Comparison of Yb-doped fiber laser with one-end and double-end pumping configuration

A high-power Ytterbium-doped fiber laser (YDFL) with homemade double clad fiber (DCF) is introduced in this paper. The output power characteristics of a linear cavity fiber laser have been studied theoretically by solving the rate equations and experimentally tested with single- and double-end-pumping configurations. When both ends of the fiber are pumped by two high-power laser diodes with a launched power of 300 W each, a maximum CW output of 444 W is obtained with a slope efficiency of 75%.     

Compact 120 TW Ti:sapphire laser system with a high gain final amplifier

A 120 TW/36 fs laser system based on Ti:sapphire chirped-pulse amplification (CPA) has been successfully established in our lab. The final four pass Ti:sapphire amplifier pumped by an energetic single-shot Nd:YAG—Nd:glass laser was designed and optimized. With 24 J/8 ns pump energy at 532 nm, 300 mJ/220 ps chirped pulse was amplified to 5.98 J in this amplifier, and a total saturated gain of 20 was achieved. The focused intensity of compressed beam could reach to 10²⁰ W/cm² with the M² of 2.0.     

Photonic generation of microwave signal using a dual-wavelength single-longitudinal-mode distributed Bragg reflector fiber laser

In this paper, a novel all-optical microwave generation technique based on a dual-wavelength single-longitudinal-mode (SLM) distributed Bragg reflector (DBR) fiber laser is proposed and demonstrated. By exploiting spatial hole burning (SHB) effect, this laser could provide stable dual-wavelength SLM operation with a wavelength separation of 0.088 nm corresponding to the microwave signal at 10.484 GHz with a 3 dB bandwidth of 28 kHz. By appropriately adjusting the pump power, dual-wavelength oscillation could be maintained at different temperatures. We have theoretically analyzed the mechanism for microwave generation of the proposed DBR laser, and the calculated microwave frequency is in good agreement with our experimental results. Furthermore, experimental observation shows both of the laser wavelengths and generated microwave signals have good stability at room temperature.     

Three-Rod Resonator for Krypton Lamp Pumped 1.8 kW Continuous-Wave Nd：YAG Laser

A three-rod series resonator cw Nd:YAG laser suitable for the industrial applications is presented. The symmetrical resonator laser has been developed and is rated at 1820-W output power with beam parameter product 24 mm.mrad. By utilizing the symmetrical resonator design, the characteristic of beam with multi-rod is not obviously decreased compared with that of a single one. The system total electro-optics efficiency of lamp pumped YAG crystal is as high as 4.0%. The main factors, which affect output power and beam quality of high power solid-state laser module, are theoretically analysed.     

Low-threshold operation of a 355-nm pumped nanosecond β-BaB2O4 optical parametric oscillator

We report the low-threshold operation of a nanosecond β-BaB₂O₄ optical parametric oscillator (OPO) pumped by the third harmonic of a Q-switched Nd:YAG laser. Using cylindrical focusing of the pump beam, a threshold pulse energy of 0.5 mJ is obtained at the signal wavelength of 560 nm, which is about sixteen times lower than that of a spherical focusing configuration. The importance of diffraction loss in the design of tightly focused OPOs is discussed in terms of a simple extension of the conventional OPO model.     

Diffractive multi-beam surface micro-processing using 10 ps laser pulses

A high repetition rate picosecond laser system is combined with a spatial light modulator (SLM) for diffractive multiple beam processing. The effect of the zero order beam is eliminated by adding a Fresnel zone lens (FZL) to defocus the un-diffracted beam at the processing plane. Chromatic dispersion, which is evident with a large bandwidth femtosecond pulses leading to the problem of distorted hole shape is eliminated due to the much narrower spectral bandwidth, 0.1 nm at 10 ps pulselength, resulting in highly uniform intensity spots, independent of diffraction angle. In addition, high-throughput processing is demonstrated by combining the high power laser output, 2.5 W at λ ≈ 1064 nm and fast repetition rate, f ≈ 20 kHz with P > 1.2 W diffracted into 25 parallel beams. This has the effect of creating an “effective” repetition rate of 500 kHz without restrictive scan speeds.     

高功率高光束质量脉冲Nd: YAG激光器

 以实现高功率、高光束质量的脉冲激光输出为目的,对非对称平-凹谐振腔的结构进行了理论分析。设计出了高功率、高光束质量非对称放置的平-凹谐振腔、双氙灯泵浦的脉冲Nd: YAG激光器。当占空比为9%时,实现输出激光平均功率近480 W,光束参数积优于12.7 mm·mrad,电光转化效率近4%,与理论分析吻合,可用芯径300 μm的光纤传输,不稳定性优于±1%。加工实验证明有较好的质量：切割材料为不锈钢,厚度为3 mm时、切割速度为0.6 m/min和厚度为1.5 mm、切割速度为1.2 m/min时,两种情况下所得切缝宽度均为250 μm,且切割上下沿光滑。     

