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In this paper, we report an external-cavity 2128 nm narrow-linewidth optical parametric oscillator involving a reflective volume Bragg grating. Based on the Sellmeier equation, we introduce the thermal expansion coefficient together with the thermally-induced output wavelength shift. When the pump power is 12.91 W, with the repetition rate being 70 kHz, a 2128 nm laser with an output power of 3.85 W is obtained, having the optical-to-optical conversion efficiency equal to 30% and the linewidth equal to 108 nm. Moreover, the output power is 2.71 W at 2128 nm and the output linewidth is compressed to 0.19 nm, when a reflective volume Bragg grating is used instead of a total reflection mirror, with the corresponding optical-to-optical conversion efficiency being 21% and the beam quality factor being $$ {\mathrm{M}}_x^2 $$ = 1.92 and $$ {\mathrm{M}}_y^2 $$ = 1.98. As a result, a 2128 nm narrow-linewidth laser is implemented.

The existence of the spherical aberration of the thermal lens in the crystal has a certain regulatory effect on the distribution of laser modes. In this paper, using the impact of this aberration on the superposition area of TEM01 and TEM10 modes, we carry out an experimental study of a 1064 nm hollow beam and its nonlinear frequency conversion providing a 532 nm hollow beam. Using a plano-concave cavity structure, under 21.92 W pump power at 808 nm, a 1064 nm hollow beam with an output power of 4.01 W is generated. Based on this result, a 532 nm hollow beam with an output power of 1.08 W is obtained by intracavity frequency doubling with type I phase matching in an LBO crystal. The conversion efficiency is 26.9%.

In this study, we measure the output current of a silicon-based positive-intrinsic-negative (p-i-n) quadrant photodetector (QPD) exposed to a millisecond-pulse laser radiation. We study the output current curve for a cell at different laser energy fluences and pulse widths. The results obtained show that the behavior of the output current involves a holding current stage as the photo-generated current stage declines with time. Based on these results and the p-i-n structure, we analyze such a behavior.

We investigate increase in the surface temperature of biased Si avalanche photodiodes (APDs) fabricated in an external capacitor circuit irradiated by a millisecond-pulse laser. The results obtained show that different external capacitance parameters have different effects on the temperature rise, the smaller the capacitance of external capacitor, the lower surface temperature increase in the APD. The reason for this phenomenon is that the external capacitor charging decreases the circuit current, which hinders the generation of Joule heat in the APD. Therefore, the laser damage resistance of Si APDs can be improved by optimizing the capacitance parameters of the external circuit.

In this study, a two-dimensional model describing thermal stress on a charge-coupled device (CCD) induced by ms laser pulses was examined. Considering the nonlinearity of the CCD’s material parameters and the melting phase transition process of aluminum electrode materials was considered by using equivalent specific heat capacity method, the physical process where a laser pulse irradiating a CCD pixel array was simulated using COMSOL Multiphysics software. The temperature field and thermal stress field were calculated and analyzed. In order to clarify the mechanism producing damage on the CCD detector, Raman spectra from silicon were measured with a micro-Raman spectrometer to determine stress change in the CCD chip. The procedure presented herein illustrates a method for evaluating strain in a CCD after laser irradiation.

In this paper, temperature change and removal depth of continuous laser removal of various coatings (alkyd paint, epoxy varnish, epoxy primer) were analyzed by finite element simulation software. The simulation results show that under the condition of continuous laser irradiation for 1 s, the optimal cleaning threshold of double-layer structure target composed of epoxy primer and epoxy varnish is 200 W/mm2, and the optimal cleaning threshold of three-layer structure target composed of epoxy primer, epoxy varnish and alkyd paint is 150 W/mm2. The reason for this phenomenon is explained by the different material properties of each layer of coating. At the same time, it is concluded that the temperature when the laser directly acts on the double-layer target is lower than that when the laser acts on the three-layer target, which is conducted by alkyd coating. The results achieved in this paper can provide a feasible process parameter for related industries.

In this article, the finite element simulation software is used to analyze the temperature change and the removal depth of the nanosecond continuous laser to remove rubber tracks from the airport runway. The simulation results show that as the continuous laser output energy in nanoseconds increases, the removal depth gradually increases and the temperature of the laser action point gradually increases, so that the glue layer peels off. of the base surface without damaging the base. is removed when nanosecond power is 200W and 150W. Depth is best. In terms of laser glue removal simulation research, the distribution of the temperature field of the glue layer under the action of a pulsed Gaussian heat source is simulated to obtain a better vaporization temperature. Among combined lasers, continuous lasers have better thermal conduction and surface heating effects, but the depth of withdrawal is worse than nanosecond lasers. The nanosecond laser has a better effect of removing mechanical vibration, the central idea of the proposed combined laser is to use high-power short-pulse lasers to quickly increase the target surface temperature, and then according to the positive correlation between material absorption rate and temperature, it can change the material surface to follow. The continuous laser energy absorption characteristics improve the coupling efficiency of the material to laser energy and achieve the expected elimination goal.

