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A high power orthogonally polarized mid-infrared (mid-IR) laser was realized by a singly resonant optical parametric oscillator (SROPO) employing two KTA crystals with the Z-axes perpendicular to each other. The SROPO was pumped by a diode-end-pumped acoustic-optically (AO) Q-switched Nd:YAG laser, and each of the KTA crystals used a differently polarized part of the fundamental wave and participated in separated frequency conversion. The maximum SROPO output power of 2.18 W including 0.98 W of signal at 1535 nm and 1.2 W of idler at 3468 nm was obtained at a repetition rate of 6 kHz and an absorbed pump power of 16.5 W, corresponding to an optical-to-optical conversion efficiency of up to 13.2 % and a slope efficiency of 19.4 %. The 3468-nm beam M2-factor of 1.6 was measured by a beam analyzer.

Two graphene oxide saturable absorbers (GO-SAs) spin coated on indium tin oxide (ITO) substrate have been prepared and their transmissivity spectra have also been measured. The performance of the diode-pumped passively Q-switched Nd:YVO4 laser with GO-SA has been investigated for the first time. The shortest pulse width of 113 ns and the highest peak power of 4.3 W are obtained at the pump power of 5.04 W. The output laser characteristics have demonstrated that graphene oxide is a promising saturable absorber for passive Q-switching.

Continuous-wave (CW) and passively Q-switched operations of laser diode-end-pumped Nd:CLTGG laser at 1.06 μm was demonstrated for the first time. The laser spectrum was found to be tri-wavelength, with respective wavelengths of 1058.4, 1060.5, and 1065.5 nm for both CW and passive Q-switching regime. The highest CW output power of 2.6 W was obtained with an optical-optical conversion efficiency of 13.9% and a slope efficiency of 17.1%. In the passive Q-switching regime, the highest output power, shortest pulse width, largest pulse energy and highest peak power were achieved as 242 mW, 45.8 ns, 1.65 μJ and 0.4 kW, respectively. The passively Q-switched tri-wavelength laser should have the potential to be used for terahertz radiation generation.

In this article, a diode-end-pumped passively Q-switched extra-cavity frequency doubled micro-type green laser by Nd:YAG/Cr4+:YAG composite crystal was demonstrated. The dependence of the average out power, pulse width and pulse repetition rate on incident pump power were measured. Under the pump power of 14 W, the minimum pulse width of 1.3 ns with repetition rate of 68.0 kHz was obtained, corresponding single-pulse energy of 8.8 μJ and peak power of 6.7 kW.

A novel nonlinear frequency conversion process was demonstrated to realize the synchronized dual-wavelength emissions at 1534 and 1572 nm by the mixed optical parametric oscillation (OPO) conversion in gray-tracking-resistance KTP (GTR-KTP) and KTA crystals. Both the two crystals were inserted into the diode-pumped Nd:YAG/Cr4+:YAG fundamental resonator, with their Y axes perpendicular to each other. This could eliminate the competition of the two OPO processes in fundamental radiation. Furthermore, the ratio between the length of GTR-KTP and KTA has also been specially designed to satisfy the same OPO thresholds. The synchronized dual-wavelength lasing with the power ratio of 1:1 between 1534 and 1572 nm was successfully realized. At an incident LD pump power of 7 W, the maximum total output power of 460 mW was achieved, with the corresponding pulse width and repetition rate measured to be 3.9 ns and 5.5 kHz, respectively. This mixed conversion opens a new door for the multi-wavelength lasing.

Diode end-pumped continuous-wave and passively Q-switched Nd:Lu x(x = 0.5) Y 1 − x VO 4 mixed crystal lasers were demonstrated. At the pump power of 12.6 W, the maximum output power of 6.7 W around 1066.5 nm was obtained with the output transmission of 27%. The optical conversion efficiency is 53.2%, corresponding to a slope efficiency of 55.8%. For pulsed operation, the shortest pulse width attained was 8.6 ns, with the pulse repetition frequency of 99 kHz, and the single pulse energy and the peak power were estimated to be 25.5 μJ and 2.96 kW, respectively.

