Adaptive pulse compression for transform-limited 15-fs high-energy pulse generation

We demonstrate the use of a deformable-mirror pulse shaper, combined with an evolutionary optimization algorithm, to correct high-order residual phase aberrations in a 1-mJ, 1-kHz, 15-fs laser amplifier. Frequency-resolved optical gating measurements reveal that the output pulse duration of 15.2 fs is within our measurement error of the theoretical transform limit. This technique significantly reduces the pulse duration and the temporal prepulse energy of the pulse while increasing the peak intensity by 26%. It is demonstrated, for what is believed to be the first time, that the problem of pedestals in laser amplifiers can be addressed by spectral-domain correction.     

New directions in sub-10-fs optical pulse generation

Sub-10-fs pulse generation has reached a maturity and robustness that gave rise to a rapid increase of new ultrafast applications. Some of these novel applications rely on the octave-spanning spectral width, the coherence properties, or the extremely high peak intensity of femtosecond lasers, which sets them apart from the traditional use of femtosecond lasers in ultrafast spectroscopy. In this review, we concentrate on the sub-10-fs regime and first discuss the state of the art in ultrashort pulse generation. We then report on ultrabroadband wavelength conversion schemes and dispersion control by chirped mirrors. We also review advances in pulse characterization methods, with which we can measure pulse properties with much higher accuracy than simple autocorrelation methods and which support even a bandwidth in the single-cycle regime. With the recent demonstrations of pulses with a duration of merely two optical cycles, a regime is entered where the relative phase between the carrier and the envelope of the pulse starts to play a role. We discuss methods to measure and control the carrier–envelope phase and point out applications in frequency metrology. A wealth of further novel directions and developments in femtosecond research is reviewed in this article.     

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.     

19-fs pulse generated by supercontinuum compression

Supercontinuum generation and compression in a length of 50-mm photonic crystal fiber with pulse of nanojoule energy are investigated theoretically and experimentally. Chirped mirror pair is used for dispersion compensation and pulse compression. Pulse characteristics are measured by frequency-resolved optical gating. And 19-fs pulse is generated.     

170 fs pulse generation by optical pulse compression at 308 nm

Pulses of 170 fs duration have been obtained by compression of 220–250 fs pulses of a hybrid excimer-dye laser setup.     

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.     

Optimization of high-order harmonic generation by adaptive control of a sub-10-fs pulse wave front

We present a method for the optimization of high-order harmonic generation based on wave-front correction of the driving laser beam. The technique exploits wave-front adaptive control by means of a deformable mirror, governed by an optimization procedure.     

27-fs extreme ultraviolet pulse generation by high-order harmonics

Autocorrelation measurement was demonstrated for the first time to our knowledge in the XUV region to measure the width of a high-order harmonic pulse. Two-photon ionization of rare gases was used as a nonlinear process for the autocorrelation measurement. The 27-fs pulse width that was obtained is, to our knowledge, the shortest in the XUV region.     

A novel-high energy pulse compression system: generation of multigigawatt sub-5-fs pulses

Received: 28 February 1997 / Revised version: 2 May 1997     

Visible pulse compression to 4 fs by optical parametric amplification and programmable dispersion control

Angular dispersion of pump frequencies is shown to be an efficient mechanism for bandwidth enhancement in a noncollinear optical parametric amplifier. We demonstrate the generation of a continuous, simultaneously phase-matched 250-THz parametrically amplified spectrum. The resultant visible-near-IR signal-wave pulses were compressed to a 4-fs duration by a micromachined flexible mirror. Feedback for an iterative computer-controlled dispersion compensation algorithm is based on pulse characterization by second-harmonic generation frequency-resolved optical gating.     

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。     

An 11-fs, 5-kHz optical parametric/Ti:sapphire hybrid chirped pulse amplification system

We developed a noncollinear optical parametric/Ti:sapphire hybrid chirped pulse amplification system, which consists of a two-pass optical parametric amplifier and multipass Ti:sapphire amplifiers with adaptive phase control. The use of the parametric amplifier instead of a regenerative amplifier broadened the final spectrum significantly, resulting in 11-fs pulses with a peak power of 18 GW at 5 kHz. PACS 42.55.-f; 42.65.Re; 42.65.Yj     

Ultrabroadband phase-matched optical parametric generation in the ultraviolet by use of guided waves

We present what is believed to be the first experimental demonstration of guided-wave phase-matched frequency mixing and harmonic conversion in gases. Broad-bandwidth ultrafast pulses, tunable around 270 nm, were generated from an ultrafast Ti:sapphire amplifier system using 2? + 2? - ? parametric wave mixing in a capillary waveguide. We achieved nonresonant phase matching by coupling both the fundamental and the second-harmonic light into the lowest-order mode. The output 3? pulses have an energy of >4muJ at a 1-kHz repetition rate. Simple extensions of this method can generate higher-energy 10-20-fs pulses tunable throughout the vacuum ultraviolet.     

Generation of broadly tunable sub-30-fs infrared pulses by four-wave optical parametric amplification

We report on the generation of sub-30-fs near-IR light pulses by means of broadband four-wave parametric amplification in fused silica. This is achieved by frequency downconversion of visible broadband pulses provided by a commercial blue-pumped beta-barium borate crystal-based noncollinear optical parametric amplifier. The proposed method produces the IR idler pulses with energy up to ～20 μJ and tunable in wavelength from 1 to 1.5 μm. The shortest pulse duration is 17.6 fs, measured at 1.2 μm.     

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)].     

Spatial-temporal coupling in grating-pair pulse compression system analysed by matrix optics

The coupling between spatial and temporal parameters of ultrashort pulsed beams propagating through a dispersive system is treated by a 6×6 matrix formalism. A typical grating-pair system that is commonly used in pulsed beam compression is analysed in detail. Numerical examples show that the spatial-temporal coupling becomes severe under some conditions.University School of Optics     

Time- and wavelength-interleaved optical pulse train generation based on dispersion spreading and sectional compression

A method to generate time- and wavelength-interleaved optical pulse trains based on dispersion spreading and sectional compression is proposed and demonstrated. A 4×2 GHz time- and wavelength-interleaved pulse train is generated from an input 2 GHz mode-locked pulse train. The advantages of the proposed scheme are its simplicity and robustness, since no microwave component or multiwavelength laser source is required. In addition, we demonstrate supercontinuum generation of an ultraflat 18 nm bandwidth spectrum with less than 0.5 dB fluctuation over the 3.2 nm central bandwidth.     

Spatial-temporal coupling in a grating-pair pulse compression system analysed by matrix optics

The coupling between spatial and temporal parameters of ultrashort pulsed beams propagating through a dispersive system is treated by a 6×6 matrix formalism. A typical grating-pair system which is commonly used in pulsed beam compression is analysed in detail. Numerical examples show that the spatial-temporal coupling becomes severe under some conditions.