Generation of sub-10-fs pulses from a Kerr-lens mode-locked Cr(3+):LiCAF laser oscillator by use of third-order dispersion-compensating double-chirped mirrors

Pulses as short as 9 fs at 220-mW average power and a 97-MHz repetition rate are generated from a cw Ti:sapphire-pumped Kerr-lens mode-locked Cr(3+)LiCAF laser oscillator employing broadband double-chirped mirrors for second- and third-order dispersion compensation. Fine adjustment of dispersion is accomplished with a fused-silica prism pair. The result demonstrates that Raman-induced self-frequency shifting of the pulse does not limit sub-10-fs pulse generation from colquiriite crystals.     

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.     

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)].     

Sub-10-fs pulse generation from a blue laser-diode-pumped Ti:sapphire oscillator

Pulses as short as 8.1 fs were generated from a blue laser-diode-pumped Kerr-lens mode-locked Ti:sapphire oscillator, with an average power of 27 m W and a repetition rate of 120.6 MHz. The full width at half-maximum exceeds 146 nm, benefitting from the dispersion management by a combination of a low-dispersion fused silica prism pair and a series of double-chirped mirrors. To the best of our knowledge, this is the first time to generate sub-10-fs pulses from a laser diode directly pumped Ti:sapphire oscillator.     

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.     

Generation of 0.66-TW pulses at 1 kHz by a Ti:sapphire laser

A 1-kHz, 0.66-TW Ti:sapphire laser has been developed. We obtained 21-fs, 14-mJ pulses with an extraction efficiency of 32% in the final amplifier. The dispersion through the system was successfully compensated for by insertion of a pair of prisms in a regenerative amplifier. The pulses were characterized by frequency-resolved optical gating and were in good agreement with dispersion calculated by three-dimensional ray tracing.     

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.     

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.     

Generation of 8-fs pulses at 390 nm

We demonstrated the generation of pulses as short as approximately 8 fs at 390 nm, with an average power of 80 mW by frequency-doubling the output of a sub-10-fs, 1.2-MW Ti:sapphire oscillator. Cross-correlation technique was employed to measure the pulse duration. To our knowledge, these are the shortest pulses produced in the violet-blue spectral range at high repetition rates so far.     

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.     

Femtosecond pulse amplification by coherent addition in a passive optical cavity

By simultaneously controlling repetition and carrier frequencies, one can achieve the phase coherent superposition of a collection of successive pulses from a mode-locked laser. An optical cavity can be used for coherent delay and constructive interference of sequential pulses until a cavity dump is enabled to switch out the amplified pulse. This approach will lead to an effective amplification process through decimation of the original pulse rate while the overall coherence from the oscillator is preserved. Detailed calculations show the limiting effects of intracavity dispersion and indicate that enhancement of sub-100-fs pulses to microjoule energies is experimentally feasible.     

Intense 8-fs pulse generation in the deep ultraviolet

By use of the recently developed technique of guided-wave frequency conversion, the generation of sub-10-fs light pulses in the UV has been demonstrated for what is believed to be the first time. Cross-phase modulation of the light in a hollow waveguide produced a bandwidth of 16nm, with a center frequency of 270 nm, at 1 kHz. A simple grating pair was used to compress the pulses to a duration of 8 fs, as measured by self-diffraction frequency-resolved optical gating. In the experiment the compressed energy was greater than 1 muJ , with a peak power of >100 MW ; the technique can be scaled to higher energy. Further improvements should make it possible to generate pulses as short as ~3 fs with this technique.     

Over 300 nm tunable broadband one-crystal noncollinear optical parametric amplification

An over 300 nm tunable broadband noncollinear optical parametric amplification in visible scale as well as the generation of blue pump pulses in one BBO crystal are demonstrated. Micro-joule energies are achieved in the signal branch, and the signal central wavelength can be tuned from 475 to 800 nm. The near-transform-limited sub-50 fs pulse duration is attainable over the whole tuning range after compression by a pair of prisms.     

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。     

Phase-preserving chirped-pulse optical parametric amplification to 17.3 fs directly from a Ti:sapphire oscillator

Phase-stabilized 12-fs, 1-nJ pulses from a commercial Ti:sapphire oscillator are directly amplified in a chirped-pulse optical parametric amplifier and recompressed to yield near-transform-limited 17.3-fs pulses. The amplification process is demonstrated to be phase preserving and leads to 85-microJ, carrier-envelope-offset phase-locked pulses at 1 kHz for 0.9 mJ of pump, corresponding to a single-pass gain of 8.5 x 10(4).     

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) .     

Sub-100 fs SDPF optical soliton compressor for diode laser pulses

We report our studies on a fiber-optic soliton compressor for generation of sub-100 femtosecond (fs) optical pulses out of picosecond (ps) diode laser pulses. The soliton compressor is rather simple and composed of a 15 ～ 20 m-long step-like dispersion profiled fiber (SDPF) in conjunction with a single Er-doped fiber amplifier (EDFA). Careful design of such a SDPF compressor was performed, leading to demonstration of 20-fs class compression performance, and experimental investigation was carried out in detail on the optical pulse propagation in the compression processes. In addition, nonlinear fiber loops were applied to suppression of pulse pedestals, resulting successfully in high quality optical pulses of the 100-fs range.     

Collinear type II second-harmonic-generation frequency-resolved optical gating for the characterization of sub-10-fs optical pulses

For the first time to our knowledge, we demonstrate a collinear frequency-resolved optical gating (FROG) technique that is suitable for the characterization of sub-10-fs pulses. This FROG variant does not suffer from geometrical blurring effects, and a temporal resolution of 1 fs can be achieved without the need for additional aperturing. The apparatus is suitable for subnanojoule pulse energies. We apply this technique for the full characterization of pulses from a Kerr-lens mode-locked Ti:sapphire laser.     

Ex vivo characterization of sub-10-fs pulses

An all-mirror dispersion-compensation setup is used to correct for quadratic and cubic phase distortions induced within a custom nonlinear optical microscope. Mouse tail tendon is used to characterize sub-10-fs pulses by interferometric autocorrelation. This is an ideal method for characterizing dispersion from the optical system, immersion medium, and wet biological sample. The generation of very short autocorrelations demonstrates the ability to compensate for phase distortions within the imaging system and efficient second-harmonic upconversion of the ultrashort pulse spectrum within collagen. Compensated autocorrelation traces are presented for biologically relevant objective lenses.