Vacuum ultraviolet pulses of 11 fs from fifth-harmonic generation of a Ti:sapphire laser

We demonstrate that in a short Ar cell, generation of the fifth harmonic from 12 fs pulses at 810 nm directly results in ultrashort vacuum UV pulses at 162 nm. They have a spectral width of approximately 5 nm and a duration of 11+/-1 fs (1.4 times the transform limit), as measured by cross correlation with the fundamental pulses. Their energy (estimated to 4 nJ) turned out to be sufficient for use as a pump in time-resolved experiments.     

Efficient generation of terahertz pulses in lithium niobate crystal with integrated matching prism

We present results of experimental studies of Cherenkov-type generation of a terahertz (THz)-pulse during propagation of a femtosecond laser pulse in LiNbO₃ crystal with a Si-prism output coupler. Application of the Si-prism allows reducing essentially the damping of THz radiation because of shortening of the path of THz pulse in the nonlinear crystal. Results of experimental studies agree sufficiently well with theoretical calculations.     

5fs驱动激光脉冲的高次谐波选择性优化

研究了在紧聚焦实验条件下, 采用5 fs激光脉冲与氩气相互作用产生的高次谐波特性. 通过优化系统色散、气体靶气压与位置等参数, 观察到在60–73 eV波段范围内高次谐波光谱接近一个量级的增强. 进一步通过对单原子模型和传播方程的数值求解及模拟相位匹配实验参数下高次谐波的产生过程, 发现相位匹配在所观察到的实验现象中起着关键作用, 得到了理论上与实验规律一致的结果. 关键词： 极紫外激光 高次谐波 超快光谱     

Hollow-fiber compression of visible, 200 fs laser pulses to 40 fs pulse duration

We demonstrate the use of a very simple, compact, and versatile method, based on the hollow-fiber compression technique, to shorten the temporal length of visible laser pulses of 100-300 fs to pulse durations shorter than approximately 50 fs. In particular, 200 fs, frequency-doubled, Nd:glass laser pulses (527 nm) were spectrally broadened to final bandwidths as large as 25 nm by nonlinear propagation through an Ar-filled hollow fiber. A compact, dispersive, prism-pair compressor was then used to produce as short as 40 fs, 150 microJ pulses. A very satisfactory agreement between numerical simulations and measurements is found.     

钛宝石激光器9.5 fs脉冲输出中的啁啾镜色散补偿

根据钛宝石激光器的要求,实验设计了中心波长800 nm带宽200 nm的啁啾镜,在700—900 nm波长范围内提供约-60 fs²群延迟色散(group delay dispersion,GDD).采用双射频离子束溅射方法进行制备,用实验室搭建的白光干涉仪进行色散性能测试,从测试结果可以看出,制备的啁啾镜的性能和设计值符合得比较好.制备得到的非成对啁啾镜在钛宝石激光谐振腔中进行色散补偿,锁模后分别获得了12 fs和9.5 fs的激光脉冲输出.这是目前报道的使用国产啁啾镜获得的最短的 关键词： 啁啾镜 群延迟色散 色散补偿 钛宝石激光器     

High-repetition-rate 12 fs pulse amplification by a Ti:sapphire regenerative amplifier system

We demonstrate the direct generation of 12 fs pulses from a Ti:sapphire regenerative amplifier system at a 1 kHz repetition rate utilizing properly designed broadband components for chirped-pulse amplification. Optimized designs of a regenerative amplifier with a multilayer gain-narrowing compensator and an adaptive dispersion compensator with a spatial light modulator contribute to the shorter pulse amplification.     

Difference-frequency generation by mixing dual-wavelength pulses emitting from an electronically tuned Ti:sapphire laser

Broadly tunable difference-frequency generation (DFG) in AgGaS₂ was achieved by mixing dual-wavelength oscillating pulses from an electronically tuned Ti:sapphire laser with a two-frequency-driven acousto-optic device. Continuous tuning from 6.5 to 8.5 μm was achieved by simultaneous dual-wavelength-tuned DFG without crystal rotation. In the dual-pulse oscillation, the shorter and longer wavelength pulses were tuned from 700 to 775 nm and from 763 to 880 nm, respectively, while keeping the phase-matching relationship for DFG. When crystal rotation was adopted, however, the tunable output range was extended from 5.3 to 12 μm by tuning the longer wavelength pump pulse, while the shorter wavelength pulse was fixed. Received: 18 November 1998 / Revised version: 5 February 1999 / Published online: 26 May 1999     

