Design and performance of a composite Tm:YAG laser pumped by VBG-stabilized narrow-band laser diode

A 2-μm composite Tm:YAG laser pumped with a narrow-band laser diode was presented. The temperature distribution and thermal lens in the Tm:YAG were numerically simulated by a finite element method and the results were used to design the special cavity, in order to achieve a high efficiency and stable output. With a 25-W incident pump power, we obtained a maximum output power of 11 W at 2018.5 nm, corresponding to a slope efficiency of 51.3% and an optical-to-optical efficiency of 44.5%, respectively. The beam quality was measured to be M_x~2= 1.8 and M_y~2= 1.6.     

Efficient Diode-Pumped Tm：YALO3 Laser with a Pump Recycling Scheme

By using a pump recycling configuration, the maximum power of 8.1 W in the wavelength range 1.935-1.938 μm is generated by a 5-ram long Tm：YAIOa （4 at.%） laser operating at 18℃ with a pump power of 24 W. The highest slope efficiency of 42% is attained, and the pump quantum efficiency is up to 100%. The Tm：YAlO3 laser is employed as a pumping source of singly-doped Ho（1%）：GdV04 laser operating at room temperature, in which continuous wave output power of greater than 0.2 W at 2.05/μm is achieved with a slope efficiency of 9%.     

High-power diode-end-pumped Tm：YAP and Tm：YLF slab lasers

Diode-end-pumped continuous-wave(CW) Tm:YAP and Tm:YLF slab lasers are demonstrated. The a-cut Tm:YAP and Tm:YLF slabs with doping concentrations of 4 at.-% and 3.5 at.-%,respectively,are pumped by fast-axis collimated laser diodes at room temperature. The maximum CW output powers of 72 and 50.2 W are obtained from Tm:YAP and Tm:YLF,respectively,while the pump power is 220 W,corresponding to the slope efficiencies of 37.9% and 26.6%,respectively.     

A Stable Diffusion-Bonded Tm：YLF Bulk Laser with High Power Output at a Wavelength of 1889.5 nm

A high power diode-pumped diffusion-bonded Tm：YLF laser operating at 1889.5nm with a FWHM linewidth of less than 0.1 nm is reported. A Brewster plate and two Fabry-Perot etalons are inserted in the laser cavity for spectral narrowing and stabilization. Under an incident pump power of 136.8 W, 46.1 W of output power is achieved, corresponding to an optical-to-optical conversion efficiency of 33.7% and a slope efficiency of 42.8%. The laser wavelength shift of only 0.07nm with the incident pump power from 20.1 W to 136.8W is observed. The M2 factor at maximum output power is calculated to be 2.3 in the x-axis and 2.0 in the y-axis, respectively.     

A Compact High Power Laser-Diode Side-Pumped Tm,Ho：YAG Laser Nearly at Room Temperature with Intracavity Tm：YAG Laser

We report a compact high power Tm,Ho：YAG laser nearly at room temperature. The laser-diode side-pumped Tm：YAG and Tm,Ho：YAG laser modules are operated in the same cavity. The laser yields 37.34 W of continuous wave output power under the temperature of 6℃, corresponding to a maximum slope efficiency of 16.7% when the output power lies from 5.1 W to 27.0 W. This is the first report on the combined Tm：YAG and Tm,Ho：YAG lasers for obtaining high power 2.1 μm laser.     

Measurement of thermal expansion coefficient of nonuniform temperature specimen

A new technique is developed to measure the longitudinal thermal expansion coefficient of C/C composite material at high temperature.The measuring principle and components of the apparatus are described in detail.The calculation method is derived from the temperature dependence of the therinal expansion coefficient.The apparatus mainly consists of a high temperature environmental chamber,a power circuit of heating,two high-speed pyrometers,and a laser scanning system.A long solid specimen is resistively heated to a steady high-temperature state by a steady electrical current.The temperature profile of the specimen surface is not uniform because of the thermal conduction and radiation.The temperature profile and the total expansion are measured with a high-speed scanning pyrometer and a laser slit scanning measuring system,respectively.The thermal expansion coefficient in a wide temperature range(1000-3800 K)of the specimen can therefore be obtained.The perfect consistency between the present and previous results justifies the validity of this technique.     

Diode-pumped high-efficiency broadband tunable Tm:YAP laser

A laser diode-pumped high-efficiency widely tunable Tm:YAP laser with excellent comprehensive properties is reported.The output power is stable at a given pump power.Under the absorbed pump power of 12.95 W,the maximum output power at 2,010 nm is 5.16 W,corresponding to a slope efficiency of 45.5%.The generated beam profile is close to the Gaussian TEM00 near the maximum pump power.Furthermore,the laser working wavelength can be continuously tuned through optimization from 1,894 to 2,066 nm,which is the widest tunable range for Tm:YAP lasers to date.     

