Lu, Gd codoped KY(WO(4))(2):Yb epitaxial layers: towards integrated optics based on KY(WO(4))(2)

Codoping KY(WO(4))(2):Yb layers with optically inert Lu and Gd ions allows a large increase of the refractive index contrast with respect to KY(WO(4))(2) substrates. This paves the way for the realization of integrated optical circuits based on this very promising material. First riblike waveguide structures have been fabricated and propagation losses below 1 dB/cm have been evaluated. A Y-junction with a splitting ratio close to 1:1 and additional losses of 1.4 dB has also been demonstrated.     

Yb-doped KY(WO4)2 planar waveguide laser

High-quality monoclinic KY(WO4)2 optical waveguides were grown by liquid-phase epitaxy, and laser operation of an Yb-doped KY(WO4)2 waveguide was demonstrated for the first time to our knowledge. Continuous-wave laser emission near 1 microm was achieved with both surface and buried planar waveguides. An output power of 290 mW was obtained in the fundamental mode and the slope efficiency was above 80%.     

Diode-pumped Kerr-lens mode-locked Yb:KY(WO(4))(2) laser

A self-starting Kerr-lens mode-locked Yb:KY(WO(4))(2) laser directly end pumped by two 1.6-W diodes is demonstrated for what is to our knowledge the first time. Pulses as short as 71 fs with 120-mW average output power, at a center wavelength of 1057 nm, were obtained at a repetition rate of 110 MHz. A 10-nm tuning range was achieved with longer pulses and higher average output power.     

Yb3+:KY(WO4)2 laser with a fast saturable absorber

Quantum-well semiconductor structures with superlattice barriers and reduced recovery time of absorption are designed and manufactured. A saturable absorption mirror based on such a structure is used in the Yb³⁺:KY(WO₄)₂ laser. The mode locking at a repetition rate of 70 MHz yields an almost bandwidth-limited pulse with a duration of about 115 fs. The maximum mean power (1.57 W) is comparable with a CW power of 1.62 W, which indicates a relatively low level of nonsaturable loss in the saturable absorption mirror.     

Yb3+掺杂KY(WO4)2激光晶体生长、结构与光谱分析

采用顶部籽晶提拉法(TSSG)生长出Yb:KY(WO4)2(Yb:KYW)激光晶体.对预烧后的原料及晶体进行了XRD分析,结果表明,分别在920℃和600℃预烧8h后的熔质和助熔剂基本上形成一相,抑止了实验中的挥发问题;所生长的晶体为β-Yb:KYW,计算其晶格常数为a=1.063nm,b=1.034nm,c=0.755nm,β=130.75°.测得不同厚度样品的吸收光谱,结果表明样品在933nm和981nm有较强的吸收峰,计算出主峰981nm的吸收截面σabs=5.34×10-20cm2.测得样品的荧光光谱,计算出主峰1030nm受激发射截面σem=3.1×10-20cm2,并估算其荧光寿命为0.56ms,与实测值0.60ms吻合.计算出激发态最小粒子数(β)、饱和抽运强度(Isat)和最小抽运强度(Imin),通过与其他掺Yb3+晶体比较,结果表明Yb:KYW晶体的Imin(0.24kW/cm2)很小.     

新型激光晶体Yb:KY(WO4)2的结构与光谱

采用顶部籽晶提拉法,以K2W2O7为助溶剂,生长了Yb:KY(WO4)2新型激光晶体.经热重-差热分析,确定晶体熔点为1045℃,相变温度为1010℃.X射线粉末衍射测试,验证所生长的晶体为β-Yb:KY(WO4)2.晶体结构分析确定Yb:KY(WO4)2晶体由WO6八面体连接而成,WO6八面体是由双氧桥(WOOW)及单氧桥(WOW)构成.晶体粉末样品室温下的红外及拉曼光谱测试,确定WO6原子基团、双氧桥及单氧桥的振动频率.晶体的吸收峰位于940nm,980nm,发射峰位于989nm-1030nm.     

