Fiber-laser-based femtosecond parametric generator in bulk periodically poled LiNbO(3)

A diode-pumped system for optical parametric generation of wavelength-tunable femtosecond pulses is demonstrated. It comprises an Er-doped fiber mode-locked laser, a fiber chirped-pulse amplifier, and a bulk periodically poled LiNbO(3) (PPLN) optical parametric generator. The parametric generator is pumped at 777 nm with frequency-doubled microjoule pulses from the fiber amplifier and produces 300-fs pulses tunable from 1 to 3microm with output energies up to ~200 nJ. Use of a PPLN nonlinear crystal substantially reduces the pump energies required for efficient parametric generation. Saturated single-pass parametric energy conversion of 38% (internal) has been achieved with only 220 nJ of pump inside the crystal. A parametric generation threshold of 54 nJ is observed, and efficient parametric conversion is obtained with repetition rates up to 200 kHz.     

Multi-millijoule, nonlinear preamplifier for high intensity femtosecond Yb:YAG chirped-pulse amplification lasers at 1030 nm

We report the highest energy broadband laser pulses at a center wavelength of 1030 nm based on optical parametric chirped-pulse amplification (OPCPA). We have demonstrated amplification of 1030 nm femtosecond laser pulses from a broadband Yb oscillator to over 6.5 mJ with a total gain of greater than 10⁷ achieved in a single pass through only 56 mm of gain material at a 10 Hz repetition rate. The amplified spectral bandwidth of 10.8 nm affords recompression to a 230 fs pulse duration following amplification. As an alternative to the regenerative amplifier (RA) this system is one of the more promising candidates for realizing compact, high intensity, direct diode-pumped, high repetition rate femtosecond Yb:YAG chirped-pulse amplification (CPA) in laser systems.     

高功率,红光至中红外可调谐腔内和频光学参量振荡器

本文利用高重复频率,高平均功率大模场面积飞秒光纤激光器作为同步抽运源,抽运以多周期极化掺氧化镁铌酸锂为非线性晶体的单共振光学参量振荡器,获得了高功率可调谐红光至中红外光,信号光调谐范围为1450—2200 nm,闲频光调谐范围为2250—4000 nm,在2 W的抽运功率下,信号光输出波长为1502 nm时获得最大输出功率374 mW,转换效率为18.7%,脉冲宽度为144 fs,此时中红外输出中心波长为3.4μm,平均功率为166 mW.再利用BBO晶体对信号光进行腔内和频,获得和频光输出波长调谐范围为610—668 nm,在4.1 W抽运的情况下,最高平均功率为615 nm处的694 mW,转换效率达16.9%.     

Synchronously pumped mid-infrared optical parametric oscillator with an output power exceeding 1?W at 4.5?��m

The generation of tunable mid-infrared picosecond laser radiation in a synchronously pumped optical parametric oscillator (OPO) based on periodically poled lithium niobate (PPLN) is reported. Numerical calculations were used to optimize the crystal length in order to balance the parametric gain and the absorption losses in the high-absorption regime of lithium niobate. Due to the numerical results, the system was systematically optimized for the mid-infrared output power. An output power of 1.1?W at 4.5???m and of more than 3?W at 3???m were achieved for 6-ps-long pulses with a repetition rate of 160?MHz and an M²<2.     

采用环形再生腔结构的飞秒激光啁啾脉冲放大研究

采用环形再生腔结构的啁啾脉冲放大技术方案, 在重复频率100 Hz,单脉冲能量33.1 mJ的532 nm激光抽运下, 从钛宝石激光中获得了单脉冲能量9.84 mJ的放大输出, 对应的斜效率达33.1%.在重复频率10 Hz的情况下, 同样获得了单脉冲能量为9.64 mJ, 对应斜效率达36.8%的高效率放大结果. 通过色散补偿压缩该啁啾激光脉冲后的单脉冲能量为6.36 mJ, 脉冲宽度为59.7 fs. 测量结果表明典型的能量不稳定度为1.85%. 关键词： 啁啾脉冲放大 再生放大 飞秒激光 环形腔     

