In this paper, a series of experiments of drilling holes and slotting micro-channels on the 1 mm-thick BK7 or 1.1 mmthick B270 glass substrates are introduced by employing three types of Q-switched lasers with the wavelength of 1064, 355, and 266 nm. Firstly, by smearing the solution of NiSO4∙6H2O on the front surface of BK7 glass plates, we successfully realized drilling holes on the glass substrates by employing a 1064 nm fundamental Nd:YAG laser. Then, we also carried out the experiments of drilling holes by utilizing a normal third-harmonic-generation (THG) 355 nm Nd:YAG laser and a 266 nm FHG (forth-harmonic-generation) laser. It can be found that the diameters of drilled holes by utilizing a 355 nm laser are larger than those by utilizing a 266 nm laser, and the holes with both two wavelengths lasers did not change a lot when the exposure time of lasers was increased from 0.5 s to 30 s. Finally, the experiments of slotting micro-channels on B270 glass plates were undertaken by utilizing both a 355 nm laser and a 266 nm laser. It has been found that the cracks around slotted micro-channels become lesser when the moving speeds are increased for both experiments. The channel widths of using the 355 nm laser are around 10 times smaller than those of using the 266 nm laser. As a conclusion, among three kinds of lasers, the 355 nm laser may be the most suitable type for the glass micro-processing with high precision in practice.
With the development of laser technology, nanosecond lasers have been widely used in material micromachining due to their advantages such as the narrow pulse width and high-power density. The high-order harmonic generation procedures have been invented to obtain 532, 355, and 266 nm radiations based on a 1064 nm Nd:YAG laser. In this paper, the influence of different sample moving speeds and laser power on the cutting effects were studied using three kinds of laser sources. It can be seen that the state of the cutting surface has not changed obviously when the laser power was increased. The self-defined cutting threshold, i.e., 2.25 W·s/mm, has been obtained by investigating the processing morphology with the power of 1.35 W at different sample moving speeds for both a 355 nm laser and a 266 nm laser. Increasing the laser power to 3.20 W, we obtained the cutting threshold of about 1.80 W·s/mm for a 355 nm laser. The scorching status of the surfaces cut by both a FHG laser and a SHG laser have been found to be more serious than that cut by a THG laser. The experiments have demonstrated that the machining efficiency increases with the laser power, but the cutting quality becomes worse at the same time. The results are thought to be useful for the PCB cutting applications in the industrial fields.
In this paper, a simple and effective method is proposed for measuring the focal length of a weak negative thermallyinduced lens. Generally, it is very difficult to measure the focal length larger than 1000 mm of a weak thermally-induced lens by utilizing the traditional procedures. In our experiment, we planned to construct a Yb:KGW laser system almost without the thermally-induced lens in which the focal length of the laser crystal should be measured precisely. With respect to the optical features of Yb:KGW crystal, the thermally-induced characteristics look like something of a negative lens with weak effects. The steps of measuring the focal length of a thermally-induced lens of the laser medium have been adopted as follows. First, the relationship between the focal length f1 of a positive assistant lens as well as the position of the assistant lens and the focal length fT of a thermally-induced lens were carefully analyzed and the experimental setup were designed through the theoretical simulation. Secondly, the variation of the spot size and post position for a He-Ne probe laser have been experimentally investigated after the probe laser beam passed through a thermally-induced lens (fT) and an assistant lens (f1) with the different drive currents of a pump LD with the wavelength of 980 nm. Then, the post position for a He-Ne laser beam can be obtained by use of a least square method, and then the focal length of a weak thermally-induced lens can be deduced with an indirect detection method. In this paper, we introduce a new technique for the measurement of the focal length with the absolute value large than 1000 mm of a negative lens, which has not been reported until now. The results might be useful for the evaluation of a weak thermally-induced lens of almost all solid-state lasers (SSLs).
