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Based on the Fourier heat conduction equation and the thermoelastic equation, the thermal-stress coupling model of the Si-CCD irradiated by millisecond pulse laser was established, the time-space distribution of the temperature field and the stress field on the Si-CCD was calculated. The results show that: the damage firstly occurred in the color filter layer; increased the laser energy density, part of the microlens and the color filters were missing; then continued to increase the laser energy density, the photosensitive area in the N-Si layer was melting; when the channels in the N-Si layer were damaged, the Si-CCD was under functional loss. In this paper, the simulation results were consistent with the experiment results. [ABSTRACT FROM AUTHOR]

Based on a combination of online experimental process detection and off-line experimental results measurement, an experimental system of a millisecond pulse laser irradiating a CCD detector was established, the interacting process between the millisecond pulse laser and the CCD detector was studied, and the formation of different damage effects was analyzed. The experimental results show that: the damage on the CCD detector firstly occurred in the color filter layer, and then extended along the depth direction. The damage sequence of the color filter layer was green, cyan, yellow and magenta color filters, and the color filters were discolored after irradiation. The damaged area from center to outside was green, cyan, burgundy and yellow in the video image; increased the laser energy density to completely destroy partial optical part, the photosensitive layer was exposed in the air, the white part appeared in the middle of the bluish green part in the video image. The connecting position between the exposed photosensitive layer and color filter layer was accompanied with heave and displacement; the changes on the optical part of CCD detector were composed of thermal damage and mechanical damage, and the changes on the electrical part of CCD detector mainly performed noise on the output signal and decrease on signal-noise ratio(SNR). [ABSTRACT FROM AUTHOR]

Continuous wave (CW) laser irradiation induces temperature changes in various phases within porous media, accompanied by phase change and gas transport. Water saturation is a crucial factor influencing this context's moisture and heat transfer process. This paper addresses this issue by establishing a theoretical model for CW laser irradiation on unsaturated porous media. Through experiments and simulations, it studies the effects of different water saturations on heat and mass transfer under laser irradiation. The results indicate that the critical depth reflects the influence of water saturation under laser irradiation on the distribution of solid-phase temperature in both time and space dimensions. Specifically, an increase in water saturation enhances the uniformity of solid-phase temperature distribution, while the gas temperature exhibits a similar distribution pattern. For mass transfer processes, it increases the evaporation rate and Darcy velocity of porous media within the effective range of laser irradiation. Lower water saturation facilitates phase change processes and accelerates gas transport rates. Importantly, this trend remains consistent even with the emergence of dry-saturation zones. Additionally, the decrease in water saturation has a coupled promoting effect on gas temperature and mass transfer processes. Lowering water saturation can increase gas temperature and consequently enhance mass transfer processes. Simultaneously, enhancing mass transfer processes benefits heat exchange between the two phases. In the four sets of experiments, the conformity of the surface temperature rise curves obtained from experiments and simulations is good, indicating that the model can accurately reflect the temperature rise patterns of sand particles. In summary, this work provides valuable research results on the effects of different water saturations on laser irradiation-induced temperature rise, phase change, and gas and moisture transport within porous media. It lays a specific theoretical foundation for laser soil remediation technology. [ABSTRACT FROM AUTHOR]

• Effective suppression of ASE by optimizing parameters in 1908.12 nm pulsed amplifier. • The three-dimensional amplification gain versus fiber lengths and wavelengths were simulated. • ASE power distributions versus time with pumping powers were simulated. • Maximum ASE suppression and total amplifier gain were 49.85 dB and 40.27 dB, respectively. • Maximum average output power of 14.62 W (linewidth of 0.65 nm) with slope efficiency of 46.0%. We proposed and demonstrated high efficiency Tm3+-doped pulsed all-fibered master oscillator power amplifier (MOPA) operating at 1908.12 nm with Amplified Spontaneous Emission (ASE) suppressed by optimizing the pumping power, seed laser power and fiber length. Considering the effect of pulsed seed laser and ASE on amplifier output characteristics, the amplifier gain and ASE suppression ratio under different conditions are simulated. Using an optimized length of 1.0 m large-mode-area (LMA) Tm-doped fiber (TDF) is used as amplifier fiber, the maximum average output power of 14.62 W (slope efficiency of 46.0%) with total amplifier gain of 24.66 dB is obtained when pumping power of 30.5 W and input signal laser power of 1.225 W. Meanwhile, ASE can be effectively suppressed with maximum ASE suppression ratio of 49.85 dB is obtained at the repetition frequency (RF) of 1 MHz and the duty cycle of 80%. Central wavelength of 1908.12 nm with linewidth of 0.65 nm and the beam quality of M x 2 = 1.35 and M y 2 = 1.51. This is, to the best of our knowledge, the maximum ASE suppression ratio in pulsed Tm3+ doped fiber laser by using acousto-optic (AO) external modulation operating at 1908.12 nm without filter. [ABSTRACT FROM AUTHOR]

