Investigation of continuous-wave and Q-switched microchip laser characteristics of Yb:YAG ceramics and crystals

Continuous-wave and passively Q-switched microchip laser performance of Yb:YAG ceramics and single-crystals was investigated. Highly efficient continuous-wave Yb:YAG laser performance was observed at 1030 nm and 1049 nm for both Yb:YAG ceramics and crystals with different transmissions of output couplers. The laser performance of Yb:YAG ceramic is comparable to that of Yb:YAG single crystal. Meanwhile, the laser performance of laser-diode pumped Yb:YAG/Cr⁴⁺:YAG all-ceramics- and all-crystals-combination passively Q-switched microchip lasers were investigated. Sub-nanosecond laser pulses with peak power over 150 kW were obtained with different Yb:YAG/Cr⁴⁺:YAG combinations. Linearly polarized laser was observed in Yb:YAG/Cr⁴⁺:YAG all-crystals combination and circular polarized laser was obtained in Yb:YAG/Cr⁴⁺:YAG all-ceramics combination. The best laser performance was obtained with Yb:YAG/Cr⁴⁺:YAG all-crystals combination.     

Passively Q-switched diode-pumped Yb:YAG laser using Cr-doped garnets

We investigate the repetitive modulation in the kHz frequency domain of a passively Q-switched, diode-pumped Yb:YAG laser, by Cr⁴⁺:YAG, Cr⁴⁺:LuAG, and Cr⁴⁺:GSGG saturable absorbers. The results presented here are focused towards the design of a passively Q-switched Yb:YAG microlaser. The free-running performance of both rod and a disk Yb:YAG is characterized and experimental parameters such as gain and loss are evaluated. These values, together with the value of the stimulated emission cross-section, e.g. σ_em=3.3×10⁻²⁰ cm² were found to fit between our experimental results and an existing numerical model which relates the experimental and physical parameters to the minimal threshold pumping power. Q-switched pulses with maximum peak power of ≈10.4 kW, with energy of ≈0.5 mJ/pulse, were extracted with 30% extraction efficiency.     

Plate-shaped Yb:LuPO4 crystal for efficient CW and passively Q-switched microchip lasers

It is demonstrated that plate-shaped crystals of Yb:LuPO₄, which are grown from spontaneous nucleation by high-temperature solution method, can be utilized to make microchip lasers operating in continuous-wave (CW) or passively Q-switched mode. Efficient operation of such a microchip laser, which is built with a 0.3 mm thick crystal plate in a 2 mm long plane-parallel cavity, is realized at room temperature. With 2.37 W of pump power absorbed, 1.45 W of CW output power is generated with a slope efficiency of 73%. When passively Q-switched with a Cr⁴⁺:YAG crystal plate as saturable absorber, the laser produces a maximum pulsed output power of 0.53 W at 1013.3 nm, at a pulse repetition rate of 23.8 kHz, the resulting pulse energy, duration, and peak power are 22.3 μJ, 4.0 ns, and 5.6 kW, respectively.     

Doubly Q-switched tape casting YAG/Nd:YAG/YAG ceramic laser

A doubly Q-switched 1.06 μm pulsed laser using a novel tape casting YAG/Nd:YAG/YAG composite ceramic with a sandwich structure was demonstrated for the first time. Compared to purely acousto-optical (AO) Q-switching, this laser using an AO Q-switch and Cr⁴⁺:YAG saturable absorber simultaneously can generate shorter pulses. The pulsed laser performance was investigated at two modulated repetition rates of 10 and 20 kHz.     

Fabrication and laser properties of transparent Yb:YAG ceramics

High optical quality transparent Yb:YAG laser ceramics have been successfully fabricated by a vacuum reactive sintering method. Commercial Al₂O₃ powder and co-precipitated Y₂O₃ and Yb₂O₃ powders were used as the raw materials. In-line transmittances at 1300 nm and 400 nm were measured to be 83.6% and 81.8% respectively for a 3 mm thick mirror polished Yb:YAG ceramics sample. Continuous wave (CW) lasing at the wavelength of 1030 nm was achieved when pumped by a 940 nm fiber coupled laser diode. A slope efficiency as high as 62.7% was obtained.     

Multi-ring modes generation in Yb:YAG ceramic laser

A short-focus glass lens with strong spherical aberration was used for mode selection in the cw LD-end-pumped Yb:YAG ceramic laser. Sequence of low to very high order Laguerre-Gaussian (LG_pl) modes with different combinations of radial, p and azimuthal, l indices (p ? 10, l ? 28), with output beam diameters 2-13 mm and power up to 30 mW was obtained. Peaked and hollow multi-ring beams with near-diffraction free propagation of the central minimum or maximum over 40 m distance from the laser resonator were observed. Mechanisms of mode selection and possible applications of the proposed laser scheme are considered.     

