Pulse-front-matched optical parametric amplification for sub-10-fs pulse generation tunable in the visible and near infrared

A noncollinear optical parametric amplifier is presented that generates transform-limited sub-10-fs pulses that are tunable in both the visible and the near infrared (NIR). The pulse-front-matched pump geometry realizes tilt-free signal amplification, and pulses as short as 6.1 fs can be obtained from 550 to 700 nm. The large angular dispersion of the idler specific to the group-velocity-matching interaction is effectively eliminated by a grating-telescope compensator, and 9-fs NIR pulses are also successfully obtained from 900 to 1300 nm. This is believed to be the first tunable sub-10-fs light source.     

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。     

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 intense 8-fs pulses at 400 nm

Frequency-doubled pulses from a sub-40-fs, 1-kHz Ti:sapphire amplifier system are spectrally broadened in an argon-filled hollow waveguide. Compression of the self-phase-modulated pulses is implemented with chirped mirrors and a prism pair, yielding 8-fs, 15-muJ pulses in the violet spectral range.     

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-100 femtosecond pulses from a SESAM modelocked thin disk laser

We present the first passively modelocked thin disk laser (TDL) with sub-100-fs pulse duration using the broadband sesquioxide gain material Yb:LuScO₃ and an optimized SEmiconductor Saturable Absorber Mirror (SESAM). In this proof-of-principle experiment, we obtained 5.1 W of average power at a repetition rate of 77.5 MHz and a pulse duration of 96 fs. We carefully explored and optimized the different parameters on the soliton pulse formation process for the generation of short pulses. In particular, SESAMs combining fast recovery time, high modulation depth and low nonsaturable losses proved crucial to achieve this result even though they are expected to only play a minor role in soliton modelocking. To our knowledge, these are the shortest pulses ever obtained with a modelocked TDL, reaching for the first time the sub-100-fs milestone. This result opens the door to sub-100-fs oscillators with substantially higher power levels in the near future.     

Dual-echelon single-shot femtosecond spectroscopy

A dual-echelon technique for performing real-time pumpprobe spectroscopy with sub-100-fs temporal resolution is demonstrated. In a single laser shot, measurements at 400 different temporal delays are recorded to cover a total temporal range of 10 ps in 25-fs steps. Data from a glass sample and an explosive single crystal, each irradiated with intensity above the permanent damage threshold, are presented.     

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.     

High-quality sub-100-fs optical pulse generation by fiber-optic soliton compression of gain-switched distributed-feedback laser-diode pulses in conjunction with nonlinear optical fiber loops

We report our investigations of a new and simpler femtosecond fiber-optic soliton compressor for chirp-compensated gain-switched diode-laser pulses and of pedestal suppression by a compound fiber loop mirror (CFLM) and nonlinear-optical loop mirrors (NOLM's), both of which are designed for sub-100-fs pulse generation of high quality. The soliton compressor, composed of a 21.1-m-long steplike dispersion profiled fiber, exhibited 44-fs pulses and a compression ratio of approximately 60. Pedestals of 100-fs soliton pulses were suppressed successfully (>20 dB) by the CFLM and the NOLM's. In particular, 63-fs pedestal-free sech(2) pulses were obtained by NOLM propagation.     

Electric-field reconstruction of femtosecond laser pulses from interferometric autocorrelation using an evolutionary algorithm

We present an evolutionary algorithm for reconstructing a femtosecond laser pulse from its interferometric autocorrelation trace and laser spectrum. The algorithm is optimized for the intensity and phase characterization of several-cycle optical pulses. We tested this algorithm with numerically-generated femtosecond pulses and then applied it to experimental data. In the experiment, a negatively chirped 31-fs pulse and a sub-10-fs pulse containing high-order phase distortion were characterized. Frequency-resolved optical gating measurements, performed for comparison, confirm the reliability of our technique.     

