An examination of the efficiencies of three commonly used nonlinear crystals (PPKTP, LBO, and BiBO) when
generating second harmonic of a Cesium laser is presented. The experiment investigates both the intracavity and single
pass second harmonic generation of 895 nm Cs laser light when operating in quasi-CW and in CW modes and pumped
by several watts. A degradation of the conversion efficiencies for each crystal was observed when high fundamental
powers or a high duty cycle of the pump were used. For a Cs laser operating at 894nm, PPKTP is found to be the optimal
crystal for intracavity SHG in both pulsed and CW modes when operating at SHG powers of several watts. At higher
powers, however, the increased absorption coefficient of PPKTP at 447nm, compared to that of BiBO or LBO, may
become significant to where another crystal will be more appropriate for this application. Maximum blue light power
obtained with PPKTP crystal was about 1.5W in CW mode and 2.5W in QCW.
A major problem of current silicon thin film solar cells lies in low carrier collection efficiency due to short carrier diffusion length. Instead of improving the collection efficiency in a relatively thick solar cell, increasing light absorption while still keeping the active layer thin is an alternative solution. Absorption enhancement in a thin film Si solar cell by incorporating a two-dimensional periodic metallic nanopattern was investigated using three-dimensional finite element analysis. By studying the enhancement effect brought by different materials, dimensions, coverage, and dielectric environments of the metal nanopattern, we found that absorption enhancement occurs at wavelength range outside surface plasmons resonance of the nanostructures. The exploitation of the nanostructures also enhances the Fabry-Perot resonance in the active layer. It plays an important role in optimizing the absorption of the solar cell.
Conference Committee Involvement (1)
Terahertz Physics, Devices, and Systems
2 October 2006 | Boston, Massachusetts, United States