Femtosecond optical Kerr effect in normal and grades of cancerous breast tissues as a new optical biopsy method.

This study reports on the first use of the optical Kerr effect (OKE) in breast cancer tissue. This proposed optical biopsy method utilizes a Femtosecond Optical Kerr Gate to detect changes in dielectric relaxation and conductivity created by a cancerous infection. Here, the temporal behavior of the OKE is tracked in normal and cancerous samples of human and mouse breast. These tissues display a double peaked temporal structure and its decay rate changes depending on the tissue's infection status. The decay of the secondary peak, attributed to ultrafast plasma response, indicates that the tissue's conductivity has doubled once infected. A slower molecular contribution to the Kerr effect can also be observed in healthy tissues. These findings suggest two possible biomarkers for the use of OKE in optical biopsy. Both markers arise from alterations in the infected tissue's cellular structure, which changes the rate at which electronic and molecular processes occur.

Femtosecond Optical Kerr Gate in tissues.

The Optical Kerr Effect is investigated for the first time in biological tissues. This nonlinear effect was explored in both human brain and avian breast tissues using a time-resolved femtosecond pump-probe Optical Kerr Gate that looks for phase changes that arise in the probe from the pump induced Kerr refractive index change. The tissue samples produced a unique ultrafast (700-800 fs) doubled peaked temporal signal, which is indicative of interplay between the different ultrafast mechanisms (electronic plasma and molecular) that make up the Kerr index. The unique profile was replicated in theoretical simulations. The properties of the temporal profile varied between samples suggesting that it could be used as a new diagnostic. Understanding this behavior can help improve the scientific understanding of nonlinear spectral diagnostic techniques and potentially create a new Kerr-based optical biopsy method.

Technical note: Monte Carlo study of the mechanism of proton-boron fusion therapy.

PURPOSE: Proton beam therapy has been found to have enhanced biological effectiveness in targets that contain the boron isotope 11 B, with the alpha particles resulting from the p + 11 B → 3α reaction being hypothesized as the mechanism; in this study, we aimed to elucidate the causes of the enhanced biological effectiveness of proton-boron fusion therapy by performing a detailed Monte Carlo study of the p + 11 B → 3α reaction in a phantom geometry. METHODS: We utilized the Geant4 toolkit to create Monte Carlo particle physics simulations. These simulations consisted of a proton beam with a range 30 mm, creating a Spread-Out Bragg Peak with a modulation width of 10 mm, directed into a water phantom containing a region of boron material. Energy deposition, particle energy, and particle fluence were scored along the path of the beam and grouped by particle species. The scoring was performed using a series of cylindrical volumes with a radius of 2.5 mm and depth of 0.1 mm, constructed such that the depth was parallel to the proton beam. Root was then used to perform the data analysis. RESULTS: Our simulations showed that the dose delivered by alpha particles produced by p + 11 B → 3α was several orders of magnitude lower than the dose delivered directly by protons, even when the boron uptake region was comprised entirely of natural boron or pure 11 B. CONCLUSIONS: Our findings do not support the theory that an alpha particle-based mechanism is responsible for the enhanced biological effectiveness of proton-boron fusion therapy. We conclude that any enhanced biological effect seen in experimental studies was not caused by fusion reactions between protons and 11 B nuclei. However, it is necessary to reproduce the past experiments that indicated significant dose enhancement.

Femtosecond anti-Stokes conical emission in BK-7 glass and O and E-wave calcite.

The angle of anti-Stokes conical emission (CE) is experimentally measured in the frequency shift span of 2000cm-1 to 9000cm-1. The experiment was performed using a 800 nm 50 fs laser pump in samples of BK-7 glass and calcite in both the O and E-wave configurations. The experimental results of angular emission are then compared to three competing models: the Alfano-Shapiro four wave mixing (FWM) model from 1970, the Luther FWM model from 1994, and the Faccio X-wave model from 2004. Results indicate that in all samples and configurations tested, the original FWM has the best agreement with experimental results in the anti-Stokes span.

Steady-state stimulated Raman generation and filamentation using complex vector vortex beams.

Stimulated Raman scattering and laser filamentation produced using nanosecond pulsed complex vector vortex beams (CVVB) are investigated in a 20 cm long methanol cell. The CVVB is generated using q-plates and is tested at orbital angular momentum (L) values of 1, 2, 3, and 4 and circular, radial, and azimuthal polarizations. The results illustrate that the stability and intensity of the generated stimulated Raman has dependence on input polarization and L value. During filamentation, the beam is also shown to break up into multiple primary filaments and that there is a reduction in small-scale filamentation when using CVVBs.

Explanation of the competition between O- and E-wave induced stimulated Raman and supercontinuum in calcite under ultrafast laser excitation.

Key optical properties of calcite were measured to unravel the difference between stimulated Raman scattering (SRS) and self-phase modulation (SPM) for the supercontinuum (SC) for ordinary (O) wave and extraordinary (E) wave. These properties are group velocity dispersion, walk-off, spontaneous Raman spectra and cross section, optical 1086cm-1 phonon linewidth, nonlinear susceptibility (χ3), steady-state and transient SRS, and SC caused from SPM. These are investigated for O-waves and E-waves from a 2.7 cm thick calcite crystal. Using 390 fs pulses (∼0.8µJ pulse energy) at 517 nm, the O-wave produced a stronger sharp SRS peak at 1086cm-1 and a weaker SC spectrum in the visible range than the E-wave. The salient difference found between the O- and E-waves for SRS and SPM in calcite is attributed to the larger Raman cross section and the size of nonlinear susceptibility (χ3) for O-waves as compared to E-waves.

Inhibition of multi-filamentation of high-power laser beams.

We experimentally demonstrate the control and complete elimination of multi-filamentation in condensed matter by varying the focusing geometry. In particular, increasing the input beam power enables the extension of the filament length without generating multi-filaments up to 1400 times the critical power in fused silica at an 800 nm wavelength. Furthermore, the generated single filament exhibits spatial solitary wave behavior.