High power LDA's in general have an emitter line dimension of 1cmx1μm and a beam divergence of 40°x10°, which could not be delivered or focused effectively with common optics. With the ever-increasing needs of high power diode laser sources, it is crucial to obtain high power high brightness diode laser beam with improved optical quality. Although it has been known that beam shaping techniques can be used to achieve this aim, it has been challenging to shape the laser beam effectively and efficiently to deliver it through an optical fiber with high brightness. By using a new beam shaping technology developed recently, however, brightness over 2.4 MW/cm<sup>2</sup>-str has been achieved by delivering 28W from a 0.1mm multimode fiber. Diode lasers are the most efficient laser comparing with other lasers, and its application in various industrial sectors will become more and more extensive.
We conducted studies of some optical imaging systems having super resolution pupil functions for 0.18 micrometers to 0.1 micrometers lithography as well as for high resolution inspections. The optical systems with these aperture stops have high transmissivity to illumination light beam if appropriate illumination optical systems are used, and have large depth of focus. When this optical imaging method is applied to optical inspection systems, the resolutions of these optical systems can be doubled. The theory of this new optical imaging method is discussed along with the theory and design of illumination optical system. The imaging method will be easy to implement, and can be used for steppers, direct writing lithography, and confocal microscopes.
By now laser conditioning has been proved to be a useful method to improve the optical coatings and raise the laser induced damage threshold of the thin film coatings. However, whatever happens during the laser conditioning process and which ever factor influences the laser conditioning effect are still not very clear. We produce a series samples with different roughness levels of the substrates, multilayer design, thin film material and the vacuum environment of the chamber. We make laser conditioning test to these samples by 1.06 micrometers laser. Photothermal deflection technology is employed to observe the conditioning process in-situ. A series of experimental data are obtained. We give our explanation. The mechanism of laser conditioning is also discussed.
Laser induced damage in optical coatings is a complicated problem, which is attributed to a lot of factors, including environment parameters, laser parameters and thin film production parameters. Among the three factors, production parameters interest us most. We produce a series of samples with different roughness levels of the substrates, thin film material and vacuum environment within the chamber, etc. Using 1.06 micrometers Nd:YAG laser as our test laser, we make 1- on-1 laser damage test to these samples. Some interesting phenomena are found. We calculate the laser induced local heating within the thin film multilayers, and make analysis to the experimental phenomena. Conclusions are given.
A new concept for roughness measurement is presented in this paper. The new concept is the mean surface that describes the summation of the shape, error and waviness of a profile surface measured by the interferometric microscope. The mean surface is fitted by the Zernike polynomials in a least squares sense. When the mean surface is subtracted from the profile data, the roughness can be calculated. The numerical simulations show that the accuracy is enough high.
The design of a pseudospark chamber, a high-voltage (>100
kV), high-current density, low-emittance and high-brightness electron
beam source which can provide high-quality beams for free-electron lasers
(FELs), driven by a modified pulse line accelerator, is presented.
Based on the hollow cathode (HC) effect and the pseudospark (PS)
empirical formula, the HC parameters, the cathode-anode separation,
and the working gas pressure region are determined. The general experimental
setup of the high-brightness PS-produced electron beam
source is shown.
The mode-matching problem of a multislab cascade laser is investigated. Optimized parameters of the multislab cascade laser resonator were derived using computer simulation. The theoretical analysis was confirmed by the experiment. High output efficiency can be achieved with properly chosen resonator parameters. The output power of the two-slab cascade laser was measured at more than 90% of the output power summation of each single-slab laser.
An expression of evanescent field of the scanning near-field optical microscope (SNOM) and a few effects on the resolving power are given. The concept about degrees of freedom of light information transmitted and resolution of SNOM are reviewed.
Here we put forward the idea of getting superresolution in confocal setup with apodization film. By this configuration we can suppress the background noise aroused by apodization film, and further avoid problem owing to non-axial points when modified lens is used solely. Also we introduce a new model based on the confocal setup to explain superior resolution mechanism in near field optical microscope. Theoretical development and skeptical comments are given in this paper.