• Utilizing an FBG to broaden the observation range. • Based on Vernier peaks accuratelying the temperature. • Utilizing the Vernier effect to improve sensitivity. An optical temperature sensing method with ultra-high sensitivity and a wide measurement range is proposed. The performance enhancements come from the high thermos-optical coefficient of liquid crystal (LC) material, and the Vernier effect produced by LC birefringence characteristics. This paper proposes and demonstrates a method to enhance the measurement range of the LC temperature sensor. A miniature LC temperature sensor was made by using an optical fiber Fabry-Perot interferometer (FPI). To compensate for and attenuation of LC and improve the contrast of the FPI, silver films are coated on one end of the optical fiber. Due to the high birefringence of the LC in the interferometer, a Vernier spectrum can be observed in the reflection. The temperature measurement range of 20–32 °C and the temperature sensitivity of the Vernier peaks of a sensor sample is about 42.18 nm/°C, which is much higher than the sensitivity of the cascaded FBG in structure. The limited measurement range is due to the free spectral range (FSR) limitation. In this context, the FBG peak can be used as a temperature reference while switching the adjacent Vernier peaks. Hence, this LC temperature sensor exhibits high sensitivity as well as a wide measuring range, which would broaden the application scope of the LC temperature sensors. [ABSTRACT FROM AUTHOR]

The effect of laser surface paint removal depends on the mechanism of paint removal. The mechanism of nanosecond laser removal of epoxy resin paint film on aluminum alloy surfaces was studied theoretically and experimentally. Firstly, a laser thermal paint removal model was established based on the heat conduction equation, Hertz-Knudsen equation, and Hooke's law. The adsorption relationship between the paint film and the aluminum alloy substrate molecules and the adsorption force between the paint film and the substrate were analyzed and calculated. A laser thermal paint removal model was solved using COMSOL finite element software. By analyzing the changes in temperature and thermal stress with laser fluence, we obtained the theoretical threshold for laser paint removal. Subsequently, experimental research was conducted on laser paint removal. Through theoretical and experimental studies, it was found that the paint removal threshold of nanosecond pulse laser is 0.47 J/cm2. The primary mechanism of nanosecond laser paint removal is thermal stress stripping. When the laser fluence is low, the nanosecond pulse laser can only ablate the paint on the surface, and the thermal stress between the paint film and the substrate makes it difficult to remove the paint film. As the laser fluence increases, the nanosecond laser will ablate the surface paint film, and the thermal stress between the paint film and the substrate will cause the stripping of the underlying paint film and the substrate. The primary mechanism of laser paint removal is stripping. [ABSTRACT FROM AUTHOR]

• A π -polarized 1084 nm laser based on Nd:MgO:LiNbO 3 crystal under modulation pulsed pumping mode was realized. • The dual-wavelength fundamental laser output range of 1084 nm and 1093 nm was modulated by adjusting the duty cycle of the pump source. • The π -polarized 1084 nm fundamental laser with a maximum average output power of 1.396 W in the whole pump range was obtained. A π -polarized （ π -pol） 1084 nm laser based on Nd:MgO:LiNbO 3 crystal under modulation pulsed pumping mode was demonstrated. The anisotropic Nd:MgO:LiNbO 3 slab crystal was end-pumped by a pulsed laser diode (LD) with a different duty cycle for experiments. The dual-wavelength fundamental laser emission range was effectively controlled within a certain pump peak power interval, and the unmatched polarized fundamental laser is completely suppressed when the duty cycle is 20 % and below. At a repetition frequency of 5 Hz and pulse width of 40 ms, the π -pol 1084 nm fundamental laser with a maximum average output power of 1.396 W in the whole pump range was obtained, and the single pulse energy was 279.2 mJ. [ABSTRACT FROM AUTHOR]

