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

Measurement of phase fluctuations in a HF chemical laser beam

1979 ◽  
Vol 50 (12) ◽  
pp. 7917-7920 ◽  
Author(s):  
C. P. Wang ◽  
R. L. Varwig
Keyword(s):  
Laser Beam ◽  
Chemical Laser ◽  
Phase Fluctuations

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.

Interferometric Study of Phase Fluctuations of a Laser Beam Through the Turbulent Atmosphere

1968 ◽  
Vol 7 (11) ◽  
pp. 2246 ◽  
Author(s):  
M. Bertolotti ◽  
M. Carnevale ◽  
L. Muzii ◽  
D. Sette
Keyword(s):  
Laser Beam ◽  
Turbulent Atmosphere ◽  
Phase Fluctuations ◽  
Interferometric Study

scholarly journals Influence of Laboratory Generated Turbulence on Phase Fluctuations of a Laser Beam

1968 ◽  
Vol 7 (6) ◽  
pp. 1121 ◽  
Author(s):  
M. Carnevale ◽  
B. Crosignani ◽  
P. Di Porto
Keyword(s):  
Laser Beam ◽  
Phase Fluctuations

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.

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.

Two-photon excitation microscopy in cellular biophysics

1995 ◽  
Vol 53 ◽  
pp. 62-63
Author(s):  
David W. Piston ◽  
Brian D. Bennett ◽  
Robert G. Summers
Keyword(s):  
Confocal Microscopy ◽  
Laser Beam ◽  
Duty Cycle ◽  
Excited Electronic State ◽  
Input Power ◽  
Two Photon ◽  
Simultaneous Absorption ◽  
Photon Excitation ◽  
Very High ◽  
Two Photon Excitation

Two-photon excitation microscopy (TPEM) provides attractive advantages over confocal microscopy for three-dimensionally resolved fluorescence imaging and photochemistry. Two-photon excitation arises from the simultaneous absorption of two photons in a single quantitized event whose probability is proportional to the square of the instantaneous intensity. For example, two red photons can cause the transition to an excited electronic state normally reached by absorption in the ultraviolet. In practice, two-photon excitation is made possible by the very high local instantaneous intensity provided by a combination of diffraction-limited focusing of a single laser beam in the microscope and the temporal concentration of 100 femtosecond pulses generated by a mode-locked laser. Resultant peak excitation intensities are 106 times greater than the CW intensities used in confocal microscopy, but the pulse duty cycle of 10-5 maintains the average input power on the order of 10 mW, only slightly greater than the power normally used in confocal microscopy.

The atomic-force microscope and its future in biology

1993 ◽  
Vol 51 ◽  
pp. 704-705
Author(s):  
Jean-Paul Revel
Keyword(s):  
Silicon Nitride ◽  
Laser Beam ◽  
Atomic Force Microscope ◽  
Scanning Tunneling Microscope ◽  
Point Of View ◽  
Scanning Tunneling ◽  
Close Relative ◽  
Tunneling Microscope ◽  
Atomic Force ◽  
Sharp Point

The last few years have been marked by a series of remarkable developments in microscopy. Perhaps the most amazing of these is the growth of microscopies which use devices where the place of the lens has been taken by probes, which record information about the sample and display it in a spatial from the point of view of the context. From the point of view of the biologist one of the most promising of these microscopies without lenses is the scanned force microscope, aka atomic force microscope.This instrument was invented by Binnig, Quate and Gerber and is a close relative of the scanning tunneling microscope. Today's AFMs consist of a cantilever which bears a sharp point at its end. Often this is a silicon nitride pyramid, but there are many variations, the object of which is to make the tip sharper. A laser beam is directed at the back of the cantilever and is reflected into a split, or quadrant photodiode.

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