scholarly journals Electrostrictive Mechanism of Radiation Self-Action in Nanofluids

2013 ◽  
Vol 2013 ◽  
pp. 1-5 ◽  
Author(s):  
Albert Livashvili ◽  
Victor Krishtop ◽  
Margarita Yakunina
Keyword(s):  
Refractive Index ◽  
Analytical Solution ◽  
Diffusion Equation ◽  
Radiation Intensity ◽  
Focal Length ◽  
Hydrodynamic Characteristics ◽  
Nonlinear Part ◽  
Self Focusing ◽  
Lens Focal Length ◽  
Dynamics Of Particles

The electrostriction mechanism of beam self-focusing in nanofluids is theoretically investigated. An analytical solution of the diffusion equation, which describes the dynamics of particles in nanofluids, was obtained and studied. Explicit expressions for the nonlinear part of the refractive index and concentration lens focal length are presented. It is shown that there is a limit on the radiation intensity associated with the physical and hydrodynamic characteristics of the phenomena in these processes.

scholarly journals Evaluating effects of focal length and viewing angle in a comparison of recent face landmark and alignment methods

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Xiang Li ◽  
Jianzheng Liu ◽  
Jessica Baron ◽  
Khoa Luu ◽  
Eric Patterson
Keyword(s):  
Focal Length ◽  
Ground Truth ◽  
Detection Methods ◽  
Viewing Angle ◽  
Deep Convolutional Neural Networks ◽  
Landmark Detection ◽  
High Performing ◽  
Detection Techniques ◽  
And Performance ◽  
Lens Focal Length

AbstractRecent attention to facial alignment and landmark detection methods, particularly with application of deep convolutional neural networks, have yielded notable improvements. Neither these neural-network nor more traditional methods, though, have been tested directly regarding performance differences due to camera-lens focal length nor camera viewing angle of subjects systematically across the viewing hemisphere. This work uses photo-realistic, synthesized facial images with varying parameters and corresponding ground-truth landmarks to enable comparison of alignment and landmark detection techniques relative to general performance, performance across focal length, and performance across viewing angle. Recently published high-performing methods along with traditional techniques are compared in regards to these aspects.

scholarly journals Nonlinear refractive index of porcine cornea studied by z-scan and self-focusing during femtosecond laser processing

2010 ◽  
Vol 18 (4) ◽  
pp. 3700 ◽  
Author(s):  
M. Miclea ◽  
U. Skrzypczak ◽  
S. Faust ◽  
F. Fankhauser ◽  
H. Graener ◽  
...  
Keyword(s):  
Refractive Index ◽  
Femtosecond Laser ◽  
Nonlinear Refractive Index ◽  
Laser Processing ◽  
Self Focusing ◽  
Femtosecond Laser Processing ◽  
Porcine Cornea

Relativistic self-focusing of a rippled laser beam in a plasma

1999 ◽  
Vol 62 (4) ◽  
pp. 389-396 ◽  
Author(s):  
M. V. ASTHANA ◽  
A. GIULIETTI ◽  
DINESH VARSHNEY ◽  
M. S. SODHA
Keyword(s):  
Refractive Index ◽  
Laser Beam ◽  
The Self ◽  
Laser Beams ◽  
Radial Dependence ◽  
Main Beam ◽  
Gaussian Laser Beam ◽  
Self Focusing ◽  
Saturation Effects ◽  
Paraxial Ray

This paper presents an analysis of the relativistic self-focusing of a rippled Gaussian laser beam in a plasma. Considering the nonlinearity as arising owing to relativistic variation of mass, and following the WKB and paraxial-ray approximations, the phenomenon of self-focusing of rippled laser beams is studied for arbitrary magnitude of nonlinearity. Pandey et al. [Phys. Fluids82, 1221 (1990)] have shown that a small ripple on the axis of the main beam grows very rapidly with distance of propagation as compared with the self-focusing of the main beam. Based on this analogy, we have analysed relativistic self-focusing of rippled beams in plasmas. The relativistic intensities with saturation effects of nonlinearity allow the nonlinear refractive index in the paraxial regime to have a slower radial dependence, and thus the ripple extracts relatively less energy from its neighbourhood.