Low threshold, diode end-pumped Nd:GdVO4 self-Raman laser

Low threshold, high efficient Raman laser output has been realized from a compact, diode end-pumped, self-stimulating Nd³⁺:GdVO₄ Raman laser. Maximum Raman output power of 100 mW was achieved at a pulse repetition frequency (PRF) of 10 kHz with 1.8 W pump power. The optical efficiency is 5.6% from diode to Raman laser and the slope efficiency is 8%. The lowest threshold for the SRS process is only 400 mW at a PRF of 5 kHz. By generating second harmonics using a LBO crystal, 3 mW 588 nm yellow laser was also produced. A strong blue emission was observed in the Nd³⁺:GdVO₄ crystal when the Raman laser output, we contribute this for the upconversion of the Nd³⁺ in the crystal.     

Photoluminescence and laser behavior of Yb:YAG ceramic

Yb:YAG transparent ceramics with different doping concentration were fabricated by the traditional solid-state diffusion route, and their fluorescence properties and laser behavior were investigated. It is found that both the fluorescence intensity and lifetime depend deeply on both the doping concentration of Yb ions and the annealing treatment. The continuous wavelength (C.W.) laser performance for 10 at.% Yb:YAG ceramic suggests that both the threshold pump power and slope efficiency increase with increasing transmittance of the output couple (T_oc). For T_oc = 15%, the threshold pump power is about 6.1 W, the slope efficiency is 25%, and the maximum output power of 2.2 W is achieved when pumped by 14.9 W.     

Fabrication and laser behavior of the Yb:YAG ceramic microchips

Highly transparent 5 at.% Yb:YAG ceramic microchips were fabricated by vacuum sintering technology. The calculated cross section of the absorption σ_abs and emission σ_em were 6.1 × 10⁻²¹ cm² at 940 nm and 1.9 × 10⁻²⁰ cm² at 1030 nm, respectively. The fluorescence lifetime of the unannealed sample was 0.618 ms, and became 1.229 ms after annealing. Laser oscillation around 1037 nm was observed when pumped by the fiber-coupled laser with 970 nm. The threshold power was 3.0 W and the slope efficiency was about 12% when using the transmission of 2.6% output coupler.     

Yb:YAG透明陶瓷的制备和激光输出

制备了高质量的Yb:YAG透明陶瓷. Yb:YAG透明陶瓷的晶粒尺寸为10μm左右且分布均匀, 晶界处和晶粒中没有杂质、气孔的存在. Yb:YAG样品中所有元素分布均匀, 不同的晶粒间, 晶粒和晶界间成分是一致的, 没有出现成分的偏析. 4mm厚样品的透过率为80％. LD泵浦获得了波长为1030nm, 最大功率为268mW的连续激光输出.     

Tri-wavelength passively Q-switched Yb3+:GdAl3(BO3)4 solid-state laser based on WS2 saturable absorber

Using the WS₂ nanosheets prepared by a facile hydrothermal reaction as saturable absorber (SA), we demonstrate a tri-wavelength passively Q-switching operation of a diode-pumped Yb:GdAl₃(BO₃)₄ (Yb:GAB) crystal laser for the first time. The single pulse energy up to 1.30 μJ with the output power of 140 mW is obtained. The corresponding pulse width and repetition frequency rate are 440 ns and 107.8 kHz, respectively. The stable pulsed laser operates at 1044.9, 1045.6 and 1048.5 nm, simultaneously. This work suggests that solvothermal synthesized WS₂ could be a promising SA to realize a simultaneously multi-wavelength laser operation.     

Passively Q-switched multi-wavelength Nd:YVO4 self-Raman laser

Abstract

Multi-wavelength self-Raman laser from a passively Q-switched c-cut Nd: YVO₄ laser at 1066.8 nm to four discrete Stokes lines at 1097.2, 1129.2, 1168.3 and 1178.8 nm is demonstrated simultaneously for the first time. With a 0.27 at% c-cut Nd:YVO₄ crystal, the total output power of Stokes lines is 267 mW at a pump power of 5.0 W.     

Narrow-linewidth passively Q-switched fibre laser based on microsphere resonator

We experimentally demonstrate a stable narrow-linewidth passively Q-switched fibre laser based on a microsphere resonator (MSR) and graphene saturable absorber (SA). The MSR made by the arc discharge method has the characteristics of easy fabrication, broad free spectral range (FSR) and flexibility. And it acts as a narrow band-pass filter to ensure narrow-linewidth operation. A stable passively Q-switched pulse with 0.016?nm narrow spectral linewidth is successfully achieved. The output pulse has the pulse width of 5.2 µs, repetition frequency of 28 kHz and high signal to noise ratio (SNR) of ～60?dB. The results demonstrate that our works may provide an effective way to achieve narrow-linewidth pulsed fibre lasers.     

Diode-end-pumped passively Q-switched Nd:YAG crystal laser with V:YAG saturable absorber at 1319 and 1338 nm

A diode-end-pumped passively Q-switched Nd:YAG laser with a V:YAG saturable absorber emitting at 1319 and 1338?nm was demonstrated for the first time. A maximum output power of 286?mW was obtained with minimum pulse duration of 13.2?ns and the highest repetition rate was 15?kHz under an incident pump power of 7.7?W. The calculated highest peak power and pulse energy were 2.1?kW and 29?μJ, respectively.     

