A. Hariharan

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.

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.

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.

Alexandrite-pumped alexandrite regenerative amplifier for femtosecond pulse amplification.

We demonstrate a regenerative amplif ier incorporating alexandrite as the gain medium that is pumped by an alexandrite laser. Temperature-altered gain permitted the 728-nm alexandrite pump laser, operating at room temperature, to pump a 780-800-nm alexandrite laser that was maintained at elevated temperatures. 200-fs pulses from a Ti:sapphire oscillator were amplif ied to the millijoule level. This system also amplif ied femtosecond pulses from a frequency-doubled Er-doped fiber laser.

Generation of diffraction-limited femtosecond beams using spatially-multimode nanosecond pump sources in parametric chirped pulse amplification systems

Summary form only given.We have shown that spatially multimode output from a large core fiber amplifier can be efficiently converted into a diffraction-limited amplified signal beam by using optical parametric amplification. This allowed us to demonstrate a compact system for generating high-energy ultrashort pulses based on large-core cladding-pumped Yb fibers. Such approach eliminates limitations on the usable fiber core-size and, therefore, is expected to provide further significant increase in pulse energies and powers from fiber-based ultrafast laser systems.

Microlaser pumped, engineerable bandwidth parametric chirped-pulse amplifier using electric-field-poled LiNbO/sub 3/

We have demonstrated the use of periodically poled LiNbO/sub 3/ as a practical diode-pumped parametric gain medium for ultrashort pulse amplification. The essential advantage is that a high single-pass gain is achievable without the need for regenerative or multiple-pass amplification. Uniquely, such an amplifier has engineerable optical properties, which potentially can provide extremely broad gain bandwidths suitable for amplification of few femtosecond pulses.

Highly efficient, low-noise Yb femtosecond fiber source

Summary form only given. With the recent availability of Raman-shifted, widely tunable Er fiber laser pulse sources, the direct injection of Yb fiber amplifiers with femtosecond pulses from a frequency-converted Er-fiber laser has become possible. The exploitation of the unique efficiency and large bandwidth of Yb fiber amplifiers thus allows the construction of highly compact ultrafast laser sources operating at W-level average powers. However, in most applications very low noise levels from such systems are needed, which may seem challenging due to the nonlinear processes involved from transferring the output of an Er fiber laser at 1.56 /spl mu/m to the 1 /spl mu/m region. We demonstrate for the first lime to our knowledge that a femtosecond Yb fiber source can be operated in an extremely low noise regime. Injected with a Raman-shifted and frequency doubled Er femtosecond fiber laser low noise performance is achieved by exploiting self-limiting nonlinear frequency conversion in both the Raman shifting stage as well as the frequency doubling stage. Reliable operation of the Yb-amplifier is obtained by employing side-pumping and polarization maintaining (PM) fibers.

Parametric chirped pulse microamplifier based on engineerable quasi-phase-matched LiNbO3

A new class of compact diode-pumped femtosecond amplifiers based on quasi-phase-matched parametric gain in LiNbO3 can provide single-pass gain of up to 80 dB and arbitrarily broad, optically engineerable bandwidth.