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1.
This paper reports on an investigation into the development of an analytical model for the quality control of laser marking/engraving of clay tiles using a high-power diode laser (HPDL). An analytical model for the laser melting of inhomogeneous workpieces with parabolic melt pool geometry being assumed was developed. The theoretical results were compared with the experimental data. The predicted melt pool depth and the experimental values were in close correlation with the parameter for values less than 15 Wmm−1 s−1/2, in spite of simplifications introduced in the model. At the relatively large values of parameter the assumption of parabolic melt pool shape and one-dimensional heat transfer no longer holds true.  相似文献   

2.
Picosecond laser single pulse ablation of Au, Al and Ti alloy (Ti6Al4V) was experimentally investigated with a laser pulse width of 10 ps at a wavelength of 1064 nm for potential industrial micromachining applications. The diameters, depths and morphologies of the drilled craters were studied. Two novel phenomena were found: as hole diameters decreased with fluence, a change of slope of the trend line indicated a change in ablation mechanism for Al and Ti alloy, metallic materials with short electron-phonon coupling times (<10 ps), while Au showed no such transition: an isolated island structure was also observed on Au due to significant melt expulsion. A one-dimensional two-temperature model has been used to discriminate different ablation phenomena. It is shown that metallic materials with different electron–phonon coupling constant have different ablation characteristics in the ps regime. This study could be very helpful for metallic material micromachining with high repetition rate ps lasers pulses which indicates that high throughput may be achieved as well as good machining quality.  相似文献   

3.
The plasma cathode design concept is applied to an Ar laser for the first time. The sliding discharge is used as a plasma cathode for the main laser discharge. The laser operates at atmospheric pressure with a gas mixture of Ar/He/SF6. Results concerning the dependence of the laser performance on the gas mixture flow rates and charging voltage are presented. The temporal behavior of the laser output is also presented. Output energies as high as 2 mJ, efficiency and specific energy extraction values up to 1.3×10−2% and 0.02 J/l respectively, at atmospheric pressure, are obtained. The spectroscopic examination of the output shows that lasing at 1.79 and 1.27 μm is obtained with approximately equal line intensities.  相似文献   

4.
Eye-protection glasses against YAG laser injury based on band gap reflection of one-dimensional photonic crystal (PC) is designed and manufactured in this paper. The laser beam (wavelength 1.06 μm) is reflected by the one-dimensional PC (with the transmission 10−7) and absorbed by the phosphatic glass substrate (with the transmission 1% for 1.06 μm), so the transmission of the device for wavelengths of1.06 μm can reach 10−9. The glasses have enough capabilities to protect the eyes from injury of ns-YAG lasers whose energy density is 1 J/cm2 for all incident angles, and also to avoid a second injury to others from the reflected laser beams. The transmission of the glasses is beyond 70% for the visible lights. The testing data of the eye-protection glasses agree well with the theoretical predictions.  相似文献   

5.
We report lasing characteristics of Rhodamine B (Rh. B) in sol–gel silica under excitation with frequency-doubled Nd:YAG laser and sensitization with Rhodamine 6G (Rh. 6G). The principle of radiative energy transfer (from Rh. 6G to Rh. B) has been utilized as a longitudinally Rh. 6G laser (at 585 nm)-pumped Rh. B laser process in the same sample. Rh. B offers a high photostable and efficient laser dye in sol–gel silica sensitized with Rh. 6G; 75,000 shots as a laser half-lifetime of the sample and 24% efficiency at pumping intensity 0.1 J/cm2 of 532 nm. Wavelength shift occurs from 606 to 630 nm in the Rh. B laser with increasing its concentration from 1×10−4 to 8×10−4 M. The measured optical gain for Rh. B sensitized with Rh. 6G in sol–gel silica is higher than that in ethanol. A new effect has been observed; at 1×10−4 M of Rh. B and 0.5×10−4 M of Rh. 6G mixture, the emitted color of laser is changed by changing the pump intensity of frequency-doubled Nd:YAG laser.  相似文献   

