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 Yb:YAG Laser with Cr(4+):YAG as the Saturable Absorber

By using a continuous-wave Ti:sapphire laser as a pumping source, we demonstrated a passively Q-switched Yb:YAG laser at room temperature with Cr(4+):YAG as the saturable absorber. We achieved an average output power of as much as 55 mW at 1.03 mum with a pulse width (FWHM) as short as 350 ns. The initial transmission of the Cr(4+):YAG has an effect on the pulse duration (FWHM) and the repetition rate of the Yb:YAG passively Q-switched laser. The Yb:YAG crystal can be a most promising passively Q-switched laser crystal for compact, efficient, solid-state lasers.     

Cr doped garnets: their properties as non-linear absorbers

A comparative research into the use of Cr⁴⁺-doped YAG, YSGG and LuAG (Lu₃Al₅O₁₂) as saturable absorbers for the 1.06 μm emission of Nd:YAG laser has been conducted. Q-switched pulses with temporal duration ranging from 23 to 52 ns (FWHM) were observed for the different garnets under investigation. Cross-sections for ground state and excited state absorption were evaluated by fitting our saturation data to Frantz-Nodvik equation.     

Yb to Er energy transfer and rate-equations formalism in the eye safe laser material Yb:Er:Ca2Al2SiO7

Rate equations formalism is used to predict the population ratio of the Er^{3+ 4}I_13/2 levels involved in the 1.55 μm laser transition in the Yb:Er:CAS laser materials. An effective Yb → Er energy transfer, favourable to the Er³⁺ 1.55 μm laser emission, is demonstrated in this laser host. Indeed, the Yb → Er transfer and the Er → Yb back transfer rates are calculated to be 6 x 10⁻¹⁶ and 0.45 x 10⁻¹⁶ cm³ s⁻¹, respectively. Attempts of codoping the system with Nd³⁺, Eu³⁺ and Ce³⁺ have been realised in order to increase the population of the Er^{3+ 4}I_13/2 laser emitting level. Best results are obtained with Ce³⁺ ion since in the sample containing 6 x 10²⁰ Ce³⁺/cm³, the Er^{3+ 4}I_11/2 level lifetime is divided by a factor of 3 while the Er^{3+ 4}I_13/2 fluorescence lifetime remains unaffected. On the contrary, codoping with Nd³⁺ or Eu³⁺ ions simultaneously decreases the Er^{3+ 4}I_11/2 and ⁴I_13/2 kinetics parameters. The role of the other parameters such as Yb/Er concentrations ratios is also discussed.     

Optically active Er–Yb codoped Y2O3 films produced by pulsed laser deposition

Optically active Er³⁺:Yb³⁺ codoped Y₂O₃ films have been produced on c-cut sapphire substrates by pulsed laser deposition from ceramic Er:Yb:Y₂O₃ targets having different rare-earth concentrations. Stoichiometic films with very high rare-earth concentrations (up to 5.5 × 10²¹ at cm^− 3) have been achieved by using a low oxygen pressure (1 Pa) during deposition whereas higher pressures lead to films having excess of oxygen. The crystalline structure of such stoichiometric films was found to worsen the thicker the films are. Their luminescence at 1.53 μm and up-conversion effects have been studied by pumping the Yb³⁺ at 0.974 μm. The highest lifetime value (up to 4.6 ms) is achieved in films having Er concentrations of ≈ 3.5 × 10²⁰ at cm^− 3 and total rare-earth concentration ≈ 1.8 × 10²¹ at cm^− 3. All the stoichiometric films irrespective of their rare-earth concentration or crystalline quality have shown no significant up-conversion.     

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.     

Laser-diode pumped passively Q-switched Nd3+:NaY(WO4)2 laser with Cr4+:YAG saturable absorber

A laser-diode pumped passively Q-switched new type crystal Nd³⁺:NaY(WO₄)₂ (known as Nd:NYW) laser with Cr⁴⁺:YAG saturable absorber has been realized. The dependence of pulse repetition rate, pulse energy, pulse width, and peak power on pump power for different small-signal transmission of Cr⁴⁺:YAG are measured. The coupled rate equations are used to simulate the Q-switched process of laser, and the numerical solutions agree with the experimental results.     

Performance of diode-end-pumped Cr, Nd:YAG self-Q-switched and Nd:YAG/Cr:YAG diffusion bonded lasers

Self-passively Q-switching of a diode-pumped Cr,Nd:YAG, where the Cr⁴⁺ is used as a saturable absorber for the 1064 nm laser emission is reported. The maximum average output power was obtained using an output coupler of R=86%. The self-Q-switched diode pumped laser yielded 1.86-W average output power with low threshold pumping power (≈1.7-W), average slope efficiency of ≈34%, pulse duration of about 14–16 ns, and modulation frequency ranging from 2.4 to 73 kHz, depending on the input pumping power. These results are the highest reported for self-Q-switched lasers. Higher slope efficiency (42%) and shorter Q-switched pulses were obtained for a Q-switched Nd:YAG/Cr⁴⁺:YAG diffusion bonded laser. A comparison of the codoped Cr,Nd:YAG laser performance, with that of a diffusion bonded laser is reported and analyzed.     

