Polarization instability of ultrashort pulses as a source of vectorial supercontinuum.

Polarization instability (PI) of ultrashort light pulses, giving rise to vectorial supercontinuum generation, is demonstrated using a subwavelength-core, highly birefringent, normally dispersive optical fiber. The evolution of ultrashort pulses in the regime of PI is shown to radically differ from polarization-instability dynamics of cw fields and longer laser pulses. As the peak power of the laser field decreases along the propagation path due to dispersion-induced pulse stretching, the Poincaré-sphere map of field dynamics is shown to evolve from the behavior typical of PI in the highly nonlinear regime toward the beating dynamics of uncoupled polarization modes, characteristic of low field intensities and cw fields.

Raman detection of cell proliferation probes with antiresonance-guiding hollow fibers.

Antiresonance-guiding hollow-core fibers are shown to enable highly sensitive detection of cell proliferation probes using Raman scattering within the region where the cellular Raman activity is minimal. We demonstrate that such fibers can substantially reduce the level of the background compared to standard index-guiding optical fibers, thus radically improving the sensitivity of Raman detection of DNA synthesis in cells and offering a powerful tool for fiber-based live-cell imaging.

Tailoring the soliton output of a photonic crystal fiber for enhanced two-photon excited luminescence response from fluorescent protein biomarkers and neuron activity reporters.

Dual-cladding photonic crystal fibers (PCFs) with two zero-dispersion points are used to enhance the two-photon excited luminescence (TPL) response from fluorescent protein biomarkers and neuron activity reporters in dye-cell experiments and in in vivo work on transgenic mice and tadpoles. The soliton transmission of ultrashort pulses through a PCF suppresses dispersion-induced temporal pulse spreading, maintaining a high level of field intensity needed for efficient TPL excitation. The soliton self-frequency shift, stabilized against laser power fluctuations by a specific PCF dispersion design, is employed to accurately match the wavelength of the soliton PCF output with the two-photon absorption spectrum of dye or fluorescent protein biomarker molecules, enhancing their TPL response and allowing the laser damage of biotissues to be avoided.

Fiber-optic probes for in vivo depth-resolved neuron-activity mapping.

Specialty fiber probes are used for in vivo depth-resolved mapping of neuron activity through the optical detection of fluorescent-protein reporters expressed inside the living brain of anesthetized transgenic mice. Supercontinuum radiation produced by highly nonlinear photonic-crystal fibers is employed to demonstrate a simultaneous multicolor interrogation of several biomarkers in a model aqueous solution system, thus suggesting the way toward a multiplex mapping of various types of neuron dynamics inside the living brain.

Raman-resonance-enhanced composite nonlinearity of air-guided modes in hollow photonic-crystal fibers.

Coherent anti-Stokes Raman scattering (CARS) is used to measure relations between the resonant (Raman) and nonresonant (Kerr-type) optical nonlinearities of air-guided modes in a hollow-core photonic-crystal fiber (PCF). We demonstrate that, due to its interference nature, CARS provides a convenient tool for measuring the contribution of the fiber cladding to the total nonlinearity sensed by air-guided modes in hollow PCFs. On a Raman resonance with molecular vibrations in the gas that fills the fiber core, a two-color laser field is shown to induce optical nonlinearities that are several orders of magnitude higher than the nonresonant Kerr-type nonlinearities typical of air-guided PCF modes.