High-power picosecond regenerative amplifier based on CW diode side-pumped Nd:YAG with high beam quality

A compact high-power picosecond regenerative amplifier based on continuous wave(CW) diode sidepumped Nd:YAG is demonstrated.Average power of 8.8 W is achieved at a repetition rate of 5 kHz at a wavelength of 1 064 nm with a pulse duration of 28 ps,corresponding to a pulse energy of 1.76 mJ and a peak power of 62.9 MW.The beam quality is close to the di?raction limit with Mx2 = 1.24,My2 = 1.03.To the best of our knowledge,this is the highest pulse energy obtained from a CW diode pumped Nd:YAG picosecond regenerative amplifier.     

High energy and long pulse generation with high-birefringence photonic crystal fibre and laser-diode pumped regenerative amplifier

We report on the generation of a high energy and long pulse for pumping optical parametric chirped-pulse amplification(OPCPA) by a high-birefringence photonic crystal fibre(HB-PCF) and a laser-diode-pumped regenerative chirped pulse amplifier.Using the femtosecond pump pulse centred at 815 nm,a 1064 nm soliton pulse is produced in the HB-PCF.After injecting it into an Nd:YAG regenerative amplifier with the glass etalons,a narrow-band amplified pulse with an energy of ～4 mJ and a duration of 235 ps is achieved at a repetition rate of 10 Hz,which is suitable for being used as a pump source in the 800 nm OPCPA system.     

Hybrid femtosecond laser system based on a Yb:KGW regenerative amplifier for N_P polarization

We report a hybrid femtosecond laser system based on a femtosecond Yb-doped fiber laser and a Yb-doped potassium gadolinium tungstate(Yb:KGW) regenerative amplifier. To match the central wavelength of the seed source, a Yb:KGW crystal is used in the regenerative amplifier for N_p polarization. We study and optimize the dynamics of nonlinear amplification to alleviate the gain narrowing effect. With optimization, the system can output 270 fs pulses with 21 μJ pulse energy at a 60 kHz repetition rate.     

Theoretical and experimental investigations of quasi-continuous wave diode array side-pumped Yb＇YAG slab laser

An analytical model of quasi-continuous wave (quasi-CW) diode array side-pumped slab laser for Yb:YAG oscillator in long-pulse free-running has been developed based on the CW model. In this model we first introduce a new parameter, pump pulse width, and make the model available for use in the quasi-CW model. We also give an analytical equation of laser delay time to calculate the laser pulse width. A detailed model is also presented for a new structure laser design, taking account of the geometry of Yb:YAG slab. A quasi-CW diode array side-pumped Yb:YAG slab laser is investigated theoretically and experimentally. Experiments yield a quasi-CW output energy up to 20.36 mJ with the laser pulse width of 654.55 μs at 1049 nm when the diode arrays operate at 25 Hz and 1 ms pulse width. The crystal dimensions are 3 mm×8 mm×1 mm and the doping density is 10 at.%. The experimental results are in good agreement with the predictions of the theoretical model.     

Flash-lamp-pumped picosecond Nd:YAG regenerative amplifier

A flasli-lamp-pumped Nd:YAG regenerative amplifier has been developed at 1.06 μm, seeded with 10-ps pulses from a diode-end-pumped and mode-locked Nd:YAG oscillator with homemade semiconductor saturable absorber mirror (SESAM). The pulse energy was amplified to 2 mJ by the regenerative amplifier at 10-Hz repetition rate. In two-stages amplifier the regenerative amplified pulse energy was amplified to 100 mJ, and 35-mJ double frequency at 532 nm was obtained by extra-cavity double frequency with a KTP crystal.     

Diode-pumped Yb:SSO chirped pulse amplifier with 1 ps pulse duration

We demonstrate a diode-pumped picosecond Yb-doped silicate Yb3+:Sc2Si O5(Yb:SSO) chirped pulse amplifier. The seed source with a pulse width of 220 fs is a diode-pumped Yb:KGW femtosecond oscillator. A single chirped volume Bragg grating is employed both as a pulse stretcher and as a compressor to improve the compactness of the system. Stretched pulse is amplified using a diode-pumped Yb:SSO regenerative amplifier. The maximum amplified pulse energy obtained at a pump power of 13.5 W is 450 μJ. The amplified pulse is centered at 1033.3 nm before compression at a frequency of 1 k Hz. After compression, the pulse energy is 315 μJ with a pulse duration of approximately 1 ps.     

Diode-side-pumped AO Q-switched Tm,Ho:LuLF laser

A diode-side-pumped Tm,Ho:LuLiF laser at 2-m wavelength obtained in a ring resonator and its amplification experiment are reported. At the maximum pump energy of 4.7 J available for the oscillator,the output energy per pulse for the oscillator decreases from 904 to 483 mJ in free running mode,and decreases from 106 to 68 mJ in Q-switched mode,with an increase of pump pulse repetition rate from 1 to 5 Hz. When considering the amplifier,99-mJ Q-switched output energy is achieved at 5-Hz repetition rate.     