Enhancement of stability and peak power in a diode-pumped doubly QML YVO4/Nd:YVO4 laser with EO and Cr:YAG saturable absorber

A diode-pumped doubly Q-switched and mode-locked (QML) YVO₄/NdYVO₄ laser is realized with the electro-optic (EO) modulator and Cr⁴⁺:YAG saturable absorber, in which the repetition rate of the Q-switched envelope is controlled by the active EO modulation while the mode-locked pulses inside the Q-switched envelope depend on both the actively modulated loss and the passive saturable absorption. The experimental results show that the doubly QML laser can generate more stable and shorter pulses with higher peak power when compared with the singly passively QML laser with Cr⁴⁺:YAG. At the pump power of 20 W and the repetition rate 1 kHz, a 21 ns Q-switched pulse envelope with a average mode-locked peak power of 544 kW is obtained, which is the shortest Q-switched pulse envelope to my knowledge. In comparison to the singly passively QML laser with Cr⁴⁺:YAG, the doubly QML laser has compressed the Q-switched envelope pulse width 70% and improved the mode-locked pulsed peak power 27 times. By using a hyperbolic secant square function and considering the Gaussian distribution of the intracavity photon density, the coupled equations for diode-pumped dual-loss-modulated QML laser is given and the numerical solutions of the equations are in good agreement with the experimental results.     

固态晶体生长及其在平面波导结构制备上的应用

研究了烧结温度、晶粒大小以及掺杂离子对固态晶体生长的影响。在热致固态晶体生长的过程中, 接近键合面的陶瓷会被单晶诱导而转变成取向一样的单晶, 同时形成稳固的键合。实验利用这种方法制备核层为12at%Yb:YAG陶瓷(100 mm), 包层为YAG晶体的平面波导结构。这种方法制备的波导结构没有Yb离子的浓度扩散现象。同时, 还测试了平面波导结构的激光性能: 通过设计平平腔实现了1.14 W, 斜率效率16.09%的激光输出; 在三镜腔中实现1.83 W, 斜率效率9.59%的激光输出。并且激光输出在1027.5 nm到1033.5 nm间连续可调。     

Electron Paramagnetic Resonance and optical absorption spectra of Cr(III) ions in alkali cadmium borosulphate glasses

The Electron Paramagnetic Resonance (EPR) spectrum at 9.205 GHz and at 300 K has been examined for a series of Cr³⁺ ions doped alkali cadmium borosulphate [R₂SO₄-CdSO₄-B₂O₃ (R=Li,Na,K or Cs)] glasses. The low field EPR spectral resonance lines are attributed to isolated Cr³⁺ ions where as the high field spectral resonance lines are attributed to exchange coupled pairs of Cr³⁺ ions. The absorption spectra of Cr³⁺ ions ions in these glasses show two broad bands characteristic of Cr³⁺ ions in octahedral symmetry. The bands are slightly shifted to higher wavelength side from Li glass to Cs glass. From the optical spectra the crystal field parameter Dq and the Racah interelectronic repulsion parameters B and C are evaluated. From the EPR and optical data, it is concluded that, the site symmetry around the Cr³⁺ ions is octahedral and the nature of bonding is predominantly covalent in nature.     

Optical absorption and nonlinear transmission of tetrahedral V (d) in yttrium aluminum garnet

The saturation of the optical absorption in V³⁺ : YAG crystal is investigated. The absorption cross section of tetrahedral V³⁺ at 1.08 μm is estimated to be 8.2±2.5x10^-18 cm². Q-switching and passive mode-locking for a number of solid state lasers with wavelengths at 747 nm, 780 nm, 1.06 μm and 1.34 μm have been obtained with a V³⁺ :YAG saturable absorber.     

Effect of ionizing radiation on optical and lasing properties of Y3Al5O12 single crystals doped with Nd, Er, Ho, Tm, Cr ions

The influence of gamma irradiation on optical and lasing properties of YAG:Er, YAG:CTH, YAG:Nd and YAG:Cr⁴⁺ single crystals were studied. For no thermal annealed rods from YAG:Er and YAG:CTH crystals the increase of laser output energy was established. The mechanisms of radiation sensibilization are discussed.     

Maximum value of the pulse energy of a passively Q-switched laser as a function of the pump power

The finite recovery time Ts of the bleached absorber is presented as one of the possible mechanisms accounting for the increase-maximum-decrease in pulse energy E with the pumping rate Wp in cw-pumped passively Q-switched solid-state lasers, by analytically evaluating the sign of the derivative partial differentialE/ partial differentialWP. The results show that, in the low pump regime (T>Ts, T is the interpulse period), the initial population density ni remains constant, the final population density nf decreases with Wp, and this results in a monotonic increase of E with Wp. In the high pump regime (T相似文献   

Optical properties and energy transfer among Nd in Nd:Ca2Al2SiO7 crystals for diode pumped lasers

