Efficient visible femtosecond optical parametric generator and amplifier using tilted pulse-front pumping

Using pulses with tilted pulse fronts to compensate for the group-velocity mismatch in three-wave interactions, we constructed an efficient 400-nm pumped femtosecond collinear typeI phase-matched beta -barium borate optical parametric generator and amplifier. The signal and idler outputs are tunable from 470nm to 2.7 microm and have pulse widths in the range of 100170fs at a 1-kHz repetition rate. A maximum output energy of 6.5 microJ and a total conversion efficiency of more than 15% were achieved.     

All-solid-state generation of 100-kHz tunable mid-infrared 50-fs pulses in type I and type II AgGaS(2)

We report the operation of an all-solid-state system for the generation of tunable mid-infrared sub-50-fs pulses. A Ti:sapphire regenerative amplifier, pumped by 10 W of power from 532-nm, diode-pumped, frequency-doubled Nd:YVO(4) lasers, produced 4-muJ energy, sub-50-fs pulses at 800 nm with a 100-kHz repetition rate. This output was used to drive a beta-BaB(2)O(4) optical parametric amplifier followed by a difference-frequency generator based on a AgGaS(2) crystal. Continuous tuning of ultrafast pulses from 2.4m to longer than 12mum was obtained. A performance comparison of difference-frequency generation in type I and type II phase-matched AgGaS(2) is reported.     

Sub-20 fs visible pulses with 750 nJ energy from a 100 kHz noncollinear optical parametric amplifier

We demonstrate the operation of a 100 kHz noncollinear optical parametric amplifier that is pumped by just a few microjoules of 800 nm pulses with 50 fs duration. The device delivers sub-20 fs pulses tunable from 460 nm to beyond 1 microm and pulse energies up to 750 nJ when it is pumped with 7 microJ of energy. The design of the single-stage amplifier has been carefully optimized, and the design considerations are discussed.     

Generation of tunable octave-spanning mid-infrared pulses by filamentation in gas media

The continued development of femtosecond mid-infrared (IR) sources with ultrabroad spectral width is critical for probing and controlling complex molecular structural dynamics on an ultrafast timescale. We report on a sub-20 fs, coherent mid-IR source with an octave-spanning spectral bandwidth (>2000 cm(-1)) tunable from 2-8 micrometers (37.5-150 THz), with energy >0.4 μJ/pulse at 1 kHz. The mid-IR pulses are generated by four-wave mixing during the filamentation of intense 800 nm and 400 nm pulses in various gas media. Spectral tunability is achieved by the choice of gas, pressure and input 800 nm pulse energy.     

Generation of 12 fs deep-ultraviolet pulses by four-wave mixing through filamentation in neon gas

Generation of deep-ultraviolet femtosecond pulses by four-wave mixing through filamentation in neon gas was demonstrated. Fundamental (omega) and second-harmonic (2omega) pulses of 25 fs Ti:sapphire amplifier output were focused into neon gas, and 20 microJ pulses with the center wavelength of 260 nm were produced by a four-wave mixing process, 2omega+2omega-omega?3omega through an ~15 cm filament. Additionally, pulses with an energy of 2 microJ at 200 nm were generated, probably by a cascaded process, 3omega+2omega-omega?4omega. The 260 nm pulses were compressed by a grating-based compressor and characterized by a dispersion-free transient grating frequency-resolved optical gating. The estimated pulse width was 12 fs.     

Tunable ultraviolet source from fifth and seventh harmonic generated by mid-infrared pulses filamentation in air

The seventh harmonic generation by tunable mid-infrared femtosecond pulses filamentation in air is observed first time. Pumped by a focused mid-infrared pulses, which pulse duration is ～50 fs and wavelength is tunable from 1300 to 2000 nm, the tunable region of the fifth and seventh harmonic generation can cover the near ultraviolet region from 180 to 400 nm.     

300 microJ noncollinear optical parametric amplifier in the visible at 1 kHz repetition rate

We demonstrate an order-of-magnitude energy scaling of a white-light seeded noncollinear optical parametric amplifier in the visible. The generated pulses, tunable between 520 and 650 nm with sub-25-fs duration, had energies up to 310 microJ with 20% blue-pump-to-signal energy conversion efficiency at 540 nm. This new ultrafast source will make possible numerous extreme nonlinear optics applications. As a first application, we demonstrate the generation of tunable vacuum ultraviolet pulses.     

