High-fidelity, 160 fs, 5 µJ pulses from an integrated Yb-fiber laser system with a fiber stretcher matching a simple grating compressor.

Although femtosecond microjoule Yb-fiber systems are attractive because of a straightforward power scalability, they inherently suffer from a lowered pulse fidelity as a result of complex dispersion and nonlinearity management. Here, we present an integrated Yb-fiber system delivering high-fidelity microjoule pulses compressible down to 160 fs. The system uses a dispersion compensating fiber stretcher that is specially designed to match the dispersion of a 1480 lines/mm grating compressor. Performance analysis suggests the further possibility of scaling the pulse energy to tens of microjoules without pulse quality deterioration using this dispersion management scheme.

Broadly tunable carrier envelope phase stable optical parametric amplifier pumped by a monolithic ytterbium fiber amplifier.

In an effort to develop a robust and efficient front end for a chirped-pulse parametric amplification chain, we demonstrate a broadband difference-frequency converter driven by a monolithic femtosecond Yb-doped-fiber amplifier and emitting carrier-envelope-offset-free pulses with the energy of tens of nanojoules tunable in the wavelength range from 1200 nm to beyond 2 mum. Next to providing these seed pulses, the system enables direct optical synchronization of Nd- and Yb-doped pump lasers for subsequent parametric amplification.

Parametric amplification of few-cycle carrier-envelope phase-stable pulses at 2.1 microm.

We demonstrate an optical parametric chirped-pulse amplifier producing infrared 20 fs (3-optical-cycle) pulses with a stable carrier-envelope phase. The amplifier is seeded with self-phase-stabilized pulses obtained by optical rectification of the output of an ultrabroadband Ti:sapphire oscillator. Energies of -80 microJ with a well-suppressed background of parametric superfluorescence and up to 400 microJ with a superfluorescence background are obtained from a two-stage parametric amplifier based on periodically poled LiNbO3 and LiTaO3 crystals. The parametric amplifier is pumped by an optically synchronized 1 kHz, 30 ps, 1053 nm Nd:YLF amplifier seeded by the same Ti:sapphire oscillator.

Generation of dual-wavelength pulses by frequency doubling with quasi-phase-matching gratings.

We demonstrate generation of two synchronized picosecond pulses at different wavelengths near 778 nm by frequency doubling of a femtosecond pulse. We use nonlinear frequency filtering with quasi-phase-matching gratings, which allow us to obtain second-harmonic spectral intensities that are higher than the spectral intensities of the pump.

Nanosecond-to-picosecond pulse compression with fiber gratings in a compact fiber-based chirped-pulse-amplification system.

A chirped, 12-cm-long fiber Bragg grating with 10-nm spectral bandwidth was employed in place of a conventional diffraction grating pair compressor in a compact fiber-based high-energy chirped-pulseamplification system. Initial nanosecond chirped pulses from a fast-tuned laser diode were compressed to produce 1.9-ps-long, 300-nJ pulses.

High-power amplification of femtosecond optical pulses in a diode-pumped fiber system.

We report a compact all-diode-laser-pumped erbium-doped fiber system consisting of an environmentally stable Kerr-type mode-locked fiber oscillator and a fiber amplifier. High-repetition-rate (38 MHz) 200-fs-duration pulses were amplified to as much as 3 nJ of energy and 150 mW of average power. Amplification of unstretched and stretched pulses was studied. Using chirped-pulse amplification, we obtained clean pedestal-free 420-fs pulses. Amplification of unstretched pulses produced 84-fs pulses with a broad pedestal.

Generation of high-energy femtosecond pulses in multimode-core Yb-fiber chirped-pulse amplification systems.

220-fs pulses with energies of ~100microJ have been generated by use of two different configurations of diode-pumped Yb-fiber chirped-pulse amplification systems. Energy scaling was demonstrated with 25-microm -core diameter fibers, in which stable diffraction-limited output (M(2)~1.1) was achieved. A two-stage fiber-amplifier system produced average powers of up to 5.5 W at ~1- MHz pulse-repetition rate. A double-pass configuration provided 53-dB gain in a single Yb-fiber amplifier stage, thus eliminating the necessity for multiple amplification stages as well as the need for using polarization-preserving fibers.

Hybrid diode-laser fiber-amplifier source of high-energy ultrashort pulses.

We demonstrate what we believe is the first compact laser system for generating ultrashort microjoule-energy optical pulses. Linearly chirped pulses from monolithic tunable Bragg-reflection laser diodes were amplified in a diode-pumped two-stage erbium-doped fiber amplifier and compressed with a grating-pair compressor. The laser diodes had their emission wavelengths at 1.538 and 1.562 microm. The highest pulse energies obtained were 2 microJ at the repetition frequencies of 1-10 kHz and were at the saturation energy level of the fiber amplifier. The shortest duration of compressed pulses is 1.8 ps.

Fiber-laser-based femtosecond parametric generator in bulk periodically poled LiNbO(3).

