Passively Q-Switched Nd,Cr:YAG Laser Simultaneous Dual-Wavelength Operation at 946 nm and 1.3μm

A diode-end-pumped Q-switched high-efficiency Nd, Cr：YAG laser with simultaneous dual-wavelength emission at 946nm and 1.3μm is demonstrated. The maximum output power of 1.93 W with simultaneous dual-wavelength operation is achieved at an absorbed pump power of 13.32 W and an absorbed slope efficiency of 15.15%. The maximum optical-optical efficiency is 14.49% with pulse widths of 16.38ns at 946nm and 26.65ns at 1.3μm. A maximum total repetition rate of 43.25 kHz is obtained.

High-Power Passively Q-Switched Nd:YAG Laser at 1112 nm with a Cr^(4+):YAG Saturable Absorber

A high-power passively Q-switched Nd：YAG laser operating at lll2nm with Cr4＋：yAO as a saturable absorber is demonstrated. Under 808 nm diode-direct pumping, the maximum average output power of 2.73 W is achieved at the pump power of 16.65 W, corresponding to an optical-to-optical conversion efficiency of 16.4%. At the same time, the pulse width, pulse repetition rate, single pulse energy and peak power are 27.2ns, 9 kHz, 303.3#3 and 11.2kW, respectively. As far as we know, the result gives the highest average output power at 1112nm generated by an 808 nm diode-end-pumped Nd：YAG laser.

Efficient Passively Q-Switched Nd:YAG/Cr4+:YAG/LBO Microchip Laser

Performance of an LD-end-pumped passively Q-switched Nd： YA G/Cr4＋ ： YA G microchip laser operating at 1123 nm is studied. A maximum average output power of 517row with an optical-to-optical conversion efficiency of 12.6% and a slope efficiency of 25.8% is obtained under a pump power of 4.1 W. A minimum pulse width of 1.1 ns with a pulse repetition rate of 20.2kHz is obtained, and the corresponding pulse energy and peak power are 25.6μJ and 23.3kW, respectively. To our knowledge, the 23.3kW peak power is the highest among 1123nm lasers. Additionally, based on the 1123 nm laser, with LBO as the frequency doubler, a 288-mW green-yellow laser at 561 nm is successfully achieved.

Efficient Diode-Pumped Actively Q-Switched Ceramic Nd:YAG/YVO4 Raman Laser Operating at 1657 nm

A diode-pumped actively Q-switched Raman laser is demonstrated, with YV04 employed as Raman active medium, based on a ceramic Nd：YAG laser operating at 1444nm. The first-stokes Raman generation at 1657nm is achieved. A maximum output power of as high as 612mW is obtained under a pump power of 20. 7 W and at a pulse repetition frequency rate of 20kHz, corresponding to an optical-to-optical conversion efficiency of 3%.

Diode Pumped High Peak Power Quasi Q-Switched and Passively Q-Switched Nd:YVO₄Lasers at 1064 nm and 532 nm using Cr:YAG and KTP crystals

Diode end-pumped solid-state lasers have the potential to yield high quality laser beams with high efficiency for laser range finding and warning receiver applications as well as day and night military laser designation systems. In this paper we presents theoretical calculations using Advanced Dynamics Professional LASCAD software and experimental studies for a high power pigtailed fiber diode laser module of 8 W operating at 808 nm with a specially designed high efficiency cooling system, end pumped high-efficiency Nd:YVO4 laser of 3 × 3 × 10 mm rod and overall cavity length of 44 mm. To the best of our knowledge a self Q-switching effects was generated in Nd:YVO4 laser by changing the cavity dimensions and the position of the intracavity KTP crystal at certain regime of operation for the first time, in which the cavity length is reduced to be 30 mm and the distance between Nd:YVO4 rod and KTP crystal is only 1mm. Self Q-switched laser pulse at 532 nm with high peak power of 96 W, pulse width of 88 ns at FWHM and repetition rate of 400 kHz was achieved. Experimental studies of a passive Q-switched Nd:YVO4 laser using Cr:YAG crystal with three different transmissions of 30%, 40% and 70% were investigated. Passive Q-switched laser pulse at 1064 nm and narrow line width of less than 1.5 nm with highest peak power of nearly 18 kW, short pulse width of less than 4 ns at FWHM and higher repetition rate of 45 kHz using Cr:YAG with transmission of 30% was achieved for the first time.

