As optics and photonics technologies advance, more energy efficient use of light will be necessary. This dissertation presents methods developed to enhance the efficiency of three different optical systems: extreme ultraviolet lithography, a hybrid solar photovoltaic/thermal collection system, and thermo-photovoltaics. Extreme ultraviolet (EUV) lithography is the leading contender to become the next industrial scale lithography technology in the semiconductor industry. Traditionally, aberration correction in extreme ultraviolet projection optics requires the use of multiple lossy mirrors, which results in prohibitively high source power requirements. This dissertation analyzes a single spherical mirror projection optical system where aberration correction is built into the mask itself through an adjoint-based optimization algorithm. This greatly reduces the power requirements for the source. Hybrid solar photovoltaic/thermal systems offer a way to convert sunlight into electricity and heat that efficiently uses different parts of the solar spectrum. Highly efficient hybrid solar photovoltaic/thermal systems are enabled by recent advances in photovoltaic technology. Record breaking photovoltaic cells have highly reflective rear mirrors to maximize luminescence efficiency. This reflectivity can also be used to create reflective optics to concentrate the reflected radiation onto a thermal absorber. This dissertation reports on a hybrid solar photovoltaic/thermal system with a thermal efficiency of 37% at a maximum absorber temperature of 365°C, and a direct solar to electric efficiency of 8%. Thermo-photovoltaics offers a method to use photovoltaic cells to efficiently convert heat to electricity. In a thermo-photovoltaic system, light is collected by photovoltaic cells from a local black body source. This dissertation reports on a thermo-photovoltaic device that recycles unused radiation from the photovoltaics with a highly reflective rear mirror. Theoretical efficiencies using this strategy are in excess of 50%. For an emitter temperature of 1207°C, this dissertation reports an experimental power conversion efficiency of 28.1%.