The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
Shengzhi Zhao - One of the best experts on this subject based on the ideXlab platform.
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1.36 W Passively Q-Switched YVO4/Nd:YVO4 Laser With a WS2 Saturable Absorber
IEEE Photonics Technology Letters, 2017Co-Authors: Wenjing Tang, Shengzhi Zhao, Tao Li, Kejian Yang, Dechun Li, Guiqiu Li, Yonggang Wang, Jia Zhao, Wenchao QiaoAbstract:By using WS2 as saturable absorber (SA), a diode-pumped passively Q-Switched YVO4/Nd:YVO4 laser is demonstrated. Under the pump power of 6.28 W, a maximum output power of 1.36 W and minimum pulse duration of 56 ns with a repetition rate of 1.03 MHz are obtained, resulting in a peak power of as high as 23.6 W. So far as we know, it is the shortest pulse duration in Q-Switched Lasers with 2-D materials. The experimental results show that WS2 is an excellent SA for all-solid-state Q-Switched Lasers.
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thermal modeling of the continuous wave end pumped Q Switched Lasers
Optics Communications, 2010Co-Authors: Tao Li, Shengzhi Zhao, Shuaiyi Zhang, Kejian Yang, Zhuang ZhuoAbstract:The transient temperature profiles in continuous-wave (cw) end-pumped Q-Switched Lasers are investigated by solving a numerical model coupling the transient heat conduction eQuation and the rate eQuations, in which the influences of the thermal time constant, the fluorescence lifetime and the repetition rate on the temperature variation are considered. Furthermore, the buildup dynamics of thermal eQuilibrium in several laser crystals are presented and compared with each other. The numerical simulation results reveal that the buildup time of thermal eQuilibrium mainly depends on the thermal time constant, however, the temperature rise is primarily influenced by the absorption cross section. Compared with the influences of the other parameters, fluorescence lifetime principally determines the thermal oscillation contrast. In addition, it is also found that the repetition rate and the pump power have significant effects on the thermal characteristics in Q-Switched Lasers.
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Optimization of GaAs semiconductor saturable absorber Q-Switched Lasers
Optik, 2010Co-Authors: Dechun Li, Shengzhi Zhao, Guiqiu Li, Kejian YangAbstract:The expressions of pulse characteristics such as output energy, peak power, and pulse width are obtained by solving the coupled rate eQuations describing the operation of GaAs semiconductor saturable absorber Q-Switched Lasers. The key parameters of an optimally coupled GaAs saturable absorber Q-Switched laser are determined and several design curves are generated from these expressions for the first time. These key parameters include the optimal normalized coupling parameters and the optimal normalized saturable absorber parameters that maximize the output energy or maximize the peak power, and the corresponding normalized energy, normalized peak power, and normalized pulse width. Using the expressions and design curves, one can predict the pulse characteristics and perform the design of an optimally coupled GaAs saturable absorber Q-Switched laser.
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Optimization of the Efficiency of GaAs Saturable Absorber Q-Switched Lasers
2010 International Conference on Artificial Intelligence and Computational Intelligence, 2010Co-Authors: Wenjing Tang, Shengzhi Zhao, Dechun Li, Guiqiu Li, Kejian YangAbstract:The laser efficiency is an important parameter, and we pay more attention to the maximum conversion efficiency of a laser in many cases. By taking into account the single-photon absorption (SPA) and two-photon absorption (TPA) processes of GaAs, the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density, and the pumping and the spontaneous emission during the pulse formation, the new normalized rate eQuations of a GaAs saturable absorber Q-Switched laser are solved numerically, and the optimum laser efficiency of GaAs saturable absorber Q-Switched laser is determined. A group of general curves are generated, which clearly show the dependence of the optimum laser efficiency on the parameters of the gain medium, the GaAs saturable absorber, and the resonator. In addition, the influence including the space variation, the pumping and the spontaneous emission is also shown. Sample calculations for a diode-pumped Nd3+:YVO4 laser with a GaAs saturable absorber are presented to demonstrate the use of the curves and the relevant formulas.