Simulation of Diode-Pumped Q-Switched Nd:YAG Laser Generating Eye-Safe Signal in IOPO Environment

Numerical simulation of diode-pumped Q-switched Nd:YAG laser leading to the generation of eye-safe signal in singly resonant Intracavity Optical Parametric Oscillator (IOPO) is presented. Starting from rate equations, the time dependent laser equations have been solved numerically, whereas the space-dependent OPO equations analytically. Our results show that 1.4 J diode laser (810 nm) pulse with 200 msec width, delivers 30 mJ Nd:YAG laser (1064 nm) pulse with 5 n-second width. This Nd:YAG laser further generates 9 mJ eye safe signal (1570 nm) pulse with 2.5 n-second width.

Development of an injection-seeded single-frequency laser by using the phase modulated technique

An injection-seeded single-frequency Q-switched Nd：YAG laser is accomplished by using a phase modulated rampfire technique. A RbTiOPO4（RTP） electro-optic crystal is selected for effective optical path length modulation of the slave self-filtering unstable resonator. This single-frequency laser is capable of producing 50 m J pulse energy at 1 Hz repetition rate with a pulse width of 16 ns. The standard deviation of laser pulse intensity for consecutive 100 shots from the mean pulse intensity is less than 1.05%. A spectral linewidth of less than 0.5 pm with a frequency jitter of about 14 fm over30 min is obtained.

Experimental study of electro-optical-switched pulsed Nd:YAG laser

We report the specification of a compact and stable side diode-pumped Q-switched pulsed Nd：YAG laser. We ex- perimentally study and compare the performance of the pulsed Nd：YAG laser in the free-running and Q-switched modes at different pulse repetition rates from 1 Hz to 100 Hz. The laser output energy is stabilized by using a special configu- ration of the optical resonator. In this laser, an unsymmetrical concave-concave resonator is used and this structure helps the mode volume to be nearly fixed when the pulse repetition rate is increased. According to the experimental results in the Q-switched operation, the laser output energy is nearly constant around 70 mJ with an FWHM pulse width of 7 ns at 100 Hz. The optical-to-optical conversion efficiency in the Q-switched regime is 17.5%.

Induction of oxidative stress in human aqueous and vitreous humors by Nd:YAG laser posterior capsulotomy

AIM： To evaluate whether the Q-switched Nd：YAG laser treatment applied in routine capsulotomy elicits oxidative stress in aqueous and vitreous humors. METHODS： Thirty-six patients who had to undergo a 25 gauge pars plana vitrectomy due to vitreoretinal disorders were enrolled, 15 of them underwent a Q-switched Nd：YAG laser capsulotomy 7 d before vitrectomy due to posterior capsule opacification（PCO）（Nd：YAG laser group） while the remaining 21 patients were not laser treated before vitrectomy（no Nd：YAG laser group）. Samples of the aqueous and vitreous humors were collected during vitrectomy from all patients for the assessment of oxidative parameters which were compared between the Nd：YAG laser group and no Nd：YAG laser group. Thiobarbituric acid reactive substances（TBARS）, a product of membrane lipid peroxidation, nitrite levels, the antioxidative activities of SOD and catalase, the 4-HNE-protein conjugate formation, indicating structural modifications in proteins due to lipoperoxidation, were assessed in aqueous and vitreous samples. RESULTS： In the human vitreous humor TBARS levels are significantly higher in the Nd：YAG laser group compared to the no Nd：YAG laser group and importantly, there is a significant correlation between the TBARS levels and the total energy of Nd：YAG laser used during capsulotomy.Moreover the anti-oxidative activities of SOD and catalase were significantly decreased by Nd：YAG laser treatment, both in aqueous and vitreous humors. In accordance with the TBARS data and anti-oxidative enzyme activities, significantly higher levels of proteins were conjugated with the lipoperoxidation product 4-HNE in the aqueous and vitreous humors in the Nd：YAG laser-treated group in comparison to no Nd：YAG laser group. CONCLUSION： These data, clearly suggest that any change that Q-switched Nd：YAG photo disruption may cause in the aqueous and vitreous compartments, resulting in a higher level of oxidative damage might be of considerable clinical significance particularly by accelerating the aging of the anterior and posterior segments of the eye and by worsening the intraocular pressure, the uveal, the retinal（especially macular） pathologies.

