(s):  
Interference Pattern ◽  
Computer Analysis ◽  
Side Band ◽  
Diffraction Plane ◽  
Illumination System ◽  
Probe Size

Recently the use of a biprism in a STEM instrument has been suggested for recording of a hologram. A biprism is inserted in the illumination system and creates two coherent focussed beams at the specimen level with a probe size d= 5-10Å. If one beam passes through an object and another one passes in vacuum, an interference pattern, i.e. a hologram can be observed in diffraction plane (Fig.1).

Reconstruction of electron holograms recorded in a non-FEG, non-biprism TEM

1995 ◽  
Vol 53 ◽  
pp. 618-619
Author(s):  
Z.L. Wang
Keyword(s):  
Electron Microscope ◽  
Single Crystal ◽  
Experimental Technique ◽  
Transmission Electron Microscope ◽  
The Other ◽  
Electron Holography ◽  
Transmission Electron ◽  
Coherent Sources ◽  
Imaging Theory ◽  
Normal Specimen

An experimental technique for performing electron holography using a non-FEG, non-biprism transmission electron microscope (TEM) has been introduced by Ru et al. A double stacked specimens, one being a single crystal foil and the other the specimen, are loaded in the normal specimen position in TEM. The single crystal, which is placed onto the specimen, is responsible to produce two beams that are equivalent to two virtual coherent sources illuminating the specimen beneath, thus, permitting electron holography of the specimen. In this paper, the imaging theory of this technique is described. Procedures are introduced for digitally reconstructing the holograms.

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