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Optimization of doubly Q-Switched Lasers with both an electro-optic modulator and a GaAs saturable absorber
International Symposium on Photoelectronic Detection and Imaging 2009: Laser Sensing and Imaging, 2009Co-Authors: Wenjing Tang, Shengzhi Zhao, Dechun Li, Guiqiu Li, Kejian YangAbstract:It has been proved theoretically and experimentally that a doubly Q-Switched laser with both an electro-optic (EO) modulator and a GaAs saturable absorber can obtain more symmetric and shorter pulse with high pulse peak power, which is more useful in some applications. Therefore it is essential to optimize this kind of doubly Q-Switched Lasers. In this paper, by combining the single-photon absorption (SPA) and two-photon absorption (TPA) processes of GaAs saturable absorber, and considering the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density as well as the influence of the electro-optic (EO) Q-switch, we introduce some new normalized parameters and provide the new normalized rate eQuations for a diode-pumped doubly Q-Switched laser with both an electro-optic (EO) modulator and a GaAs saturable absorber, which are solved numerically. The key parameters of an optimally coupled doubly Q-Switched laser are determined, and a group of general curves are generated for the first time. These key parameters include the optimal normalized coupling parameter, the optimal normalized saturable absorber parameters, and the normalized parameters of the electro-optic (EO) Q-switch, which can maximize the output energy. Meanwhile, the corresponding normalized energy, the normalized peak power and the normalized pulse width are given. The curves clearly show the dependence of the optimal key parameters on the parameters of the gain medium, the GaAs saturable absorber, the electro-optic (EO) Q-switch, the resonator and the spatial distributions of the intracavity photon density. These optimal results are compared with those of the optimized single Q-Switched Lasers. Sample calculations for a diode-pumped Nd:YVO 4 laser with both an electro-optic (EO) modulator and a GaAs saturable absorber are presented to demonstrate the use of the curves and the relevant formulas.
O G Okhotnikov - One of the best experts on this subject based on the ideXlab platform.
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High-Repetition-Rate Q-Switched Holmium Fiber Laser
IEEE Photonics Journal, 2012Co-Authors: Yu. A. Chamorovskiy, A. V. Marakulin, A. S. Kurkov, T. Leinonen, O G OkhotnikovAbstract:Pulses of 118 nJ at the repetition rate of 170 kHz and central wavelength of 2097 nm have been produced by holmium fiber laser Q-Switched by carbon nanotube saturable absorber. Efficient operation of holmium fiber with fairly high-doping level has been demonstrated by using refined preform fabrication, which allowed for short-length cavity laser. The results demonstrate the practical potential of holmium fibers for Q-Switched Lasers with high-repetition rate operating above 2 μm wavelength.
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dynamic gain induced pulse shortening in Q Switched Lasers
Optics Letters, 2008Co-Authors: Robert Herda, S Kivisto, O G OkhotnikovAbstract:We describe a novel mechanism of pulse shortening in a Q-Switched laser induced by the gain compression effect under strong pumping conditions. The pulse shortening reQuires a large variation of the gain excursion during the saturation process and benefits from the large volume of the gain medium. The effect has been experimentally demonstrated using a passive Q-Switched Tm/Ho-doped fiber laser that shows gain-induced pulse compression from 800 ns down to 160 ns when the pump threshold is exceeded by 15 times.
Joop M Grevelink - One of the best experts on this subject based on the ideXlab platform.
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comparison of the Q Switched alexandrite nd yag and ruby Lasers in treating blue black tattoos
Dermatologic Surgery, 1999Co-Authors: Mia L Leuenberger, Maria W Mulas, Tissa R Hata, Mitchel P Goldman, Richard E Fitzpatrick, Joop M GrevelinkAbstract:Background. A new generation of highly selective short-pulsed Lasers has emerged in recent years for the treatment of tattoos. Several studies (including reports by the present investigators) have proven the efficacy of each of the three commercially available, FDA approved devices; namely, the Q-Switched alexandrite, Q-Switched Nd:YAG and Q-Switched ruby Lasers. Considerable differences among the three have been reported in relation to the rate of clearing of the tattoo ink particles, tissue effects, beam profile, wound healing, and side effects. Objective. This study was primarily conducted to examine and compare the clinical response of patients with blue-black tattoos simultaneously treated with three different Q-Switched Lasers (alexandrite, Nd:YAG, ruby) with a focus on the percentage of tattoo lightening/clearance and the occurrence or non-occurrence of pigmentary change as a side effect. Methods. A total of forty-two blue-black tattoos seen at two laser centers (Massachusetts General Hospital Dermatology Laser Center and Laser and Skin Surgery Center of La Jolla) were simultaneously treated with three types of Q-Switched Lasers: a Candela Q-Switched alexandrite laser (755nm 50-100 nanoseconds, 3.0mm spot size, 6-8 J/cm2); a Continuum Biomedical Q-Switched Nd:YAG laser (1064nm, 10-20 nanoseconds, 3.0mm spot size, 5-10 J/cm2); and a Spectrum Q-Switched ruby laser (694nm, 25-40 nanoseconds, 5.0mm spot size, 4-10 J/cm2). Paired t-tests and McNemar tests were used to compare the treatment outcome and pigmentation side effects between sites per tattoo, with each site representative of one of the three Lasers. The statistical significance level was set at p < .05. Results. Overall, the Q-Switched ruby laser had a significant difference in tattoo lightening versus the Q-Switched Nd:YAG and Q-Switched alexandrite Lasers. An increase in the number of treatments paralleled a statistically significant increase in tattoo clearance for all three Q-Switched Lasers. Conclusion. The Q-Switched ruby laser had the highest clearance rate in blue-black tattoos and the highest incidence of longlasting hypopigmentation. The Nd:YAG had no incidence of hypopigmentation.
