All-solid-state Cr:forsterite laser generating 14-fs pulses at 1.3 mum

We report the generation of 14-fs pulses at 1.3mum with 80-mW average power at 100-MHz repetition rate by an all-solid-state Kerr-lens mode-locked Cr:forsterite laser. The laser spectrum covers wavelengths of 1230-1580 nm, with a FWHM of 250 nm. Since 1.3-mum wavelengths are close to the zero dispersion wavelength of Cr:forsterite, higher-order dispersion is the main factor limiting pulse durations. We use specially designed and fabricated double-chirped mirrors in combination with high-index PBH71 prisms to compensate for the intracavity dispersion over almost 300 nm.     

Femtosecond quadrature-squeezed light generation in CdSe at 1.55 mum

We generated pulsed quadrature-squeezed light by cross-phase modulation in single-crystal hexagonal CdSe at wavelengths of 1.4 to 1.55mum . We measured 0.4-dB squeezing (0.7 dB is inferred at the crystal) with 100-fs laser pulses. The wavelength and the intensity dependence, as well as variations in the local oscillator configuration, are examined. At higher intensities squeezing is shown to deteriorate owing to competing nonlinear processes.     

Second-harmonic generation frequency-resolved optical gating analysis of low-intensity shaped femtosecond pulses at 1.55 mum

We illustrate observation and characterization of medium- and low-intensity shaped ultrashort pulses at lambda=1.55mum through single-shot geometry (multishot-average) second-harmonic generation-frequency-resolved optical gating. The pulses are shaped by amplitude filters in the Fourier plane of a compact folded shaper. Sensitivity to pulses with energies of less than 20 pJ and high dynamic range is reported for this configuration. Application of this method to the propagation of ~170-fs pulses through a 50-m fiber link is also illustrated.     

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.     

Parametric generation of short acoustic pulses

A method of parametric generation of short sound pulses with controllable duration upon excitation of steady-state vibrations of the acoustic field in the resonator under conditions of modulation of the amplitude of high-frequency variations in the speed of sound in a resonator material was proposed and theoretically studied.     

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.     

40-GHz pulse-train generation at 1.5 mum with a chirped fiber grating as a frequency multiplier

Pulse-train multiplication based on the temporal Talbot effect in a linearly chirped fiber Bragg grating has been experimentally demonstrated. A 40-GHz repetition-rate, nearly transform-limited 10-ps duration optical pulse train at 1.533 mum has been obtained from a 2.5-GHz mode-locked Er- Yb:glass laser by use of a 100-cm-long linearly chirped apodized fiber grating.     

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.     

Parametric four-photon generation of picosecond light at high conversion efficiency

Parametric four-photon interaction in isotropic media was studied in the saturation range. Up to 10% of input laser energy could be converted into a broad frequency spectrum ranging from the ultraviolet to the infrared. Parameters which influence the conversion efficiency are discussed.     

Optimal generation of single-dispersion precompensated 1-fs pulses by molecular phase modulation

We show how an optimal control approach can be combined with the pump-probe technique for pulse compression by molecular phase modulation in hollow-core fibers to generate single 1-fs pulses in the visible. Varying the intensity and duration of the Gaussian-shaped pump pulse at the input induces optimal rotational response of the molecules. The probe pulse, which scatters off of the resulting time variation of the refractive index, is shaped at the input for optimal compression at the output, including dispersion to all orders.     

All-optical square-pulse generation and multiplication at 1.5 mum by use of a novel class of fiber Bragg gratings

A new class of linearly chirped fiber Bragg gratings, suitable for all-fiber optical multiplication and reshaping of picosecond pulse trains, is proposed and experimentally demonstrated. Repetition-rate multiplication, based on the temporal Talbot effect, is achieved by accurate control of the grating chirp, and a suitable design of the index-modulation depth profile allows for simultaneous square-pulse shaping. A 50-ps squarelike optical pulse train at 10-GHz repetition rate is obtained, starting from a 2.5-GHz Gaussian pulse train emitted by a mode-locked Er-Yb laser.     

Nonlinear source for the generation of high-energy few-cycle optical pulses

We investigate the evolution of optical pulses in a hollow waveguide filled with noble gas at pulse intensities for which tunnel ionization dominates the nonlinear response of the gas. A numerical analysis reveals that the spectral chirp generated by the plasma nonlinearity is to a good approximation linear over the whole pulse spectrum and can be compensated in a dispersive delay line. Our calculations predict the generation of 3-4-fs optical pulses with energies of a few milijoules. To our knowledge, these energies are an order of magnitude greater than the pulse energies that have been realized to date in hollow-fiber compressors based exclusively on the nonlinear Kerr effect.     

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

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

Complete pulse characterization at 1.5 mum by cross-phase modulation in optical fibers

Cross-phase modulation in optical fibers has been used for complete characterization of ultrashort pulses by a modified frequency-resolved optical gating (FROG) measurement technique. This technique has been used for characterization of picosecond pulses at 1.5mum with energy as low as 24 pJ, and the results are in excellent agreement with second-harmonic generation (SHG)-FROG characterization. The use of an optical waveguide gives measurement sensitivity comparable with that of SHG-FROG but without any temporal ambiguity in the retrieved pulse.     

Guiding and high-harmonic generation of sub-10-fs pulses in hollow-core fibers at 1015 W/cm2

15 W/cm². The high resistance of fused silica to damage in the sub-10-fs regime allows stable reproducible operation without degradation of the capillary waveguide. In preliminary experiments, we demonstrate kHz-repetition-rate guided-wave high-harmonic generation in helium down to the 10-nm range. The reported experiments open up the way to realizing high-field interactions with plane-wave excitation at intensity levels in excess of 10¹⁵ W/cm² under well-controlled conditions. Received: 28 May 1998     

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)].     

Practical all-fiber source of high-power, 120-fs pulses at 1 micrometre

Amplification of femtosecond pulses at 1.03 micrometre in a standard Yb-doped single-mode fiber is reported. A pulse energy of 8 nJ and an average power of 400 mW are obtained, limited by available pump power. To our knowledge these are the highest pulse energy and average power obtained from an integrated, single-mode fiber amplifier. After dechirping, 120-fs, 6-nJ pulses are obtained. A practical fiber-based source with performance comparable with that of a bulk solid-state laser is thus demonstrated, and scaling to substantially higher powers will be possible.     

Multi-terawatt laser system generating 12-fs pulses at 100 Hz repetition rate

We have developed a laser system generating high peak-power ultrashort pulses based on the chirped pulse amplification of a Ti:sapphire laser. The pulse duration of the laser is reduced to 12 fs, owing to the successful compensation of gain narrowing during amplification with novel optics. The pulse energy and the repetition rate are 40 mJ and 100 Hz, respectively, as a consequence of sufficient energy extraction from a laser medium in the final stage of a multipass amplifier chain, which is designed to balance focusing with a thermal lens against defocusing with convex mirrors without cryogenic cooling for Ti:sapphire crystals. The laser pulses delivered from this laser system are suitable for generating an intense attosecond pulse train in a vacuum ultraviolet or extreme ultraviolet region.