Evaluation of laser-induced damage in optical coatings employing a surface inclusion adhesion layer model is presented. The effects of thermal and optical absorption of an inclusion adhesion layer on a coating surface irradiated by a laser pulse can induce coating damage. The effects of the adhesion layer extinction coefficient, thickness, and heat conductivity on the laser-induced damage threshold of the coating are investigated by thin-film temperature field distribution analysis. Laser-induced damage on high-reflectance (HR) multilayer and ion-beam-sputtered coatings are analyzed.
In this paper, aberrations in reconstruction are analyzed, and aberration elimination method are discussed, and the feasibility of direct reconstruction of lensless Fourier transform x-ray hologram with visible light is investigated.
A new type of cavity, a distributed feedback cavity from periodically rippled walls is developed. The Raman free electron laser (400 KeV/800 A) with the new cavity is studied. The spectral measurements using a microwave grating spectrometer are presented. The frequency selection, narrowed spectral bandwidth with central wavelength at 8 mm, and output power enhancement show that oscillation happened.
One compact optical architecture for implementation of second-order neural network, which get rid of some redundant terms of the input vectors and the interconnection matrix without reducing its associative memory, is put forward.
The earliest laser application in medicine has occurred in ophthalmology. In 1965,the Shanghai Institute of Optics and Fine Mechanics, Academia Sinica, suy developed the first laser retina photocoagulator in China. It was an experimental prototype. Then the laser ophthalmic experiment for animal and for clinical demonstration were carried out at the Shanghai No. 6 People's Hospital. Since 1970 ,further effort has been made to improve the performances of this experimental system, and the ruby laser retina photocoagulator has been produced for clinic application. In 1972 ,a ruby laser photodisruptor was developed ,and was used for clinic peripheral iridectomy one year later. Since 1970,in addition to Shanghai,mo.st of the large cities of China,such as Beijing ,Shenyang,Guangzhou ,Hefei ,Chengdu and Xumou etc. successively started laser ophthalmology. Now the laser ophthalmology has become widespread medical application in China. The municipal hospitals of all provinces except Tibet and the suburban county hospitals have set up their laser ophthalmic clinics. As a regular medical technology ,laser has provided effective treatment for over thousand of the eye diseases patients every year. Among all cities of China , Shanghai is the leading and mo.st developed city in ophthalmology. 220 hospitals in Shanghai set up their laser clinics,and most of them has laser ophthalmic treatment divisions. Recently ,the Shanghai Research Center for Laser Medicine has been established in the Shanghai Second Medical University. The Center has assembled many famous laser medical experts and laser engineering experts. The ophthalmic laser application is its major effort.
Femtosecond pulse have an appreciable spectral width and it is not possible to satisfy the phase matching condition for all the possible frequency components in the spectrum. This allows pulse propagation with a group velocity that differs from the phase velocity. The difference in the group velocity between the fundamental and harmonic radiation complicates the second harmonic generation. In this paper, the characteristics of SHG from femtosecond optical pulse are discussed. Analytical solutions for the harmonic pulse shape and conversion efficiency in non-depletion condition are presented. In time domain coupled equations in general condition are solved by numerical method. Phase mismatching effect on the harmonic pulse shape and conversion efficiency is analyzed.
A novel polymer film doped with natural active chloroplastin was formed by spin coating backings. The nonlinear refractive index of this composite polymer was measured by picosecond laser pulses. Comparing our experimental setup for measuring nonlinear refractive index and the response time of our samples with the original Z-scan system proposed by M. Sheik-Bahae et al., we added a variable time delay path and a tunable probe beam into this system to implement the measurement of the response time and spectra of n<SUB>2</SUB>. The nonlinear refractive index and response time of the polymer film ((alpha) equals 1.29 cm<SUP>-1</SUP>) is about 4.9 X 10<SUP>-8</SUP> esu and 85 ps. When we put a F-P filled with the polymer film into a nanosecond pulse laser path, we observed optical bistability phenomena. The rising time was less than 1 ns and the recover time was about 2.5 ns. Analyzing and comparing the nonlinearities of chloroplastin derived from heat effects and (pi) -electron transition, we found that the heat effects, reorientation, and redistribution of the chloroplastin molecule can be neglected and the large optical nonlinearities of the film were of electronic origin.