Broadband difference frequency mixing between visible and near-infrared pulses for few-cycle pulse generation with stable carrier-envelope phase

Difference frequency generation between broadband visible noncollinear optical parametric amplifier (NOPA) pulses and the fundamental pump laser pulses allows the generation of ultrashort infrared pulses with passively stabilized carrier-envelope phase. A simple prism compressor for the visible NOPA pulses is sufficient to generate few-cycle pulses in the infrared and no additional compression is needed. We theoretically investigate the concept, explain the principles, and demonstrate it for high repetition rate, long pulse durations, and various wavelengths by applying it to a Ti:sapphire and an Yb:KYW-based laser systems. For the latter sub-15 fs phase stable pulses around 1.8 μm with an energy of 100 nJ are obtained at 100 kHz repetition rate.     

光纤激光泵浦MgO:PPLN高功率中波红外光参量振荡器

为实现高效率、高功率中波红外激光输出,研制基于MgO:PPLN晶体的中波红外光参量振荡器（OPO）,泵浦源为基于主振荡功率放大（MOPA）结构的线偏振掺Yb光纤激光器（YDFL）。实验结果表明:YDFL可实现最高79.1 W的1064.1 nm脉冲线偏振激光输出;在YDFL泵浦下,通过优化输出镜曲率半径和泵浦光束腰直径,该OPO实现最高9.15 W的3.754 μm脉冲激光输出,光光转换效率为11.57%,重复频率为300 kHz,脉冲宽度约为110 ns。     

Generation of high-contrast and high-intensity laser pulses using an OPCPA preamplifier in a double CPA, Ti:sapphire laser system

We demonstrate a high-contrast, high-intensity double chirped-pulse amplification (CPA) Ti:sapphire laser system using an optical parametric chirped-pulse (OPCPA) pre- amplifier. By injecting cleaned microjoule seed pulses into the OPCPA, a temporal contrast greater than 10¹⁰ within picosecond times before the main femtosecond pulse is demonstrated with an output pulse energy of 1.7 J and a pulse duration of 30 fs, corresponding to a peak power of 60 TW at a 10 Hz repetition rate. This system uses a cryogenically-cooled Ti:sapphire final amplifier and generates focused peak intensities in excess of 10²⁰ W/cm².     

1.5 mJ, 6.4 fs parametric chirped-pulse amplification system at 1 kHz

We demonstrate an optical parametric chirped-pulse amplification (OPCPA) system with the pulse energy of 1.5 mJ at a 1 kHz repetition rate. The newly developed 100 ps Ti:sapphire pump laser system, which was optically synchronized with OPCPA seed pulses, delivered 10 mJ, 400 nm pump pulses. After three-stage parametric amplification, recompression of the amplifier output from 45 ps to 6.4 fs was performed. The pulse width of 6.4 fs is, to our knowledge, the shortest ever obtained by OPCPA, and the average power of 1.5 W (1.5 mJ, 1 kHz) is believed to be the highest among few-cycle OPCPA systems.     

高激光损伤阈值Ge-As-S硫系玻璃光纤及中红外超连续谱产生

测量了Ge-As-S系列硫系玻璃在中红外波段的飞秒激光损伤阈值,研究了它与玻璃化学组成的关系.基于优化的玻璃组成,采用棒管法制备了芯径为15μm的阶跃折射率非线性光纤.采用飞秒脉冲抽运光纤,研究了光纤中超连续谱(supercontinuum,SC)的产生特性.在研究的Ge-As-S硫系玻璃中,具有化学计量配比的Ge0.25As0.1S0.65玻璃显示出最高的激光损伤阈值.以该玻璃作为纤芯材料、以与其相匹配的Ge0.26As0.08S0.66玻璃作为包层材料制备的光纤的数值孔径约为0.24,背景损耗<2 dB/m.采用4.8μm的飞秒激光抽运长度为10 cm的光纤,获得了覆盖2.5-7.5μm的SC.这些结果表明,Ge-As-S硫系玻璃光纤是一种有潜力的中红外高亮度宽带SC产生的非线性介质.     