• Direct emitting visible dual-wavelength double pulse laser. • Control the dual-wavelength intensity ratio by adjusting the insertion angle of F-P etalon. • Control the master–slave pulse energy ratio by adjusting acoustic-optic Q-switch step loss. A theoretical model of dual-mode rate equation has been developed to accurately describe the oscillation mechanism of a visible dual-wavelength double pulse Pr:YLF laser. The insertion angle of F-P etalon and the two-step loss of Q-switching are found to be critical factors in controlling dual-wavelength intensity ratio and master–slave pulse energy ratio. Experimental results demonstrate that tuning these parameters enables the production of a dual-wavelength double-pulse laser, with a maximum output power of 98mW, a pulse width of 100 ns, and a PRF of 10 kHz. To the best of our knowledge, this is the first investigation of a visible dual-wavelength double pulse Pr:YLF laser. [ABSTRACT FROM AUTHOR]

Raman and absorption features all-trans- β -carotene (β -Car) liquefied in dimethyl sulfoxide (DMSO) of 10−6 concentration at temperature range from 333K to 263K are recorded. The usage of density functional theory (DFT) calculations could meticulously anticipate the molecular vibration mechanism. The calculation of CC bond length alternation (BLA) and graphic illustration of the highest occupied molecular orbital (HOMO) of β -Car can help decipher the vibration mechanism during phase transition. The Raman scattering cross section (RSCS) of the CC single and double bonds roughly increases when temperature decreases during pure liquid- solid phase condition due to extended effective conjugation length (ECL). The RSCS sharply drops during the phase transition because the β rings are very likely rotated from 0° to 90°. Electronic transition energy (0-0) of absorption spectra declining lead to the amplified resonance effect. This research is counted upon to be valuable by using DFT calculations to investigate the influence of phase transition on resonance Raman character of β -Car. [ABSTRACT FROM AUTHOR]

Highlights • The Pulse-LD-intermittent-pumped acousto-optically Q-switched Tm:YAG laser is proposed. • The technology relies on precise time control among pulse laser diodes and Q-switch. • The technology relieves the thermal effect of Tm:YAG crystal. • Output pulse energy increases while ensuring the operation repetition of Tm:YAG laser. Abstract 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 M x 2 is 1.48 and M y 2 is 1.59. The stability is larger than 98%. [ABSTRACT FROM AUTHOR]

• The compact 3.8 µm self-optical parametric oscillator is realized. • The high repetition rate 1.59 W 3.8 µm laser is obtained. • The self-optical parametric oscillator is able to flexible adjustment of wavelength output. A compact mid-infrared self-optical parametric oscillator (SOPO) based on thermally boosted direct pumped (4I 9/2 Z3→ 4F 3/2 R2) is realized for the first time (to our knowledge). The SOPO that measures only 60 mm is achieved. When the absorbed pump power is 28.4 W, the maximum average power of 1.59 W is obtained, corresponding to a pulse repetition rate of 119.57 kHz and pulse width of 6.71 ns, respectively. The wavelength of the SOPO is controlled at 3834.3 nm within the entire pump region by adjusting the TEC's cooling temperature, leveraging the reduction in thermal effects achieved through the thermally boosted direct pumped technique. Furthermore, the SOPO wavelength could be tuned from 3816.7 to 3846.1 nm. This work obtains the highest average power in the compact mid-infrared SOPO and provides an efficient method to generate mid-infrared pulsed laser, which has important applications in far-infrared laser generation, gas detection, and laser medicine. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We present a real-time solution to the phase diversity problem when the observed objects are extended scenes. It utilizes an iterative linearization of the optical transfer functions (OTF) in at least two diversity planes by a first-order Taylor expansion to reconstruct initial wavefront. Vast simulation experiments are processed to verify the presented algorithm, including comparing our algorithm with the analytic estimator method, demonstrating that our method has high wavefront detection accuracy and large linearity range. [ABSTRACT FROM AUTHOR]