A diode-pumped system for optical parametric generation of wavelength-tunable femtosecond pulses is demonstrated. It comprises an Er-doped fiber mode-locked laser, a fiber chirped-pulse amplifier, and a bulk periodically poled LiNbO(3) (PPLN) optical parametric generator. The parametric generator is pumped at 777 nm with frequency-doubled microjoule pulses from the fiber amplifier and produces 300-fs pulses tunable from 1 to 3microm with output energies up to ~200 nJ. Use of a PPLN nonlinear crystal substantially reduces the pump energies required for efficient parametric generation. Saturated single-pass parametric energy conversion of 38% (internal) has been achieved with only 220 nJ of pump inside the crystal. A parametric generation threshold of 54 nJ is observed, and efficient parametric conversion is obtained with repetition rates up to 200 kHz.

Engineerable compression of ultrashort pulses by use of second-harmonic generation in chirped-period-poled lithium niobate.

We demonstrate the use of an aperiodic quasi-phase-matching (QPM) grating to generate second-harmonic pulses that are stretched or compressed relative to input pulses at the fundamental frequency. We frequency doubled an externally chirped erbium-doped fiber laser generating 17-ps (FWHM) pulses at 1560nm to produce near-transform-limited 110-fs (FWHM) pulses at 780nm by use of a 5-cm-long lithium niobate crystal poled with a QPM grating chirped from an 18.2- to a 19.8-microm period.

High-energy femtosecond pulse amlification in a quasi-phase-matched parametric amplifier.

A new type of solid-state femtosecond amplifier is demonstrated that is based on quasi-phase-matched parametric amplification. Such gain media are different from conventional solid-state amplifiers in that their amplification bandwidths and pump and signal wavelengths can be engineered. Furthermore, high gain is characteristic of parametric amplification, permitting extraction of high energies without the need to resort to multiple-pass configurations. We report a parametric chirped pulse amplification system in which femtosecond pulses from a mode-locked Er-doped fiber laser system are amplified to 1-mJ energies in a single pass by use of a 5-mm-long periodically poled LiNbO(3) (PPLN) crystal. This amplifier is pumped by 5-mJ and 0.5-ns pulses at 786 nm, demonstrating that limitations associated with a low optical-damage threshold for long pump pulses can be overcome because of the high nonlinearity of PPLN and that relatively simple Q -switched lasers can be used with such parametric amplifiers.

Engineerable femtosecond pulse shaping by second-harmonic generation with Fourier synthetic quasi-phase-matching gratings.

We describe a pulse-shaping technique that uses second-harmonic generation with Fourier synthetic quasi-phase-matching gratings. We demonstrate both amplitude and phase tailoring by generating a picosecond squarelike pulse as well as trains of femtosecond pulses with a terahertz-range repetition rate from either a compressed or a chirped pump pulse.

Chirped-pulse-amplification circuits for fiber amplifiers, based on chirped-period quasi-phase-matching gratings.

A new type of compact chirped-pulse-amplification circuit for high-power amplification of femtosecond pulses in an optical fiber is demonstrated. This circuit is based on a novel pulse compressor, chirped-period quasi-phase-matching gratings in electric-field-poled lithium niobate. The main advantages of this circuit are simplicity, the small number of components, compactness, and wavelength conversion of Er-doped fiber output to the technologically important 780-nm wavelength region.

High-power 100-fs pulse generation by frequency doubling of an erbium ytterbium-fiber master oscillator power amplifier.

Frequency doubling of an erbium-ytterbium-fiber master-oscillator-power-amplifier system is demonstrated. Simultaneous amplification and pulse compression in multimode erbium-ytterbium-doped fibers produces high-quality near-diffraction and near-bandwidth-limited 100-fs pulses at a wavelength of 1.62microm with an average power of 230 mW at a repetition rate of 52 MHz. Periodically poled LiNbO(3) allows for frequency doubling with a conversion efficiency of 51%, producing near-bandwidth-limited 105-fs pulses with an average power of 117 mW and a pulse energy of 2.3 nJ at a wavelength of 810 nm.

Frequency doubling of femtosecond erbium-fiber soliton lasers in periodically poled lithium niobate.

We report efficient frequency doubling of passively mode-locked femtosecond erbium-fiber lasers. Quasi-phase-matched second-harmonic generation in periodically poled lithium niobate is used to generate 8.1 mW of 190-fs (FWHM), 90-pJ pulses at 777 nm with a conversion efficiency greater than can be obtained with existing birefringently phase-matched nonlinear materials. A dispersion-compensation-free soliton oscillator generating transform-limited 230-fs (FWHM) pulses at 1554 nm is used as a pump laser.

Ultrawide tunable Er soliton fiber laser amplified in Yb-doped fiber.

A Raman-shifted and frequency-doubled high-power Er-fiber soliton laser for seeding an efficient high-power Yb fiber femtosecond amplifier is demonstrated. The Raman-shifted and frequency-doubled Er-soliton laser is tunable from 1.00 to 1.070microm and produces bandwidth-limited 24-pJ pulses at a repetition rate of 50 MHz with a FWHM pulse width of 170 fs at 1.040microm . The Yb(3+) amplifier has a slope efficiency of 52% and generates 3-ps linearly chirped pulses with an average power of 0.8 W at 1.05microm . After pulse compression, 74-fs bandwidth-limited pulses with an average power of 0.4 W and a pulse energy of 8 nJ are generated.