Continuum Generation In Fibers Research Articles

Static third-harmonic lines in widely variable fiber continuum generation.

An intriguing phenomenon of third-harmonic generation under fiber continuum generation is the emission of an anharmonic signal. One popular interpretation of this effect has developed into a general theory of fiber third-harmonic generation. Here we produce "static" third-harmonic Unes dictated fully by fiber properties independent of pump parameters, in contrast to the signals of all known phase-matched nonlinear optical processes that vary dynamically with these parameters. We argue that the anharmonic signal is an illusion of the continuum generation, that it is in fact harmonic, and that this theory should be reevaluated.

Cross-validation of theoretically quantified fiber continuum generation and absolute pulse measurement by MIIPS for a broadband coherently controlled optical source

The predicted spectral phase of a fiber continuum pulsed source rigorously quantified by the scalar generalized nonlinear Schrödinger equation is found to be in excellent agreement with that measured by multiphoton intra-pulse interference phase scan (MIIPS) with background subtraction. This cross-validation confirms the absolute pulse measurement by MIIPS and the transform-limited compression of the fiber continuum pulses by the pulse shaper performing the MIIPS measurement, and permits the subsequent coherent control on the fiber continuum pulses by this pulse shaper. The combination of the fiber continuum source with the MIIPS-integrated pulse shaper produces compressed transform-limited 9.6 fs (FWHM) pulses or arbitrarily shaped pulses at a central wavelength of 1020 nm, an average power over 100 mW, and a repetition rate of 76 MHz. In comparison to the 229-fs pump laser pulses that generate the fiber continuum, the compressed pulses reflect a compression ratio of 24.

Dual-spectrum laser source based on fiber continuum generation for integrated optical coherence and multiphoton microscopy

A single-laser dual-spectrum source designed for integrated optical coherence and multiphoton microscopy is demonstrated. The source implements the laser characteristics needed to optimally perform both modalities while extending the spectral range for this imaging technique. It consists of a widely tunable, mode-locked, Ti-sapphire laser with a portion of its output spectrally broadened via continuum generation in a photonic crystal fiber. The continuum-broadened beam allows for enhanced optical sectioning with optical coherence microscopy, while the unbroadened beam from the ultrashort-pulse Ti-sapphire laser optimally excites fluorescent markers. The noise power of the continuum-broadened beam is less than 1.1 dBmHz higher than the Ti-sapphire laser in the range from 1 Hz to 25 MHz, and the fiber shows no sign of damage after approximately 100 h of use. We demonstrate the use of this source across a wide spectral range by imaging green fluorescent protein-transfected mouse fibroblast cells costained with fluorescent dyes that are maximally excited at various wavelengths. Images of unstained in vivo human skin are also presented. This source extends the feasibility of this integrated imaging modality and will facilitate new investigations in in vivo microscopy, tissue engineering, and cell biology.