Sub-20-fs terawatt-class laser system with a mirrorless regenerative amplifier and an adaptive phase controller

We have developed an ultrabroadband regenerative amplifier with a mirrorless cavity to eliminate the limitation of bandwidth of dielectric coats on cavity mirrors. The large amount of material dispersion in the Pellin-Broca prisms that are used instead of cavity mirrors is compensated for with a hybrid technique that uses Brewster prism pairs in the regenerative amplifier and an adaptive phase controller of a liquid-crystal spatial light modulator. We obtained a 16-fs pulse width with an energy of 13 mJ, which is to our knowledge the highest energy obtained in the sub-20-fs regime by use of an adaptive phase controller.     

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.     

Generation of isolated attosecond pulses with a specific waveform two-color laser field

We theoretically propose a new method for generating intense isolated attosecond pulses during high-order harmonic generation (HHG) process by accurately controlling electron motion with a two-color laser field,which consists of an 800-nm,4-fs elliptically polarized laser field and a 1400-nm,～43-fs linearly polarized laser field.With this method,the supercontinua with a spectral width above 200 eV are obtained,which can support a ～15-as isolated pulse after phase compensation.Classical and quantum analyses explain the controlling effects well.In particular,when the pulse duration of the 800-nm laser field increases to 20-fs,sub-100-as isolated pulses can be obtained even without any phase compensation.     

Pulse characteristics of an optical parametric oscillator pumped by sub-30-fs light pulses

We obtained nearly transform-limited light pulses of 34 fs near 1.2 microm by pumping an optical parametric oscillator with a 2-mm-long KTP crystal by 26-fs pulses from a Ti:sapphire laser. The average power of the pulses that were obtained was greater than 50 mW, at an 80-MHz repetition rate. Attempts to downscale the pulse duration by decreasing the pump-pulse duration revealed remarkable limitations of the attainable pulse length for sub-30-fs pump pulses, in accordance with a recent theoretical study [J. Opt. Soc. Am. B 17, 741 (2000)].     

Optical parametric amplification of a shaped white-light continuum

Phase-locked two-color sub-40-fs double pulses in the visible are produced by noncollinear parametric amplification of white light tailored in a pulse shaper with a liquid-crystal mask. The carrier phase between the pulses is conserved during the amplification process and can be adjusted, as can the temporal separation and the center of wavelengths of the pulses.     

Generation of sub-6-fs blue pulses by frequency doubling with quasi-phase-matching gratings

We demonstrate the generation of sub-6-fs pulses centered at 405 nm by frequency doubling of 8.6-fs Ti:sapphire laser pulses. The frequency doubling is carried out in a nonlinearly chirped quasi-phase-matching grating fabricated in a lithium tantalate substrate. This device simultaneously provides frequency conversion and pulse compression of the positively prechirped fundamental pulses. The second-harmonic pulses are characterized in a cross-correlation setup, and their pulse shapes are retrieved by two iterative phase-reconstruction algorithms. The generated second-harmonic spectrum spans a bandwidth of 220 THz. To our knowledge, these are the shortest pulses ever generated in the blue spectral region.     

Two-color pump-probe ionization spectroscopy of gaseous water enhanced by preliminary impulsive Raman excitation

We use sub-10-fs pulses at 400 nm and 15-fs pulses at 800 nm to ionize water molecules and their isotopomers HDO and D₂O in a pump–probe scheme. Pulses are generated via spectral broadening of 25-fs pulses of a 1-kHz Ti:sapphire amplifier system by self-phase modulation in a noble-gas-filled hollow waveguide and subsequent compression using chirped mirrors. At this time scale vibronic excitation of the first bending mode of water in the electronic ground state by impulsive Raman scattering is possible (e.g. the fundamental bending mode of H₂O: t_vib=20 fs). The effect of this pre-excitation on the ionization rate is shown. Received: 14 May 2001 / Revised version: 24 August 2001 / Published online: 19 September 2001     

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.     

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.