Study of diode-pumped Yb:YAG disk lasers at low temperature

A Yb:YAG disk laser with V-shaped stable resonator and active-mirror configuration,end-pumped by a 940-nm InGaAs laser diode array,is demonstrated.Performances and optimization of the disk laser at low temperature over a range of 130-200 K are investigated theoretically and experimentally.Laser output energy of 1.46 J/pulse operating at 10-Hz repetition rate is obtained with the optimum output coupler transmission of 30%,and the corresponding optical-to-optical efficiency is 48.7%.     

Laser diode end-pumped Nd：YVO4 regenerative amplifier for picosecond pulses

A diode dual-end-pumped Nd:YVO4 regenerative amplifier is reported. The influence of the cavity stability on the performance of the regenerative amplifier is studied. The experimental results match well with the analysis at high pump power. The mode locking seed pulses with 15 ps pulse width and 10 nJ single pulse energy at 86 MHz are amplified up to 4.7 mJ at 1 kHz, corresponding to the maximum amplification about 0.5 × 106 , by our regenerative amplifier. And an average power of 4.7 W is obtained at the repetition rate from 1 kHz to 10 kHz.     

Generation of 170-fs Laser Pulses at 1053nm by a Passively Mode-Locked Yb:YAG Laser

A novel method is developed to obtain 1.05μm laser operation with a Yb：YAG laser. By using a Yb：YAG crystal with proper length and doping concentration, a femtosecond Yb： YAG laser is realized at the central wavelength of 1053nm. The measured pulse duration and spectral bandwidth （FWHM） are 170fs and 7nm; the repetition rate is 80 MHz. Under a power pump of 2 W, an average mode-locking power of 180mW is achieved.     

Highly efficient cryogenically-cooled Yb:YAG laser

A MOPA laser system for high pulse energy and high average power has been developed by using a cryogenic Yb:YAG. In the regenerative amplifier with our original TRAM architecture, the high pulse energies of 6.5 and 1.5 mJ were obtained at the repetition rate of 200 Hz and 1 kHz, respectively. An optical efficiency was as high as η_o-o = 9.3% with an excellent beam quality of M ² < 1.1, which ensured that a cryogenic Yb:YAG TRAM had a high thermal strength. The following four pass power amplifier with a cryogenic Yb:YAG rod showed 140 mJ at 100 Hz. Both a high optical efficiency of η_o-o = 30% and a high slope efficiency of η_s = 44% showed that an efficient laser operation could be realized for a power amplification with both a high pulse energy and a high average power by using a cryogenic Yb:YAG.     

Picosecond pulses from a cryogenically cooled, composite amplifier using Yb:YAG and Yb:GSAG

A cryogenic Yb amplifier using two laser materials, Gd3Sc2Al3O12 and Y3Al5O12 (YAG), has been used to obtain 70 W average power at 5 kHz pulse repetition frequency; the output was compressed to 1.6 ps, compared with an input compressible to 1.4 ps. The gain broadening obtained by combining two media enables shorter pulses than using Yb:YAG alone but retains the power-scaling advantages of cryogenic Yb:YAG.     

激光二极管泵浦的重复频率大能量低温Yb:YAG激光器设计

为实现重复频率大能量激光输出,基于Yb:YAG激光介质低温下良好的热特性和激光特性,设计了12kW高功率激光二极管(LD)阵列泵浦的V型腔低温Yb:YAG激光器(液氮温度)。对于泵浦耦合系统和散热结构两个关键点,分别使用光线追迹方法和有限元方法进行了分析,提出了楔形真空窗口和低温热管等解决方案。模拟结果表明,该设计的激光器热效应较低,可实现重复频率大能量输出。     

低温Yb:YAG放大器增益与热畸变特性实验研究

为了研究低温条件下Yb:YAG放大器的增益和热特性,搭建了一套液氮冷却的低温放大器,开展了实验研究。测量了不同泵浦强度下的小信号增益以及低温和常温下的介质热致波前畸变。结果表明:低温条件下,可以用更少的泵浦能量得到高于常温的增益;常温下泵浦电流200A、脉冲宽度1200μs的小信号增益为1.59;低温下泵浦电流200A、脉冲宽度400μs的小信号增益为1.82,光光效率显著提高。自发辐射放大(ASE)问题在低温下更加显著,采用短脉冲泵浦有利于降低ASE的影响。低温的热管理效果较常温有显著提高,可以在更高的平均功率下运行。     

Sub-kHz cryogenic Yb:YAG regenerative amplifier by using a total-reflection active mirror

The first pulse operation using a total-reflection active mirror (TRAM) with a cryogenic Yb:YAG/YAG monolithic composite ceramics was demonstrated in a regenerative amplifier scheme. More than 5.0 mJ of output pulse energy was obtained for repetition rates between 10 and 450 Hz. A high energy fluence of 3.5 J/cm² on the active media was realized by separating input and output surfaces of the TRAM.     