Integral plug-in RF module in a CO2 hybrid-waveguide laser: Its performance and overall evaluation

This work describes the performance of a compact “in-house built” radio–frequency (RF)-excited CO₂ slab waveguide laser which has the innovation of having a plugged-in RF generator–amplifier module directly connected into the positive electrode of the laser head. The design circuit parameters include a matching circuit and a feed-through element as a whole. The overall laser performance takes into account the waveguide dimension (y-axis) as approximately one-tenth of the free space transverse dimension (x-axis). The optical resonator is calculated to be in the regime of the negative branch for unstable confocal resonators, having focal lengths of and with geometrical amplification of 1.108. Optical output coupling mirror was set to 9.7%. The calculated waveguide length is 37.73 cm whilst the total resonator length was adjusted to 42 cm to allow coupling losses less than 1%. The laser operational efficiency was about 12% and the output beam quality of 1.13 which is close to the ideal Gaussian beam. The optical output power was accomplished by playing with different gas compositions to have a final optimized gas proportion of 1:1:2.7:0.3 correspondingly to CO₂, N₂, He and Xe as admixture.     

Repetitive operation of a helium-free mini TEA CO2 laser

A helium-free mini TEA CO₂ laser has been operated at a repetition rate of 100 Hz wherein the gas re-circulatory loop consisting of heat exchanger and catalytic converter, mandatory for conventional repetitive operation of such lasers, have been totally dispensed with. The laser utilized inexpensive molecular gases alone that were simply flown out transversely through the inter-electrode region by an open gas flow system. The active medium was energized by making use of a spiker-sustainer excitation scheme. At this repetition rate, the laser produced an average power of 3.50 W.     

Edge-pumped, folded zig-zag Nd:YAG slab laser

 We report the design and performance of conduction-cooled, edge-pumped, folded zig-zag continuous wave Nd:YAG slab laser. The Nd:YAG slab is pumped with waveguide coupled laser diode bars. The coupling efficiency of waveguide to laser diode radiation is 97%. In a folded zig-zag resonator, a maximum output power of 37 W in multimode operation is achieved for an incident pump power of nearly 180 W on the Nd:YAG slab. This corresponds to an optical-to-optical conversion efficiency of 20% and slope efficiency of 32%. We obtained more than 10 W of output power with the beam quality factors in the width dimension and in the thickness dimension equal to 8.     

Beam quality considerations of high power Nd:YAG lasers

High power Nd:YAG lasers with fiber optic beam delivery have introduced new capabilities for material processing applications. Here, we present the stable resonator design for high power Nd:YAG lasers to optimize beam quality for fiber optic transmission. Dependence of beam parameters on position and dioptric power of thermal lens has been investigated and optimized to achieve efficient fiber optic beam delivery. With the optimum resonator configuration, an efficient fiber optic beam delivery over the entire operating range of input power has been achieved. The results of stable resonator design with good beam quality and output power have been presented.     

Experimental study on tandem pumped fiber amplifier

We present the experimental results of a 1083 nm fiber amplifier tandem pumped by 1030 nm fiber laser. The output characteristics of the tandem pumped amplifier with cladding-pump and core-pump schemes are both investigated. The 1083 nm signal laser has not been efficiently amplified when cladding-pumped by 1030 nm laser for the weak absorption of the gain fiber. The core-pump scheme works well with the amplifier. The output properties with different gain fiber length are experimentally investigated. The maximum output power is 2.4 W with power conversion efficiency of 60%.     

30-W Yb<Superscript>3+</Superscript>-pulsed fiber laser with wavelength tuning

We have investigated various pulsed operation regimes of a diode-pumped Yb³⁺-doped fiber laser with both an acoustooptic filter and a shutter inside the resonator. To imbed the polarization-sensitive acoustooptic-tunable spectral filter into the polarization-nonmaintaining resonator, based on an “isotropic” single-mode fiber without “polarization’ losses, we have used a CaCO₃ single-crystal nondispersive thermostable polarization splitter. Stable smooth bell-shaped laser pulses were obtained in the Q-switch generation regime across the entire wavelength tuning band. Their duration depended on the resonator travel time and their repetition rate was determined exclusively by the outer high-frequency generator controlling the acoustooptic shutter. A pulsed laser radiation tuning bandwidth of more than 20-nm at a repetition rate band of 10–100 kHz was observed in the amplification band of the Yb³⁺-doped fiber. A stable average power of 30 W of the pulsed 70-ns 100-kHz laser radiation in a near Gaussian beam was reached by means of the two-stage amplifier based on Yb³⁺-doped fibers with an enlarged mode field diameter (14 μm). The amplifier was pumped by λ = 975 nm CW multimode laser diodes with a maximum average power of 42 W.     

