Ultrahigh-resolution optical coherence tomography using continuum generation in an air-silica microstructure optical fiber.

We demonstrate ultrahigh-resolution optical coherence tomography (OCT) using continuum generation in an air-silica microstructure fiber as a low-coherence light source. A broadband OCT system was developed and imaging was performed with a bandwidth of 370 nm at a 1.3-mu;m center wavelength. Longitudinal resolutions of 2.5 microm in air and ~2 microm in tissue were achieved. Ultrahigh-resolution imaging in biological tissue in vivo was demonstrated.

Visible continuum generation in air-silica microstructure optical fibers with anomalous dispersion at 800 nm.

We demonstrate experimentally for what is to our knowledge the first time that air-silica microstructure optical fibers can exhibit anomalous dispersion at visible wavelengths. We exploit this feature to generate an optical continuum 550 THz in width, extending from the violet to the infrared, by propagating pulses of 100-fs duration and kilowatt peak powers through a microstructure fiber near the zero-dispersion wavelength.

Optical properties of high-delta air silica microstructure optical fibers.

We analyze the waveguide properties of microstructure optical fibers consisting of a silica core surrounded by a single ring of large air holes. Although the fibers can support numerous transverse spatial modes, coupling between these modes even in the presence of large perturbations is prevented for small core dimensions, owing to a large wave-vector mismatch between the lowest-order modes. The result is an optical fiber that can appear single mode with propagation properties that can be achieved only in multimode waveguides.

Breakdown of the slowly varying envelope approximation in the self-focusing of ultrashort pulses.

We show theoretically and experimentally that with ultrashort pulses much longer than a single optical cycle, the effects of self-steepening and space-time focusing are important for describing the nonlinear dynamics of self-focusing. Asymmetric temporal splitting of the pulse envelope is observed in which the relative magnitudes of the peaks are reversed as the input power is increased.

Femtosecond ultraviolet autocorrelation measurements based on two-photon conductivity in fused silica.

We utilize the two-photon conductivity of a fused-silica substrate to produce a photoconductive switch for use in an intensity autocorrelator for ultraviolet ultrashort pulses. We perform measurements at 267 nm with pulse durations in the range of 110-330 fs and with energies as weak as 10 nJ. Based on the bandgap of fused silica, this device can potentially operate in the wavelength range of 140-280 nm.

Autocorrelation measurement of 6-fs pulses based on the two-photon-induced photocurrent in a GaAsP photodiode.

We experimentally characterize the two-photon response of a GaAsP photodiode by use of a femtosecond Ti:sapphire laser tuned below the diode bandgap. The photodiode is shown to be highly suitable for real-time second-order autocorrelation measurements of pulses as short as 6fs in duration and with energies as small as a few picojoules.

Measurements of the tensor properties of third-order nonlinearities in wide-gap semiconductors.

We extend the z-scan technique to provide for measurements of the sign and the magnitude of all the independent components of chi((3)) for isotropic and cubic-symmetry materials. This technique is used to measure the dispersion of the tensor components of the real and the imaginary parts of chi((3)) for various wide-gap semiconductor materials by use of femtosecond laser pulses. Our measurements of the polarization dichroism of the nonlinear-index and two-photon absorption coefficients are in fair agreement with recent theoretical calculations; however, substantial discrepancies exist between the measured and predicted values for the corresponding anisotropy parameters.