Diode end-pumped continuous wave (CW) and passively Q-switched (PQS) laser performances of the mixed Nd:Gd0.33Lu0.33Y0.33VO4 crystal are investigated for the first time. At the pump power of 9 W, the highest output power is 3.66 W, with an optical conversion efficiency of 40.7% and a slope efficiency of 43.6%. For pulsed operation, the minimum pulse width of 9.2 ns with Cr4+:YAG as saturable absorber is attained with the repetition rate of 81.8 kHz, and the single pulse energy and peak power are estimated to be 9.78 J and 1.06 kW, respectively.

This paper reported a broadband tuning intracavity optical parametric oscillator (IOPO), based on the multiple grating periodical poled lithium niobate (PPLN) pumped by a acoustic-optical (AO) Q-switched Nd:YVO4 laser. The widely tunable OPO output signal wavelength range from 1390 to 1605 nm, which was obtained by changing PPLN poling period from 27.8 to 31.6 μm at a certain temperature of 46°C, while the continuous tuning range was measured from 1475 to 1592 nm with the PPLN poling period of 30 μm by varying the temperature of nonlinear crystal PPLN from 50 to 120°C. The maximum output power of 0.92 W at 1534 nm with the minimum pulse width of 5.17 ns was generated under the incident pump power of 9.6 W at 808 nm. The corresponding peak power and single pulse energy were calculated to be 5.94 kW and 30.7 μJ, respectively. The M2-factor was measured to be 2.01 at the signal power of 0.4 W.

The simultaneous stimulated Raman scattering (SRS) and optical parametric oscillation (OPO) for the 1064 nm radiation were realized in one KTP crystal for the first time. At an incident diode laser power of 8.6 W, the maximum average output powers at 1096 nm and 1572 nm were 1.1 W and 0.36 W, respectively. The conversion efficiency to Stokes with respect to the incident diode power was as high as 12.8%. The corresponding minimum pulse widths at 1096 nm and 1572 nm were 2.8 and 1.1 ns, respectively.

The efficient dual-wavelength oscillation at 1064 and 1342 nm in the passively Q-switched laser based on Nd:YVO4/V3+:YAG is successfully obtained, as demonstrated in this paper. A total average output power of 2.2 W is obtained with 1.3 W for 1064 nm and 0.9 W for 1342 nm under the incident pump power of 7.7 W, corresponding to a total optical-optical conversion efficiency of 28.2%. The pulse widths are 58 and 54 ns for 1064 and 1342 nm, respectively, with the repetition rate of 89 kHz. Moreover, a rate equation model considering the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density is presented to characterize the dual-wavelength passive Q-switching operation.

We report a passively mode-locked Yb:Y2Ca3(BO3)4 (Yb:CYB) laser with a partially reflective semiconductor saturable-absorber mirror. The minimum pulse duration of 244-fs with a repetition rate of ~ 55 MHz has been obtained at the central wavelength of 1044.7 nm (8.1 nm full width at half maximum (FWHM)). The measured average output power amounts to 261 mW under the absorbed pump power of 7.0 W. To our best knowledge, this is the first demonstration of a femtosecond Yb:CYB laser.

A simultaneous dual-wavelength eye-safe laser at around 1.9 and 1.7 μm based on only a single KTiOAsO4 (KTA) intracavity optical parametric oscillator (IOPO) is firstly reported. The dual-wavelength-IOPO is driven by an acousto-optic (AO) Q-switched Nd:YAG laser, which is simultaneously oscillated at the radiations of 1.3 and 1.06 μm. Within the KTA-IOPO cavity, the signal output waves of IOPO at the wavelength of 1.9 and 1.7 μm are pumped by the 1.3 and 1.06 μm radiations from Nd:YAG laser, respectively. With the laser diode pumped power of 100 W and the pulse repetition rate of 4 kHz, the maximum average output power of 1.3 W at 1895 nm with the pulse duration of 30 ns and that of 0.9 W at 1715 nm with the pulse duration of 18 ns are obtained. With different diode pump power, the central wavelength of IOPO signal light at 1.9 μm is tunable from 1850 to 1895 nm, while the other signal wave at 1.7 μm is from 1650 to 1715 nm.