高功率高光束质量脉冲Nd: YAG激光器

以实现高功率、高光束质量的脉冲激光输出为目的,对非对称平-凹谐振腔的结构进行了理论分析。设计出了高功率、高光束质量非对称放置的平-凹谐振腔、双氙灯泵浦的脉冲Nd: YAG激光器。当占空比为9%时,实现输出激光平均功率近480 W,光束参数积优于12.7 mm·mrad,电光转化效率近4%,与理论分析吻合,可用芯径300 μm的光纤传输,不稳定性优于±1%。加工实验证明有较好的质量：切割材料为不锈钢,厚度为3 mm时、切割速度为0.6 m/min和厚度为1.5 mm、切割速度为1.2 m/min时,两种情况下所得切缝宽度均为250 μm,且切割上下沿光滑。     

Mode competition in acousto-optically Q-switched planar waveguide lasers

Multi-mode rate equations have been developed to investigate mode competition in high-power acousto-optically Q-switched planar waveguide lasers. The mode competition arises from coupling effects and temporal losses in the transform between guided modes and free-space propagation. Pulse-to-pulse instability and temporal beam distortions are enlarged by mode competition when the laser works in the multi-mode regime. The influence of parasitic oscillation is also discussed. A Nd:YAG planar waveguide laser has been established with a folded hybrid/unstable resonator. A maximum average power of 83 W with a beam propagation factor is obtained. The theoretical simulation agrees well with the experimental observation.     

Efficient Raman frequency conversion of high‐power fiber lasers in diamond

We report high‐power frequency conversion of a Yb‐doped fiber laser using a double‐pass pumped external‐cavity diamond Raman oscillator. Pumping with circular polarization is shown to be efficient while facilitating high‐power optical isolation between the pump and Raman laser. We achieved continuous‐wave average power of 154 W with a conversion efficiency of 50.5% limited by backward‐amplified light in the fiber laser. In order to prove further scalability, we achieved a maximum steady‐state Raman‐shifted output of 381 W with 61% conversion efficiency and excellent beam quality using 10 ms pump pulses, approximately a thousand times longer than the transient thermal time‐constant. No power saturation or degradation in beam quality is observed. The results challenge the present understanding of heat deposition in Raman crystals and foreshadow prospects for reduced thermal effects in diamond than originally anticipated. We also report the first experimental evidence for stimulated Brillouin scattering in diamond.

     

四棒串接连续灯泵浦Nd:YAG大功率激光器

 报道了一种符合工业应用的四棒谐振腔连续Nd:YAG激光器。实验中采用对称放置方式四棒串接谐振腔得到2 105 W的平均功率输出，光束参数积24 mm·mrad，系统总光电转换效率达到3.5%。还对影响激光器工作的因素进行了理论分析。     

High repetition rate mid-infrared laser source

An efficient, high-power mid-infrared laser source based on ZnGeP₂ (ZGP) optical parametric oscillator (OPO) is presented. Using a Q-switched Ho:YAG laser as the pump source a total output power of 10.6 W was obtained in the 3–5 μm band at 10 kHz and 8.5 W at 20 kHz. The Ho:YAG laser was pumped by two diode-pumped polarization coupled Tm:YLF lasers. Optical-to-optical efficiency achieved is >8.8% (laser-diode 792 nm to mid-IR 3–5 μm). With a commercial PtSi infrared camera (256×256 pixel focal plane array, 24 μm pitch) the pointing stability of Ho pump, signal and idler beam was measured to be better than 30 μrad. Whilst propagating the OPO beams over 100 m, little absorption for the idler beam was observed, resulting in a significant higher peak-to-peak value of ±22%, whereas the peak-to-peak stability of the signal pulses remained unchanged (±13%). To cite this article: M. Schellhorn et al., C. R. Physique 8 (2007).     

Electronic stopping power of polymers for heavy ions in the ion energy domain of LSS theory

LSS based computed electronic stopping power values have been compared with the corresponding measured values in polymers for heavy ions with Z = 5–29, in the reduced ion velocity region, v_red ≤ 1. Except for limited v_red  0.6–0.85, the formulation generally shows significantly large deviations with the measured values. The ζ factor, which was approximated to be Z₁^1/6, involved in LSS theory has been suitably modified in the light of the available experimental stopping power data. The calculated stopping power values after incorporating modified ζ in LSS formula have been found to be in close agreement with measured values in various polymers in the reduced ion velocity range 0.35 ≤ v_red ≤ 1.0.     

High spatial intensity 10 W-CuBr laser with hydrogen additives

High beam quality output has been demonstrated from a single medium-scale (2 cm dia. × 50 cm) CuBr laser with hydrogen additives. The addition of hydrogen leads to beam divergence reduction and laser power lift-up finally yielding 5-fold increase in laser power spatial intensity compared with the case of no hydrogen added. With a simple positive-branch unstable resonator practical (pulse-average) divergence of 80 rad is achieved. The easy-feasible sealed-off version of CuBr laser makes it an attractive source for many high-quality laser beam applications.