Glass is one of the most important materials in industrial applications because of its high hardness, high thermal stability, and high transparency in the visible band. In general, it is very difficult to process glass with near-infrared, visible, and near-ultraviolet lasers. Physically speaking, the absorption coefficient of the glass sheet is one of the most crucial factors for processing efficiency, and it can be influenced by the temperature of a glass sheet. Therefore, to obtain the optimal processing efficiency, the influence of the temperature on the absorption coefficient should be studied in detail. In this paper, we theoretically and experimentally studied the relationship between the absorption coefficient and the temperature to improve the processing efficiency. A tunable near-ultraviolet Nd:YAG frequency-tripled harmonic laser with the wavelength ranging from 270 to 400 nm was utilized to measure the absorption coefficient, and a Peltier temperature controller was used to heat the glass sheet. It has been demonstrated that controlling the temperature is an efficient method to process the transparent glass sheet.
A serious rust phenomenon has been observed in an enclosed laser cavity. To figure out the reason which induces the rust, some experiments were carried out by recording the variation of the temperature and relative humidity at different positions. Thus, the vapor density can be numerically deduced by using the measured physical features. To avoid the undesirable rust phenomena occurring again, the exchange windows were chiseled out on an inner cover of the enclosed laser cavity in order to decrease the difference between the vapor density inside the cover and that outside the cover, which relates to the efficiency of dehumidification. The results validate that such a difference of the vapor density is a function of the area of exchange windows. Then, the curves of the vapor density versus the area of exchange windows have been plotted. It has been demonstrated that adding the area of exchange windows, which were pasted by some particulate air filters to prevent external dust particles from entering, on an inner cover might be a feasible method to avoid rust near the water cooling elements. Such a study might be useful for laser technicians to pay much more attention to the protection of undesirable vapor-induced rusting.
Laser processing plays a key role in treating a lot of materials. The visible nanosecond laser processing based on a tripartite-interaction system has been proved to be an effective method of processing materials with high optical transparency, which has the advantages of low cost, high efficiency, and simplicity over the direct processing by using a femtosecond laser. However, further studies on the theoretical mechanism and parameter optimization keep to be rear for the hybrid tripartite-interaction laser processing. In this study, we have carried out the confirmatory experiment and numerical simulation of laser processing with a tripartite-interaction system, which includes a visible nanosecond laser (19 ns@532 nm), a piece of transparent glass, and a copper foil. The experiment indicates that drilled holes can be obtained on the glass sheets by using the visible nanosecond laser. The numerical results, which have been obtained by an approach named as constrained interpolation profile, reveal that the processing mechanism is based on the heat conduction, generation of stress and ablation between the glass and the copper foil. Our results could to be useful for the development of visible nanosecond laser processing in industrial applications.
It has always been difficult to process a metal film with high reflectivity in the field of manufacture, industry, medicine, and military, etc. Since much of the laser energy can be reflected especially when the reflectance of the target film surface is high, it is hard to process such a metallic film by laser radiation as the energy absorbed by the film material is very little. In this paper, we used a nanosecond pulsed laser to scribe some patterns on a smooth titanium (Ti) film, and investigated the surface morphology of a Ti film ablated by different laser spot sizes and laser energy. In our experiments, it has been found that the Ti film can be efficiently processed although the surface reflectance of the Ti film is about 57% at the wavelength of 532 nm. We also see that the processing range of the Ti film will decrease when the diameter of a laser beam increases. The experimental results show that the ablated status of the surface of a Ti film for a just-focus beam is much better than that for a defocus beam under the same laser power. Furthermore, the higher the laser power, the larger the processed area. By using the optimal parameters we obtained, we also produced some hole matrices and line patterns on a glass-based Ti film by employing a short pulsed laser. The processed samples were observed with a reflecting microscope and a transmitting microscope, respectively. Our research results can play an important role in the selection of laser parameters for laser processing of some materials with a high reflectivity.
Terahertz wave is generally an electromagnetic wave at the wavelength of 0.1-10 THz (30-3000 μm). The terahertz laser is a new type of radiation source with many unique advantages and has broad applications. Generally, the size of a normal laser cavity is from a few of to several hundred millimeters, and the size of a micro-cavity is mainly from a few of to several hundred micrometers in the wavelength region of ultraviolet, visible, and near-infrared. However, if the wavelength increases to the terahertz region, the wavelength is of the order of the micro-cavity size. The power distributions inside and outside the cavity of a terahertz laser are significantly different from those for a conventional laser cavity. In this paper, a theoretical model is established to study the outputted and leaked power of a micro-cavity in the terahertz band. We assume that the wavelength of an emission terahertz source is 240 μm and simulate the output features of a micro-cavity laser with the Finite-Difference Time-Domain (FDTD) algorithm. The output characteristics of a micro-cavity have been analyzed by using two types of material and different thicknesses of the sidewall. It has been found that when the thicknesses of both silver and aluminum sidewalls are reduced to around 16 μm, the power leaking from the micro-cavity begins to increase with the decrease of the sidewall thickness. In this way, the sidewall no longer restrains terahertz radiation inside the cavity. The simulation results might be referred for the design of a terahertz laser with the micro-cavity.