A novel high-average-power pulsed CO2 laser with a unique electrode structure is presented. The operation of a 5-kW transverse-flow CO2 laser with the preionized pulse-train switched technique results in pulsation of the laser power, and the average laser power is about 5 kW. The characteristic of this technique is switching the preionized pulses into pulse trains so as to use the small preionized power (hundreds of watts) to control the large main-discharge power (tens of kilowatts). By this means, the cost and the complexity of the power supply are greatly reduced. The welding of LF2, LF21, LD2, and LY12 aluminum alloy plates has been successfully achieved using this laser.
A measurement interferometer available for wafer stage metrology of lithography has been investigated by means of resolution-extending of optical subdivision based on commercial interferometers. Factors that determine the accuracy, linearity and repeatability of nanometer-scale measurements of displacements exceeding hundreds of millimeters and of target velocities exceeding hundreds of millimeters per second are also discussed.
A fiber-optic biosensor is developed based on the principle of evanescent wave while light propagates in optical fiber. The biosensor uses a red laser diode at 636.85 nm for exciting Cy5 fluorescent dye. Sensitivity limit of 0.01 nnmol/l is obtained from the detection of serial Cy5 solutions with various concentrations. In log-to-log plot, excellent linear response characteristic is seen in the Cy5 concentrations ranging from 0.01 nmlo/l to 100 nmol/l. And a good result of signal-to-noise ratio of 4.61 is obtained when the biosensor is used to measure Legionella pneumophila solution of 0.01 μmol/l. All the results are comparable with those that are obtained by a commercial biochip scanner GeneTAC 1000.
KEYWORDS: Laser optics, Control systems, Humidity, Lenses, Device simulation, Optical simulations, Carbon dioxide lasers, High power lasers, Temperature metrology, Sensors
Lasers are now widely used in various industrial circumstances with changeable room conditions. If the humidity and the temperature in an operation room are not well controlled, a thin layer of water can be formed on the surfaces of laser optics by the effect of "dewfall," which could cause damages of expensive laser optics such as output coupler and/or focusing lenses. In this work, we design and develop an alarm device to monitor and control the dewfall for industrial CO2 lasers; however, the device is also useful in other cases which require alarm and control of dewfall.
Using a high power pulse transverse flow CO2 laser developed in our lab, a series of thin Al alloy plates were successfully welded. Effects of processing parameters (beam quality, laser power, welding speed and assisting gas et al) on weldability of Al alloy plates were given. A key technique, artificial keyhole caused by the gap between two Al alloy butt plates is successfully used, which helped to break through their high reflectivity at 10.6 μm wavelength and enhanced the energy coupling efficiency. The weld thickness of Al alloy plates reached 4 mm with 3 kW CO2 laser average output power. Microhardness and tensile tests showed that for some Al alloys, mechanical properties of the welds could be near or equal to base material with the artificial keyhole technique and suitable processing parameters.
The focusing characteristics of higher-order mode Gaussian beams in flying optics were investigated in detail. On the basis, a novel adaptive laser processing system for flying optics was developed. In the system, a lens with long focal length and two adaptive deformable mirrors controlled by hydraulic were employed. The lens was near the laser source for some distance and the two adaptive mirrors were integrated together with parabolic focusing mirror. The system has the advantages of compact structure and easy control. The system can keep the focus position and the focus radius constant for long distance laser processing.
KEYWORDS: Resonators, Mirrors, Reflectivity, Reflectors, Laser resonators, Xenon, Gas lasers, Energy efficiency, Pulsed laser operation, Chemical species
A folded resonator for pulsed reactor-pumped lasers (RPL) is presented, which has a zigzag propagation inside and high coupling efficiency with the nuclear reactor. The equivalent length of gain cell in this device is multiplied. Thus higher optical intensity may be coupled out when high reflectors are available. For a 3He/Ar/Xe system, the energy loading is relatively uniform and the appropriate size for resonator can be easily achieved by calculations. A method for optimizing of outcoupling is discussed in the work as well.
Research on change of Rayleigh range ZR of output beams and effect of focusing characteristics caused by the dynamic process of resonator deformation especially for the HR coupler in high power CO2 Laser is given in this paper. An adaptive optics system which can compensates the change of Rayleigh range ZR was used. The real-time control of focus position was achieved.
Review on recent progress of laser precision microfabrication in China is given in this paper. The universal fields of the LPM mostly using short pulse and short wavelength lasers in China are as follows: new materials, advanced manufacturing technology, information technology, biological technology, medical treatment and so on, which are given priority to the development in high-tech fields in China.
A laser-diode based optical sensor for laser particle counter is described,nd some calculated and test results are reported in this paper. A low-powered 650 nm laser diode is used as the light source. The optical system of the sensor is a right- angle scattering optics, which consists of an illumination system and a wide-angle collection system for scattered light. The sensor features high counting efficiency and high signal- to-noise ratio for smaller particles.