Temperature distributions of Ti02 single layer irradiated by iOns,
1. 06 m wavelength laser pulse were calculated with thermal transfer
equation. Following conclusions were obtained: To improve thermal
parameters of coating can reduce the peak temperature obviously; The
thermal parameters of substrate have little effect on temperature
response of coating; Temperature distribution of thin film depends on
the electrical field distribution, The peak temperature of quarter
-wavelength coatings is lower than that of half-wavelength coatings.
Centroid and geometric center methods are suggested for tracing the center location of an irregular interferogram in this paper. The methods remove limitations of general software which may only analyze straight or quasi-straight fringe patterns. The F-test method is used to control accuracy of fringe analysis. The speed and accuracy of the software depend upon the quality of the fringe pattern and a number of sample points.
The thermal conduction theory based on uniform heating in the slab laser has been presented before, but results from the theory are very different from the results of experiments. In this paper, a non-uniform heating model based on the absorption law of the medium is proposed. According to the model, the temperature distribution in the slab laser under CW and pulse pumping is solved. Thermal stress and fracture limitation of the slab are given. The new model is in good accordance with the experimental results.
A rotating pipe geometry laser is one of the schemes for obtaining high average-power output. The theory on thermal effects of the laser is proposed and the corresponding experimental results are given. An output power of 200 W is obtained from this laser at 20 Hz with laser efficiency of 2.2% and slope efficiency of 3.5%. Finally, the parameters of the laser of KW are discussed.
TiO<sub>2</sub> and ZrO<sub>2</sub> coatings were prepared by ion beam sputter deposition. Refractive indices, optical absorptions, and laser-induced damage thresholds of the films were investigated. The optical absorptions of thin films are decreased obviously.
High quality ZnSe-ZnS strained-layer superlattices (ELSs) were grown by molecular beam epitaxy (MBE). Photoluminescence and Raman-scattering measurements were carried out to evaluate the optical properties of the SLSs.
Design and construction of a deep-UV projection lens for use in sub-micron excimer laser lithography is reported. Its spectral band is wide enough for an unnarrowed excimer laser used as an illumination source.
This family of optical systems is developed from the Wynne-Dyson system, which can be used in UV and deep-UV lithography systems. Its numerical aperture is larger than 0.4, its spectral bandwidth is wide, so the unnarrowed excimer laser or mercury lamp can be used as an illuminator in these lenses and even the through-lens alignment system can be used in the lithography systems in which these lenses are used.
Pulsed phototherinal deflection technique (pulsed-PDT) is employed to make insitu investigations of laserinduced damage in optical coatings. Preliminary experiniental results show that the technique is capable of providing a lot of new information about not only the damage thresholds but also the damage processes of which of particular interest are the transient damage 1ehavior and the cumulative effect. key words: laser damage optical coating in-situ investigation photothermal deflection pulse duration and wavelength effect thermal property. 1 .
In this paper wavelength dependent damage phenomena in SiO2 overcoats on TiO2/SiO2 and ZrO2/SiO2 HR coatings are systematically investigated with the help of various techniques, including a dynamical study of the damage process by time-resolved photothermal deflection technique, microscopic analysis of the absorption sites by CW-modulated photothermal microscopy, and observation of the coating microstructures and damage morphology by TEM and Nomarski optical microscopy. From the data for 355 nm and 1.06 micron radiation and a theoretical calculation of the temperature distribution inside the coating, we conclude that damage occurs first either in the HR coating or in the overcoat depending on the wavelength of the incident radiation.