In this paper, a simulation model is established to study the temperature rises of the rust layer surface and the metal substrate surface when the continuous laser and nanosecond laser act on the rust layer surface, and draw the temperature charts of the rust layer surface and the metal substrate surface, so as to analyze the temperature rising process of laser cleaning rusty steel plate. The temperature rising process of the rust layer surface and the metal substrate was studied. The simulation results show that: when the continuous laser power is 239W, the peak temperature of the rust layer surface is 1772.1K. At this time, the temperature of the rust layer surface is close to the melting point, but the temperature of the substrate surface has no significant rise. When the power of nanosecond pulse is 5135kW, the peak temperature of the rust layer surface is 1772.8K. At this time, the surface temperature of the rust layer is close to the melting point, but the substrate surface temperature has no significant rise. The results of this paper not only provide a theoretical basis for laser cleaning of rusty steel plate, but also provide a theoretical support for the application of laser cleaning technology.

Aluminum alloy is widely used to make building panels, doors and windows, curtain walls, automobile decorative parts and aircraft skin due to its corrosion, surface treatment, beauty and durability. There is usually a dense oxide film on the surface of aluminum alloy. The oxide film has many pores, and the pore size becomes larger from the inside to the outside. It has good adsorption capacity and strong adhesion with the substrate. Therefore, it is necessary to pretreat and clean the oxide film of aluminum alloy. Compared with the traditional cleaning method, laser cleaning is an advanced environmental protection cleaning technology. Laser cleaning method has the characteristics of less environmental pollution, no contact, less wear on the substrate, high flexibility and stability, which can realize automatic cleaning, wide application range and good cleaning effect. But the key problem of cleaning is to determine the laser cleaning threshold and damage threshold. Firstly, the experiment of laser cleaning aluminum alloy oxide film was simply carried out, and the cleaning threshold and damage threshold were roughly determined by the morphology characteristics. In the theoretical part, the cleaning threshold is obtained by heat conduction model and numerical calculation analysis. Finally, it is found that the theoretical calculation results are consistent with the experimental results.

Green-red (500nm-660nm) laser is widely used in laser projection, laser color display, lithography and laser communication. It is a relatively simple and effective method to obtain the green, orange and red laser from Pr3+:YLF crystal pumped by blue laser diode (LD). In this paper, the influence of output mirror with different transmittance and different curvature radius on the output power of green laser is analyzed. The green laser is achieved with the maximum output power of 960mW at 522nm, when the full pumping current is 2.269A, the absorption power of a-cut Pr3+:YLF crystal is 7.44W.

In this study, different coatings (gray epoxy primer, white epoxy varnish and red alkyd paint) of 7075 aluminum alloy are cleaned with a 500 W continuous-wave (CW) fiber laser. We analyzed the influence of the laser power density on the temperature evolution and target surface morphology. Under the condition of continuous laser irradiation for 1 s, the experimental results indicated that the suitable cleaning thresholds of epoxy primer, epoxy primer and epoxy varnish, as well as epoxy primer, epoxy varnish and alkyd paint were 177.74, 192.89 and 147.44 W/mm2. The results show that the cleaning threshold of thicker three-layer paint target was smaller than the single-layer paint layer, and we analyze the mechanism of this phenomenon.

An evaluation model for optimizing system parameters was established in this study using longitudinal-mode pre-lase selection technology. By solving the rate equation and calculating the evaluation function, we determined the evaluation efficiency of a single-longitudinal-mode operation using this scheme. The optimal condition for the characteristics of the single-longitudinal Q-switched laser was also analytically calculated in detail. We observed that the evaluation function derived using the two-step signal of the Q-switch modulation time and other resonator parameters significantly influenced the output characteristics of the single-longitudinal-mode Q-switched laser operation. Furthermore, the experimental results were consistent with the simulations.