• The 1.5 μm self frequency conversion OPO based on Nd3+ doped MgO:PPLN with the multi-focus pumping mode was realized. • The multi-focus pumping mode effectively dispersed the thermal effect of the crystal. • The oscillation of the σ-polarized 1093 nm laser was suppressed. • The signal light with an average output power of 183 mW was obtained in the double-focus pumping mode. A 1.5 μm passively Q-switched self frequency conversion optical parametric oscillator based on Nd3+ doped MgO:PPLN with the multi-focus end-face coupling pumping mode is reported. The reason for the generation of dual-wavelength fundamental frequency laser is explained by Nd:MgO:PPLN laser characteristics and energy level theory, and a multi-focus pumping thermal model is established to numerically simulate the temperature field distribution under different pumping injection modes. Compared with the traditional single-focus pumping mode, the multi-focus coupling pumping mode effectively disperses the thermal effect of the Nd:MgO:PPLN crystal, the oscillation of the σ-polarized 1093 nm laser is suppressed, the single-wavelength output of the π-polarized 1084 nm laser is realized. Thereby the more efficient 1514 nm signal light is obtained. In the experiment, the 1514 nm signal light with an average output power of 183 mW is obtained when the repetition frequency is 5.4 kHz, the pulse width is 6.8 ns and the pulse energy is 34 μJ in the double-focus pumping mode. In the triple-focus pumping mode, the 1514 nm signal light with an average output power of 165 mW is obtained when the repetition frequency is 5.6 kHz, the pulse width is 7.2 ns and the pulse energy is 30 μJ. Overall evaluation of the experimental effects of the two kinds of pumping modes shows that the double-focus pumping mode is superior to the triple-focus pumping mode. [ABSTRACT FROM AUTHOR]

• The extra-cavity multi-optical parametric oscillator is a technique to generate multi-wavelength tunable laser output. • The back conversion and power differential are compared between the adjusting transmittance and the adding EO PCs. • Adjusting transmittance and adding EO PCs can suppress the back conversion and reduce the power differential. • Adding EO PCs can obtain a balanced multi-wavelength laser output for higher output power and conversion efficiency. The extra-cavity multi-optical parametric oscillator (MOPO) using MgO-doped aperiodically poled lithium niobite (MgO:APLN) is a technique to generate multi-wavelength tunable laser output, in which the back conversion and power differential can reduce the output power and conversion efficiency. A comparison of the back conversion and power differential between the two methods is presented in this paper. One approach is to adjust the mirror transmittance to change the parametric light's power density involved in the oscillation. With 1.47 μm transmittance of 20 % and 3.30 μm transmittance of 60 %, the 3.30 μm output power is 0.95 W, the 3.84 μm output power is 0.94 W, and the power ratio is 1.01. The other approach is to add two electro-optical polarization mode converters (EO PC) to change the parametric light's polarization. When the electric fields of two EO PCs are 66 V/mm and 15 V/mm, the 3.30 μm and 3.84 μm output powers are 2.54 W and 2.49 W, the conversion efficiencies are 10.3 % and 10.0 %, and the power ratio is 1.02. The comparison results confirm that both methods have the capability of back conversion suppression and power differential reduction. Compared with the adjusting transmittance, adding EO PCs has higher output power and conversion efficiency, which is the first reported method for better balanced multi-wavelength laser output. [ABSTRACT FROM AUTHOR]

• With the proposed laser, a Q-switching pre-lase single-longitudinal-mode pulsed laser output has been achieved with 10.25 μJ of output energy and 77.66 ns pulse duration at a repetition of 20 kHz. • The spectral linewidth of the single-longitudinal-mode pulsed laser was approximately 18 MHz. • By optimizing the parameters of the inserted components in the laser cavity, the problem of single-longitudinal-mode oscillation during high energy injection being unstable can be solved. In this article, a single-longitudinal-mode pulsed laser with a center wavelength of 639.7 nm was developed by using a 444 nm laser diode end face continuously pumped Pr:YLF crystal, with the method of inserting the Q-switching pre-lase technology and a Fabry-Perot etalon set in the resonant cavity. Experimental results show that by optimizing the parameters of the inserted components in the laser cavity, the problem of single-longitudinal-mode oscillation during high energy injection being unstable can be solved. With the proposed laser, a Q-switching pre-lase single-longitudinal-mode pulsed laser output has been achieved with 10.25 μJ energy and 77.66 ns pulse duration at a repetition of 20 kHz. The spectral linewidth of the single-longitudinal-mode pulsed laser was approximately 18 MHz. [ABSTRACT FROM AUTHOR]

• A 4.3 W π -polarized 1084 nm single-wavelength CW laser with a single circular spot output is obtained. • The oscillation of σ -polarized 1093 nm laser is suppressed successfully. • The thermal model of Nd:MgO:LN under different pumping modes is established. • The single circular spot laser is realized based on the double-focus coupling pumping mode by optimizing the design of the resonator. A π -polarized 1084 nm continuous wave(CW) laser based on a-cut Nd3+ doped MgO:LiNbO 3 (Nd:MgO:LN) with the end-face double-focus coupling pumping mode is reported. The reason for the dual-wavelength laser is explained from the perspective of Nd:MgO:LN energy level, the thermal model of Nd:MgO:LN is established, the temperature field distribution in the crystal under different pumping modes is analyzed, and the laser spot morphology of the output mirror at different positions is simulated. In the experiment, compared with the traditional end-face single-focus pumping mode, it is experimentally verified that the thermal management of Nd:MgO:LN can be effectively realized with the end-face double-focus coupling pumping mode, σ -polarized 1093 nm laser is suppressed successfully, the phenomenon of orthogonally polarized dual-wavelength alternating output or simultaneous output does not appear, the advantage is obvious under high-power pumping. And the single circular spot laser is realized based on the double-focus coupling pumping mode by optimizing the design of the resonator. Finally, a 4.3 W π -polarized 1084 nm single-wavelength CW laser with a single circular spot output is obtained. [ABSTRACT FROM AUTHOR]