In lightcraft vehicle system, a ringy laser beam is focused by a 90 degree off-axis annular parabolic mirror. In this paper, methods are applied combining the geometrical optics and the physical optics. The effects of the angular misalignment of the optical axis and divergent angle on the focal power density are analyzed. Ray tracing shows that a pair of vertical focal lines is produced due to the angular misalignment. Basing on this, and from the theory of diffraction optics, we can know that the incident Gaussian beam will become the beam that is similar to the elliptical Gaussian mode for the misalignment. Moreover, the focal power density is decreased due to the angular misalignment. The parabolic mirror is very sensitive to misalignment of the incident beam, and the misalignment angle on the order of magnitude of mrad magnitude is enough to decrease peak power density down to the half. The tolerance of the misalignment angle down rapidly with the incident beam diameter increasing. When the incident angle has a divergent angle, coma is produced that also decrease the power density at focal plane.
In a general way, study on the distributions of laser modes is under the condition that the modes are regularly distributed. In fact, because of the misalignment of resonator, sometimes the output laser modes are irregular, and because of the superposition of laser modes, and the disturbance of the atmosphere in the process of propagation, laser beams output are partially coherent. In this paper, with the aid of the computer, the far field distributions of some laser modes and the influence of spatial coherence on the distributions are discussed.
Study on focus characteristics of the laser beam for long distance propagation in atmosphere is very important for many laser applications, especially for lightcraft vehicle, laser weapon. In this paper, the influence of atmospheric turbulence and thermal blooming on focus characteristics of laser beam is given for several typical lasers with different wavelength. The excursion of the laser beam axis for long distance propagation in atmosphere is also obtained for several laser beam axes. The calculations coincide with the experimental result.
KEYWORDS: Aluminum, Carbon dioxide lasers, Laser welding, Particles, High power lasers, Crystals, Laser crystals, Reflectivity, Absorption, Chemical elements
By means of a transverse flow 5 kW CO2 laser with low- order mode laser beam output, 1 - 4 mm thick aluminum alloy plates 6063 and LY12 were successfully butt welded. The result shows that the butt weldability and the weld quality of the aluminum alloy plates are mainly dependent on incident laser power density, laser beam defocused distance and shielding gas. The relationship between the weld quality of the aluminum alloy plates and the welding parameters is discussed. The macrostructure and microstructure of the welded seams are analyzed. The mechanical properties of the welded seams are discussed.
A keyhole enhances the absorption coefficient greatly and helps the laser energy to penetrate deeper into the material in laser welding on aluminum alloys. We set up a simple model to estimate the threshold conditions to form a keyhole and analyzed the effects of various parameters on laser welding theoretically and experimentally. By the measurement of the spectral signals the laser welding state can be monitored during processing.
KEYWORDS: Cladding, Annealing, Aluminum, Scanning electron microscopy, Transmission electron microscopy, Crystals, Gas lasers, Coating, Thermal analysis, Chemical elements
This paper deals with amorphous structures in the laser cladding. A kind of Ni-Cr-Al alloy was sprayed on the substrate, which was ZL111 alloy, to be the coating material. The coating was clad by 5 kW transverse flow CO2 laser. The observation of SEM and TEM revealed that in the laser cladding there were amorphous structures which appeared two different morphologies: one was space curved flake-like, which existed in the white web-like structures; the other was fir leaf-like, which existed in the grain-like structures. Differential thermal analysis (DTA) was used to semi- quantitatively determine the content of the amorphous structures. A curve relation was obtained between the content of amorphous structures and the dimensionless laser cladding parameter C. The changes of the amorphous structures after annealing were also shown.
Generally, the ABCD law for the complex parameter q of the TEM00 Gaussian beam is not valid for high-order modes. The focussing of a Gaussian beam means imaging of the beam waist. Under this condition, the spot size in the virtual part of the parameter q should be substituted by the Rayleigh range of a certain resonator. Thus, the ABCD law of the parameter q can be used for the high-order modes or their superposition. The calculation shows that when the focus lens moves along the optical axis, the change of focal length and focal depth is not relative to the orders of the Gaussian beam modes for an ideal resonator without distortion. For high power gas lasers or solid lasers, the distortion of the resonator components can change the resonator parameters, and also the Rayleigh range. In this situation, for a certain resonator, its focus characteristics, including the change of focal length and focal depth, are relative to the output power. It's important for the applications of the laser space craft vehicle and flying optical processing.
In high power cw-CO2-laser welding, assisting gas is necessary. It has a great effect on the welding results, such as penetration depth, cross section, size of the heat affected zone and welds surface. Much has been done on discussing the influence of its kind and flow rate on the welding results, but little attention was given to its configurations. In this article, several configurations of assisting gas were tried and the according welding results were given. Especially, a new gas assisting configuration including three gases was suggested. Their influences on the topography and cross sections were qualitatively analyzed. Experimental results showed that the best welds were obtained with the new three-gas-configuration.
The thermal deformation in penetration welding with a laser has been investigated as a factor which results in the elevation on the surface of the weld. Qualitative analysis of the course of thermal deformation during which elevation is made has been presented in detail. A series of comparison laser welding experiments was done with a 5kW CO2 laser. The experimental results showed that there were always a slight warp and a lateral shrinking of the workpiece together with the elevation on the surface, which had been predicted by the analysis. The influence exerted by shielding gas on the topography of the weld has also been discussed. The shielding gas is supposed to affect the pressure above the surface of the welding pool. The shape of the surface of the welding pool is determined by the difference between pressures on both sides of the surface in term of Laplace equation. When the distribution of the gas pressure was homogeneous within the range of the welding pool, a fairly smooth topography was experimentally obtained. Otherwise, obvious ripples were observed along the weld.
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