Multistep third-harmonic generation of femtosecond laser pulses in periodically-poled and chirped-periodically-poled lithium niobate

Simultaneous generation of the second and third harmonics in periodically-poled and chirped-periodically-poled lithium niobate (PPLN and CPPLN) is studied numerically taking into account mismatches and dispersions of the group velocities of interacting laser pulses. It is shown that CPPLN frequency converters can be successfully used for creating multicolor short laser pulses.     

Waveguides in lithium niobate fabricated by focused ultrashort laser pulses

We report on investigations of the bulk microstructuring of lithium niobate crystals with intense femtosecond laser pulses. In different crystal cuts, optical waveguides were produced whose properties depend strongly on the processing parameters. To explore the origin of the refractive index changes, we subjected the crystals to different conditions (like temperature, illumination, etc.) while monitoring the waveguide output. This way several mechanisms for the change in refractive index could be singled out. These include the photorefractive effect, inhomogeneous ion concentrations and stress in the crystalline lattice. As an application, we demonstrate frequency doubling of 1064 nm laser radiation in a microstructured phase-matched waveguide.     

Ablation induced by single-and multiple-femtosecond laser pulses in lithium niobate

We present results on the surface-damage threshold of lithium niobate after single-and multiple-femtosecond laser pulse irradiation at the pulse duration of 80 fs, with a 800-nm wavelength, and a repetition rate of 1 kHz. The surface-ablation threshold was found to decrease significantly with an increase in the pulse number applied to the surface until reaching an almost constant level due to an incubation effect, which is attributed to the laser-induced defect formation. The threshold of lithium niobate under a single shot is found to be 2.82 J/cm², and the threshold fluence for an infinite number of pulses F _th(∞) converges to a common value of 0.52 ± 0.06 J/cm² for N > 80. The results have the potential for application in laser micromachining and the fabrication of related optical devices and applications in frequency conversion by a femtosecond laser in lithium niobate.     

Sub-6-fs pulses from a SESAM-assisted Kerr-lens modelocked Ti:sapphire laser: at the frontiers of ultrashort pulse generation

Well-characterized pulses in the two-optical-cycle regime are demonstrated using a Kerr-lens modelocked (KLM) Ti:sapphire laser and phase-sensitive diagnostics. The oscillator employs double-chirped mirrors (DCMs) for dispersion compensation, spectral shaping via wavelength-dependent output coupling, and a semiconductor saturable absorber mirror (SESAM) for reliable operation at up to 300 mW output power and with a repetition rate of ~90 MHz.In the discussion of the experimental results we emphasize how spectral shaping can be used most efficiently in the generation of the shortest possible pulse supported by the Ti:sapphire gain bandwidth.     

The generation of intense, transform-limited laser pulses with tunable duration from 6 to 30 fs in a differentially pumped hollow fibre

We have investigated experimentally the energy transmission and spectral broadening of 30-fs, 700-μJ laser pulses in a neon-filled, 250-μm inner diameter hollow fibre. We implement a differentially pumped fibre, where a vacuum is maintained at the fibre entrance, and compare this to a statically filled fibre. We obtain significantly higher transmission and increased spectral broadening in the differentially pumped case due to a reduction of ionisation defocusing at the fibre entrance. This arrangement provides a method for the generation of near-transform- limited pulses with smoothly varying pulse duration whilst maintaining constant pulse energy, by simple adjustment of the gas pressure. Compression of ∼450-μJ pulses from the differentially pumped fibre to a duration of 6.5 fs has been achieved for pulses with spectra spanning 650–900 nm, by use of negatively dispersive chirped mirrors. PACS 42.65.Re; 42.65.Jx; 42.65.-k     

Analysis of tunable picosecond pulse generation from a distributed feedback Ti：sapphire laser

A distributed feedback Ti:sapphire laser (DFTL) pumped by a 532nm Q-switched pulse is proposed for the generation of tunable picosecond pulses. With coupled rate equation model, the temporal characteristics of DFTL are obtained. The numerical solutions show that the DFTL pulse with a 50-ps pulse duration and as much as 3.SmJ pulse energy can be obtained under 40-m J, 5-ns pulse pumping. The dependence of output pulse width on the laser crystal‘s length, pumping pulse duration, and pumping rate is also discussed in detail.     