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 $\sim $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.     

A ring ZnGeP2 optical parametric oscillator pumped by a Ho:LuAG laser

We have demonstrated that we believe to be the first ring ZnGeP₂ (ZGP) optical parametric oscillator (OPO) pumped by a pulsed Ho:LuAG laser. The maximum output power of the ring ZGP OPO laser was 5.51 W at 13.1 W incident Ho pump power, corresponding to a slope efficiency of 59.0 %. The ZGP OPO laser produced 14 ns mid-infrared pulses in the 3.72–4.01 and 4.37–4.75 μm spectral regions simultaneously. In addition, the continuous wave Ho:LuAG laser generated 26.5 W of linearly output at 2,094.4 nm at the absorbed Tm pump power of 49.9 W.     

Broadband femtosecond OPCPA system driven by the single-shot narrow-band iodine photodissociation laser SOFIA

A two-stage optical parametric amplifier driven by a frequency-tripled beam from the high-energy iodine laser system SOFIA was built. This single-shot Optical Parametric Chirped Pulse-Amplification facility (OPCPA) and the system synchronizing the pump and signal pulses are described in detail. The chirped seed pulse of a Ti:sapphire oscillator running at the central wavelength of 800?nm is amplified in the two-stage (LBO and KDP) optical parametric amplifier over 10⁸ times. The amplified spectral bandwidth of 68?nm corresponds to the pulse duration of 14?fs when a transform-limited pulse is assumed. This implies a compressed pulse of TW power. Systematic gain measurements reveal a good match with the theoretical predictions. Signal and idler beam fluence profiles are presented. The suitability of the iodine photo-dissociation laser as a pump source for the OPCPA technique is thus proved for the first time experimentally. A distinctive feature of the iodine laser is its very narrow gain bandwidth (<0.1?cm^?1) and, therefore, the conventional chirped-pulse amplification technique does not lead to pulse durations at the femtosecond level.     

70-W average-power doubly resonant optical parametric oscillator at 2 μm with single KTP

We have demonstrated a high-power intra-cavity-pumped doubly resonant optical parametric oscillator (OPO) at 2 μm with single-type II phase-matched KTP. A linearly polarized Q-switched solid-state Nd:YAG laser was used as the intra-cavity pump source, of which the output power and beam quality were improved by cascading two laser rods for compensating the thermal birefringence as well as by placing double acoustic-optical Q-switches orthogonally, and the output power of the doubly resonant OPO was studied versus the temperature of KTP and the repetition rate of the Q-switch. The output power was insensitive to the temperature of KTP in a wide range, and 70-W average power was obtained at 2 μm with the repetition rate of 5 kHz. The stability of the OPO laser was measured to be <3.5 % root mean square at the output power of 70 W for 400 s.     

Visualization of high-order dispersion for compression of few-cycle pulses

We present a visually intuitive method for higher-order dispersion compensation based on multi-photon interpulse interference pulse scans. The dispersion values obtained from these scans are fed back as a correction to an acousto-optical programmable dispersive filter to compensate residual higher-order dispersions up to fifth order. This method is applied to the dispersion management of a non-collinear optical parametric chirped-pulse amplifier. A grism-pair stretcher is designed based on a global dispersion balance which provides a large stretching factor and supports a spectral bandwidth of up to 320 nm. It is implemented in a two-stage three-pass non-collinear optical parametric chirped-pulse amplifier and stretches 6-fs seed pulses to about 80 ps from 700 to 1,000 nm. The amplified pulses are compressed by material dispersion. Pulses of less than 10-fs duration with a pulse energy of 125 μJ are obtained at 20-kHz repetition rate.     