Nonlinear Refractive Index of Silicon Nanoparticles: A Short Review

2014 ◽  
Vol 1 (2) ◽  
pp. 87-97
Author(s):  
Sudakshina Prusty
Keyword(s):  
Refractive Index ◽  
Nonlinear Refractive Index ◽  
Phase Modulation ◽  
Silicon Nanoparticles ◽  
Nonlinear Coefficient ◽  
Short Review ◽  
Self Phase Modulation ◽  
Physical Mechanisms ◽  
Self Focusing ◽  
Physical Phenomena

This article discusses the nonlinear refractive index of silicon nanoparticles starting from the basic formalism to some of the consequent physical phenomena like self focusing and self phase modulation. Several experimental techniques mainly based on Z-scan are discussed to measure the nonlinear refractive index. Another less explored technique for silicon nanoparticles, which studies the far-field optical fringe pattern formed by spatial self-phase modulation, is also discussed. Computation of the nonlinear refractive index is shown in detail by employing these two techniques. While Z-scan can estimate the nonlinear coefficient of a medium in a chosen time scale, the optical fringe method can predict the overall nonlinear refractive index due to all possible physical mechanisms. Some of the recent results for silicon nanoparticles using these two techniques are also discussed.

scholarly journals Resolution and Sensitivity in the Eye of the Winkle Littorina Littorea

1992 ◽  
Vol 170 (1) ◽  
pp. 57-69
Author(s):  
JAN-OLOF SEYER
Keyword(s):  
Electron Microscopy ◽  
Refractive Index ◽  
Focal Length ◽  
Light And Electron Microscopy ◽  
Geometrical Model ◽  
Radius Ratio ◽  
Visual Performance ◽  
Littorina Littorea ◽  
Marine Animals ◽  
Lens Radius

The winkle Littorina littorea (L.) has camera-type (simple) eyes. Light and electron microscopy were used to generate an accurate geometrical model of the eye, and this was used to predict the eye's visual performance. The lens is spherical with a diameter of 112 μm, and examination of images formed by isolated lenses indicates a mean focal length in water of 126 μm. These images are crisp and apparently aberration-free. This, in addition to a shorter than expected focal length, implicates the presence of a gradient of refractive index in the lens. The lens has a focal length to lens-radius ratio of 2.3, which is close to the ‘Matthiessen ratio’ of 2.5 found in the aplanatic lenses of many other marine animals. The lens is predicted to focus images within the retina only when the eye is submerged in water: in air, images are focused distal to the retina. In the central retina, the inter-receptor angle is 1.8° and the rhabdom diameter is 4 μm (5.5 times larger than the diffraction blur-circle), indicating a retinal array coarser than that necessary to sample all the information contained in the image. In addition, a low F-number (1.2) and the large possible angles of incidence of rays striking the retina (up to 40°) mean that the eye is likely to suffer substantial spreading of light between rhabdoms (which are unshielded) and further degradation of resolution. Possible behavioural roles for the eyes are discussed.

scholarly journals Relativistic ponderomotive self-focusing of quadruple Gaussian laser beam in cold quantum plasma

2018 ◽  
Vol 36 (3) ◽  
pp. 353-358 ◽  
Author(s):  
Richa ◽  
Munish Aggarwal ◽  
Harish Kumar ◽  
Ranju Mahajan ◽  
Navdeep Singh Arora ◽  
...  
Keyword(s):  
Refractive Index ◽  
Laser Beam ◽  
Electron Temperature ◽  
Density Perturbation ◽  
Beam Width ◽  
Quantum Plasma ◽  
Gaussian Laser Beam ◽  
Self Focusing ◽  
Linear Differential ◽  
Paraxial Ray