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clinical and histological responses of congenital melanocytic nevi after single treatment with Q Switched Lasers
Archives of Dermatology, 1997Co-Authors: Joop M Grevelink, R L Van Leeuwen, Rox R Anderson, H R ByersAbstract:Background: Laser irradiation of congenital melanocytic nevi is a controversial treatment. Recurrence of lesions after laser treatment appears to be the rule, and the effects of laser irradiation on cellular biological behavior and the possible mutagenic responses of nevomelanocytes that have received nonlethal doses of irradiation are still unclear. Without treatment, there is an increased potential for malignant degeneration over a lifetime. The purpose of this study was to examine the effects of Q-Switched Lasers on congenital nevi and to explain the mechanism(s) behind the response of the nevi to laser treatment. Five congenital nevi were divided into 3 eQual parts: 1 part was treated with the Q-Switched ruby laser at a wavelength of 694 nm, 1 part was treated with the Q-Switched neodymium:YAG laser at a wavelength of 1064 nm, and 1 part was left untreated to serve as control. At intervals ranging from 3 days to 3 months after laser irradiation, the lesions were excised and evaluated by routine staining. This clinical study was conducted entirely at the Massachusetts General Hospital Dermatology Laser Center, Boston, Mass. Observations: Both the superficial and the deep protions of the congenital melanocytic nevi were affected by the 2 Lasers, as evidenced by macroscopic inspection as well as microscopic evaluation. However, the Q-Switched laser treatment did not destroy all nevomelanocytes, particularly in the deeper, less pigmented portions of the lesions. Conclusions: Both the Q-Switched ruby laser and the neodymium:YAG laser often removed only the superficial portion of the congenital melanocytic nevi. The Q-Switched ruby laser (694 nm) appeared to be more effective in removing nevomelanocytes than the Q-Switched neodymium:YAG laser (1064 nm). Arch Dermatol. 1997;133:349-353
Moshe Lapidoth - One of the best experts on this subject based on the ideXlab platform.
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Tattoo removal
Basics in Dermatological Laser Applications, 2011Co-Authors: Maurice A. Adatto, Shlomit Halachmi, Moshe LapidothAbstract:Over 50,000 new tattoos are placed each year in the United States. Studies estimate that 24% of American college students have tattoos and 10% of male American adults have a tattoo. The rising popularity of tattoos has spurred a corresponding increase in tattoo removal. Not all tattoos are placed intentionally or for aesthetic reasons though. Traumatic tattoos due to unintentional penetration of exogenous pigments can also occur, as well as the placement of medical tattoos to mark treatment boundaries, for example in radiation therapy. Protocols for tattoo removal have evolved over history. The first evidence of tattoo removal attempts was found in Egyptian mummies, dated to have lived 4,000 years BC. Ancient Greek writings describe tattoo removal with salt abrasion or with a paste containing cloves of white garlic mixed with Alexandrian cantharidin. With the advent of Q-Switched Lasers in the late 1960s, the outcomes of tattoo removal changed radically. In addition to their selective absorption by the pigment, the extremely short pulse duration of Q-Switched Lasers has made them the gold standard for tattoo removal.
Xingyu Zhang - One of the best experts on this subject based on the ideXlab platform.
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modeling of passively Q Switched Lasers
Journal of The Optical Society of America B-optical Physics, 2000Co-Authors: Xingyu Zhang, Shengzhi Zhao, Qingpu Wang, Bernd Ozygus, Horst WeberAbstract:The intracavity photon density and the initial population-inversion density in the diode-pumped passively Q-Switched laser rate eQuations are assumed to be Gaussian spatial distributions. These space-dependent rate eQuations are solved numerically, and a group of general curves are generated. These curves clearly show the dependence of the pulse characteristics on the pump- to laser-mode size ratio and the parameters of the gain medium, the saturable absorber, and the resonator. They can also be used to estimate the pulse parameters of an arbitrary diode-pumped passively Q-Switched laser and to determine the optimal pump- to laser-mode size ratio. In addition, these curves are not limited to diode-pumped Lasers. Sample calculations for a diode-pumped Nd3+:YVO4 laser and a flash-lamp pumped Nd3+:YAG laser are presented to demonstrate the use of the curves and the related formulas.
