We have studied the third order optical nonlinearities of Ge-As-Se-based glasses. The glasses have high melting and glass transition temperatures that offer the potential for integration with traditional compound oxide glasses into highly nonlinear, high-index-contrast fibers. We used z-scan and femtosecond pump-probe techniques to measure the nonlinear refractive index and two-photon absorption coefficient of the glasses at telecommunication wavelengths. Nonlinearities as high as ϳ900ϫ that of silica were measured at 1540 nm in Ge 35 As 15 Se 50 with a glass transition temperature of 380°C.
Carbon dioxide (CO2) lasers have become one of the most common surgical lasers due to excellent tissue interaction properties that offer precise control of cutting and ablation depth, minimal thermal damage to surrounding tissue, and good hemostasis. However, realization of the benefits offered by using surgical CO2 lasers in many endoscopic, minimally invasive surgical procedures has been inhibited by the absence of reliable, flexible fiber laser beam delivery systems. Recently, novel hollow-core photonic bandgap optical fibers for CO2 lasers were developed that offer high flexibility and mechanical robustness with good optical performance under tight bends. These fibers can be used through rigid and flexible endoscopes and various handpieces and will allow surgeons to perform delicate and precise laser surgery procedures in a minimally invasive manner. This paper describes the basic design of laser beam delivery system, different surgical fiber designs and their characteristics, and usage with existing surgical CO2 laser models. A few examples of successful CO2 laser surgeries performed with these fibers are presented.
Inelastic and superelastic electron scattering from the optically prepared 3 2 P 3͞2 state of sodium has enabled atomic collision parameters to be deduced for the 4S-3P deexcitation and the 3S-3P excitation processes. These data are compared with convergent close coupling and second order distorted wave Born calculations. For excitation, both theories agree with experiment, whereas for deexcitation the close coupling theory is in better agreement. A long-standing proposal relating to the sign of the transferred angular momentum is not supported. [S0031-9007 (98)07775-8] PACS numbers: 34.80.DpExtensive studies of electron collision-induced atomic transitions involving the ground state performed over the last 25 years have resulted in a substantial body of experimental data and have stimulated the development of a number of theoretical models ([1-3], and references therein). By contrast, few investigations have been devoted to electron-impact excitation of transitions between excited atomic states [4][5][6][7]. Theoretical models of electron-impact excitation, developed for atoms initially in the strongly bound ground state, may not be applicable for transitions between excited states that are less strongly bound to the atomic core. Electron excitation involving excited states plays an important role in electrical discharges, astrophysics, and in many branches of plasma physics, and so the study of these processes is of relevance in a number of different fields.Experimental techniques, such as electron-photon coincidence and superelastic methods, allow measurements of comprehensive sets of observables called the atomic collision parameters (ACPs), which directly relate to the complex scattering amplitudes. ACP measurements complement excitation differential cross section (DCS) measurements while providing more sensitive tests of different theoretical models. When the spin of the incident and scattered electron is not measured, a subset of the complete set of collision parameters is obtained. For transitions between S and P states for which spin-orbit interactions are negligible, four spin unresolved ACPs are required: the angular momentum transferred perpendicular to the scattering plane L Ќ , the degree of anisotropy of the atomic charge cloud P ᐉ , the charge cloud alignment angle g, and the degree of coherence P 1 [3].Of particular interest is the behavior of L Ќ as a function of scattering angle [8][9][10]. An analysis of general trends in the behavior of this parameter was performed in 1981 by Madison and Winters [11]. By expressing this parameter in terms of a Born series expansion for the transition matrix up to second order, their analysis indicated that for a ground S state to excited P state transition, L Ќ should be positive at small scattering angles and negative at larger angles. This qualitative prediction was supported for sodium by calculations using a second order distorted wave Born (DWB2) theory [12] and by experiment [13].Madison and Winters further proposed that for a positive projectile (i.e.,...
Abstract.Experimental apparatus and measurement technique are described for precision absorption measurements in sodium -noble gas mixtures. The absolute absorption coefficient is measured in the wavelength range from 425 nm to 760 nm with ±2% uncertainty and spectral resolution of 0.02 nm. The precision is achieved by using a specially designed absorption cell with an accurately defined absorption path length, low noise CCD detector and double-beam absorption measurement scheme. The experimental set-up and the cell design details are given. Measurements of sodium atomic number density with ±5% uncertainty complement absorption coefficient measurements and allow derivation of the reduced absorption coefficients for certain spectral features. The sodium atomic number density is measured using the anomalous dispersion method. The accuracy of this method is improved by employing a least-squares fit to the interference image recorded with CCD detector and the details of this technique are given. The measurements are 1 aimed at stringent testing of theoretical calculations and improving the values of molecular parameters used in calculations.
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