A mini eye-safe KTiAsO 4 intracavity optical parametric oscillator (IOPO) employing the shared cavity configuration and driven by a diode-end-pumped composite Nd:YAG/Cr 4+ :YAG laser is demonstrated in this paper. Under an incident laser diode power of 11 W, a maximum average output power of 424 mW at 1534 nm was obtained. The corresponding signal pulse width and repetition rate were 1.2 ns and 16.7 kHz, respectively. The fluctuation of the average signal output power over long-term operation was found to be ±3.0%. A theoretical model for the compact IOPO was also presented in this paper.

The character of a diode-pumped passively Q-switched Nd:GdVO4/V3+:YAG 912 nm laser was demonstrated for the first time to our knowledge. With an absorbed pump power of 7.4 W, an average output power of 360 mW with a Q-switched pulse width of 328 ns at a pulse repetition rate of 163 kHz was obtained. The Q-switching efficiency was found to be 32.7%. Our work further indicated V3+:YAG could be an effective fast passive Q-switch for 0.9 μm radiation.

A gray-trace resistance KTP (GTR-KTP) second Stokes Raman laser intracavity driven by a diode-pumped acousto-optic Q-switched Nd:YVO4 laser was first demonstrated in this paper. With an incident pump power of 9.5 W, the intracavity GTR-KTP Raman laser, operating at the repetition rate of 20 kHz, produced the maximum average output power of 860 mW at 1129 nm. The minimum pulse width obtained in this GTR-KTP Raman laser was 10.8 ns. When the GTR-KTP was substituted with a common KTP, a lower average output power of 720 mW and longer pulse width of 15.9 ns were obtained in the common KTP Raman laser under the same pump condition and cavity setup as the GTR-KTP Raman laser. Experimental results indicated that the decreased absorption at the fundamental and Stokes wave in GTR-KTP was beneficial to improve the stimulated Raman scattering performance.

A widely continuous tunable eye-safe laser based on periodical poling lithium niobate (PPLN) crystal, driven by a diode-end-pimped acoustic-optical (AO) Q-switcher Nd:YVO4 laser was demonstrated. Under the pumped power of 7.74 W at 808 nm and the frequency repetition rate of 45 kHz, the maximum output power of 0.58 W at 1534 nm with the minimum pulse duration of 7.53 ns was obtained. The corresponding peak power and single pulse energy were calculated to be up to 1.71 kW and 12.9 μJ, respectively. By changing 20 different channels with poling period between 27.8 to 31.6 μm, we measured widely continuously tunable wavelength coverage from 1390 to 1605 nm.

The continuous wave (CW) and passively Q-switched Nd:Gd3AlxGa5-xO12 (Nd:GAGG) laser operation at 938 nm have been realized for the first time. The maximum CW output power of 0.44 W was obtained under the absorbed pump power of 8.54 W, corresponding to the slope efficiency of 7.8% and optical-to-optical efficiency of 5.2% respectively. A V3+:YAG saturable absorber crystal with the initial transmission of 97% was used for the passive Q-switching regime. The maximum average output power of 0.19 W was achieved with the minimum pulse width of 358 ns and Q-switched repetition rate of 116 kHz. The corresponding single pulse energy and pulse peak power were determined to be 1.6 μJ and 4.6 W, respectively.

Q-switching and Q-switched mode-locked Yb:Y2Ca3B4O12 lasers with an acousto-optic switch are demonstrated. In the Q-switching case, an average output power of 530 mW is obtained at the pulse repetition rate of 10.0 kHz under an absorbed pump power of 6.1 W. The minimum pulse width is 79 ns at the repetition rate of 1.7 kHz. The pulse energy and peak energy are calculated to be 231 μJ and 2.03 kW, respectively. In the Q-switched mode-locking case, the average output power of 64 mW with a mode-locked pulse repetition rate of 118 MHz and Q-switched pulse energy of 48 μJ is generated under the absorbed pump power of 6.1 W.

A compact efficient diode-end-pumped acousto-optically Q-switched intracavity-frequency-tripled Nd:YVO4 355 μm ultraviolet laser was realized. Intracavity sub-resonators with anti-reflection and high-reflection coated mirrors were used to get higher efficiency of third harmonic generation. With two LBO crystals used in frequency doubling and tripling processes, greater than 1.46 W 355 nm average output power was obtained under the absorbed pump power of 13.9 W and the repetition rate of 10 kHz. The corresponding pump-to-ultraviolet conversion efficiency was determined to be as high as 10.5%. At 10 kHz, the minimize pulse width was obtained to be 12 ns with the peak power of 10.4 kW and single pulse energy of 146 μJ.

