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.     

Generation of 10 to 50 fs pulses tunable through all of the visible and the NIR

Noncollinearly phase-matched optical parametric amplifiers (NOPAs) pumped by the blue light of a frequency-doubled Ti:sapphire regenerative amplifier are a convenient source of continuously tunable ultrashort pulses in the visible and near infrared for spectroscopic experiments. We present the underlying principles, report recent improvements and describe the experiences gained from the routine use of a number of NOPAs in our laboratories. We find that the setup can easily be optimized for the given experimental requirements. Typical output-pulse energies in the visible are 5 to 10 μJ and a few μJ in the NIR from 200 μJ regenerative-amplifier pulses at 800 nm. From 460 to 700 nm, pulse lengths between 10 and 20 fs are routinely achieved, while the length increases monotonically from about 20 fs at 900 nm to just below 50 fs at 1600 nm. In all cases this corresponds to a dramatic shortening compared to the length of the pump pulses of around 100 fs. First results show that the 700 to 900 nm region can be accessed with sub-50-fs pulse lengths by use of an intermediate white-light generator in a two-stage setup. Received: 29 November 1999 / Published online: 5 July 2000     

All-fiber integrated 10 GHz repetition rate femtosecond laser source based on Raman compression of pulses generated through spectral masking of a phase-modulated diode

We report the development of a 10?GHz repetition rate all-fiber integrated femtosecond source tunable around 1.55?μm. A phase modulator and sharp spectral filter are used to convert the output of a tunable CW diode to a 10?GHz pulse train. These pulses are compressed using Raman soliton adiabatic compression in a 21?km long length of fiber to generate sub-300-fs duration pulses at a 10?GHz repetition rate. By tuning the wavelength of the diode and appropriate filtering, similar performance was achieved over a 20?nm bandwidth.     

Femtosecond ultraviolet pulses generated using noncollinear optical parametric amplification and sum frequency mixing

We demonstrate the generation of ultraviolet 33-fs pulses with a shot-to-shot energy fluctuation of less than 3% using sum frequency mixing of visible pulses of a noncollinear optical parametric amplifier with sub-40-fs pulses of a 1-kHz Ti:sapphire-amplified system. The pulses are transform-limited (ΔνΔτ=0.36) and tunable in the range from 315 nm to 355 nm with energy above 1 μJ (2.6 μJ at 330 nm). Received: 21 July 2000 / Published online: 8 November 2000     

Soliton self-frequency shift of 6-fs pulses in photonic-crystal fibers

Raman soliton phenomena in photonic crystal fibers are shown to allow efficient tunable frequency shifting of sub-10-fs laser pulses. Soliton self-frequency shift in a photonic-crystal fiber with a core diameter less than 2 μm is used to transform the spectrum of a 6-fs 2-nJ Ti: sapphire-laser pulse, dominated by a 670-nm peak, into a spectrum featuring a well-resolved intense spectral component centered at 1064 nm, which is ideally suited as a seed for Nd: YAG- and ytterbium-based laser devices.     

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.     

Ultrafast intrachain photoexcitation of polymeric semiconductors

We report on excited state dynamics in isolated poly(9,9-dioctylfluorene) chains obtained by embedding the polymer in an inert plastic matrix. Early events (<300 fs) of intrachain photophysics are detected by pump-probe spectroscopy using tunable UV 25-fs pump pulses and sub-10-fs visible probe pulses. We show that higher-lying optical states, reached by multiphoton transitions, give rise to on-chain charge separation on the ultrafast time scale. The intrachain charge pair decays geminately within 500 fs to the lowest singlet state. Characteristic time scales for internal conversion and intramolecular vibrational redistribution are also determined.     