Mid-infrared difference-frequency generation of ultrashort pulses tunable between 3.2 and 4.8 microm from a compact fiber source

We report single-pass difference-frequency generation of mid-infrared femtosecond pulses tunable in the 3.2-4.8 microm range from a two-branch mode-locked erbium-doped fiber source. Average power levels of up to 1.1 mW at a repetition rate of 82 MHz are obtained in the mid infrared. This is achieved via nonlinear mixing of 170 mW, 65 fs pump pulses at a fixed wavelength of 1.58 microm, with 11.5 mW, 40 fs pulses tunable in the near-infrared range between 1.05 and 1.18 microm. These values indicate that the tunable near-infrared input component is downconverted with a quantum efficiency that exceeds 30%.     

基于单个BBO晶体载波包络相位稳定的高效率光参量放大器

基于单个BBO非线性晶体,利用非共线光参量放大技术,研究了载波包络相位稳定的高效率可调谐近红外脉冲产生.以载波包络相位稳定的飞秒激光放大系统产生的白光作为种子光,注入一个二类匹配的二级光参量放大器,在1350 nm波段获得抽运-信号光34%的转换效率.利用f—2f光谱相干测量技术,放大脉冲载波包络相位的抖动30 min内小于137 mrad.该方法提供了一种简单高效的载波包络相位稳定的红外脉冲产生技术.     

Sub-20-fs pulses tunable across the visible from a blue-pumped single-pass noncollinear parametric converter

Femtosecond pulses with center wavelengths between 470 and 750 nm are generated in a single-stage type I BBO optical parametric amplifier pumped by a frequency-doubled 1-kHz Ti:sapphire amplifier. A high-quality white-light continuum is used as the seed. Pulse durations as short as 16 fs and pulse energies of as much as 11 microJ are observed. The quantum efficiency is ~25% for both 7- and 40-microJ pump pulses. This unique combination of ultrashort pulse duration and high conversion is made possible by noncollinear phase matching that permits a sufficiently large amplification bandwidth. Simultaneously the group velocities of the signal and the idler are effectively matched. As a result widely tunable sub-20-fs pulses can be generated in a nonlinear crystal as thick as 2 mm.     

Formation mechanisms of uniform arrays of periodic nanoparticles and nanoripples on 6H-SiC crystal surface induced by femtosecond laser ablation

Uniform arrays of periodic nanoparticles with 80-nm period are formed on 6H-SiC crystal irradiated by circularly polarized 400-nm femtosecond laser pulses. In order to understand the formation mechanism, the morphology evolvement as a function of laser pulse energy and number is studied. Periodic nanoripples are also formed on the sample surface irradiated by linearly polarized 400-, 510- and 800-nm femtosecond laser pulses. All these results support well the mechanism that second-harmonic generation plays an important role in the formation of periodic nanostructures. PACS 79.20.Ds; 42.62.Cf; 61.80.Ba; 81.05.Cy; 78.30.Am     

Generation of narrowband subpicosecond mid-infrared pulses via difference frequency mixing of chirped near-infrared pulses

The widely used setup for the generation of femtosecond infrared (IR) pulses based on parametric amplifiers (OPAs) and difference frequency mixing (DFM) is extended to produce tunable narrowband mid-IR pulses. The insertion of pairs of silicon prisms after the OPA induces adjustable chirp, which leads to the generation of narrowband pulses in the DFM stage. Rapid tunability of the mid-IR wavelength via a computer-controllable actuator can be achieved in a range of approximately 200 cm(-1) at a bandwidth of the IR-pulses between approximately 15 and approximately 50 cm(-1) and pulse energies up to 0.4 microJ. The narrowband mid-IR pulses are well suited for 2D IR spectroscopy.     

Stretcher-free high energy nonlinear amplification of femtosecond pulses in rod-type fibers

We report on the study of direct amplification of femtosecond pulses in an 80 mum core diameter microstructured Yb-doped rod-type fiber amplifier in the nonlinear regime. The system includes a compact single grating compressor for the compensation of the small dispersion in the amplifier. With a 1250 line/mm (l/mm) grating-based compressor, pulses as short as 49 fs with 870 nJ pulse energy and 12 MW peak power are obtained. Alternatively, the use of a 1740 l/mm grating allows the production of higher quality pulses of 70 fs, 1.25 microJ pulse energy, and 16 MW peak power.     