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Modeling of diode-pumped actively Q-Switched Lasers
IEEE Journal of Quantum Electronics, 1999Co-Authors: Xingyu Zhang, Shengzhi Zhao, Qingpu Wang, Bernd Ozygus, Horst WeberAbstract:The intracavity photon density and initial population inversion density in the diode-pumped actively Q-Switched laser rate eQuations are assumed to be Gaussian distributions. These space-dependent rate eQuations are solved numerically and a group of general curves are generated. By using these curves and the related formulas, the pulse parameters of an arbitrary actively Q-Switched laser can be easily estimated and an optimally coupled Q-Switched laser can be designed. A sample calculation for a Q-Switched Nd/sup 3+/:YVO/sub 4/ laser is presented to demonstrate the use of the curves and the related formulas.
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optimization of cr sup 4 doped saturable absorber Q Switched Lasers
IEEE Journal of Quantum Electronics, 1997Co-Authors: Xingyu Zhang, Shengzhi Zhao, Qingpu Wang, Qidi Zhang, Shaojun ZhangAbstract:Cr/sup 4+/-doped saturable absorbers are characterized by long excited state lifetime and appreciable excited state absorption. In the paper, we first solve the three coupled rate eQuations describing the operation of Cr/sup 4+/-doped saturable-absorber passively Q-Switched Lasers to obtain the expressions of pulse characteristics such as output energy, peak power, and pulsewidth. We then determine the key parameters of an optimally coupled passively Q-Switched laser as functions of two variables concerning the amplifying medium, saturable-absorber medium, and pump level, and generate several design curves. These key parameters include the optimal normalized coupling parameter and the optimal normalized saturable-absorber parameter which maximize the output energy (or maximize the peak power, or minimize the pulsewidth), and the corresponding normalized energy, normalized peak power, and normalized pulsewidth. The results are valid for not only Cr/sup 4+/-doped saturable-absorber Q-Switched Lasers but also any other Lasers passively Q-Switched by saturable absorbers with long excited state lifetime and appreciable excited state absorption. Using the expressions and design curves, with the aid of a simple hand calculator, one can predict the pulse characteristics and perform the design of an optimally coupled passively Q-Switched laser.
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Optimization of Cr/sup 4+/-doped saturable-absorber Q-Switched Lasers
IEEE Journal of Quantum Electronics, 1997Co-Authors: Xingyu Zhang, Shengzhi Zhao, Qingpu Wang, Qidi Zhang, Shaojun ZhangAbstract:Cr/sup 4+/-doped saturable absorbers are characterized by long excited state lifetime and appreciable excited state absorption. In the paper, we first solve the three coupled rate eQuations describing the operation of Cr/sup 4+/-doped saturable-absorber passively Q-Switched Lasers to obtain the expressions of pulse characteristics such as output energy, peak power, and pulsewidth. We then determine the key parameters of an optimally coupled passively Q-Switched laser as functions of two variables concerning the amplifying medium, saturable-absorber medium, and pump level, and generate several design curves. These key parameters include the optimal normalized coupling parameter and the optimal normalized saturable-absorber parameter which maximize the output energy (or maximize the peak power, or minimize the pulsewidth), and the corresponding normalized energy, normalized peak power, and normalized pulsewidth. The results are valid for not only Cr/sup 4+/-doped saturable-absorber Q-Switched Lasers but also any other Lasers passively Q-Switched by saturable absorbers with long excited state lifetime and appreciable excited state absorption. Using the expressions and design curves, with the aid of a simple hand calculator, one can predict the pulse characteristics and perform the design of an optimally coupled passively Q-Switched laser.
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Optimization of dye Q-Switched Lasers
IEEE Journal of Quantum Electronics, 1994Co-Authors: Xingyu Zhang, Shengzhi Zhao, Qingpu Wang, Jiyang WangAbstract:Analytical expressions for all key parameters of the optimally coupled Q-Switched laser are derived. These parameters include the optimal reflectivity of the output mirror, the optimal initial transmission of the dye, and the maximum attainable output energy and corresponding peak power and pulse width for a given pump level. Meanwhile, according to the optimization theory of dye Q-Switched Lasers, a NAB miniature dye Q-Switched laser is studied experimentally and experiment shows a good agreement with the theory.