Using V3+:YAG crystal as the saturable absorber, a diode-pumped passively Q-switched and mode-locked Nd:GGG laser operating at 1.3 μm is realized for the first time. The mode-locking modulation depth of nearly 100% has been achieved. The maximum output power and the single Q-switched pulse energy are 410 mW and 8.3 μJ. The mode-locked pulse inside the Q-switched pulse has a repetition rate of 349 MHz, and its average pulse width is estimated to be about 750 ps.

An efficient, eye-safe, high-repetition-rate, single-resonant intracavity optical parameter oscillator, driven by a laser-diode (LD) end-pumped acousto-optically Q-switched Nd:YVO4 laser, based on high gray-trace resistance KTiPO4 (GTR-KTP), was demonstrated. With a pump power of 13.8 W and frequency repetition rate of 40 kHz, the maximum power of 1.72 W with pulse width of 2.09 ns at signal wavelength 1572 nm is obtained. The corresponding peak power and single pulse energy is calculated to be 21 kW and 43 μJ, respectively. And the conversion efficiency from incident pump power at 808 nm to output power at signal wavelength 1572 nm is about 12.5%. The output instability is measured only to be 1% within 1 h.

A high power, quasi-continuous wave ultraviolet laser at 355 nm was obtained by intracavity frequency tripling of a diode side-pumped acousto-optic (AO) Q-switched Nd:YAG laser. Type II critical phase-matched KTP and LBO crystals were used for the second harmonic generation and the third harmonic generation, respectively. Under the pump power of 180 W, 7.8 W average output power at 355 nm was obtained at 8 kHz with the pulse width of 50 ns, corresponding to the pump-to-ultraviolet conversion efficiency of 4.3%. The peak power and single pulse energies were estimated to be 18.8 kW and 938 μJ. Its far-field divergence was measured to be about 3.8 mrad. The instability of the 355 nm laser was less than 1% at an output power of 6.3 W for 2 h operation.

By exploiting the diode-end-pumped Nd:GGG/Cr4+:YAG laser as the pump source, a high peak power gray-trace resistance KTP intracavity optical parametric oscillator at eye-safe wavelength was first demonstrated (to our knowledge). Under the incident diode power of 10 W, the maximum average output power of 320 mW at 1567 nm was obtained with the T = 33% output coupler. The corresponding signal pulse width and repetition rate were respectively 1.4 ns and 5.8 kHz. Due to the greatly reduced pulse repetition rate and short pulse width, the signal peak power was estimated to be as high as 39.4 kW.

A compact, high power and high beam quality diode-end-pumped CW Nd:YVO4 slab 1064 nm laser with a hybrid resonator is demonstrated. The maximum output power of 23.0 W is obtained under the pump power of 66.7 W, which gives the slope efficiency and optical conversion efficiency of 52.0 and 34.0%, respectively. The beam quality M2 factors are measured to be 1.5 in the unstable direction and 1.7 in the stable direction. The power stability of the LD end-pumped slab laser at an output power of 19 W is measured to be 0.7% for half an hour operation.

A diode-pumped passively Q-switched Nd:LuVO4 1.34 μm laser using Co:LMA saturable absorber was successfully demonstrated. The average output power, pulse width, repetition rate of a-cut and c-cut Nd:LuVO4 lasers were studied with different output couplers. The maximum average output power of 164 mW was obtained at the pump power of 10.3 W and the narrowest pulse width of 168 ns was achieved at repetition rate of 457 kHz under pump power of 8.59 W in a-cut Nd:LuVO4 laser with T = 8%.

A diode-end-pumped simultaneously Q-switched and mode-locked intracavity frequency doubled Nd:GdVO4/LBO red laser with an acousto-optic Q-switch was realized. The maximum red laser output power of 250 mW was obtained at the incident pump power of 8.3 W and the repetition rate of 10 kHz. At 5 kHz, the maximum mode-locking modulation depth of about 80% was achieved with the Q-switched pulse width of 440 ns. The red mode-locked pulse inside the Q-switched pulse had a repetition rate of 115 MHz, its average pulse width was estimated to be about 350 ps.