Nonlinear refractive properties of Yb3+-doped KY(WO4)2 and YVO4 laser crystals

The nonlinear refractive indices of Yb³⁺: KY(WO₄)₂ and Yb³⁺:YVO₄ laser crystals are characterized using a Z-scan technique at a wavelength of 1.08 μm for different polarizations. The results reveal that the nonlinear refractive index of Yb³⁺:YVO₄ is superior to that of Yb³⁺:KY(WO₄)₂ and is found to be 1.9×10^-15 cm²/W and 1.5×10^-15 cm²/W for E⊥c and E∥c polarizations, respectively. PACS 42.65.Hw; 42.55.Rz; 42.65.Re; 42.70.Hj     

High-peak-power pulses from a cavity-dumped Yb:KY(WO4)2 oscillator

We report generation of 1.35 microJ femtosecond laser pulses with a peak power of 3 MW at 1 MHz repetition rate from a diode-pumped Yb:KY(WO4)2 laser oscillator with cavity dumping. By extracavity compression with a large-mode-area fiber and a prism sequence, we generate ultrashort pulses with a duration of 21 fs and a peak power of 13 MW.     

Highly efficient 1 GHz repetition-frequency femtosecond Yb3+:KY(WO4)2 laser

We present a highly efficient, diode-pumped, femtosecond Yb3+:KY(WO4)2 (Yb:KYW) laser operating at a 1.024 GHz repetition rate. The output was centered at a wavelength of 1042 nm and had a bandwidth of 3.8 nm, leading to transform-limited pulses with durations of 278 fs determined by fringe-resolved autocorrelation measurements. The optical-to-optical conversion efficiency and slope efficiency were 61% and 69%, respectively, and the relative intensity noise was <0.1%.     

Directly diode-pumped Yb:KY(WO(4))(2) regenerative amplifiers

Two Yb(3+) -doped KY(WO(4))(2) regenerative amplifiers, one end pumped by two 1.6-W single-stripe diodes at 940 nm and the other side pumped by one 20-W diode bar at 980 nm, are demonstrated. When the regenerative amplifiers are injected, 40-muJ , 400-fs and 65-muJ , 460-fs pulses at a 1-kHz repetition rate are obtained following compression from the end- and side-pumped amplifiers, respectively.     

Efficient femtosecond green-light source with a diode-pumped mode-locked Yb3+:KY(WO4)2 laser

Efficient generation of femtosecond pulses at 524 nm is demonstrated by the extracavity frequency doubling of the output of a diode-pumped femtosecond Yb3+:KY(WO4)2 laser using a periodically poled LiTaO3 crystal. An average second-harmonic power of 120 mW is produced at an internal conversion efficiency of 40%. The temporal characteristics of the frequency-doubled pulses as a function of focusing conditions in a thick nonlinear crystal are investigated experimentally, and pulses as short as 225 fs are generated at a pulse repetition frequency of 86 MHz.     

240-fs pulses with 22-W average power from a mode-locked thin-disk Yb:KY(WO(4))(2) laser

We demonstrate what is to our knowledge the first passively mode-locked thin-disk Yb:KY(WO(4))(2) laser. The laser produces pulses of 240-fs duration with an average power of 22 W at a center wavelength of 1028 nm. At a pulse repetition rate of 25 MHz, the pulse energy is 0.9microJ , and the peak power is as high as 3.3 MW. The beam quality is very close to the diffraction limit, with M(2)=1.1 .     

Ultrafast thin-disk Yb:KY(WO4)2 regenerative amplifier with a 200-kHz repetition rate

We report an Yb:KYW thin-disk amplifier system that provides ultrashort pulses in the 10-microJ energy range at high repetition rates. The thin-disk concept uses large laser beam cross sections to avoid high peak intensities. Without using a traditional diffraction-grating stretcher, pulse energies of approximately 9 microJ with pulse durations of 280 fs at repetition rates of 200 kHz were generated.     