Investigation of the Emission Cross-sections and the Spectra of (Cr4+, Yb3+): YAG Crystal

The emission and the lifetime data of Cr, Yb: YAG and Yb: YAG were reported. The effective peak stimulated-emission cross section of chromium and ytterbium-co-doped yttrium-aluminum garnets (Cr, Yb: YAG) has been determined to be 8.98 × 10-20 cm2 at room temperature. The luminescence spectrum of Cr, Yb: YAG is the same as that of Yb: YAG. The luminescence lifetime of Cr, Yb: YAG at room temperature is 0.3 ms (Yb: YAG, 1.48 ms ). The causes of the differences in the fluorescence spectra and the stimulated emission cross-section between Yb: YAG and Cr, Yb: YAG crystals were discussed. Also the potential of Cr, Yb: YAG as a self Q- switched laser crystal was discussed.     

Investigation of the Emission Cross-sections and the Spectra of (Cr~(4 ), Yb~(3 ) ): YAG Crystal

l introductionIn recent years, Cr4 --doped crystals have attracted a great deal of attention aspassive Q--,wit,h.,[l~4]. These Cr4 --dOPed crystals include Cr4 : YAG[l'21 ) Cr4 :GSGG[s], Cr4 : YSO['] etc. They have a large absorption cross section and lOwsaturable intensity at the laser wavelength. In comparison with previously usedsaturable absorbers such as dyes['] and LiF: FZ-- [6] cOlor center crystals, Cr4 -dopedcrystals are more photO--chemically and thermally stable and h…     

Polarization manipulated solid-state lasers with crystalline-orientations

The polarization states of 〈111〉-cut Yb:YAG crystal microchip lasers were investigated by pumped with the elliptically polarized pump beam from fiber-coupled laser-diode. The manipulated polarized lasers were achieved in laser-diode pumped Yb:YAG microchip laser by controlling the crystalline-orientations in 〈111〉-growth Yb:YAG crystal. Generally elliptically polarized lasers were obtained in laser-diode pumped Yb:YAG microchip lasers. However, crystalline-orientation manipulated linearly polarized laser was obtained when six different sites with different crystalline orientations were set to parallel to the major axis direction of the elliptically polarized pump beam. Six different sites in Yb:YAG crystal were separated with 30° and 90°, which were responsible for the linearly polarized laser oscillations. Circularly polarized lasers were observed when a Yb:YAG crystal was aligned to a special position between two sites responsible for linearly polarized laser oscillation. Effects of the polarization states of pump source on the laser polarization states of Yb:YAG microchip lasers and polarization direction of different polarized lasers with respect to Yb:YAG crystal rotation was addressed.     

Effect of ytterbium concentration on cw Yb:YAG microchip laser performance at ambient temperature – Part II: Theoretical modeling

A theoretical model based on a quasi-four-level system is modified to investigate the effect of Yb concentration on performance of continuous-wave Yb:YAG microchip lasers by taking into account temperature-dependent thermal population distribution, temperature-dependent emission cross-section and concentration-dependent fluorescence lifetime, thermal loading, thermal conductivity, and thermal expansion coefficient. The local temperature rise in Yb:YAG crystal caused by the absorbed pump power plays an important role in the laser performance of Yb:YAG microchip lasers working at ambient temperature without actively cooling the sample. The output wavelengths dependent on output coupling, Yb concentration, and pump power level were analyzed quantitatively. The numerical simulation of Yb:YAG microchip lasers is in good agreement with experimental data. The optimized laser operation for Yb:YAG microchip lasers is proposed by varying the thickness and output coupling for different Yb concentrations. The effect of thermal lens, thermal deformation effect, and saturated inversion population distribution inside the Yb:YAG crystal on performance of heavy-doped Yb:YAG microchip lasers are also addressed. PACS 42.55.Xi; 42.70.Hj; 42.55.Rz     

Comparison of spectroscopic properties of Yb:YAP and Yb:YAG crystals

The Yb:YAG and Yb:YAP crystals have been grown by Czochralski method. The absorption spectra and the fluorescence spectra of Yb:YAG and Yb:YAP crystals have been investigated. It is shown that the Yb:YAG crystal has better laser properties and smaller threshold power than Yb:YAP crystal. In addition, the absorption cross-section of the Yb:YAP crystal is 2.16 times of that of the Yb:YAG crystal,so laser diode pumped Yb:YAG lasing can be easily realized. Because YAP single crystal is anisotropic, it is provided with polarization characteristics.