An integrated droplet digital polymerase chain reaction (ddPCR) gene chip that can quantify nucleic acid absolutely was constructed to avoid problems such as droplet fusion, fragmentation and sample contamination during pipetting. The integrated ddPCR gene chip was fabricated by photolithography and cyclic olefin copolymer (COC) injection mold. The 20 μL sample was distributed to about 60,000 water-in-oil droplets with a diameter of about 87 μm within 3 min by flow focus microstructure, and the volume of each droplet was about 0.27 nL. The generation of bubbles was reduced by reducing the width of the collection chamber and increasing the deceleration step. In addition, the efficiency of PCR was improved using COC materials. The sample of human epidermal growth factor receptor (EGFR) exon18 gene was quantitatively detected by this chip. Experimental results show that the detection signal has a good linear relationship with the DNA concentration from 101 to 105 copies/μL (R2 = 0.999) so that the integrated ddPCR gene chip can realize absolute quantification of nucleic acid. It is verified that the integration of droplet generation, PCR amplification and fluorescence detection are realized on one chip, reduce bubble generation and improve PCR efficiency. Compared with the current independent split chip, the integrated ddPCR gene chip ensures a high degree of anti-pollution performance, avoids the operation of droplet movement, reduces human interference, and standardizes the results. It has wide application prospects in nucleic acid quantification and trace detection.

In this paper, the effect of injected energy on low energy single longitudinal mode (SLM) pre-lase Q-switched is analyzed and the optimization procedure is shown in detail. Here, taking the Pr:YLF laser as an example of low energy laser, and the parameters of Pr:YLF laser by using pre-lase have been shown. Compared with normal Q-switched laser, the single pulse energy reaches 60.16% and the pulse width exceeds 39.73% when the same maximum energy is injected and SLM is achieved in pre-lase. The analysis results show that pre-lase is suitable for low energy laser to obtain SLM and there be an optimal performance to achieve the optimal energy output.

An innovative pulse-diode-intermittent-pumped 2-µm acousto-optically Q-switched Tm:YAG laser is presented for the first time, which can improve the output energy, while ensuring the operation repetition of laser. Maximum output energy of 6.83 mJ and minimum pulse width of 367.7 ns at Q-switched repetition rate of 200 Hz is obtained at pump energy of 86.2 mJ. The output wavelength is 2014.9 nm. The beam quality factor Mx2 is 1.48 and My2 is 1.59. The stability is larger than 98%.

The application of laser fabrication of fiber-reinforced polymer (FRP) has an irreplaceable advantage. However, the effect of the plasma generated in laser fabrication on the damage process is rarely mentioned. In order to further study the law and mechanism of laser processing, the laser process was measured. CFRP and GFRP materials were damaged by a 1064 nm millisecond pulsed laser. Moreover, the propagation velocity and breakdown time of plasma plume were compared. The results show that GFRP is more vulnerable to breakdown than CFRP under the same conditions. In addition, the variation of plasma plume and material surface temperature with the number of pulses was also studied. The results show that the variation trend is correlated, that is, the singularities occur at the second pulse. Based on the analysis of experimental phenomena, this paper provides guidance for plasma phenomena in laser processing of composite materials.

As a common alloy material, aluminum alloy has a good application prospect in the fields of construction, automobile, electric power and aerospace.There is a layer of high melting point oxide film on the surface of aluminum alloy, which will hinder the laser energy transfer, lead to poor welding stability, and easily lead to welding defects such as porosity and inclusion in the weld; the surface of aluminum alloy has high reflectivity of laser, which makes the utilization rate of laser energy low, which is easy to cause welding defects such as incomplete penetration and incomplete fusion. Therefore, the surface of aluminum alloy should be pretreated before laser welding. Laser cleaning is an advanced and environmentally friendly cleaning technology. A Nd: YAG laser with 1064 ns pulse width was used to study the morphology of aluminum alloy under the action of nanosecond laser pulse cleaning.The laser-treated surfaces were characterised using metallurgical microscope. Successful oxide removabove certain thresholds that defined the lower end of the process operating window for pulse operation . The ablationechanisms involved in the removaloxide firom 1064nm and found to combineboth thermal and mechanical effects , the surface melting first occurring at fluences lower than those at which cleaning is initialised.In the process of laser cleaning, new oxide layer is formed.

In the industrial field, in order to protect the metal, the metal surface is painted. However, when metals need to be welded, coating becomes a problem. Since the solid polymer coating sublimates during the high temperature welding process, pores are generated in the weld bead[1] .So removal coating is very importance in industry and there have numerous ways to removal coating. Paint removal by laser ablation is favoured among cleaning techniques due to its high efficiency. How to predict the optimal laser parameters without producing damage to substrate still remains challenging for accurate paint removal [2] .In this paper, based on the laser ablation morphology, combined with experiments and numerical simulations, the mechanism and optimal conditions of laser ablation for paint removal are deeply studied. Our studies suggest that laser removal have many physics and chemistry phenomenon including the redox reaction, carbonization, melting and gasification. The threshold value of laser paint removal is 30W obtained from the laser cleaning experiment. The model of laser temperature rise is established, and it is found by numerical simulation that the theory is in good agreement with the experiment