• A mid-infrared narrow linewidth optical parametric oscillator based on composite intra-cavity pumping is studied for the first time. • The narrow linewidth laser output of idler wavelength is realized indirectly through the function of F-P etalon on fundamental wavelength and signal wavelength. • The combined action of dual F-P etalons on signal wavelength can suppress adjacent modes of idler wavelength. • The narrow linewidth mid-infrared laser with the central wavelength of 3811.84 nm and the linewidth of 0.73 nm was obtained. A compact, multiple F-P etalon and narrow linewidth intra-cavity single-resonant mid-infrared optical parametric oscillator based on MgO:PPLN is reported, which is composed of a 1064 nm gain cavity and a mid-infrared frequency conversion cavity. The narrow linewidth at 3.8 μm can be obtained indirectly through the linewidth compression at the fundamental wavelength and the signal wavelength. The linewidth at 3.8 μm is 0.73 nm without adjacent mode when the fundamental wavelength is acted by the single F-P etalon with the thickness of 2.5 mm and the signal wavelength is acted by the dual F-P etalon with the thickness of 2.5 mm and 0.5 mm. Meanwhile, the output power of 1.06 W is obtained, corresponding to the conversion efficiency of 2.41%, the pulse width of 11.17 ns is obtained synchronously, and the beam quality factor M2 at 3.8 μm are M x 2 = 1.92 and M y 2 = 1.87, respectively. It provides a method for intra-cavity pumped mid-infrared linewidth compression. [ABSTRACT FROM AUTHOR]

• A intracavity pumped dual-wavelength optical parametric energy conversion model based on MgO:APLN was set up for the first time. • The effect of the ratio between resonant signal wavelengths on the gain of idler wavelengths was simulated. • The maximum output powers of 1.43 W at 3.30 μm and 2.47 W at 3.84 μm were obtained. An intracavity pumped dual-wavelength optical parametric oscillator based on a single MgO:APLN crystal at approximately 3.30 and 3.84 μm was studied using a folded-type double cavity, which consists of a 1.06 μm resonator and dual-wavelength optical parametric oscillator. With the maximum incident diode power of 43.84 W, the maximum output powers of 1.43 W at 3.30 μm and 2.47 W at 3.84 μm were obtained under T = 70%@1.57 μm and T = 25%@1.47 μm at a repetition rate of 40 kHz, corresponding to conversion efficiencies of 3.26% and 5.63%, respectively. The pulse widths of 11.35 ns at 3.30 μm and 13.17 ns at 3.84 μm were obtained synchronously. A dual-wavelength optical parametric energy conversion model was set up to simulate the influence of the transmittance at resonant signal wavelengths on the output power of idler wavelengths. Both theoretical and experimental results demonstrated that the relationships in output power between 3.30 and 3.84 μm can be affected by adjusting the transmittance at signal wavelengths. [ABSTRACT FROM AUTHOR]

• HG mode conversion and etalon are used to achieve wavelength tuning of vortex laser. • Continuous wavelength tuning of 1.9 μm vortex beam is realized. • There is no obvious change of the vortex beam during the wavelength tuning process. In this paper, HG mode conversion and etalon are used to achieve a 1.9 μm vortex beam output in a Tm:YLF laser while achieving a certain range of wavelength continuous tuning. In theory, the wavelength tuning characteristic and tuning capability of the etalon are analyzed. In the experiment, the HG 1,0 mode laser is achieved by off-axis pump, and the optical field distribution and beam quality are relatively consistent with the theoretical state. After the HG 1,0 mode laser passes through the π/2 mode converter, the LG 1,0 vortex beam output is realized. The optical field distribution and beam quality of the vortex beam are relatively close to the theoretical state. The threshold of the laser at LG 1,0 mode is 3.2 W, the slope efficiency is 37.7%, the optical–optical conversion efficiency is 34%, and a laser output of 8.6 W is obtained at the highest pump power of 25.3 W. On this basis, the continuous wavelength tuning of the LG 1,0 mode vortex beam from 1937 nm to 1921 nm was achieved by rotating the etalon. Through comparison, it can be found that the optical field distribution and output power of each wavelength are relatively close during the wavelength tuning process. Finally, the topological charge of the vortex beam is measured by the interference of the vortex beam with the spherical wave and the plane wave. This article is of great significance for the further research of multi-dimensional tuning to realize large-capacity optical communication. [ABSTRACT FROM AUTHOR]