High-peak-power passively Q-switched Nd:YAG/Cr^(4+):YAG composite laser with multiple-beam output

We report on the design, realization, and output performance of a diode-pumped high-peak-power passively Q-switched Nd:YAG∕Cr^(4+):YAG composite medium monolithic laser with four-beam output. The energy of a laser pulse was higher than 3 m J with duration of 0.9 ns. The proposed system has the ability to choose independently the focus of each beam. Such a laser device can be used for multipoint ignition of an automobile gasoline engine, but could also be of interest for ignition in space propulsion or in turbulent conditions specific to aeronautics.

High-peak-power passively Q-switched 1.3 μm Nd:YAG/V^(3+):YAG laser pumped by a pulsed laser diode

We demonstrate a high-pulse-energy, short-pulse-width passively Q-switched（PQS） Nd：YAG∕V3t：YAG laser at 1.3 μm, which is end-pumped by a pulsed laser diode. During the PQS regime, a maximum total output pulse energy of 3.3 m J is obtained under an absorbed pump pulse energy of 21.9 m J. Up to 400 μJ single-pulse energy is realized with the shortest pulse width of 6.16 ns and a pulse repetition frequency of 34.1 k Hz,corresponding to a peak power of 64.9 k W. The high-energy laser pulse is operated in the dual wavelengths of 1319 and 1338 nm, which is a potential laser source for THz generation.

Primary Investigation into the Laser Triggering Multi-Gap Multi-Channel Gas Switch in a Single Test Module Facility

A high precision laser trigger system is built up in the single test module of Primary Test Stand （PTS） facility. A fourth harmonic, with a wavelength A of 266 nm, Q-switched Nd：YAG laser was used to trigger the 5 MV multi-gap multi-channel gas switch which was filled with high pressure SF6-N2 mixture gas. The maximum deviation and the standard deviation in the jitter time of the trigger system is 4- 0.7 ns and 0.3 ns respectively. The maximum deviation and the standard deviation in the jitter time for the multi-gap multi-channel laser triggering switch is 4- 2.4 ns and 1.5 ns respectively. The curve of switch delay-time versus laser energy is obtained, which is helpful for the choice of fitting laser energy. The successful test with two lasers indicated that the design of using twenty-four lasers to trigger twenty-four switches respectively is feasible in ＂PTS＂.

Three-nanosecond-equal interval sub-pulse Nd:YAG laser with multi-step active Q-switching

We demonstrate a three-nanosecond equidistant sub-pulse multi-step Q-switched Nd:Y3 Al5 O12(Nd:YAG) laser.In the time interval of 100–1000 ns, three pulses with the same nanosecond interval and the same peak power are obtained at the pulse width of 24 ns, 28 ns, and 36.6 ns, respectively.The energy is 32.5 m J, and the optical efficiency is 10.8%.The multi-step Q-switched method does not require the insertion of other optical elements into the traditional Q-switched laser, and it is very suitable to obtain pulse group output with several nanosecond pulse intervals.

