Non-iterative characterization of few-cycle laser pulses using flat-top gates.

We demonstrate a method for broadband laser pulse characterization based on a spectrally resolved cross-correlation with a narrowband flat-top gate pulse. Excellent phase-matching by collinear excitation in a microscope focus is exploited by degenerate four-wave mixing in a microscope slide. Direct group delay extraction of an octave spanning spectrum which is generated in a highly nonlinear fiber allows for spectral phase retrieval. The validity of the technique is supported by the comparison with an independent second-harmonic fringe-resolved autocorrelation measurement for an 11 fs laser pulse.

Femtosecond coherent seeding of a broadband Tm:fiber amplifier by an Er:fiber system.

We generate broadband pulses covering the Yb: and Tm:silica amplification ranges with a passively phase-locked front end based on Er:fiber technology. Full spectral coherence of the octave-spanning output from highly nonlinear germanosilicate bulk fibers is demonstrated. Seeding of a high-power Tm:fiber generates pulses with a clean spectral shape and a bandwidth of 50 nm at a center wavelength of 1.95 µm, pulse energy of 250 nJ, and repetition rate of 10 MHz.

All-passive phase locking of a compact Er:fiber laser system.

A passively phase-locked laser source based on compact femtosecond Er:fiber technology is introduced. The carrier-envelope offset frequency is set to zero via difference frequency generation between a soliton at a wavelength of 2 µm and a dispersive wave at 860 nm generated in the same highly nonlinear fiber. This process results in a broadband output centered at 1.55 µm. Subsequently, the 40 MHz pulse train seeds a second Er:fiber amplifier, which boosts the pulse energy up to 8 nJ at a duration of 125 fs. Excellent phase stability is demonstrated via f-to-2f spectral interferometry.

Ultrabroadband background-free coherent anti-Stokes Raman scattering microscopy based on a compact Er:fiber laser system.

We demonstrate a scheme for efficient coherent anti-Stokes Raman scattering (CARS) microscopy free of nonresonant background. Our method is based on a compact Er:fiber laser source. Impulsive excitation of molecular resonances is achieved by an 11 fs pulse at 1210 nm. Broadband excitation gives access to molecular resonances from 0 cm(-1) up to 4000 cm(-1). Time-delayed narrowband probing at 775 nm enables sensitive and high-speed spectral detection of the CARS signal free of nonresonant background with a resolution of 10 cm(-1).

Compact coherent anti-Stokes Raman scattering microscope based on a picosecond two-color Er:fiber laser system.

We present a compact coherent anti-Stokes Raman scattering microscope based on a widely tunable picosecond Er:fiber laser. Intense and bandwidth-limited 1 ps pump pulses at a center wavelength of 775 nm are generated via frequency mixing within the broadband fundamental at 1.55 microm. Narrowband Stokes pulses are obtained by frequency shifting of solitons in a highly nonlinear bulk fiber and subsequent second-harmonic generation. The tuning range from 850 nm to 1100 nm gives access to vibrational resonances between 1150 cm(-1) and 3800 cm(-1). A first imaging application in the spectral region of CH stretch vibrations is demonstrated.

8-fs pulses from a compact Er:fiber system: quantitative modeling and experimental implementation.

We demonstrate an all-fiber turnkey source of extremely stable 2-cycle pulses at a center wavelength of 1.17 microm. Taylor-cut highly nonlinear germano-silica bulk fibers (HNFs) provide smooth supercontinua with a bandwidth of 560 nm and a spectral shape precisely controlled by the dispersion of the fiber and the phase of the 1.55 microm pump pulses. Alternatively these fibers are capable of generating pulses with central wavelengths continuously tunable from 0.9 microm up to 1.4 microm. These results are based on parameter-free simulations of nonlinear pulse propagation including higher-order dispersion as well as instantaneous Kerr and retarded Raman contributions.