6.
Plasmas generated during incipient laser ablation of aluminum in air were studied using emission spectroscopy. A plasma emission model was developed, invoking one-dimensional radiative transfer, to describe the observed emission spectra, while taking into account the effects of continuum radiation. Theoretical spectra were calculated and compared to experimental spectra in the range 387–406 nm. Satisfactory agreement was found between the experimental and predicted spectra, especially at delay times of 30–200 ns, thus providing plasma temperatures and electron number densities as functions of delay time and laser irradiance (1.8–8.0 GW/cm2). In general, both the plasma temperature and electron number density rise at greater laser irradiances but drop at increasing delay times, with a more rapid drop for delay times less than 60 ns. PACS 42.62.Fi; 52.25.-b  相似文献   

7.
The etching of n-GaAs in aqueous solutions of hydroxides stimulated by HeNe and HeCd laser light was studied. It was found that at low laser-power densities (5–10 W · cm–2) the etched depths do not depend on the wavelength of the incident light. This conclusion is related to the concentration of the photogenerated holes on the semiconductor surface. The diffusion length and absorption depths for HeNe and HeCd lasers are compared.  相似文献   

8.
The interaction of laser radiation with matter leads to the certain kinds of modelling of its surface or volume. These effects have been demonstrated for a lot of materials, even causing the formation of new scientific and industrial domain, which is undoubtedly laser material processing and as well as laser cleaning of artworks. Those applications lie in the so-called “low' region of laser energy densities, represented for short laser pulses by power densities below 109 W/cm2. Paper presents set of equations describing in one-dimensional (1D) model phenomena accompanying to laser–matter interaction. Target geometry includes two and four layers of different materials, irradiated by ns laser pulses. Effects of radiation absorption and transport, heat conductivity, target transit to plastic state, melting and evaporation are taken into consideration. The part of the paper is devoted to the discussion of numerical results, selected in such a way to illustrate the phenomenon of radiation interaction with materials as well as to show, in whole, possibilities of computer simulation methods.  相似文献   

9.
Ajay K. Sharma  Sandeep K. Arya 《Optik》2009,120(15):773-781
In this paper, the improved analysis for SRS- and XPM-induced crosstalk has been reported. The modified expression for XPM-induced crosstalk has been obtained and SRS- and XPM-induced crosstalks have been reported at varied walkoff parameter, modulation frequency, input optical power and transmission distance. It has been observed that there is exponent decrease in SRS-induced crosstalk with the increase in modulation frequency from 0 to 2.0 GHz. It varies with the increase in length and lie in the range of (−114 to −122.4) dB and (−115.5 to −124.4) dB at 20 and 100 km, respectively. Moreover, it increases exponentially with the increase in input optical power and lies in the range of (−121.6 to −130.6) dB at 10 mW and grows exponentially up to the range of (−114 to −122.8) dB at 60 mW optical powers at walkoff parameter of (13.6, 27.2, 54.4 and 81.6) ps/km. It has been observed that the XPM-induced crosstalk increases exponentially with the increase in transmission distance and modulation frequency for 2OD and 3OD. Furthermore, it has been found that the total SRS- and XPM-induced crosstalk rises exponentially with fluctuations with the increase in modulation frequency and transmission length in the presence of combined effect of 2OD and 3OD at varied walkoff parameters.  相似文献   

10.
The temporal pulse train modulation during laser percussion drilling was found to effect significant changes to the material ejection processes. In particular, distinct differences in the material ejection processes have been observed between a temporal pulse train shaping technique termed as sequential pulse delivery pattern control (SPDPC) and the normal delivery pattern (NDP), wherein the parameters of successive laser pulses were constant. Due to the reduced upward material removal fractions in SPDPC drilling, the spatter deposition area was reduced from approximately 6.7 to 2.7 mm2. In addition, the melt layer thicknesses at the hole bottom were significantly increased from 11–61 to 18–369 μm. Such changes were identified as being due to the low laser pulse intensities before beam breakthrough associated with the SPDPC method. It was observed that the use of the linearly increasing SPDPC method increased the downward material removal fractions, from 20% to 28% observed in NDP drilling, to 34%–39%. Such an increase in the downward material ejection mechanism in SPDPC drilling was identified as being primarily due to the pointed blind-hole profile generated before the onset of beam breakthrough. The work has shown that modulating the entire pulse train in laser percussion drilling could control the material ejection processes. Furthermore, the fundamental elements of the SPDPC technique are given in terms of the rate of energy deposition and total pulse train energy.  相似文献   

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