飞秒强激光在充气毛细管中产生三次谐波的效率

利用描写飞秒强激光在充气毛细管中产生三次谐波的一个理论模型讨论了三次谐波产生的信号-压强曲线.结果发现：在毛细管参量和激光参量确定的条件下，三次谐波效率受管内气压，三次谐波模式，走离效应（walk-off）和相调制效应的影响.同时，发现，得到的三次谐波效率接近实验值. 关键词： 效率 三次谐波 飞秒激光 充气毛细管     

High-contrast, high-intensity laser pulse generation using a nonlinear preamplifier in a Ti:sapphire laser system

We report a high-contrast, high-intensity Ti:sapphire chirped-pulse amplification system that incorporates a nonlinear preamplifier based on optical parametric chirped-pulse amplification (OPCPA). By cooling the Ti:sapphire crystal in the final amplifier down to 77 K, the chirped-pulses are amplified to 2.9 J at a 10 Hz repetition rate without a thermal lensing effect. Pulse compression down to 19 fs duration obtained after amplification indicates a peak power of 80 TW. With the OPCPA, the temporal contrast is significantly improved to better than 7x10(-9) in a few picoseconds interval prior to the main laser pulse.     

多脉冲序列飞秒钛宝石激光的啁啾脉冲放大

在数太瓦钛宝石啁啾脉冲放大系统中（极光Ⅱ升级装置）,对多脉冲序列的放大过程进行了详细的实验研究,获得了多脉冲序列的放大输出.每一个放大脉冲串中包含有19个独立的飞秒单脉冲,其相邻间隔为14.8 ns,对应的重复频率为67.5 MHz.脉冲串的总能量约为122 mJ,各单脉冲能量从20 mJ指数衰减至0.5 mJ,脉宽约为60fs,对应的峰值功率约为10¹¹—10¹⁰W.这种脉冲序列在产生长寿命激光等离子体、激光微加工等方面有重要应用前景.     

Widely tunable, narrow-linewidth, subnanosecond pulse generation in an electronically tuned Ti:sapphire laser

Widely tunable subnanosecond Ti:sapphire laser radiation pumped with a cw Q -switched laser-diode-pumped Nd:YAG laser has been demonstrated in a simple laser system with a configuration of variable cavity length. Laser wavelengths can be continuously tuned by adjustment of the rf of an intracavity acousto-optic tunable filter with a computer through the whole range of the laser gain. During tuning of the whole spectral range, there is no need to realign any optics in the laser, except for moving the mirror to track the change of the rf. The peak powers of the output pulses at a pump level of 300 mW are comparable with those of conventional tunable picosecond Ti:sapphire lasers at a cw pump level of almost 10 W.     

Fiber delivery of femtosecond pulses from a Ti:sapphire laser

We propose a way to deliver nanojoule-energy, 100-fs pulses at 800 nm through a few meters of standard optical fiber. Pulses from a mode-locked laser are compressed temporally, and then spectrally, to produce the desired pulses at the end of the fiber. Initial experiments agree well with calculations and demonstrate the benefits of this technique: For an energy of ~0.5 nJ , the delivered pulses are ~5 times shorter than those delivered by other techniques. The issues that must be addressed to scale the technique up to delivered pulse energies of 5 nJ are identified, and the apparatus employs only readily available components. Thus we expect it to find use in the many applications that would benefit from fiber delivery of femtosecond pulses.     

Fully efficient adiabatic frequency conversion of broadband Ti:sapphire oscillator pulses

By adiabatic difference-frequency generation in an aperiodically poled nonlinear crystal-a nonlinear optical analog of rapid adiabatic passage in a two-level atomic system-we demonstrate the conversion of a 110?nm band from an octave-spanning Ti:sapphire oscillator to the infrared, spanning 1550 to 2450?nm, with near-100% internal conversion efficiency. The experiment proves the principle of complete Landau-Zener adiabatic transfer in nonlinear optical wave mixing. Our implementation is a practical approach to the seeding of high-energy ultrabroadband optical parametric chirped pulse amplifiers.