Wavelength-Locked 878.6 nm In-Band Pumped Intra-Cavity 2.1 μm Optical Parametric Oscillator

We report herein a high-power folded intra-cavity 2.1μm optical parametric oscillator(ICOPO)which is the first example of an ICOPO that utilizes a wavelength-locked 878.6 nm in-band pumped Nd:YVO_4 laser as the pump source.The thermal effect of PPMgLN crystal and the divergence angle of the incident laser are considered comprehensively to determine the 2128 nm degenerate temperature.In the experiment,the functions of different output coupler transmittances and different repetition rates on the parametric laser output power are studied,respectively.The temperature versus parametric laser output power in an in-band p umped non-wavelength-locked880 nm laser diode(LD)and in a wavelength-locked 878.6 nm LD is compared.A maximum output power of 5.87 W is obtained at the pump power of 56.9 W when the repetition rate is 80 kHz.The corresponding conversion efficiency is 14.55%,with a linewidth of 73.65 nm and pulse width of 3.62 ns.The wavelength-locked 878.6 nm LD in-band pumping technology can stabilize the 2.1μm laser output power of Nd:YVO_4 crystal effectively in the environment of intense temperature change.     

Diode-pumped Tm:LuAG laser at room temperature

The lasing characteristics of Tm：LuAG at room temperature are reported. The maximum output power at 2.023-μm wavelength is 4.91 W and the slope efficiency is 25.39%. The mode matching between pump mode and laser mode is optimized by changing the pump beam waist radius and its location. Different output couplers are used to realize the optimal laser output. The relationship between operation temperature and output power is also discussed.     

High power CW and diode-side-pumped Q-switched operation of a Nd：YAG 1319-nm laser

We demonstrated the highly efficient continuous wave （CW） and Q-switched infrared laser from a diode- side-pumped Nd：YAG crystal. A CW output as high as 66 W at 1319 nm was achieved under the pump power of 460 W, corresponding to a coversion efficiency of 14.3%. A maximum average power of 8.9 W of TEM00 mode was obtained in Q-switched operation at the repetition rate of 8 kHz. The performance of the laser considering the thermal lens effect induced by pump power was also analyzed.     

Analytical modelling of end thermal coupling in a solid-state laser longitudinally bonded by a vertical-cavity top-emitting laser diode

The intrinsic features involving a circularly symmetric beam profile with low divergence, planar geometry as well as the increasingly enhanced power of vertical-cavity surface-emitting lasers (VCSELs) have made the VCSEL a promising pump source in direct end bonding to a solid-state laser medium to form the minimized, on-wafer integrated laser system. This scheme will generate a surface contact pump configuration and thus additional end thermal coupling to the laser medium through the joint interface of both materials, apart from pump beam heating. This paper analytically models temperature distributions in both VCSEL and the laser medium from the end thermal coupling regarding surface contact pump configuration using a top-emitting VCSEL as the pump source for the first time. The analytical solutions are derived by introducing relative temperature and mean temperature expressions. The results show that the end contact heating by the VCSEL could lead to considerable temperature variations associated with thermal phase shift and thermal lensing in the laser medium. However, if the central temperature of the interface is increased by less than 20~K, the end contact heating does not have a significant thermal influence on the laser medium. In this case, the thermal effect should be dominated by pump beam heating. This work provides useful analytical results for further analysis of hybrid thermal effects on those lasers pumped by a direct VCSEL bond.     

High power external-cavity surface-emitting laser with front and end pump

High power optically pumped vertical-external-cavity surface-emitting lasers with front and end pump are reported. The gain chip consists of 15 repeats of In_(0.26)GaAs/GaAsP_(0.02) multiple quantum wells and 30 pairs of Al_(0.2)GaAs/Al_(0.98)GaAs distributed Bragg reflectors. The maximum output power of 3 W, optical-to-optical conversion efficiency of 22.4%, and slope efficiency of 29.8% are obtained with 5-℃ heatsink temperature under the front pump,while the maximum output power of 1.1 W, optical-to-optical conversion efficiency of 23.2%, and slope efficiency of30.8% are reached with 5-℃ heatsink temperature under the end pump. Influences of thermal effects on the output power of the laser with front and end pump are discussed.     

A Continuous-Wave Ho：YA103 Laser with Output 8.5 W Pumped by a 1.91μm Laser at Room Temperature

A cw high efficient Ho：YAI03 laser pumped by 1.91 μm diode-pumped Tm：YLF laser at room temperature is realized. The maximum output power reaches 8.5 W when the incident pump power is 15.6 W. The slope efficiency is 63.7%, and the Tm：YLF to Ho：YAP optical conversion efficiency is 54.5%. The laser wavelength is 2118.3nm when the transmission of output coupler is 30%. The beam quality factor is M2 -1.39 measured by the traveling knife-edge method.     