An efficient eye-safe GTR-KTP IOPO with the shared cavity configuration and excited by a diode-end-pumped composite Nd:YAG/Cr4+:YAG laser was demonstrated. Under the incident LD power of 8.4 W, the maximum average output power of 900 mW at 1572 nm was obtained with the T=33% output coupler, corresponding to a diode-to-signal conversion efficiency of 10.7%. The corresponding signal pulse width and repetition rate were respectively 2.2 ns and 12 kHz, with the peak power and single pulse energy estimated to be 34.1 kW and 75 µJ, respectively. The instability of the average signal output power over hours-long operation was found to be 2.0%. As for the common KTP IOPO at the same pump condition and cavity design, a lower average output power of 640 mW with a longer pulse width of 4.6 ns was obtained. The corresponding diode-to-signal conversion efficiency was reduced by 28.8% compared with that obtained in GTR-KTP IOPO. A theoretical model for the compact GTR-KTP IOPO was also presented in this paper. Theoretical analysis on the pulse characteristics of the signal was performed, which showed a good agreement with that obtained experimentally.

The diode-pumped passively Q-switched and Q-switching mode-locked Yb:Y2Ca3B4O12 lasers with V:YAG as saturable absorber are demonstrated in this paper. In the Q-switched regime, an average output power of 150 mW is obtained under the absorbed pump power of 6.6 W; the pulse width is 46 ns with the pulse repetition rate of 11 kHz, corresponding to the single pulse energy and peak power of 14 μJ and 296 W, respectively. For the Q-switched mode locking, the average output power of 223 mW is obtained with a repetition rate of 112 MHz. Moreover, due to the reabsorption effect, the emission wavelengths vary evidently with the different operation situation.

With V3+:YAG as saturable absorber, the simple and highly efficient 1.06 μm Q-switched and mode-locked (QML) Nd:GdVO4 laser is realized. The dependence of the output power, envelop repetition rate, and pulse width on the pump power, output coupler transmission, or cut direction of Nd:GdVO4 (a-cut or c-cut) are investigated. Employing a-cut Nd:GdVO4 and the output coupler with transmission of 27%, the maximum average output power of 3.57 W with a slope efficiency of 46% is obtained.

A diode-end-pumped Q -switched mode-locking Nd:GdVO4 laser operating at 1.34 μm with an acousto-optical (AO) Q-switch in a compact V-type cavity was realized in our experiment for the first time. When the AO Q-switch repetition rate was 10 kHz, the maximum average output power of 750 mW and the pulse energy of 75 μ were obtained at the maximum incident pump power of 9 W. The mode-locking modulation depth of about 100% was obtained at certain pump power over the threshold. The mode-locked pulse inside in the Q-switched pulse had a repetition rate of 341 MHz, and its average pulsewidth was estimated to be about 350 ps. A developed rate equation model for the Q -switched and mode-locked lasers with an AO Q-switch were proposed by using the hyperbolic secant functional methods. The results of numerical calculations of the rate equations were in good agreement with the experimental results.

A diode-pumped passively Q-switching mode-locked Nd:Gd0.5Y0.5VO4 laser at 1.34 μm using V3+:YAG as the saturable absorber has been demonstrated for the first time to the best of our knowledge. At the pump power of 7 W, the maximum average output power of 0.83 W and Q-switched pulse repetition rate of 140 kHz were obtained with absorber's initial transmission of 96%, with the corresponding Q-switched pulse energy estimated to be 6 μJ. The duration of mode-locked pulse within Q-switched envelop was estimated to be 750 ps with 333.3 MHz repetition rate.

In this paper, the output performances at 1.34 μm in continuous wave operation and passive Q-switching regime of a diode-end-pumped Nd:Gd 0.5 Y 0.5 VO 4 laser have been investigated. The passive Q-switching regime was achieved with Co 2+ :LaMgAl 11 O 19 (Co 2+ :LMA) saturable absorbers crystals. A maximum average output power of 230 mW was recorded with a Co 2+ :LMA with initial transmission of 81%. The minimum pulse duration was 116 ns, which corresponded to a repetition rate of 360 kHz, the single pulse energy of 2.1 μJ and the pulse peak power of 5.5 W.