Abstract: Experiments of photodiodes irradiated by laser at various energy densities are performed in this study. The laser-induced changes in photocurrent and dark current are monitored, the degradation process of responsivity as a function of the laser energy density is obtained. Morphological examinations were done with a scanning electron microscope (SEM), and damaged depth was performed using a step profiler. The results indicate that the relative responsivity of photodiodes for He Ne probe beam gradually reduced with the increase of intense laser energy density. The mechanism of various degradation of responsivity was analyzed. The obvious decrease of responsivity mainly contributes to an increase in the surface recombination velocity caused by defects and thermal breakdown of PN junction. The results were significant for the study of interaction laser with material. [Copyright &y& Elsevier]

• The 2.1 μm self frequency conversion optical parametric oscillator with Nd3+ doped MgO:PPLN was realized for the first time. • Design the resonator cavity can suppress 1093 nm laser. • The temperature of Nd:MgO:PPLN is controlled to obtain a degenerate laser of 2168 nm. • The 2.1 μm parametric light pulse width is 7.793 ns. A 2.1 μm integrated self frequency conversion optical parametric oscillator which based on Nd3+ doped MgO:PPLN with intra-cavity acousto-optic Q-switched is reported. Under different thermal focal lengths of Nd3+ doped MgO:PPLN, the focusing parameter ratio of 1084 nm and 2168 nm and the spot radius of 1084 nm are simulated, and the optimal parameters of the composite resonant cavity are determined. According to the quasi-phase matching principle, 1093 nm is effectively suppressed by the design of the composite resonator, and a single-wavelength output of 1084 nm is obtained. The 2.1 μm self frequency conversion optical parametric oscillator with Nd3+ doped MgO:PPLN is realized for the first time, the output power is 1.21 W, the highest down-conversion efficiency from 1084 nm to 2.1 μm is 15.1%. The pulse width of 2168 nm is around 7.8 ns when the repetition rate is 40 kHz. [ABSTRACT FROM AUTHOR]

• A self-optical parametric oscillator with composite resonator is proposed. • The focusing parameter ratio and 1084 nm spot radius are simulated. • 1512 nm laser pulse of 15.3 μJ is realized. 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. [ABSTRACT FROM AUTHOR]

• A MOPO based on two electro-optical polarization mode conversions is reported. • Two EO PCs can rotate the polarization states of 1.47 μm and 3.3 μm. • The MOPO can obtain 3.3 μm and 3.84 μm output simultaneously without back conversion. The multi-optical parametric oscillator (MOPO) based on electro-optical polarization mode conversion is reported in this paper, which get two idle lights at 3.3 μm and 3.84 μm simultaneously. In the optical parametric cavity, two electro-optical polarization mode converters are placed to rotate the parametric light polarization. When the electric field intensity of electro-optical polarization mode converters are 11.5 V/mm and 34.9 V/mm respectively, the maximum output power of 3.3 μm and 3.84 μm are 2.03 W and 2.25 W, the conversion efficiency to 1064 nm is 8.3% and 9.2%, and the power ratio of 3.3 μm to 3.84 μm is 0.90. The experimental results confirm that the electro-optical polarization mode converters can regulate the conversion of MOPO, resulting in the suppression of back conversion, and the adjustment of parametric light gain. [ABSTRACT FROM AUTHOR]

• Dual-wavelength alternating output under the same Q-switched voltage is achieved. • Relationship between loss and gain in each cavity is compared as the criterion. • This criterion is used to select the same EO Q-switched voltage. • It opens the possibility for further research using other gain mediums. 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. [ABSTRACT FROM AUTHOR]

• First demonstration of a SLM Q-switched Pr:YLF laser operating at 639.5 nm. • The output energy was 3.94 μJ, with pulse width of 81.1 ns and PRF of 10 kHz. • The SLM emission linewidth was 33 MHz at the maximum output. 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. [ABSTRACT FROM AUTHOR]