Narrow-band seeding of an optical parametric amplifier in the femtosecond regime

Nearly transform limited femtosecond pulses tunable between 2.56 and 3.16 m have been generated by optical parametric amplification. The single stage parametric amplifier is pumped by a tunable high power femtosecond Ti:sapphire laser system at 1 kHz repetition rate and seeded by quasi-continuous wave (cw) radiation from the Q-switched Nd:YLF laser used to pump the regenerative amplifier. The 100 fs idler pulses are shorter than the pump pulses. The mechanism of the achieved pulse compression is discussed and experimental results are compared with numerical simulations.     

Optical parametric oscillator pumped by relaxation oscillation pulses of a mechanically Q-switched Nd:YAG laser

We report the generation of mid-infrared pulsed radiation between 2.2 and 3 μm range using a singly-resonant optical parametric oscillator (SR-OPO) based on a 40-mm-long crystal of periodically-poled LiNbO₃ (PPLN) pumped by mechanically Q-switched pulses from a Nd:YAG laser, obtained by chopping the beam inside the laser resonator over a 1–10 kHz duty cycle. An appreciable reduction in pulse width as well as the number of relaxation oscillation pulses of the Nd:YAG pump laser is observed when the frequency of the Q-switch chopper is increased up to 10 kHz. Sub-nanosecond relaxation oscillation pulses of about 170–210 ns duration are generated under the width of the idler envelope varying from 4.6 to 8.55 μs. The same behavior is observed for the signal wave. A maximum extraction efficiency of 22 % is obtained for the idler, corresponding to 785 mW of output power at 10 kHz. The tuning of the signal and idler beams were performed by temperature variation of the PPLN crystal within 100–200 °C range.     

Study on broadly tunable optical parametric oscillator based on MgO-doped periodically poled LiNbO3 crystal

An efficient source of all-solid-state broadly tunable mid-infrared optical parametric oscillator based on a periodically poled MgO-doped lithium niobate is reported. The pump source is a 1064nm acousto-optically Q-switched diode-pumped Nd:YAG laser. A broadly tunable mid-infrared output from 1.56 to 1.67 μm were generated, with corresponding idler wavelengths of 3.34 to 2.93 μm by temperature tuning from 40 to 200°C. When the average pump power is 1.61 W with about 70 ns pulse duration operating at a repetition rate of 10 kHz, the maximum signal output power of the PPMgLN-OPO is about 211 mW at 1631 nm.     

Highly efficient optical parametric chirped-pulse amplification based on BiB3O6 and β-BaB2O4 crystals at low pump intensity

We report a very high signal gain of 1.13 × 10⁷ at a low pump intensity of 260 MW/cm² in a two-stage optical parametric chirped-pulse amplifier (OPCPA), which is used as a pre-amplifier for a short-pulse front-end Nd: glass high-energy laser system. A signal energy of 0.17 nJ was amplified to 2 mJ with a central wavelength of 1053 nm and a repetition rate of 10 Hz using the OPCPA with a 15 mm-long BBO crystal at optical parametric amplifier (OPA) stage 1 and a 12 mm-long BiBO crystal at OPA stage 2.     

High-energy, high-contrast, multiterawatt laser pulses by optical parametric chirped-pulse amplification

We describe a compact, reliable, high-power, and high-contrast noncollinear optical parametric chirped-pulse amplifier system. With a broadband Ti:sapphire oscillator and grating-based stretching and compression, the chirped pulses are amplified from 0.1 nJ to 122 mJ in type I beta-barium borate optical parametric chirped-pulse amplifiers with a total gain of over 10(9) at 10 Hz repetition rate. Pulse compression down to 19-fs duration achieved after amplification indicates a peak power of 3.2 TW at an average power of 0.62 W. The prepulse contrast is measured to be less than 10(-8) on picosecond time scales.