Comparison of fluorescence spectra of Yb:Y3Al5O12 and Yb:YAlO3 single crystals

Yb:Y₃Al₅O₁₂ (Yb:YAG) single crystals with Yb doping concentration 0.5 at.%, 5 at.%, 15 at.%, 25 at.%, 50 at.%, 100 at.% and Yb:YAlO₃ (Yb:YAP) single crystals with Yb doping concentration 0.5 at.%, 5 at.%, 15 at.%, 30 at.% were grown by the Czochralski process. The fluorescence spectra of these crystals and the effects of self-absorption on the shape of the fluorescence spectra were studied. Through comparing the fluorescence spectra of Yb:YAG and Yb:YAP, all results indicate that the effects of self-absorption on the fluorescence spectra of Yb:YAP are remarkably stronger than that of Yb:YAG at the same Yb concentration.     

Watt-level Q-switched Nd:LuVO4 laser based on a graphene oxide saturable absorber

The demonstration is reported of a diode-pumped passively Q-switched Nd:LuVO₄ laser at 1064 nm using a transmission-type graphene oxide as the saturable absorber. The graphene oxide saturable absorber with a modulation depth of 10% was fabricated using a vertical evaporation method. With a pump of 11.5 W, a maximum output power of 1.353 W was obtained with 186-ns pulse duration and 336.7-kHz repetition rate, corresponding to a maximum pulse energy of 4 μJ per pulse.     

微晶玻璃的制备与光谱特性

高温熔制摩尔组分为32CaO-12Y₂O₃-24Al₂O₃-31SiO₂-1Yb₂O₃的玻璃, 制得的玻璃于950、1050、1100℃三个不同温度进行热处理, 用XRD分析热处理后样品的相变, 用TEM观察1050℃热处理后的样品, 并研究了1050℃热处理前后样品的光谱特性. 研究结果表明: 玻璃在1050℃热处理后, 在玻璃中产生单一YAG相微晶颗粒; 热处理前后样品光谱特性的变化表明热处理后掺杂的Yb ³⁺离子择优进入到YAG晶格位, 制备得到了透明Yb:YAG微晶玻璃.     

水溶性NaYF4:Yb,Er纳米颗粒的溶剂热合成及其上转换发光性能

稀土上转换发光纳米材料具有极好的生物应用前景,但其应用的前提是能制备出水溶性、发光效率高的稀土纳米材料.以乙二醇为溶剂、稀土氯化物和NaP为反应物,采用简易的溶剂热法一步制备出水溶性的NaYF4:Yb,Er纳米颗粒.NaYF4:Yb,Er样品以粒径为25~40nm的球形颗粒为主,同时含有少量直径为25~40nm、长度为50～100nm的虫状纳米颗粒.该样品具有立方相结构,样品表面上的乙二醇配体使其能够很好地分散于水中.在980nm激光器激发下,NaYF4:Yb,Er纳米颗粒水溶液展现了强的黄绿色上转换发光.因此该样品拥有良好的生物应用潜力.     

Pump beam waist-dependent pulse energy generation in Nd:YAG/Cr4+:YAG passively Q-switched microchip laser

Abstract

The incident pump beam waist-dependent pulse energy generation in Nd:YAG/Cr⁴⁺:YAG composite crystal passively Q-switched microchip laser has been investigated experimentally and theoretically by moving the Nd:YAG/Cr⁴⁺:YAG composite crystal along the pump beam direction. Highest pulse energy of 0.4 mJ has been generated when the Nd:YAG/Cr⁴⁺:YAG composite crystal is moved about 6 mm away from the focused pump beam waist. Laser pulses with pulse width of 1.7 ns and peak power of over 235 kW have been achieved. The theoretically calculated effective laser beam area at different positions of Nd:YAG/Cr⁴⁺:YAG composite crystal along the pump beam direction is in good agreement with the experimental results. The highest peak power can be generated by adjusting the pump beam waist incident on the Nd:YAG/Cr⁴⁺:YAG composite crystal to optimize the effective laser beam area in passively Q-switched microchip laser.     

Analysis of output characteristics of the actively Q-switched intracavity optical parametric oscillator considering Gaussian distribution of intracavity photon densities

By considering the Gaussian spatial distribution of the initial population-inversion density and the intracavity photon densities of the fundamental, the signal and the idle lights, the rate equations of a LD-pumped actively Q-switched intracavity optical parametric oscillator (IOPO) are derived. The influence of the pump rate, the thermal effect in the gain medium and the change of the photon density along the cavity axis have also been taken account in the equations. By numerically solving these coupled equations, the dependences of pulse width, pulse energy and peak power on incident pump power for the generated-signal light are obtained. In the experiment, a laser-diode-pumped actively Q-switched Nd:GdVO₄/KTP IOPO with an acousto-optic (AO) modulator is realized and the experimental results agree with the theoretical calculations.