This paper studied semiconductor parameters for the thermal effect of laser to the others quadrants when the millisecond-pulsed laser interacted with one quadrant of the Si-based p-i-n QPD. The thermal model and intrinsic carrier model were built on the basis of the semiconductor physics and thermal conduction theory, and a 3-D simulation model was built by the method of finite element, using COMSOL Multi-physics simulation software. It was taken into consideration that when the carrier was mainly derived from impurity ionization, the intrinsic carrier concentration is lower than impurity concentration at least an order of magnitude, it means that the concentration of intrinsic carrier is no more than 5×1014cm-3, and Si-Based semiconductor detector limit working temperature is 520K. The concentration distribution of intrinsic carrier and temperature distribution of all quadrants of QPD were simulated, and got rules which they changed over time. The conclusion was gotten, the thermal-induced failure time of the other quadrants of QPD decreased with the increase of laser energy density under the same laser spot. The thermal-induced failure time of the others quadrants of QPD extended with the increase of the lengths from every quadrant to the point of peak energy when the laser energy density was same. This paper provided important data basis for further research on the study of the interaction between laser and silicon-based semiconductor detectors.

In order to ensure the detection accuracy of laser-induced fluorescence detection, the micro droplet digital PCR material was required to have weak autofluorescence. The autofluorescence characteristic of micro droplet digital PCR chip was studied in this paper. Firstly, the chip was designed according to the principle of micro droplet digital PCR. Cycloolefin copolymers (COP) and cycloolefin polymers (COP) in organic polymers were selected as the materials of the chip because of their excellent biological characteristics. The laser induced fluorescence device was build. The excitation laser wavelength were FAM (Emission band:522nm, Excitation band:470nm) and HEX (Emission band:553nm, Excitation band:530nm) respectively. The fluorescence image of chip under different exposure time and different band was extracted by COMS camera. And read the fluorescence value through the computer software ImageJ. The glass plate was used as the reference for autofluorescence measurement of chip. From the test results, COC chip showed a good autofluorescence property compared with COP chip, which has lower autofluorescence value under laser excitation. Therefore, for the quantitative detection of trace nucleic acid, the high fluorescent background noise of COP chip will increase the threshold of negative positive discrimination which cloud lead to discrimination error and influence the requirements of detection accuracy. The research results provide a basis for the selection of high-precision micro droplet digital PCR chip materials.

A diode-pumped acousto-optic Q-switched crystal Raman laser operating at multi-wavelength is reported, in which a c-cut Nd:YVO4 crystal was used as the self-Raman medium and a c-cut GdVO4 crystal was used as the other Raman medium. Benefited from the overlapping gain at the Raman shift of 259 cm−1 in the two crystals, the corresponding cascade Stokes light efficiently oscillated, and the 1177, 1178 nm lights corresponding to the primary Raman-shifts of the two crystals oscillated with the 1097 nm laser. The laser configuration was investigated at pulse repetition frequencies (PRFs) of 10, 20, and 30 kHz. With an incident pump power of 8.62 W, the highest average Raman laser output of 1.31 W composed of 1097, 1129, 1177 and 1178 nm lights was obtained at the PRF of 20 kHz. The 1163 nm light corresponding to the third-Stokes light of the Raman shift of 259 cm−1 only arose at the PRF of 10 kHz when the incident pump power exceeded 6.37 W.

In this paper, the surface temperature rise and damage morphology of biased Si avalanche photodiodes (APDs) fabricated in external capacitor circuit irradiated by 1.0ms and 1.5ms pulse width laser are studied. The effects of external capacitance on surface temperature rise and damage morphology of APD irradiated by pulsed laser under different laser energy densities were compared and analyzed. Compared with the absence of external capacitance, the existence of external capacitance reduces the surface temperature of Si-APD and has a certain impact on the damage morphology. The results show that under the same external capacitance and laser energy density, the surface temperature rise of APD treated by 1.5ms pulsed laser is lower than that of 1.0ms pulsed laser, and the surface temperature rise of APD decreases with the decrease of external capacitance.The results show that the existence of external capacitance can further improve the laser damage resistance of Si-APD.

We develop a theoretical model of multimode rate equation that accurately describes mode evolution mechanism of prelase Q-switched Pr3+:YLF single longitudinal mode (SLM). We find that it is important to consider the effect of gain difference when calculating the mode competition time accurately. We identify that there is an optimal parameter for the two step signal of acoustic-optic modulator which determines the stability of SLM output. Then, a visible light direct oscillation Q-switched SLM Pr3+:YLF laser at 639.5 nm is obtained, and the experimental results is agree with the simulation very well.