With a non-critically phase-matched high gray-trace resistance KTP (GTR-KTP) crystal, a high-power intracavity optical parametric oscillator (IOPO) emitting at the wavelength of 1.5 μm and pumped by a diode-side-pumped acousto-optically Q-switched Nd:YAG laser is experimentally demonstrated. At the frequency repetition rate of 6 kHz, the maximum average power of 6.36 W at signal wavelength 1570 nm with a pulse width of 9.94 ns is obtained from IOPO based on GTR-KTP, corresponding to a peak power of 107 kW and a single-pulse energy of 1.06 mJ, respectively. We have compared the GTR-KTP IOPO with common KTP IOPO using the same scheme. At the same cavity design, frequency repetition rate and pump condition, only 5.42 W average output power with pulse width 13.82 ns is obtained from IOPO based on common KTP. Besides the higher output power, the output stability of GTR-KTP IOPO is much better than that of common KTP OPO. The output instability of GTR-KTP IOPO is 0.83% versus 6.7% of the common KTP IOPO.

A compact diode-end-pumped passively Q-switched intra-cavity frequency doubled Nd:YAG/Cr4+:YAG composite crystal laser was demonstrated. The pulsed laser at 532 nm was produced and the dependence of the average out power, pulse width and pulse repetition rate on incident pump power were measured. Under the pump power of 14 W, the minimum pulse width of 3.5 ns with repetition rate of 27.5 kHz was obtained, corresponding single-pulse energy of 18 μJ and peak power of 5.3 kW.

High efficient CW lasers at 1064 nm and 1342 nm were realized in a compact diode-end-pumped Nd:YVO4 slab. The maximum 1064 nm output power of 22.5 W was obtained under the pump power of 56.0 W, corresponding to the maximum optical conversion efficiency and slop efficiency of 40.1% and 50.1%, respectively. When the pump power was 34.7 W, the maximum output power at 1342 nm was obtained to be 4.4 W. The corresponding slope efficiency and the optical conversion efficiency were 17.9% and 12.6%, respectively.

We reporte a passively Q-switched and mode-locked Nd:Y0.5Gd0.5VO4 laser at 1.34 μm with Co2+:LaMgAl11O19(Co:LMA) crystal as the saturable absorber. With the incident pump power of 6.56 W, a maximum output power of 242 mW was obtained. Q-switched mode-locking pulses with modulation depth nearly 100% were obtained. The width of the mode-locked pulse was estimated to be less than 600 ps.

A compact diode-end-pumped passively Q-switched composite Nd:YAG/Cr4+:YAG laser was demonstrated in this paper. At the incident pump power of 11.8 W, the shortest pulse width of 2.05 ns was obtained, corresponding to average output power of 1.15 W and repetition rate of 17.1 kHz. The single-pulse energy and peak power were estimated to be 67.3 μJ and 32.8 kW, respectively.

The generation of passively Q-switched mode-locking (QML) pulse has been obtained from a diode-pumped Nd:GdVO4 laser with a LT-InGaAs wafer as saturable absorber as well as output coupler. Under the incident pump power of 10 W, an average output power of QML was 1.8 W with a Q-switched repetition rate of 280 kHz. The pulse duration of Q-switched pulse is about 160 ns and mode-locked pulse within the Q-switched envelope had a repetition rate of 410 MHz. It is indicated that the present LT-InGaAs is a very promising device in the field of mode locking solid-state laser, and we are sure that it will be complete pure cw mode locking with single beam output easily after further optimizing in the parameter such as saturation fluence, modulation depth, recovery time and damage threshold in semiconductors.

By using a 15 mm-long type I phase-matching LBO crystal, a maximum quasi-continuous wave red laser output power of 12 W has been obtained by intra-cavity second-harmonic generation (SHG) in a compact acousto-optically Q-switched diode-side-pumped Nd:YAG laser. The corresponding optical-optical conversion efficiency is 6.6%. The power instability at the maximum output power is observed to be less than 4.62% during half an hour. The beam quality factor M2 is measured to be 9.9 ± 1.0 by the knife-edge method. The spectrum of the red radiation is also measured and discussed.