AbstractIn the present paper, we have investigated self-focusing of the quadruple Gaussian laser beam in underdense cold quantum plasma. The non-linearity chosen is associated with the relativistic mass effect that arises due to quiver motion of electron and electron density perturbation caused by ponderomotive force. The non-linearity modifies the plasma frequency in the dielectric function and hence the refractive index of the medium. The focusing/defocusing of the quadruple laser depends on the refractive index of the medium. We have set up non-linear differential equation that controls the beam width parameter by using well-known paraxial ray approximation and Wentzel–Krammers–Brillouin approximation. The effect of intensity parameter and electron temperature is observed on laser beam self-focusing in the presence of cold quantum plasma. From the results, it is revealed that electron temperature and the initial intensity of the laser beam control the profile dynamics of the laser beam.

The receptive fields of Daphnia ommatidia

1976 ◽  
Vol 64 (1) ◽  
pp. 185-202
Author(s):  
S. Young ◽  
A. C. Downing
Keyword(s):  
Refractive Index ◽  
Direct Observation ◽  
Focal Length ◽  
Receptive Fields ◽  
Ray Optics

1. The focal length and positions of the principal planes of an isolated Daphnia lens were determined, and the refractive index of the rhabdom was measured. 2. The lens can form an image, but this always lies well behind the rhabdom. This was confirmed by direct observation of images inside a clear-eye mutant Daphnia eye. 3. The rhabdom was shown to be unlikely to function as a waveguide, and a ray optics model is proposed to enable the prediction of ommatidial receptive fields from the lens data. 4. The predicted receptive fields have wide plateaus and steep sides, and there are virtually no totally blind gaps between neighbouring ommatidia.

Absorption efficiency analysis and optical resonator simulation of Ho:YLF laser pumped with Tm:fiber laser

Laser Physics ◽  
2021 ◽  
Vol 32 (1) ◽  
pp. 015001
Author(s):  
Majid Babaiy Tooski ◽  
Abbas Maleki ◽  
Abdolah Eslami Majd ◽  
Hassan Ebadian
Keyword(s):  
Slope Efficiency ◽  
Doping Concentration ◽  
Continuous Wave ◽  
Focal Length ◽  
Beam Width ◽  
Absorption Efficiency ◽  
Optical Resonator ◽  
Threshold Power ◽  
Continuous Wave Operation ◽  
Lens Focal Length

Abstract In this paper, a Tm:fiber laser pumped Ho:YLF laser is simulated. The absorption efficiency, optimum crystal length, and optical resonator are analytically studied and simulated using LASCAD software, and the atomic-level degeneracies are considered in evaluating the absorption efficiency. In this way, the absorption efficiencies of 65% and 87% are obtained for single-pass 30 mm Ho:YLF crystal with doping concentration 0.5% and 1% respectively. These calculated efficiencies are verified by our experimental measurements and they coincide with acceptable errors. To estimate a proper length for the Ho:YLF crystal with specified doping concentration, the up-conversion, and the reabsorption effects are considered. As a result, we find the 30 mm length crystal is suited for reducing the absorption threshold and prohibiting reabsorption while saturation is controlled. The threshold power and slope efficiency for 65 W pumped powers are calculated by LASCAD software, and the thermal lens focal length of −665 mm is obtained. For a nearly constant beam width inside the cavity and suitable beam overlap efficiency, a concave-concave configuration is chosen for the optical resonator. In the continuous-wave operation, the output power is funded to be 38.4 W and the slope efficiency would be 66%.

Measurement of Lens Focal Length with Hartmann-Shack Wave Front Sensor Based on 4F System

Applied laser ◽  
2013 ◽  
Vol 33 (2) ◽  
pp. 212-215
Author(s):  
许江华 Xu Jianghua ◽  
朱岚 Zhu Lan ◽  
陈家璧 Chen Jiabi ◽  
庄松林 Zhuang Songlin
Keyword(s):  
Wave Front ◽  
Focal Length ◽  
Lens Focal Length
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