Peter E. Andersen

Power Scaling of Nonlinear Frequency Converted Tapered Diode Lasers for Biophotonics

Diode lasers have proven to be versatile light sources for a wide range of applications. Nonlinear frequency conversion of high brightness diode lasers has recently resulted in visible light power levels in the watts range enabling an increasing number of applications within biophotonics. This review provides an overview of the developments within nonlinear frequency converted high power laser diodes in the visible spectral range. Single-pass nonlinear frequency doubling is presented as a nonsophisticated method to achieve watt-level output powers and possible routes to higher power and efficiency are included. Application examples within pumping of mode-locked Ti:sapphire lasers and implementation of such lasers in optical coherence tomography are presented showing the application potential of these lasers.

A novel diode laser system for photodynamic therapy

In this paper a novel diode laser system for photodynamic therapy is demonstrated. The system is based on linear spatial filtering and optical phase conjugate feedback from a photorefractive BaTiO3 crystal. The spatial coherence properties of the diode laser are significantly improved. The system provides an almost diffraction limited output which is efficiently coupled into a 50 micrometers core diameter fiber. The optical power transmitted through the fiber is increased by a factor of six when the feedback is applied to the diode laser. 85 percent of the power from the freely running laser diode is extracted in a high-quality beam and 80 percent of the output power is extracted through the fiber. The power transmitted through the fiber scales linearly with the power of the laser diode, which means that a laser diode emitting 1.7 W multi-mode radiation would provide 1 W of optical power through a 50 micrometers core diameter fiber. The system is compact, portable, stable, and easy to operate.

Local diffuse reflectance from three-layered skin tissue structures

We consider two different skin structure models. The first structure consists of epidermis, dermis/blood, and subcutaneous tissue. The second structure consists of epidermis/dermis, adipose tissue and muscle tissue. A new solution based on diffusion theory of the cw local diffuse reflectance from a three-layered skin tissue structure is presented. Comparisons with Monte Carlo simulations are carried out favorably. It is shown that the functional form of the radial dependence of the diffuse reflectance from multilayer and single layer models are identical. We use a modified expression originating from diffusion theory to fit the diffuse reflectance. We discuss the sensitivity of the local diffuse reflectance as a function of the optical properties of separate layers in both structures. Moreover, we investigate the influence on the local diffuse reflectance with changes in the optical properties corresponding to normal changes in tissue glucose concentration and blood volume. The necessity of multilayer models lies within their ability to provide a detailed description of the light-tissue interaction rate than their applicability to practical data analysis of the local diffuse reflectance measurements.

Comment: On the relative heats of formation of C 3 H 7 O + ions. An ab initio molecular orbital [G2(MP2) and CBS-Q] study

The heats of formation of the four C3H7O+ ions have been calculated using the G2(MP2) and CBS-Q theoretical procedures, to resolve a discrepancy between experimentally determined values.