We present a method for enhancing the light conversion efficiency of a luminescent solar concentrator by putting a prism film on the upper surface for receiving the incoming light. The luminescent solar concentrator under study was composed of a thick glass with a luminescent film deposited on the top surface and a solar cell attached to the lateral surface. The prism film will deflect the incident light into two different directions. Dependence of the conversion efficiency on the incident angle of the sunlight and influence of the rotation of the prism film on the conversion efficiency were also investigated. Experimental results show that the prism film will increase the light falling on the solar cell in our luminescent solar concentrator.
In this paper, the luminescent solar concentrator comprises a thick glass with a spectrally-selective optical coating deposited on the bottom surface and an inorganic phosphor layer contacted on the coating surface. A solar cell is contacted to the lateral surface of the thick glass. Spectrally-selective coatings are applied to reflect and redirect the invisible solar radiation to the edges of luminescent solar concentrators. These coatings also transmit the visible solar light and the emission light of the inorganic phosphor. The short-circuit current of the solar cell is measured in a flashing-mode solar simulator with metal-dielectric heat mirrors and dielectric edge filters coated on the thick glass of the luminescent solar concentrators respectively. Experimental results show that the dielectric edge filter will increase the short-circuit current of the solar cell and the invisible light falling on the solar cell in our luminescent solar concentrator. The metal-dielectric coatings, silver-based transparent heat mirrors, will not increase the short-circuit current of the solar cell in our luminescent solar concentrator due to absorption of metal films.
By using a light-emitting diode as the probing light source and a Shack-Hartmann wave-front sensor to execute a relative measurement, we present a simple and sensitive method for measuring surface fluctuation of a nominally flat sample. We used an epitaxial wafer for test. The reflected wave front from the surface of the sample was first calibrated to be a planar surface. The surface fluctuation of the test sample could be estimated from the increment on the variance of the wave-front surface to its regression plane after the sample had been shifted by a small distance by using the Bienaymé formula.
Conventionally, it is a tedious work to measure the beam quality factor for a laser beam because one needs to move a camera-based beam profiler from one location to another for many times to record intensity profiles at different positions around the beam waist. We present a simple method for determining the laser beam quality factor from only two laser intensity profiles at different cross sections around the waist. We first used an iterative phase-retrieval algorithm, based on the Huygens-Fresnel principle, to reconstruct the phase profiles at the two cross sections where the intensity profiles had been measured. Once the optical field amplitude (the square root of intensity) and phase distribution functions at certain cross section of a laser beam had been determined, we can propagate the light wave at this cross section by using the Fresnel diffraction formula to obtain the intensity profiles at different positions, from which the beam quality factor can be determined. Using a HeNe laser for test, we had experimentally demonstrated the feasibility of our idea by showing that the result from our proposed method is in good agreement with that obtained from the conventional method. Our setup is capable of executing a real-time measurement of the beam quality factor because the two intensity profiles can be simultaneously recorded by using a beam splitter and two beam-profilers controlled by the same computer.