Sub-10-fs Ti:sapphire Kerr-lens Mode Locked Oscillator

Assembly of a sub-10-fs Ti:sapphire oscillator using only optical components commercially available in catalogues is reported. It was demonstrated that stable sub-10-fs optical pulses near 800 nm can be generated from a Kerr-lens mode locked oscillator equipped with a pair of prisms to compensate group delay dispersions (GDD) in the cavity. For the GDD control in a 10fs-pulse oscillator it was concluded that chirped mirrors are not always necessary, and a pair of prisms is still available.     

Spectral analysis of high-order harmonics generated by 30-fs and sub-10-fs laser pulses

The spectral properties of harmonic radiation generated in neon by laser pulses with duration from 30 fs down to 5 fs have been investigated. In the 30-fs temporal regime we have achieved continuously tunable sub-20-nm radiation by changing the gas jet position relative to the laser beam waist. We show that the results of a one-dimensional propagation code partially including three-dimensional focusing effects are in good agreement with the experimental results. Finally, we have performed a spectral characterization of harmonic radiation in the sub-10-fs temporal regime.     

Generation of high-energy broadband femtosecond deep-ultraviolet pulses by highly nondegenerate noncollinear four-wave mixing in a thin transparent solid

We present a simple and efficient technique for the generation of ultrashort deep-ultraviolet pulses based on four-wave mixing of noncollinear laser pulses in a thin solid. Sub-30-fs pulses (Fourier-limit of 13 fs) centered at 270 nm, with energies up to 6 μJ, were obtained by mixing the fundamental and the second harmonic of a Ti:sapphire amplifier in fused silica. Temporal characterization was performed with a dispersionless self-diffraction FROG setup. Spectra as broad as 20 nm were also obtained that can in principle support sub-4-fs deep-ultraviolet pulses.The results are well described by two-dimensional numerical simulations.     

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.     

Diode-pumped Yb:Sr(3)Y(BO(3))(3) femtosecond laser

We have developed a diode-pumped Yb(3+)Sr(3)Y(BO(3))(3) (Yb:BOYS) laser generating 69-fs pulses, at a central wavelength of 1062 nm. This laser is mode locked by use of a semiconductor saturable-absorber mirror and emits 80 mW of average power at 113 MHz. This is, to our knowledge, the first mode-locked Yb:BOYS laser and the shortest duration obtained from an ytterbium laser with a crystalline host. The central wavelength can be tuned from 1051 to 1070 nm, for sub-100-fs pulses. We have also achieved an average power as high as 300 mW with pulse duration of 86 fs at 1068 nm.     

Tunable sub-100 femtosecond dye-laser pulses generated with a nanosecond pulsed pumping

Subpicosecond pulses at a fixed wavelength produced with a low-Q cavity dye laser pumped by a single, nanosecond laser (Q-switched Nd:YAG) are converted into tunable high-power sub-100 femtosecond pulses by generation, spectral selection, amplification and compression of a supercontinuum. The tunable, chirped, high-energy pulses obtained are compressed with a prism pair. Energies up to 50 J in sub-100 fs pulses were obtained in the 540 to 650 nm range using 40 mJ of the Nd: YAG-laser pumping pulses at 532 nm. The whole sub-100 fs system including the low-Q dye laser uses only one Nd:YAG laser as a pump source.     

超宽带近红外和蓝光飞秒激光脉冲产生的实验研究

增益介质中泵浦光束提供的软光阑效应对于实现克尔透镜稳定锁模及其超宽带光谱脉冲的产生具有非常重要的作用.实验上首先对半导体泵浦全固化钛宝石飞秒激光器的锁模动态特性进行了研究,在4 W绿光泵浦状态下获得了平均输出功率为570 mW、中心波长在794 nm～835 nm范围内调谐、光谱带宽最大可达135 nm的近红外光脉冲输出,其相应的时域变换极限脉冲宽度均小于10 fs.另外,将光束聚焦在超薄BBO晶体上,获得了中心波长在418 nm～429 nm之间调谐、光谱宽带时域变换极限小于15 fs的蓝光飞秒脉冲.     