A diode-pumped passively Q-switched intracavity Raman laser is experimentally investigated, in which a c-cut Nd:GdVO4 crystal is used as a self-Raman medium and a c-cut Nd:YVO4 crystal is only used as a Raman medium. Simultaneous laser pulse outputs at 1096, 1176, 1177 nm corresponding to the first-Stokes light at 259, 882 and 890 cm−1 are acquired. 1128 nm light corresponding the second-Stokes light at 259 cm−1 is obtained and occupies the majority of the output power. The Stimulated Raman Scattering at 259 cm−1 takes place in both the GdVO4 and the YVO4 crystals. With an incident pump power of 7.74 W and a pulse repetition frequency of 30.5 kHz, the average output powers at 1096, 1128, 1176 and 1177 nm are 47.6, 446, 27 and 44.2 mW, respectively.

A Tm:YAP slab laser with double-end-pumped and high efficiency under room temperature is introduced. Considering the cooling of the end faces and lateral faces of the crystal, analyses of the thermal effects in which all six faces cooled by the convection cooling mechanism was assumed to solve the equations of heat conduction. By using the double-concave geometry to offset thermal lens effect, the maximum output power was 25.02W at the incident pump power of 75.97W, corresponding to the optical-to-optical efficiency of 37.05% and slope efficiency of 35.85%. F-P etalon is inserted in the cavity to control laser FWHM line width of 0.44nm at 1938.7nm. And the optical beam quality is measured when pumped power is 20W,which is the beam quality factor of M2 was estimated of 3.25 in x-direction and 2.79 in y-direction.

In this paper, we investigated the passively Q-switched Nd:GdTaO4 laser based on tungsten disulfide (WS2) saturable absorber (SA). The preparation method of WS2 SA was to attach the WS2-alcohol dispersion onto the quartz substrates. The diode-pumped passively Q-switched Nd:GdTaO4 laser operated at a central wavelength of 1066 nm. The stable pulse output could be obtained at the single pulse width of 560 ns. In a word, WS2 seems to be a suitable saturable absorber for solid state lasers.

We report a new compact high efficient CW Tm:YLF laser dual-end-pumped by an equidirectional-polarizing fiber coupled laser diode at room temperature. The maximum output power was 15.2 W at 1907.6 nm with the incident pump power of 47.4 W, corresponding to the optical-to-optical efficiency of 32.1% and the slope efficiency of 37.2%, the beam quality factors were M2 x = 3.19 and M2 y = 3.29, respectively.

This paper presents a high repetition rate and high power 1.57 μm and 3.84 μm multiple optical parametric oscillator based on a single MgO:APLN crystal and pumped by a pulsed 1.064 μm MOPA laser for the first time. In the experiment, with a repetition rate of 200 kHz, a maximum average output powers of 6.5 W at 1.57 μm and 4.3 W at 3.84 μm were obtained under 49 W of 1064 nm pump power, corresponding to optical–optical conversion efficiencies of 13.3% and 8.8%, respectively. The pulse widths were 12.8 and 11.2 ns for 1.57 μm and 3.84 μm, respectively, at the maximum output power.

Carbon fiber reinforced polymers (CFRP) are a widely used composite material applied in both commercial and industrial utilization. Based on the heat conduction theory, a theoretical model for the temperature rise of braided CFRP irradiated by long pulse laser is established in this work, and the time required for the maximum temperature rise of CFRP (with different thicknesses) to be acted by long pulse laser with different energy densities and pulse widths is simulated. At the same time, the temperature rise experiment and damage morphology of a long pulse laser with braided CFRP were carried out. The theoretical simulation results are in good agreement with the experimental results, which verifies the correctness of the theoretical model. The results of this paper will provide a theoretical basis for laser processing of CFRP.

The self-optical parametric oscillator with composite resonator based on Nd3+-doped MgO:PPLN is reported in this paper, which can achieve 1.5 μm eye-safe laser. Under different thermal focal length of Nd:MgO:PPLN, the focusing parameter ratio of 1084 nm to 1512 nm, and 1084 nm spot radius are simulated, which settle the best parameters of the resonator. By 813 nm double-end pumping, a laser pulse of 15.3 μJ at 1512 nm is realized with 60 kHz Q-switched repetition rate. The conversion efficiency of 1084 nm to 1512 nm is 33.7%, the peak power is 1.26 kW, and the power fluctuation is 3.1% respectively.