Parametric amplification of few-cycle carrier-envelope phase-stable pulses at 2.1 microm

We demonstrate an optical parametric chirped-pulse amplifier producing infrared 20 fs (3-optical-cycle) pulses with a stable carrier-envelope phase. The amplifier is seeded with self-phase-stabilized pulses obtained by optical rectification of the output of an ultrabroadband Ti:sapphire oscillator. Energies of -80 microJ with a well-suppressed background of parametric superfluorescence and up to 400 microJ with a superfluorescence background are obtained from a two-stage parametric amplifier based on periodically poled LiNbO3 and LiTaO3 crystals. The parametric amplifier is pumped by an optically synchronized 1 kHz, 30 ps, 1053 nm Nd:YLF amplifier seeded by the same Ti:sapphire oscillator.     

Mid-infrared pulses generated from the mixing output of an amplified, dual-wavelength Ti:sapphire system

We demonstrate the generation of femtosecond mid-infrared pulses by direct difference-frequency mixing in a AgGaS(2) crystal of two intense pulses from a dual-wavelength oscillator that have been simultaneously amplified in a single regenerative amplifier. A pulse energy of as much as 1.6 muJ was achieved at wavelengths of 9-11 mum.     

用于宽带啁啾脉冲光参量放大系统精确同步的新方法

基于非共线光参量放大,以波长800 nm飞秒激光的倍频光为抽运光,以激光二极管640 nm连续波激光为信号光,产生了与800 nm飞秒激光精确同步的无直流本底的1064 nm脉冲光。实验结果显示该1064 nm的光脉冲在脉冲能量和空间光束质量上均可作为1064 nm波长脉冲放大器的种子光。仅通过一级简单紧凑的非共线参量放大就可实现光周期量级的光参量啁啾脉冲放大系统的抽运激光和种子光的精确同步。     

Generation of 14.8-fs pulses in a spatially dispersed amplifier

We demonstrate amplification and compression of 110-nm broad spectra in a spatially dispersed amplifier for what is believed to be the first time and generate 14.8-fs pulses with 450 microJ of energy at a repetition rate of 1 kHz. The amplifier concept is scalable in energy and allows for spectral shaping, which was demonstrated and compared with numerical simulations and showed excellent agreement.     

基于氧化镁晶体中级联四波混频过程的紫外飞秒光脉冲产生

紫外波段飞秒激光脉冲是研究超快化学和超快物理相关过程的重要工具,实现波长可调谐的宽带紫外飞秒光脉冲将有助于推动超快动力学及相关领域的研究.本文报道了以两束400 nm的飞秒光脉冲作为级联四波混频的抽运源,在氧化镁晶体中产生9阶频率上转换和5阶频率下转换边带信号的实验结果.边带波长范围从350 nm到450 nm连续可调谐,这些边带信号的发散角和波长与级联四波混频理论预测结果吻合.紫外边带相对于入射光的整体转化效率约为1.2%.同时,高阶边带的光谱形状呈现高斯型,其谱宽理论上支持傅里叶转换极限脉宽为20—50 fs.本文展示了一种高效产生波长可连续调谐的紫外飞秒光脉冲的便捷方法,为基于紫外超短脉冲的相关研究提供了有效工具.     

Programmable amplitude- and phase-modulated femtosecond laser pulses in the mid-infrared

We present a scheme to produce programmable phase- and amplitude-modulated femtosecond laser pulses in the mid-infrared regime of 3-10mum by difference frequency mixing. The 80-fs signal output of an optical parametric amplifier is shaped with a liquid-crystal mask and mixed in an AgGaS(2) crystal with a temporally stretched idler pulse. Without changing the mechanical alignment, we produce programmable amplitude modulations and chirped pulses at lambda=3mum with energy as high has thas 1muJ . This scheme, further, allows the generation of controllable pulse sequences. The results are in good agreement with theoretical simulations.     

Half-cycle pulses in the mid-infrared from a two-color laser-induced filament

Four-wave mixing (FWM) of femtosecond near-infrared laser pulses and its second harmonic in the filamentation regime is shown to give rise to ultrashort field waveforms in the mid-infrared with pulse widths as short as a half of the field cycle and produce ultrabroadband supercontinuum spectra stretching from the mid-IR to the terahertz region. Generation of 7-fs pulses centered at 4.35 μm is demonstrated by a two-color filamentation experiment, where the 25-fs, 800-nm fundamental-wavelength output of a Ti: Sapphire laser is mixed with its second harmonic. The spectral and temporal properties of the mid-IR waveforms, as well as their emission pattern, are consistent with the FWM scenario of frequency conversion generalized to include the Kerr effect and ionization-induced refractive-index modulation.