By exploiting the intracavity frequency conversion configuration, a diode end-pumped acousto-optic (AO) Q-switched Nd:YVO 4 355 nm laser was demonstrated in this paper. Two LBO crystals were inserted in the cavity to realize the frequency tripling operation, a cascade of the second harmonic generation (SHG) and sum frequency mixing (SFM). Under the absorbed pump power of 13 W, the maximum average output power at 355 nm was obtained to be 1.32 W at the repetition frequency of 17 kHz, with the optical-to-optical conversion efficiency of 10.2%. The corresponding pulse width was 10.2 ns, with the energy of a single pulse and corresponding peak power estimated to be 77.6 μJ and 7.61 kW, respectively.

The intermittent oscillation of 1064 nm and 1342 nm was demonstrated in a diode-pumped doubly passively Q-switched Nd:YVO4/Cr4+:YAG/V3+:YAG laser for the first time to our best knowledge. By exploiting a three-mirror configuration and choosing appropriate reflectivity values for the two wavelengths on the output couplers, the dual-wavelength pulsed operation was obtained. The maximum dual-wavelength average output power was 428 mW, corresponding to an optical-to-optical conversion efficiency of 8.5%. The corresponding physical explanations for the intermittent oscillation as well as the related phenomena are also given in this paper.

In this paper, continuous wave (CW) and passive Q-switching characteristics of a diode-end-pumped Nd:GGG laser at 1331 nm have been demonstrated. The maximum CW output power of 2.08 W was obtained under the incident pump power of 11 W, and the maximum slope efficiency and optical–optical conversion efficiency were 20.5% and 19%, respectively. By using a V3+:YAG crystal with initial transmission of 94% as the saturable absorber, the maximum average output power of the passively Q-switched laser at 1331 nm was 460 mW, and the minimum pulse width of 19 ns and the repetition rate of 39 kHz were achieved, corresponding to pulse peak power of 0.62 kW and single pulse energy of 11.8 μJ, respectively.

In this paper, the output performances at 1331 nm in continuous-wave (CW) operation and the passive Q-switching regime of a Nd:Gd3Ga5O12(Nd:GGG) laser crystal have been investigated under pumping with diode lasers. A maximum CW output power of 1.5 W was reached at an incident pump power of 7.5 W; the overall optical-to-optical efficiency and the slope efficiency with respect to the pump power were 21.5% and 19.4%, respectively. The passive Q-switching regime was achieved with Co2+:LaMgAl11O19 (Co2+:LMA) saturable absorber (SA) crystals. A maximum average output power of 183 mW was recorded with a Co2+:LMA SA with initial transmission Ti of 90%. The pulse energy was 18.7 μJ and the pulse duration was 26.1 ns, which correspond to a pulse peak power of 0.7 kW. With a Co2+:LMA SA with Ti=81%, the average power decreased to 131 mW. However, the pulse energy increased to 21.4 μJ, the pulse duration was 16.4 ns and the pulse peak power increased to 1.3 kW.

The continuous-wave (cw) and passive Q-switching operation of a diode-end-pumped gadolinium gallium garnet doped with neodymium (Nd:GGG) laser at 1062 nm was realized. A maximum cw output power of 6.9 W was obtained. The corresponding optical conversion efficiency was 50.9%, and the slope efficiency was determined to be 51.4%. By using Cr4+:YAG crystals as saturable absorbers, Q-switching pulse with average output power of 1.28 W, pulse width of 4 ns and repetition rate of 6.2 kHz were obtained. The single-pulse energy and peak power were estimated to be 206 μJ and 51.6 kW, respectively. The conversion efficiency of the output power from cw to Q-switching operation was as high as 84.7%.

A diode-end-pumped passively Q-switched mode-locked Nd:GdVO4 laser operating at 1.34 μm by using the Co2+:LaMgAl11O19 (Co2+:LMA) as the saturable absorber in a Z-type cavity has been demonstrated in our experiment for the first time. The repetition rate of the Q-switched pulse envelop increases from 4.2 kHz to 17 kHz as the pump power increases from 3.8 W to 8.9 W, and a maximum Q-switched and mode-locked fundamental mode average output power of 126 mW is obtained. The mode-locked pulse inside the Q-switched pulse has a repetition rate of 114 MHz, and its average pulse width is estimated to be about 280 ps.

