Investigation of Transient Signals in Nonuniform Media Based on Diffusion Approximation

2009 ◽  
Author(s):  
Sheng-gang Wang ◽  
Li-ming Ruan ◽  
Hong Qi ◽  
Xi-ying Wang ◽  
Bing-xi Li
Keyword(s):  
Optical Properties ◽  
Diffusion Approximation ◽  
Near Infrared ◽  
Short Pulse ◽  
Numerical Models ◽  
Optical Tomography ◽  
Laser Pulses ◽  
Biological Tissues ◽  
Infrared Light ◽  
Short Laser Pulses

With the development of the ultra-short laser technology, a new optical detection field based on the transient laser pulse signals will emerge in the future. Ultra-short laser pulses have been used in biological fields to obtain the optical properties of vivo tissues. There are many numerical models to simulate the propagation of short laser pulses in tissue medium. However, since most biological tissues show a high scattering and low absorption characteristics for near-infrared light, the most popular model is diffusion approximation method. Although with many limitations, its greatest advantage is higher computational efficiency. The propagation of short pulse laser in two dimension nonuniform medium is simulated based on the diffusion approximation model in present paper. The numerical method is validated by comparing the numerical results with the theoretical analysis results in semi-infinite uniform slab medium. Then diffusion approximation is used to simulate the transfer process of ultra-short pulses in two dimensional inhomogeneous medium. Finally, The influences of inclusions with different sizes and optical properties on time-resolved reflected signals are presented. This can help to choose suitable detection parameters in diffuse optical tomography.

scholarly journals DEVELOPMENT OF ULTRA-SHORT HIGH INTENSITY LASERS FOR THE VISIBLE SPECTRA RANGE

2020 ◽  
Vol 17 (35) ◽  
pp. 739-752
Author(s):  
Hayder J. ABDULRAHMAN ◽  
Suzan B. MOHAMMED
Keyword(s):  
High Intensity ◽  
Laser Processing ◽  
Near Infrared ◽  
Laser Pulses ◽  
Dielectric Materials ◽  
Infrared Light ◽  
Near Infrared Light ◽  
Visible Spectra ◽  
Short Laser Pulses ◽  
Micro Tools

Ultra-short laser pulses are particularly suitable for processing micro tools made of ultra-hard and dielectric materials. Ultra-short laser pulses provide a contact-free and precise fabrication of heat-sensitive materials such as visible spectra range. Visible spectra range has unique properties, which makes it an essential material in the tool, jewelry, and semiconductor industries. The processing of visible spectra range by ultra-short laser pulses is complex, as visible and near-infrared light is generally not absorbed. However, the intensity of ultra-short laser pulses is extremely high, so that the absorption scales nonlinearly with the intensity and, thus, visible or near-infrared light can be absorbed. The complexity also results from many partially interdependent process variables, such as the repetition rate, pulse overlap, track overlap, and scan speed. Excellent knowledge of the process is, therefore, essential for the production of micro tools. To make the laser processing accessible to a broader user field, the operator can be supported by a computer-aided design (CAD). The aim of this research was to the modeling of an ultra-short high-intensity laser for the visible spectra range in different environments of the angle of incidence, scanning speed, pulse, and track overlap. The experimental process included ultra-short pulsed laser processing of visible spectra range and surface analysis concerning modifications and ablation of the ultra-short laser. Ablation volumes were analyzed for single pulses, multi-pulses, and pockets. Pump-probe experiments reveal transient optical properties such as transmission or reflectivity. It was concluded that ultraviolet laser pulses are best suited to induce damage or modifications to visible spectra range surfaces. Additionally, shorter wavelengths have further advantages such as potentially longer Rayleigh lengths and smaller spot sizes.

scholarly journals Imaging System Based on Silicon Photomultipliers and Light Emitting Diodes for Functional Near-Infrared Spectroscopy

2020 ◽  
Vol 10 (3) ◽  
pp. 1068 ◽  
Author(s):  
Giovanni Maira ◽  
Antonio M. Chiarelli ◽  
Stefano Brafa ◽  
Sebania Libertino ◽  
Giorgio Fallica ◽  
...  
Keyword(s):  
Infrared Spectroscopy ◽  
Human Brain ◽  
Near Infrared Spectroscopy ◽  
Near Infrared ◽  
Light Emitting Diodes ◽  
Optical Tomography ◽  
System Optimization ◽  
Infrared Light ◽  
Functional Near Infrared Spectroscopy ◽  
Light Emitting

We built a fiber-less prototype of an optical system with 156 channels each one consisting of an optode made of a silicon photomultiplier (SiPM) and a pair of light emitting diodes (LEDs) operating at 700 nm and 830 nm. The system uses functional near-infrared spectroscopy (fNIRS) and diffuse optical tomography (DOT) imaging of the cortical activity of the human brain at frequencies above 1 Hz. In this paper, we discuss testing and system optimization performed through measurements on a multi-layered optical phantom with mechanically movable parts that simulate near-infrared light scattering inhomogeneities. The baseline optical characteristics of the phantom are carefully characterized and compared to those of human tissues. Here we discuss several technical aspects of the system development, such as LED light output drift and its possible compensation, SiPM linearity, corrections of channel signal differences, and signal-to-noise ratio (SNR). We implement an imaging algorithm that investigates large phantom regions. Thanks to the use of SiPMs, very large source-to-detector distances are acquired with a high SNR and 2 Hz time resolution. The overall results demonstrate the high potentialities of a system based on SiPMs for fNIRS/DOT human brain imaging applications.