The energy levels of neodymium in the Nd³⁺:Ca₂Al₂SiO₇ (CAS) laser material with gehlenite structure are reported. As the Nd³⁺:Ca₂Al₂SiO₇ compound presents a broad absorption around 806 nm, it is a good candidate for diode pumped laser. The ⁴F_3/2→⁴I_9/2 and ⁴F_3/2→⁴I11/2 emission have been recorded and the fluorescence branching ratios calculated from the Judd-Ofelt analysis are 0.41 and 0.47 respectively. The emission cross section at 1.06 μm (⁴F_3/2→⁴I11/2 transition) is 5 × 10^-20 cm². The decay profiles of the Nd³⁺ emission have been analyzed for several Nd³⁺ concentrations using the kinetic microparameters related to the cross relaxation ( and R₀≈6 Å) and the energy migration probabilities ( ). In the Nd:CAS laser material, the optimal concentration corresponding to the maximum of the fluorescence intensity is determined to be around 2.7 × 10²⁰ Nd³⁺ ions cm^-3. The Nd³⁺-Nd³⁺ interactions are not very strong in this material as the optical concentration value is two times higher than in the Nd:YAG laser material.     

Color centers and charge state recharge in γ-irradiated Yb:YAP

Gamma-ray irradiation induced color centers and charge state recharge of impurity and doped ion in 10 at.% Yb:YAP have been studied. The change in the additional absorption (AA) spectra is mainly related to the charge exchange of the impurity Fe²⁺, Fe³⁺ and Yb³⁺ ions. Two impurity color center bands at 255 and 313 nm were attributed to Fe³⁺ and Fe²⁺ ions, respectively. The broad AA band centered at 385 nm may be associated with the cation vacancies and F-type center. The transition Yb³⁺ → Yb²⁺ takes place in the process of γ-irradiation. Oxygen annealing and γ-ray irradiation lead to an opposite effect on the absorption properties of the Yb:YAP crystal. In the air annealing process, the transition Fe²⁺ → Fe³⁺ and Yb²⁺ → Yb³⁺ take place and the color centers responsible for the 385 nm band was destroyed.     

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.     

混合尖晶石型Zn6Ga8TiO20:Cr3+荧光粉的合成、结构表征与发光性能

采用高温固相法合成新型红色荧光粉Zn₆Ga_8-xTiO₂₀:xCr³⁺。用XRD、XRF和TEM对样品的成分和晶体结构进行表征, 发现所合成的荧光粉为单一的混合尖晶石结构, Cr³⁺能有效地掺杂进入基质Zn₆Ga₈TiO₂₀中, 并占据八面体格位。荧光光谱分析表明, 激发谱由四个峰组成, 峰值分别为281、337、420和555 nm, 其中281 nm对应Cr³⁺离子的⁴A₂→⁴T₁(4P)跃迁, 337 nm来自O^2-的2p轨道电子向Ga³⁺的4s4p轨道迁移跃迁, 420和555 nm分别对应Cr³⁺离子的⁴A₂→⁴T₁和⁴A₂→⁴T_2g的跃迁。发射光谱是由²E→⁴A₂的跃迁辐射零声子线(689 nm, R锐线)、处于畸变的环境中Cr³⁺发射的N线(696 nm)以及由晶格振动导致的声子伴随发射峰组成。这种荧光粉是一种可能应用在白光LED上的红色荧光粉。     

Optical properties and laser performance of neodymium doped fluoroapatites SrxCa5−x(PO4)3F (x = 0, 1, 2, 3, 4, and 5)

Nd doped fluoroapatites Sr_xCa_5−x(PO₄)₃F(S_xC_5−xPF, X = 0, 1, 2, 3, 4, and 5) single crystals have been grown by the Czochralski technique. Their polarized absorption and emission spectra have been recorded at room temperature and used to calculate the absorption and stimulated emission cross sections. Broadening of the absorption and emission bands is observed for Nd³⁺ in the solid solutions SPF-CPF compared to Nd³⁺ in CPF or SPF. 1% Nd:S_xC_5−xPF, X = 0, 2, 3, 4, and 5, laser rods have been tested in a cavity longitudinally pumped by a 1 W AlGaAs laser diode and compared to Nd:YAG and Nd:YVO₄ rods. All fluoroapatites exhibit very good laser performance with low thresholds and high slope efficiencies, higher than in the case of YAG and equal to the YVO₄ samples. The dependance of the laser output power versus the diode temperature has also been measured for all materials. The laser output was found to be as sensitive to the diode temperature fluctuations for fluoroapatites as for YAG.     

Fluorescence line narrowing study of Cr ions in cordierite glass nucleating MgAl2O4 nanocrystals

The luminescence of Cr³⁺ ions in cordierite glass nucleating MgAl₂O₄ nanocrystallites has been investigated. The time resolved fluorescence line narrowing measurements and the temperature dependence of the homogeneous line width show that most Cr³⁺ ions are inside the nanocrystallites. Cr³⁺ ions occupy non-equivalent crystal sites, due to the Mg²⁺–Al³⁺ inversion effect. The values of the homogeneous line width compare well with those of previous studies in crystals. No surface effect has been observed due to the large size of the crystals.