Prediction of the irradiation doses from ultrashort laser-solid interactions using different temperature scalings at moderate laser intensities

The ionizing radiation created by high intensity and high repetition rate lasers can cause significant radiological hazard. Earlier defined electron temperature scalings are used for dose characterization and prediction using Monte Carlo modeling. Dosimetric implications of different electron temperature scalings are investigated and the resulting equivalent doses are compared. It was found that scaling defined by Beg et al.(1997) predicts the highest electron temperatures for given intensities, and subsequently the highest doses. The atomic number of the target, x-ray generation efficiency and interaction volume are the other parameters necessary for the dose evaluation. The set of these operational parameters should be sufficient to characterize radiological characteristics of ultrashort laser pulse based x-ray generators and evaluate radiological hazards of the laser processing facilities.

A Numerical Method for Pulse Propagation in Nonlinear Dispersive Optical Media

In this work, the pulse propagation in a nonlinear dispersive optical medium is numerically investigated. The finite difference time-domain scheme of third order and periodic boundary conditions are used to solve generalized nonlinear Schr¨odinger equation governing the propagation of the pulse. As a result a discrete system of ordinary differerential equations is obtained and solved numerically by fourth order Runge-Kutta algorithm. Varied input ultrashort laser pulses are used. Accurate results of the solutions are obtained and the comparison with other results is excellent.

Nonlinear Absorption and Refraction of Picosecond and Femtosecond Pulses in HgTe Quantum Dot Films

We report measurements of the saturated intensities, saturable absorption, and nonlinear refraction in 70-nm thick films containing 4 nm HgTe quantum dots. We demonstrate strong nonlinear refraction and saturable absorption in the thin films using tunable picosecond and femtosecond pulses. Studies were carried out using tunable laser pulses in the range of 400–1100 nm. A significant variation of the nonlinear refraction along this spectral range was demonstrated. The maximal values of the nonlinear absorption coefficients and nonlinear refractive indices determined within the studied wavelength range were −2.4 × 10−5 cm2 W−1 (in the case of 28 ps, 700 nm probe pulses) and −3 × 10−9 cm2 W−1 (in the case of 28 ps, 400 nm probe pulses), respectively. Our studies show that HgTe quantum dots can be used in different fields e.g., as efficient emitters of high-order harmonics of ultrashort laser pulses or as laser mode-lockers.

Ultrafast spectroscopy of C-H vibrations in pathogenic bacteria in 3-μm spectral range

Dynamic optical density spectra were obtained under multipulse excitation of bacterial cultures of S. aureus and P. aeruginosa by 3 μm mid-infrared ultrashort laser pulses, corresponding to the vibrational excitation of the C–H bonds of the bacterial cell. These spectra demonstrated pronounced laser intensity-dependent blue spectral shift, presumably associated with the breaking of hydrogen bonds, which are responsible for the formation of secondary and tertiary protein structures.