Optical diagnostics of laser-produced plasmas with ultra-short laser pulses

1980 ◽  
Vol 298 (1439) ◽  
pp. 407-414 ◽  
Keyword(s):  
Short Pulse ◽  
Laser Pulses ◽  
Laser Fusion ◽  
Light Pressure ◽  
Laser Plasma Interaction ◽  
Short Laser Pulses ◽  
Short Pulse Lasers ◽  
Pellet Density ◽  
Laser Heated ◽  
Interaction Problem

In laser fusion experiments the interesting phenomena occur on a picosecond timescale. Short-pulse lasers in combination with high resolution optics offer a powerful diagnostic tool. After a short description of the principles and experimental techniques I discuss three specific areas of the laser-plasma interaction problem, namely heat transport in the corona of a laser heated pellet, density profile steepening by light pressure and the generation of magnetic fields.

scholarly journals Generalized Beer–Lambert model for near-infrared light propagation in thick biological tissues

2016 ◽  
Vol 21 (7) ◽  
pp. 076012 ◽  
Author(s):  
Manish Bhatt ◽  
Kalyan R. Ayyalasomayajula ◽  
Phaneendra K. Yalavarthy
Keyword(s):  
Light Propagation ◽  
Near Infrared ◽  
Biological Tissues ◽  
Infrared Light ◽  
Near Infrared Light ◽  
Lambert Model

Theoretical and experimental analysis of scan angle-depending pulse front tilt in optical systems for laser scanners

2016 ◽  
Vol 5 (1) ◽  
Author(s):  
Lasse Büsing ◽  
Tobias Bonhoff ◽  
Lars Behnke ◽  
Jochen Stollenwerk ◽  
Peter Loosen
Keyword(s):  
Experimental Analysis ◽  
Short Pulse ◽  
Laser Pulses ◽  
Industrial Applications ◽  
Optical Systems ◽  
Full Potential ◽  
Pulse Front ◽  
Laser Scanners ◽  
Short Laser Pulses ◽  
Ultra Short Pulse

AbstractFor realising fast and highly dynamical laser-based material processing, scanner systems are already utilised for many different industrial applications. Furthermore, ultra-short pulsed (<1 ps) laser sources provide possibilities of processing most different materials with highest accuracy. Owing to the large spectral bandwidth of ultra-short laser pulses, dispersion in optical components becomes relevant. The dispersion in optical systems for laser scanners may lead to scan angle-depending pulse properties as, for example, pulse front tilt. The investigation of these effects is not state of the art today but absolutely necessary to exploit the full potential of laser scanners for ultra-short pulse applications. By means of an exemplary focusing lens, the simulation and experimental analysis of scan angle-depending pulse front tilt is presented for the first time.

Anisotropic optical properties of oriented silver nanorice and nanocarrots in stretched polymer films

Nanoscale ◽  
2015 ◽  
Vol 7 (19) ◽  
pp. 8858-8863 ◽  
Author(s):  
Xia Tong ◽  
Hongyan Liang ◽  
Yanlong Liu ◽  
Long Tan ◽  
Dongling Ma ◽  
...  
Keyword(s):  
Optical Properties ◽  
Polymer Films ◽  
Spectral Region ◽  
Near Infrared ◽  
Infrared Light ◽  
Near Infrared Light

Oriented arrays of silver nanorice or nanocarrots in stretched polymer films show polarization-dependent transmission of near-infrared light over a wide spectral region.

Decreased cerebral haemodynamic response to cognitive and physiological tasks in mood disorders as shown by near-infrared spectroscopy

2002 ◽  
Vol 32 (6) ◽  
pp. 1029-1037 ◽  
Author(s):  
K. MATSUO, ◽  
N. KATO ◽  
T. KATO
Keyword(s):  
Infrared Spectroscopy ◽  
Mood Disorders ◽  
Near Infrared Spectroscopy ◽  
Near Infrared ◽  
Poor Response ◽  
Biological Tissues ◽  
Functional Brain Imaging ◽  
Infrared Light ◽  
Invasive Technique ◽  
Physiological Tasks

Background. Hypofrontality has been demonstrated in mood disorders by functional brain imaging methods such as positron emission tomography. However, the neurobiological basis of hypofrontality has not been well clarified. Near-infrared spectroscopy (NIRS) is a non-invasive technique for continuous monitoring of alterations in oxygenated (oxyHb) and deoxygenated (deoxyHb) haemoglobin using near-infrared light, which penetrates biological tissues.Methods. We used NIRS during cognitive and physiological tasks to investigate alterations of haemoglobin oxygenation in the frontal region of euthymic patients with mood disorders (major depressive disorder (MD) and bipolar disorder (BP)) and in controls.Results. The increase of oxyHb during a verbal fluency task was significantly less in the MD and the BP groups than in the controls. The MD group showed a significantly smaller decrease of oxyHb during hyperventilation than the controls. The BP group also showed a similar trend.Conclusions. These findings suggest that the hypofrontality in mood disorders may be associated with a poor response in the cerebral blood vessels to neuronal and chemical stimuli.

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