Simultaneous all-solid-state multi-wavelength lasers——a promising pump source for generating highly coherent terahertz waves

A diode-end-pumped Nd：YAG dual-wavelength laser operating at 1319 and 1338 nm is demonstrated. The maximum average output power of the quasi-continuous wave linearly polarized dual-wavelength laser is obtained to be 2.1 W at a repetition rate of 50 kHz with an output power instability of less than 0.38% and beam quality factor M^2 of 1.45. Using the two lines, the highly coherent and narrow linewidth terahertz radiation of 3.23 THz can be generated in an organic 4-N, N-dimethylamino-methyl-stilbazolium tosylate （DAST） crystal. Meanwhile, the multi-wavelength red laser at 659.5, 664 and 669 nm is generated by frequency doubling and sum frequency processes in a lithium triborate （LBO） crystal. The average red laser output power is enhanced up to 1.625 W at a repetition rate of 15 kHz with an output power instability of better than 0.53% and beam quality factor M^2 of 6.05. Using the three lines, it is possible to generate the multi-wavelength THz radiation of 3.3, 3.43 and 6.73 THz in an appropriate difference frequency crystal.

Quantitative evaluation of enhanced laser tattoo removal by skin optical clearing

Lasers have been widely used for tattoo removal,but the limited light penetration depth calused by high skin scattering property restricts the therapeutic outcome of deep tattoo.Skin optical clearing method,by introducing optical clearing agent(OCA)into skin,has shown some im-provement in the effect of laser tattoo removal.In this study,the enhanced laser tattoo removal has been quantitatively assessed.OCA was applied to the skin of tattoo animal model and Q switched Nd:YAG laser(1064 nm)irradiation was used to remove the tattoo.The skin evaluation instrument(Mexameter probe,MPA580)was applied to measure the content of tattoo pigment before and after laser treatment,and then the clearance rate of pigment was calculated.Further,Monte Carlo(MC)method was utilized to simulate the efecet of skin optical clearing on light transmission in tattoo skin model.By comparing the pigment change of tattoo areas respectively treated with OCA plus laser and single laser,it was found that pigment clearance of the former tattoo area was increased by 1.5-fold.Further,the MC simulation verifed that the reduced light scattering in skin could increase the effective dose of lumninous fux reaching to the deep tattoo regions.It can be concluded from both experiment and theoretical simulations that skin optical clearing technique could improve the outcome of laser tattoo re moval,which should be beneficial for clinical laser tattoo removal and other laser pigment elimination.

Effects of Q-Switched Laser Treatments on Acquired Bilateral Nevus of Ota-Like Macules: A Retrospective Comparative Study

Objective:Q-switched lasers,including 1064-nm Nd:YAG nansecond laser (QSNYL),755-nm alexandrite nanosecond laser (QSAL),and 694-nm nanosecond ruby laser (QSRL),are clinically available for the treatment of acquired bilateral nevus of Ota-like macules (ABNOM).However,no reliable evidence from large-scale comparative studies identifies which type of laser works best.This study aims to determine the differences in the effectiveness,complications,and risk factors of QSNYL,QSAL,and QSRL in the treatment of ABNOM,further to provide evidence for clinician to make optimal choice according to the condition of patients.Methods:We collected the data from 685 ABNOM patients,including clinical features,medical treatments,and follow-up,since 1999 to 2014.The Kruskal-Wallis test was used to compare therapeutic differences between the three groups.The risk factors were analyzed using univariate analysis (x2 test) and multivariate logistic regression analysis.Results:The overall treatment efficiency of the QSNYL group (52.5%) and QSAL group (51.9%) was higher than that of the QSRL group (39.5%) (x2 =17.468,P < 0.001).The onset time of the QSRL and QSAL groups was shorter than that of the QSNYL group.The factors influencing efficacy in the QSNYL group were age at first treatment,number of treatments,coexistence with melesma,and the presence of hyperpigmentation;in the QSAL group was the number of treatments;and in the QSRL group was the number of treatments and hyperpigmentation.The prevalence of hyperpigrnentation in the QSNYL group (30.5%) and the QSAL group (27.5%) was lower than that of the QSRL group (47.3%) (X2=6.576,P<0.001).Concluslon:The QSNYL,QSAL,and QSRL are all effective and safe treatments for ABNOM.Considering the overall efficacy,duration of treatment,side effects,and risk factors,the QSAL is an optimal choice for ABNOM treatment.