A high power, high stability, eye-safe intracavity optical parametric oscillator (IOPO) working at the signal wavelength of 1534 nm was demonstrated, in which a type of non-critically phase-matched KTiOAsO4 (KTA) crystals were pumped by a diode-side-pumped acousto-optically Q-switched Nd:YAG laser. When a 25 mm-long KTA crystal was employed, a maximum average output power of 5.35 W and the minimum pulse width of 3.71 ns were obtained at the maximum 808 nm pump power of 143 W and the repetition rate of 6 kHz, giving an optical-optical conversion efficiency of 31.1% between the signal light at 1534 nm and the fundamental light at 1064 nm. To our best knowledge, it's the highest conversion efficiency for the KTA IOPO driven by diode-side-pumped Nd-doped lasers. The single pulse energy and peak power were determined to be 892 μJ and 287 kW, respectively. The power instability at the maximum output power was observed to be less than 1.72% during one hour.

Researches indicate that foggy weather is one of the most critical factors that restrict human’s traffic activities and cause traffic accidents. It will reduce the visibility of traffic message board, which could cause the insecurity of transportation. Commonly, light-emitting diodes (LEDs) were used as light source for variable message sign, which could not be seen clearly in the foggy low visibility condition. A high-brightness light source which could be used for variable information board was firstly put forward in this paper. And a new type of variable message sign used in low visibility condition was also introduced. Besides, the attenuation characteristics of laser diode (LD) and light-emitting diode (LED) were analyzed respectively. Calculation and simulation show that the attenuation of red light source is fastest, and the yellow LED light has the better transmittance property. In the experiment, LDs were used to make variable message board for verifying image definition. A 16*16 array structure composed of LDs was designed and could display Chinese characters. By comparing the display effect of LDs and LEDs driven with same power, they were placed in fog chamber of the visibility less than 5 meters. And experiment results show that the penetrability of red LD light is better than that of red LED. So traffic variable message sign based on LDs could improve the image definition and the information could be seen more clearly in the foggy weather. In addition to the high-brightness, good coherence, good direction, experimental results show that traffic variable message board based on LD has better visual effect in low visibility condition.

In this letter, intracavity frequency-tripling of a diode-end-pumped passively Q-switched Nd:YAG/Cr4+:YAG composite laser has been demonstrated for the first time. Under the absorbed pump power of 7.2 W, the maximum UV output power of 110 mW is obtained with the beam quality parameter M2 of 2.95. The minimum pulsewidth and the highest repetition rate are 23.9 ns and 19.6 kHz, respectively. The corresponding single pulse energy and pulse peak power are 5.6 μJ and 0.23 kW. The fluctuation of the average output power at 110 mW within an hour operation is tested and determined to be 4.7%.

It has been demonstrated that shared cavity optical parametric oscillator (OPO) could improve power stability in comparison with that of coupled cavity OPO. By theoretically calculating the spectral transmissions induced by the etalon effect, it has been found that the shared cavity OPO had much wider transmission bandwidth than that of coupled OPO. The corresponding experimental results agreed with the theoretical analysis. Furthermore, the OPO and fundamental laser resonator have nearly the same longitudinal mode spacing in the shared cavity configuration. The above two factors can account for the improved performance of the shared OPO operation.

With a non-critically phase-matched KTA crystal, a high-power intracavity optical parametric oscillator (IOPO) driven by a diode-side-pumped acousto-optically Q-switched Nd:YAG laser has been realized. The maximum average output power of 13.6 W at the signal wavelength of 1534 nm and 3 W at the idler wavelength of 3472.7 nm were obtained with the repetition rate of 18 kHz, giving the optical–optical conversion efficiency of about 5.7% from diode-power at 808 nm to OPO signal output, which was the highest conversion efficiency for intracavity KTA OPO with diode-side-pumping configurations to our best knowledge. At the highest output power of 13.6 W, the signal pulse duration of 5.46 ns was obtained, corresponding to the single pulse energy of 756 μJ and peak power of 138 kW, respectively.