Proc. SPIE. 9142, Selected Papers from Conferences of the Photoelectronic Technology Committee of the Chinese Society of Astronautics: Optical Imaging, Remote Sensing, and Laser-Matter Interaction 2013
Based on the heat transfer theory and finite element method, the macroscopic ablation model of Gaussian beam laser irradiated surface is built and the value of temperature field and thermal ablation development is calculated and analyzed rationally by using finite element software of ANSYS. Calculation results show that the ablating form of the materials in different irritation is of diversity. The laser irradiated surface is a camber surface rather than a flat surface, which is on the lowest point and owns the highest power density. Research shows that the higher laser power density absorbed by material surface, the faster the irritation surface regressed.
Proc. SPIE. 7658, 5th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optoelectronic Materials and Devices for Detector, Imager, Display, and Energy Conversion Technology
KEYWORDS: Signal to noise ratio, Wavelet transforms, Image processing, Wavelets, Denoising, Light scattering, Linear filtering, Image filtering, Electronic filtering, Mathematical morphology
In this paper, an image-denoising method is presented based on mathematical morphology and wavelet transform. Highfrequency
coefficients are processed by mathematical morphology firstly. Then, according to the respective
characteristics, high frequency sub-band images at horizontal, vertical and angular directions are denoised by three
different filter templates after wavelet transform. We take measures to protect edge information and detail of image.
Experiment result shows that the noise of the image is removed effectively. At the same time, the detail of the image is
kept well. The method has better denoising effect.
Terahertz (THz) technology, as new research topic and technology field which is paid more and
more attention by the researchers and governments, has some unique properties which is different
from other electromagnetic wave. THz wave is regarded to have potential application in many fields.
Existing and emerging applications of terahertz technology in imaging, medicine, biology, space
exploration, covert communications, compact radar ranges, industrial controls, terahertz microscopy,
terahertz tomography, and homeland security have stimulated intensive research effort in photonics
and electronics technologies bracketing the famous terahertz gap from the high and low frequency
sides, respectively. Cutoff frequencies and maximum frequencies of operation of InGaAs-based
Heterostructure Bipolar Transistors and High Electron Mobility Transistors are now approaching or
even exceeding 600 GHz. New ideas of using plasma resonances of two-dimensional electrons for
tunable detection and emission of terahertz radiation are being explored and proven experimentally.
Plasma effects in polarization-induced electrons and holes in granular pyroelectric/semiconductor
heterostructures hold promise of an active THz medium tunable by external electric field or light.
Laser cleaning technology has great advantages. The influence of beam incidence angle was studied in the case of
the removal weakly absorbing particles on absorbing particles on absorbing Si wafers by 248 nm DUV light pulse.
By decreasing the beam incidence angle from 80° to 10°, the removal efficiency of 0.15-0.30 µm Si<sub>3</sub>N<sub>4</sub> particles
was increased by 30-45%, while no improvement was observed with 0.3 μm SiO<sub>2</sub> particles. Theoretical
calculations show that decreasing the incidence angle from 80° to 10° results in a 30-fold increase of the horizontal
component of the radiation pressure force, whereas the vertical component remains unchanged as the beam width
must be decreased to keep a constant fluence at the workpiece. This force would help removing particles by
making them roll. Based on theoretical calculations, it is proposed that the enhanced removal of particles at grazing
incidence is caused by the horizontal component of the beam radiation pressure. The difference between Si<sub>3</sub>N<sub>4</sub> and
SiO<sub>2</sub> particles is attributed to the influence of particle shape on van der Waals adhesion forces: the adhesion force
of irregularly shaped Si<sub>3</sub>N<sub>4</sub> particles would be comparable to the horizontal component of the radiation pressure
force, whereas the adhesion force of spherical SiO<sub>2</sub> particles would be higher.
Along with the development and application of nanometer technology, a machine that allows deterministic position and manufacturing at the atomic level is required. An optical microscope of the machine was designed particularly to locate line features on a grid plate. It was designed to achieve nanometer level repeatability. The microscope uses a modulated light-emitting diode as its light source. It has two channels for optical imaging: one consists of two slits for precision measurement of line positions and the other of a camera for direct visual observation. A lock-in amplifier is used for demodulating the electrical signal from the photodiodes behind the slits. Initial experiments locating crosses on a grid plate indicate a repeatability of approximately 1 nm, one standard deviation. It was found that the measured line position is related not only to the focus but also to the illumination. There exists a particular orientation of the illumination where the measured line position is relatively insensitive to the focus, because of which the microscope is able to achieve nanometer level repeatability. Repeated measurements were performed on both an uncalibrated and a calibrated plate. Repeatabilities of better than 1 nm were obtained over time periods of several days; however, the ultimate accuracy of the machine still has to be demonstrated.
The principles of laser ultrasonic generation and measurements with pulsed laser are presented. There are two kinds of means to actuate ultrasonic pulse: elasticity actuating and ablation actuating. The progress in laser ultrasonic about laser ultrasound generation, detection, propagation and its applications is introduced briefly. Applications in the field of Non-Destructive Testing (NDT) are reviewed. In the field of Non-Destructive Testing, according to the principle, the laser ultrasonic testing system consists of laser system, laser interferometer, photoelectric detector and receiving system with signal amplifier. Thus, long-range and non-contact on-line detection of ultrasonic testing system was realized. In view of some of the problems, the developing trends of such techniques are analyzed.