We demonstrate a narrow linewidth Tm:YLF laser with a volume Bragg grating (VBG) that was pumped by an equidirectional-polarization fiber-coupled laser diode using a dual-end-pumping configuration. For an optimized output coupler with a radius of curvature of 150 mm and transmission of 15% at a wavelength of 1.91 μm, the maximum output power was 15.6 W for an absorbed pump power of 51.7 W at 1,907.93 nm, and the output had a narrow linewidth of 0.22 nm. This corresponds to an optical-to-optical conversion efficiency of 30.2% and the slope efficiency was 36.7%.

Terahertz wave radiation has important applications in medical instrumentation, optical communication, and so on. In this paper, we demonstrate a dual-wavelength (659.6 nm/669.4 nm) light output of a compact intracavity frequency-doubling Nd:YAG laser. We achieve a maximum output power of 1.3 W at central wavelengths of 659.6 and 669.4 nm with linewidths of 57 and 74 pm, respectively. The power instability at the maximum output power is less than 1%, and the beam quality is 1.5. This dual-wavelength laser provides a potential source for generating a coherent terahertz wave radiation of 6.46 THz by the nonlinear optical difference frequency method.

A continuous-wave 1.57 and 3.84 μm intracavity multiple optical parametric oscillator based on a single MgO:APLN crystal is reported for the first time. The synchronized dual-wavelength laser is obtained by using a folded-type double cavity, which consists of a 1064-nm resonator and a multiple optical parametric oscillator. With T = 10% at 1.47 and 3.3 μm output couplers, maximum output powers of 3.13 W at 1.57 μm and 0.85 W at 3.84 μm are obtained, corresponding to slope efficiencies of 6.8% and 1.9%, respectively. The power stabilities are better than 1.8% and 3% at the maximum output power in half an hour.

In this paper, we established a two-dimensional spatial axisymmetric finite element model to simulate the laser-supported absorption wave(LSAW) induced millisecond pulsed laser on aluminum alloy, obtained the relationship among velocity of LSAW, laser energy density and pulse width. And the finite element analysis software, COMSOL Multiphysics, was utilazed in the research. we simulated the generation and propagation procedure of LSAW based on hydrodynamic theory. All the important physical process were considered in the model which were inverse bremsstrahlung, thermal radiation, heat conduction and thermal convection. We simulated aluminum alloy irradiated by long pulse laser with different energy densities and pulse widths, the results showed that the time when the velocity reached maximum was increased with the growth of laser energy density, after laser irradiation, the velocity of LASW decreased immediately to zero, and the velocity of LSAW become slower by increasing the pulse width while the laser energy density was unchanged, moreover, the velocity of LSAW increased by increasing the laser energy density while the pulse width was unchanged. The results of the study can be applied in the laser propulsion and laser enhancement technology, etc.

In this paper, we established a two-dimensional spatial axisymmetric finite element model to simulate the laser-supported absorption wave(LSAW) induced millisecond multiple pulsed laser on aluminum alloy, made theoretical investigation. And the finite element analysis software, COMSOL Multiphysics, was utilized in the research. we simulated the generation and propagation procedure of LSAW based on hydrodynamic theory. All the important physical process were considered in the model which were inverse bremsstrahlung, thermal radiation, heat conduction and thermal convection. We simulated aluminum alloy irradiated by long pulse laser with 35J energy, 1ms pulse width and 1mm spot radius in the case of different pulse number, we first obtain the simulation result of velocity fields and temperature fields of LSAW, the results showed that there was a certain temperature cumulative effect near target material; Aiming at obtaining the relationship between the generation time of LSAW and laser pulse number. We keep the laser pulse width, energy density and pulse frequency unchanged, the pulse number was 3, 5, 10 respectively; the results showed that the generation time of LSAW become shorter by increasing the laser pulse number. The results of the study can be applied in the laser propulsion and laser enhancement technology, etc.

In this work, a 1. 9 μ m Tm:YLF high-order vortex laser output is realized for the first time based on LD off-axis pumping technology. By adjusting the off-axis displacement of the output coupling mirror accurately, the maximum topological charge up to m = 20 for stable Hermite–Gaussian (HG m,0 ) mode is achieved. The conversion of high-order HG m,0 to Laguerre–Gauss (LG m,0 ) modes are further realized by a π /2 mode converter, and the topological charge and chirality of LG m,0 modes are measured by the Mach–Zehnder (MZ) interferometer system. The maximum output power of the LG 1,0 mode vortex laser was measured to be 8.5W with the central wavelength of 1908.8 nm. The wavelength and the power instability are less than 0.72 nm and better than ± 5.9%, respectively. This work proves that the 1. 9 μ m Tm:YLF laser has the potential to achieve continuous tuning and easy chirality control for the high-order vortex optical mode output, and lays a foundation for high-power mid-infrared vortex laser applications.