Er/Yb∶KY(WO_4)_2晶体的各向吸收光谱和上转换发光特性

测试了Er/Yb∶KY(WO4)2晶体在室温下3个轴Ng,Np,Nm方向上的吸收光谱,分析比较光谱特性,并计算出各能级跃迁的吸收截面,其中沿Np轴方向有最强的吸收和较大的吸收截面,这有利于激光上能级的粒子数堆积,增大跃迁几率,加强荧光输出。由于掺入Yb3+离子,晶体在980 nm附近有很强的吸收和较大的半峰宽。该晶体在980 nm激光泵浦下有上转换绿光和红光,3个晶轴Np,Ng,Nm轴方向的上转换荧光,波峰位置相差甚微,强弱区别明显,且呈现的各向异性,其中Np方向最强。     

单斜结构的Yb:KLu(WO4)2晶体光谱和激光性质的各向异性

研究了Yb:KLu(WO4):晶体对非偏振抽运光的吸收以及连续波激光振荡性质.晶体结构的低对称性导致晶体光谱呈强烈各向异性,最强的吸收和发射都发生在平行于Nm.主轴的偏振方向上.Ng切向晶体具有最高的非偏振抽运光吸收效率和最大的激光功率产生潜力,2mm长的晶体产生的最高连续波输出功率为11 W,相对于吸收抽运功率,光一光转换效率为68%,而斜率效率则达80%.     

Crystal growth, spectral and laser properties of Yb3+:NaGd(WO4)2 crystal

Yb³⁺-doped NaGd(WO₄)₂ (Yb:NGW) crystal has been successfully grown by Czochralski method. The rocking curves from (400) plane of as-grown Yb:NGW crystal was measured and the full-width values at half-maximum was 21″. The polarized absorption spectra, the fluorescence spectra and the fluorescence decay lifetime of Yb:NGW crystal were measured at room temperature. The spectroscopic parameters of Yb:NGW crystal are calculated and compared, with those of Yb:YAG crystal. A continuous wave output power of 3.01 W at 1048 nm was obtained with a slope efficiency of 71% by use of diode pumping.     

Pulsed laser operation of Y b-dope d KY(WO(4))(2) and KGd(WO(4))(2)

Spectroscopic properties and laser performance of Y b-doped tungstates at pulsed Ti:sapphire laser pumping are reported. Room-temperature lasing near 1025nm is demonstrated in Yb:KY(WO(4))(2) and Yb:KGd(WO(4))(2), with a slope efficiency as great as 86.9%.     

Continuous-wave lasing of a stoichiometric Yb laser material: KYb(WO4)2

For the first time to the authors' knowledge, continuous-wave laser emission of the stoichiometric crystal KYb(WO4)2 was achieved at 1068 nm. The 125-microm-thin sample was directly water cooled and pumped at 1025 nm by a Ti:sapphire laser. The maximum output power at room temperature was 20 mW.     

Microjoule pulses from a passively mode-locked Yb:KY(WO(4))(2) thin-disk oscillator with cavity dumping

We demonstrate, for the first time to our knowledge, a passively mode-locked femtosecond thin-disk oscillator with cavity dumping. A beta-barium-borate-based pockels cell imposes cavity dumping at a repetition rate of 1 MHz. The laser generates pulse energies up to 3 microJ with a pulse duration of 680 fs in a diffraction-limited beam.     

Thin-disk Yb:KLu(WO(4))(2) laser with single-pass pumping

Single-pass pumping of a thin disk consisting of an only 50 microm thick epitaxial layer of 32 at.% Yb-doped KLu(WO(4))(2) grown on a 0.35 mm thick undoped KLu(WO(4))(2) substrate is demonstrated. The thin-disk laser delivered 9 W of continuous wave output power near 1030 nm with a slope efficiency of 77%.