Tunable visible and near-infrared pulse generator in a 5 fs regime

Transform-limited (TL) visible pulses with as short a duration as 4.7 fs with a 5 7J pulse energy have been generated for the first time from a novel noncollinear optical parametric amplifier (NOPA). Both signal-idler group-velocity matching and pulse-front matching are essential to generate coherent down-converted pulses compressible to the TL pulse with more than a 150-THz bandwidth. Tunable operation with bandwidth-limited sub-10-fs pulses in the visible (550-700 nm) and near-infrared (900-1300 nm) ranges, achieved by increasing the seed chirp, is also a remarkable property. The NOPA is believed to be on useful light source for ultrafast spectroscopy on an extremely short time-scale.     

A three-wavelength Ti:sapphire femtosecond laser for use with the multi-excited photosystem II

We have constructed a three-wavelength Ti:sapphire femtosecond laser with an independent tunable wavelength (λ₁) and two variable central wavelengths (λ₂ and λ₃) for use with the multi-excited photosystem II. Stable sub-40-fs pulses are generated. The λ₁-wavelength pulses can be tuned independently from 750 nm to 850 nm. The center wavelengths λ₂ and λ₃ can be varied from 760 nm to 840 nm. Received: 14 April 2000 / Revised version: 5 September 2000 / Published online: 27 April 2001     

Amplitude and chirp characterization of high-power laser pulses in the 5-fs regime

Frequency-resolved optical gating (FROG) based on second-harmonic generation has been demonstrated to be capable of high-fidelity measurement of the electric-field envelope and of the temporal evolution of the instantaneous carrier frequency of 0.1-TW 5-fs pulses without the need for any correction for systematic experimental errors. At a 1-kHz repetition rate, pulse energies of a few microjoules are sufficient for reliable FROG characterization of pulses with durations down to the single-cycle regime. The results obtained reveal that carefully designed hollow-fiber chirped-mirror compressors are able to deliver high-power sub-10-fs pulses with a smooth Gaussianlike leading edge that has an intensity contrast of approximately 10(-2) .     

Sum frequency generation of continuously tunable blue pulses from a two-branch femtosecond fiber source

We report on the generation of femtosecond blue pulses from a two-branch mode-locked erbium-doped fiber source. This is achieved by sum-frequency mixing in β-barium borate between the frequency doubled laser radiation at 770 nm and a tunable near-infrared component generated inside a highly nonlinear fiber. Small angle tuning of the nonlinear crystal leads to a continuously variable output wavelength in the visible band between 460 nm and 500 nm. Average power levels exceeding 1.5 mW were collected throughout the entire tuning range of our device, which delivered sub-300-fs pulses at a repetition rate of 98 MHz. These values indicate that the input near-infrared radiation is up-converted with a photon efficiency of 20%.     

High-power sub-100-fs UV pulse generation from a spectrally controlled KrF laser

High-power sub-100-fs UV pulses were generated from a KrF excimer laser by spectral control and chirped-pulse amplification. The spectral width was broadened to 1.6 nm, resulting in 72-fs, nearly transform-limited pulses. The average output powers at 1 kHz were 0.6 and 1.2 W for pulse widths of 72 and 110 fs, respectively.     

用于产生亚12fs脉冲的脉冲波前匹配的超宽带光学参量啁啾脉冲放大器

研究和建议了一种用于产生亚12fs脉冲的基于脉冲波前匹配的LBO超宽带光学参量啁啾脉冲放大器。实验结果表明LBO超宽带光学参量啁啾脉冲放大器可以输出大于60nm(FWHM)的增益光谱带宽，为了利用这种放大器产生转换限制的脉冲输出，给出了一种将超宽带光学参量啁啾脉冲放大器与脉冲波前匹配相结合的方法，这种方法等价于信号光脉冲波前无斜置的放大，克服了超宽带参量啁啾脉冲放大器中由于信号光的脉冲波前斜置而导致很难获得最短压缩脉冲输出的缺陷，从而允许产生转换限制的亚12fs脉冲。