The damage morphologies of silicon induced by ms-ns combined-pulse laser with different pulse delay are investigated, based on the experimental investigations of the temperature, plasma plume, and damage morphology. The splashing phenomenon began to be obvious when the pulse delay was 0.8 ms, and the small holes were formed on the center of damage morphology. It was found that the process of droplet ejection might occurred after the irradiation of ns laser. The mechanism of damage morphology induced by ms–ns combined-pulse laser with different pulse delays was discussed.

The stable zones of the first three low-order modes of the LD end-pumped laser dynamically controlled by spherical aberration are proposed. Considering the temperature dependence of thermal conductivity, an aberration factor representing spherical aberration is calculated. Based on the multiples of the thermal focal lengths of the fundamental mode, TEM01 and TEM10, their dynamic stable zones were confirmed. An asymmetrical LD end-pumped Nd:YVO4 laser wavefront information measurement experiment was performed. The primary spherical aberration, the beam quality factor and the output power were measured, and their changes with the pumping power were analyzed to determine the dynamic stable zone. The experimental results agree well with the theoretical simulations.

The spectral super-broadening of backward stimulated Raman scattering (SRS) in four liquid samples ( C C l 4 , dimethyl sulfoxide, acetone, and C H 2 C l 2 ) have been observed under the pump conditions of using 532-nm and ∼ 11 - n s pulsed laser beams from a frequency-doubled and multilongitudinal mode Pockels Q-switched Nd:YAG laser device. Under the same pump conditions, in acetone the observed maximum broadening range was ≥ 450 c m − 1 for the backward SRS, while it was ≤ 45 c m − 1 for the forward SRS. The physical origin of this observed effect is essentially related to the detailed temporal structure of the 532-nm pump pulse that consists of a series of subpulse of ∼ 50 p s width, owing to the randomly beating effect among a large number of longitudinal modes of the Pockels Q-switched laser source. Each backward SRS subpulse undergoes multiple cross-phase modulation (XPM) by interacting with a certain number of forward pump subpulses, and consequently manifests a super-broadened spectral distribution. In contrast, each forward SRS subpulse interacts only with a single pump subpulse and therefore experiences a much limited XPM influence, resulting in a much smaller spectral broadening. Furthermore, when the 532-nm pump beam was from a single-longitudinal mode-seeded Nd:YAG laser, there was no beating-effect-induced subpulse structure of the pump pulse, and thereby no noticeable spectral broadening for both backward and forward SRS could be observed.

A 3.8 μm secondary mid-infrared parametric amplifier based on MgO:PPLN crystal was analyzed. At a repetition frequency of 140 kHz and an initial amplified signal source power of 1 W, the maximum output power of the first-level 3.8 μm laser is 3.03 W. Perform second-level OPA experiment to obtain higher output power. Under the premise that the initial amplified signal source power is 2.5 W, the output power of the 3.8 μm laser is 4.69 W, the output wavelength line width is 3.58 nm, the optical-to-optical conversion efficiency is 7.3%, and the beam quality factor M2 = 1.82, The 3.8 μm laser calibration amplification output was achieved.

Transparent conductive electrode (TCE) platforms are required in many optoelectronic devices, including organic light emitting diodes (OLEDs). To date, indium tin oxide based electrodes are widely used in TCEs but they still have few limitations in term of achieving flexible OLEDs and display techniques. In this paper, highly-flexible and ultra-thin TCEs were fabricated for use in OLEDs by combining single-layer graphene (SLG) with thin silver layers of only several nanometers in thickness. The as-prepared SLG + Ag (8 nm) composite electrodes showed low sheet resistances of 8.5 Ω/□, high stability over 500 bending cycles, and 74% transmittance at 550 nm wavelength. Furthermore, SLG + Ag composite electrodes employed as anodes in OLEDs delivered turn-on voltages of 2.4 V, with luminance exceeding 1300 cd m-2 at only 5 V, and maximum luminance reaching up 40 000 cd m-2 at 9 V. Also, the devices could work normally under less than the 1 cm bending radius.

Laser characteristics of acousto-optic Q-switched operation of 1319 nm/1338 nm dual-wavelength composite Nd:YAG laser were studied. Maximum output power of 5.77 W was achieved in CW operation. Under Q-switched operation, the maximum peak power of 3.96 kW and minimum pulse width of 65.6 ns was obtained at repetition frequency of 20 kHz with the duty ratio of 96%. The influence of the duration of the ultrasonic field acted on the Q-switch to the output characteristics of dual-wavelength composite Nd:YAG laser had been reported first time.

