Multiphoton microscopy (MPM) has found a niche in the world of biological imaging as the best noninvasive means of fluorescence microscopy in tissue explants and living animals. Coupled with transgenic mouse models of disease and 'smart' genetically encoded fluorescent indicators, its use is now increasing exponentially. Properly applied, it is capable of measuring calcium transients 500 microm deep in a mouse brain, or quantifying blood flow by imaging shadows of blood cells as they race through capillaries. With the multitude of possibilities afforded by variations of nonlinear optics and localized photochemistry, it is possible to image collagen fibrils directly within tissue through nonlinear scattering, or release caged compounds in sub-femtoliter volumes.

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Nonlinear magic: multiphoton microscopy in the biosciences

This Review explains the concept of dissipative solitons and their application to high-energy mode-locked fibre laser cavities. Dynamics and effects such as dissipative soliton ‘explosions’ and ‘rain’ are summarized, and an outlook of the field is also provided.

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Dissipative solitons for mode-locked lasers

Dual-comb spectroscopy is an emerging new spectroscopic tool that exploits the frequency resolution, frequency accuracy, broad bandwidth, and brightness of frequency combs for ultrahigh-resolution, high-sensitivity broadband spectroscopy. By using two coherent frequency combs, dual-comb spectroscopy allows a sample’s spectral response to be measured on a comb tooth-by-tooth basis rapidly and without the size constraints or instrument response limitations of conventional spectrometers. This review describes dual-comb spectroscopy and summarizes the current state of the art. As frequency comb technology progresses, dual-comb spectroscopy will continue to mature and could surpass conventional broadband spectroscopy for a wide range of laboratory and field applications.

Dual-comb spectroscopy

Self-similar propagation of ultrashort, parabolic pulses in a laser resonator is observed theoretically and experimentally. This constitutes a new type of pulse shaping in mode-locked lasers: in contrast to the well-known static (solitonlike) and breathing (dispersion-managed soliton) pulse evolutions, asymptotic solutions to the nonlinear wave equation that governs pulse propagation in most of the laser cavity are observed. Stable self-similar pulses exist with energies much greater than can be tolerated in solitonlike pulse shaping, and this has implications for practical lasers.

https://arxiv.org/pdf/physics/0402013.pdf

Self-similar evolution of parabolic pulses in a laser.

A modelocked fiber laser is designed to have strong pulse-shaping based on spectral filtering of a highly-chirped pulse in the laser cavity. The laser generates femtosecond pulses without a dispersive delay line or anomalous dispersion in the cavity.

All-normal-dispersion femtosecond fiber laser

A modelocked Yb-doped fiber laser without an anomalous dispersive segment is demonstrated. Pulse-shaping is based on spectral filtering of a highly-chirped pulse in the cavity. The laser generated 170-fs pulses with 3-nJ pulse energy. Article not available.

All-Normal-Dispersion Femtosecond Fiber Laser

A series of experiments aimed at determining the maximum pulse energy that can be produced by a femtosecond fiber laser is reported. Exploiting modes of pulse propagation that avoid wave breaking in a Yb fiber laser allows pulse energies up to 14?nJ to be achieved. The pulses can be dechirped to sub-100-fs duration to produce peak powers that reach 100?kW. The limitations to the maximum pulse energy are discussed.

Femtosecond fiber lasers with pulse energies above 10 nJ.

We report the generation of 6-nJ chirped pulses from a mode-locked Yb fiber laser at 1.03 μm . A linear anomalous-dispersion segment suppresses wave-breaking effects of solitonlike pulse shaping at high energies. The dechirped pulse duration is 50 fs, and the energy is 5 nJ. This laser produces twice the pulse energy and average power, and approximately five times the peak power, of the previous best mode-locked fiber laser. It is to our knowledge the first fiber laser that directly offers performance similar to that of solid-state lasers such as Ti:sapphire.

J.R. Buckley

Papers

Self-similar evolution of parabolic pulses in a laser.

All-normal-dispersion femtosecond fiber laser

All-Normal-Dispersion Femtosecond Fiber Laser

Femtosecond fiber lasers with pulse energies above 10 nJ.

Generation of 50-fs, 5-nJ pulses at 1.03 μm from a wave-breaking-free fiber laser