Although aluminum processing with lasers has become popular in industrial applications, machining some blind grooves or blind holes with a required size in aluminum sheets is also a difficult task for laser technicians. In this paper, blind grooves with the depth of about 0.1 mm and the width of less than 0.1 mm on a 0.24 mm thick aluminum sheet have been realized by using two kinds of nanosecond Q-switched lasers without burning the coating polymer layer. The effects of the laser wavelength, average power, and scanning speed on laser processing have been investigated in detail. The groove machining of aluminum sheets has been carried out at different laser power and machining speeds by use of two Q-switched lasers with the wavelengths of 532 nm and 355 nm. The experiment result shows that the faster the scanning speed, the better the processing efficiency. And the status of blind grooves processed by a 355 nm laser is cleaner and smarter. In summary, the optimal laser parameters for processing grooves on the aluminum surface are the peak power density of 2.27×108 W/cm2 with the scanning speed of 0.1 mm/s for a 355 nm nanosecond laser. The results of our study might be of great importance as a reference for processing blind grooves on aluminum sheets in some industrial applications.
Laser processing plays a key role in the industrial manufacture. The transparent material processing with a visible nanosecond laser based on a tripartite-interaction procedure has proven to be an effective method, which has the advantages of low cost, high efficiency, and simplicity over the traditional direct processing by using a femtosecond laser. In our pre-study, by using an assisted metal foil attached to the rear surface of a transparent glass sheet, some holes can be drilled on the glass sheet with a visible nanosecond laser. Such a physical mechanism is based on the heat conduction, generation of stress and ablation among the laser beam, the glass sheet and the metal foil. However, the processing quality of the glass sheet during the previous process is still dissatisfied and remains to be improved. In this study, we demonstrated a new tripartite-interaction procedure among the laser beam, glass sheet and copper foil, i.e. attaching an assisted copper foil on the front surface of the glass sheet, to further improve the processing quality of the hybrid tripartite-interaction processing. The experimental results are compared with those of our previous work, indicating that drilled holes and grooves with less crack and better quality can be obtained by using the new procedure. Moreover, to analyze the reasons of obtaining less cracks and better quality, we have carried out a series of theoretical studies on simulating such a new tripartite-interaction process. According to some specific simulation results of the temperature and density variations in the glass and copper, we can analyze that the reduction of thermal damage on the glass sheet and the improvement on processing quality might be attributed to the thermal transfer induced by attenuated laser energy in such a configuration. Our results could be useful for the development of visible nanosecond laser processing in industrial applications.
Laser drilling has been more and more widely used in laser machining process. Therefore, optimizing the quality of laser drilling becomes extremely important. We know that laser drilling can be achieved by using high power density of a laser. As light waves with different waveforms represent the different energy distributions in time domain, we believe that the quality of laser drilling should be related to the laser waveform. At present, a laser used in the laser processing usually hasthe waveform with a Gaussian or a Lorentzian distribution. In this study, we numerically simulated the punching quality of a pulsed laser with the Gaussian distribution and a pulsed laser with the top-flat distribution (we called it as a square-shaped laser pulse) at the same energy. It mainly refers to the changes of density, temperature, and pressure of the target materials under the same energy for different waveforms. The constrained interpolation profile algorithm has been used to simulate the machining process. Until now, there are few studies on the features of laser drilling with different waveforms in time domain. This paper provides a new method to optimize the quality of laser drilling.
Laser processing plays a key role in treating a lot of materials. The mechanism of laser stealth dicing (SD) is based on irradiation of a laser beam which is focused inside the brittle material. The laser beam scans along the predetermined path, so that the characteristics of the interior brittle material can be changed, the stress layer can be therefore formed. Finally, an external force is applied to separate the brittle material. Since only the limited interior region of a wafer is processed by the laser irradiation, the damages and debris contaminants can be avoided during the SD process. SD has the advantages of a high speed for thinner wafers without any chipping, the smooth section without dust and slag, and completely dry process, which has been widely used in large scale integrated circuits and microelectronic manufacturing systems. However, further studies on the simulation analyze and parameter optimization have kept to be rear for SD so far. In this study, an approach named as constrained interpolation profile (CIP) was adopted, which has the advantages of compactness, stability, and low dissipation in computational fluid dynamics compared with other simulation procedures. We have finished a theoretical simulation to obtain the physical features of the temperature, pressure, density of the silicon substrate at different focal depth where a nanosecond pulsed laser is irradiated, then we found a suitable focal depth with a good dicing quality by analyzing these physical features.
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