This paper proposes a blue LD pumping Pr:YLF crystal acousto-optic Q-switched double pulse laser with 639 nm red light output. The output principle of the Pr:YLF double pulse laser is demonstrated, and a four level differential rate equation model is established to describe the distribution of the double pulse sequence at a high repetition frequency. When the laser repetition frequency is 10 kHz, the double step signal generator, as the modulator of the acousto-optic Q-switching, turns on the Q-switching twice in one pumping period, and obtains the maximum output power of 144 mW, pulse energy of 7.1μJ and the output of visible light double pulse with the pulse interval of 20 μs.

We report on an intra-cavity optical parametric oscillator (OPO) based on MgO-doped periodically poled lithium niobate (MgO:PPLN) crystal in-band pumped by a wavelength-locked 878.6 nm laser diode (LD). A narrow linewidth 2.1 μm laser output is obtained by using a reflection volume Bragg grating (VBG). The stability of the resonator under high pump power and the spot mode matching of the parametric laser oscillation process are considered comprehensively to determine the optimal cavity parameters. In the experiment, a narrow linewidth of 2.1 μm maximum output power of 4.7 W is obtained with the pulse duration of 8.55 ns, the linewidth of 1.89 nm at 80 kHz repetition rate, corresponding to the maximum optical-optical conversion efficiency of 11.6%.

The dual-wavelength alternating output laser using double laser gain mediums and single electro-optic (EO) Q-switched crystal with the same EO Q-switched voltage is obtained. A rate-equation model is developed, accounting for dual-wavelength alternating output laser based on the same EO Q-switched voltage. In numerical simulation, the relationship between loss and gain value in each cavity is compared as the criterion for selecting the same Q-switched voltage. Using this method, the dual-wavelength alternating output laser of 1319 nm and 1064 nm, the pulse widths of 15.88 ns and 14.58 ns, and the energies of 42.37 mJ and 43.6 mJ respectively, is stably achieved under the same Q-switched voltage of 1000 V with the maximum pump current of 90 A and 70 A, respectively.

This letter presents a visible light direct oscillation Q-switched single-longitudinal-mode Pr:YLF laser output at 639.5 nm by using the Q-switching pre-lase technology combined with the Fabry–Perot etalon. The experimental results show that the single-longitudinal-mode oscillation can be generated in a low-energy injection state. The proposed laser overcomes the problem associated with the Q-switched Pr:YLF laser, which cannot produce high-efficiency single longitudinal mode owing to the high loss of inserted elements. With the proposed laser, a Q-switched single-longitudinal-mode pulsed laser output has been achieved with 3.94 μJ energy and 81.1 ns pulse duration at a repetition of 10 kHz. The spectral linewidth of single-longitudinal-mode pulse laser was approximately 33 MHz.

In this study, by combining the voltage-increased and voltage-decreased electro-optic (EO) Q-switched technologies, a dual-wavelength coaxial alternating output solid-state laser operating at 1064 and 1319 nm is demonstrated. Two wavelengths are generated from different gain medias, and combined together with a shared EO Q-switcher which is accomplished by using a double-crystal RbTiOPO4 (RTP). The coaxial alternating 1064 nm and 1319 nm Q-switch pulses with 200 μs delay are obtained. This produces a maximum output energy of 38.96 mJ with a pulse width of 15.7 ns for the 1319 nm component, and a maximum output energy of 38.73 mJ with a pulse width of 14.7 ns for the 1064 nm component at a pulse repetition frequency (PRF) of 10 Hz when the pumping current are 90 A and 70 A, respectively.

A method for judging the locations of dynamic stable zones boundaries and mode separations is presented by spherical aberration “transient variation” Experiments on spherical aberration in dynamic stable zones of an end-pumped laser are carried out. Based on the inversion of the wavefront information, the “beam quality deterioration zone” is investigated. The multiple relationships among the thermal focal length of the low-order modes are calculated. Based on the discussion of experimental results, the changing law of the sign of spherical aberration is studied. A theoretical model of the relation among the cavity configuration, spherical aberration and beam quality can be established in addition. The experimental results agree well with the theory.

A high-repetition-rate and double-end pumped electro-optic Q-switched Tm:YAlO3 (Tm:YAP) laser is reported. The Tm:YAP slab crystal cut by c-axis is used as the laser gain medium, and the RbTiOPO4(RTP) crystal is selected as the electro-optic Q-switched crystal. Choosing volume Bragg gratings (VBG) as the input mirror to narrow the output line width. When the pump power is 79.2 W, at a repetition rate of 10 kHz, maximum average-output-power of 21.96 W is achieved, with the pulse width of 20.64 ns and output energy of 2.20 mJ. The output peak power is 107.3 kW and the slope efficiency is 29.2%. The center wavelength is 1937.87 nm and the line width is 0.73 nm. The beam quality in the x direction is 1.48, and in the y direction is 1.50.