550-W diode-pumped Nd:YAG disk laser

When a thin laser crystal disk is used with a nearly flat-top pump profile, the heat flux can be considered to be one-dimensional. This results in a homogeneous temperature and stress profile within the laser medium leading to reduction of thermal effects. A nearly flat-top pump profile is achieved with a two-pass cylindrical-lens coupling system. An average output power of 550 W is obtained by an average pumping power of 1650 W with a 40-mm diameter Nd:YAG disk. The optical-optical efficiency is 33%.     

Approximate formulas of temperature and stress distributions and thermal induced effects in a heat capacity slab laser

Approximate formulas of transient temperature and stress distributions in the slab of a two-side pumped heat capacity laser are attained by solving the heat diffusion equation. Based on the formulas, the distributions of temperature and stress during the pump period of a two-sided symmetrically laser diode array (LDA) pumped Nd:GGG slab laser with 5-kW average output power are numerically simulated. The results show that the temperature in the slab will averagely increase by more than 70 ℃ after operating for 10 seconds; the stress and maximum of the temperature difference in the slab are about 30 MPa and 24 ℃, respectively. The thermal induced effects are discussed also.     

Diode-pumped Tm:LuAG laser at room temperature

The lasing characteristics of Tm:LuAG at room temperature are reported.The maximum output power at 2.023-μm wavelength is 4.91 W and the slope efficiency is 25.39%.The mode matching between pump mode and laser mode is optimized by changing the pump beam waist radius and its location.Different output couplers are used to realize the optimal laser output.The relationship between operation temperature and output power is also discussed.     

High power vertical-external-cavity surface-emitting laser

<正>A high power optically-pumped vertical-external-cavity surface-emitting laser with a diamond heatspreader is demonstrated.Owing to the good thermal conductivity,diamond can accelerate the dissipation of heat in the active region and increase the output power significantly.The effects of the curvature radius,the transmission of output coupler,the spot size of the pump,and the temperature of the heat sink on the output power are investigated.A maximum output power of 880 mW is obtained under the conditions of 10℃temperature,15-mm curvature radius,3%transmission of the output coupler,and 8500-mW pump power.The slope efficiency and the optical-to-optical conversion efficiency of the laser are about 17%and 15%,respectively.     

Judd-Oflet analysis of spectrum and laser performance of Ho：YAP crystal end-pumped by 1.91μm Tm：YLF laser

The Ho:YAP crystal is grown by the Czochralski technique.The room temperature polarized absorption spectra of Ho:YAP crystal was measured on a c cut sample with 1 at% holmium.According to the obtained Judd-Ofelt intensity parameters Ω2 = 1.42 × 10-20 cm2,Ω4 = 2.92 × 10-20 cm2,and Ω6 = 1.71 × 10-20 cm2,this paper calculated the fluorescence lifetime to be 6 ms for 5I7 →5 I8 transition,and the integrated emission cross section to be 2.24×10-18 cm2.It investigates the room temperature Ho:YAP laser end pumped by a 1.91 μm Tm:YLF laser.The maximum output power was 4.1 W when the incident 1.91 μm pump power was 14.4 W.The slope efficiency is 40.8%,corresponding to an optical to optical conversion efficiency of 28.4%.The Ho:YAP output wavelength was centred at 2118 nm with full width at half maximum of about 0.8 nm.     

A narrow-linewidth continuous wave Ho：YAL03 laser with Fabry-Perot etalons

A narrow linewidth continuous wave Ho：YAP laser with two Fabry-Perot etalons pumped by a Tm：YLF laser is reported. The maximum output power reaches 8.3 W when the incident pump power is 15.8 W, with 52.5% optical-to- optical conversion efficiency and 62.6% slope efficiency. A stable laser output at 2118.1 nm is achieved, with a linewidth less than 0.4 nm （full width at half maximum）. The beam quality factor is M2- 1.25, measured by the traveling knife-edge method.     

LD-pumped 6 W cw Tm^3＋-Doped Silica Double-Cladding Fibre Laser

We report a thulium-doped silica fibre laser that generates a maximum cw output power of 6 W in a 2 μm wavelength range when cladding-pumped by a laser diode （LD） operating at approximately 791 nm at room temperature. The slope efficiency with respect to the launched pump power is 50% and 38.4%, with and without an output coupler mirror, respectively. The corresponding thresholds are 2.8 W and 4.8 W, respectively. The beam qualities Mx^2 and My^2 are 1.26 and 1.32, respectively. The experimental results are also analysed.