An ultrafast optical shutter was used to image ultrasmall objects hidden behind scattering walls by a procedure that selects in time the ballistic component and rejects the scattered diffusive light. Scattering walls used in this experiment included human breast tissue, chicken breast tissue, and a water suspension of polystyrene particles with scattering coefficients up to 21.7. Submillimeter resolution was achieved for two-dimensional ballistic images of a single point, a double-point fluorescence source, and a bar test chart in or behind these different turbid media.

No abstract

A novel noninvasive second-harmonic-generation tomographic method of mapping the structure of animal tissues by use of 100-fs laser pulses at 625nm is described. Subsurface structures were measured with this approach, which is potentially a symmetry-sensitive tool for optical histological reconstruction.

Nonlinear optical imaging with femtosecond (10 ؊15 -second) laser technology was used to evaluate the subsurface tumor progression in control, dysplasia, and cancerous 7,12-dimethylbenz[a]anthracene-treated hamster cheek pouch mucosa tissues. Two-dimensional images of hamster cheek pouch mucosa tissues were obtained by scanning the second harmonic signal at various sagittal and axial positions. The spatial mapping of the second harmonic signals showed depth differentiation between normal, dysplasia, and a more advanced cancerous state. This nonlinear optical method offers a noninvasive in situ imaging tool to the medical community.The medical community is searching for new and noninvasive in situ methods to better characterize the mucosal tissues of the cervix, colon, ear, nose, throat, oral cavity, and esophagus, where disease starts at the epithelial layer a few hundred micrometers beneath the surface. Second harmonic generation (SHG) imaging is a nonlinear optical technique that produces images of subsurface structures, rendering in situ histological information of tissues without surgery. The imageforming signal depends on the morphological symmetry of the molecules and the local intra-and intercellular matrices of the tissue. This symmetry dependence is derived from the secondorder, nonlinear optical susceptibility 2 tensor component that has been used to study phenomena both in the interior region and at surfaces or interfaces in various materials, including biological samples (1-6).SHG tomography can provide information about tissue structure in addition to that offered by other linear optical microscopy techniques, such as optical coherence tomography (OCT) and reflectance confocal microscopy (7,8). Both of these latter methods depend on the reflectance changes caused by local variations in the indices of refraction. Imaging techniques such as ultrasound and MRI with surface coils (100-m in spatial resolution) are limited in their ability to provide submicrometer resolutions that are comparable to linear and nonlinear optical microscopy (9, § ). The application of localized excitation makes it possible to use optical sectioning and image mapping in evaluating tissue in situ. This nonlinear optical technique allows imaging that is not restricted to signals emitted from fluorescent molecules. The illumination needs not correspond to a particular absorption band of a molecule; the wavelength can be selected to optimize excitation and imaging conditions. The SHG signal is proportional to the reflective coefficient and dependent on the reciprocal of quadratic powers of the index of refraction (6). This useful property provides a higher optical contrast for visualizing matrix structures than does reflectance microscopy such as OCT, in which the signal is proportional to the reflective coefficients.In this report, we demonstrate the applicability of the SHG imaging technique for the evaluation of subsurface tumor progression from normal to advanced cancer states. This technology provides a noninvasive h...

The temporal profiles of ultrashort light pulses propagating through turbid media of different lengths were measured with a streak camera. Various Fourier spatial filters were used to select the spatial frequencies of the scattered pulses. The temporal profiles of the pulses scattered by a 0.4% Intralipid solution in a cell of 5-cm thickness were signif icantly narrowed because of the removal of the higher-frequency components by a Fourier spatial filter.

Second- and third-harmonic generations of femtosecond and picosecond laser pulses have been measured from chicken skin, muscle, and fat tissues. The magnitude of the harmonic signals showed a strong structural dependence with the signal from skin interface being the strongest. The polarization dependence of the signal was also measured and found to be consistent with the fact that the tissue samples were highly scattering random media. The second-harmonic- and third-harmonic-generation conversion efficiencies were found to be in the range of ~10(-7) to ~10(-10).

Spectral broadening of a weak 80-microJ picosecond 530-nm laser pulse in a BK-7 glass has been enhanced over the entire spectral band by the presence of an intense millijoule picosecond 1060-nm laser pulse. The spectral distributions of the self-phase modulation and the induced-phase modulation signals are similar. The dominant enhancement mechanism for the induced supercontinuum was determined to be caused by an induced-phase modulation process, not by stimulated four-photon scattering.

Infrared supercontinua spanning the range 3-14 microm were observed when an intense pulse generated from a CO(2) laser was passed into GaAs, AgBr, ZnSe, and CdS crystals. These supercontinua have been qualitatively compared with theoretical predictions.