Thermophotovoltaic generation of electricity : Sixth Conference on Thermophotovoltaic Generation of Electricity, TPV6, Freiburg, Germany, 14-16 June, 2004 / by Conference on Thermophotovoltaic Generation of Electricity (6th : 2004 : Freiburg, Germany), Gopinath, Ashok, Coutts, T. J., Luther, J., United States. Naval Sea Systems Command