Minority carrier diffusion length is a key parameter of material quality and gives an indication of diode performance. It is also one important parameter when considering the increase of the effective optical sensitive area caused by the lateral diffusion and the crosstalk between individual detectors on a focal plane array (FPA). In this paper, we perform diffusion length measurements with two methods on short wavelength infrared (SWIR) HgCdTe photovoltaic devices. One method is based on the different behaviors of electrons and holes in a variation magnetic field B and their effects on the saturation current density J0. The other method is an optical characterization technique called Laser Beam Induced Current (LBIC). The results were in good agreement with each other.
In this paper, we use diffractive superresolution technology to design a pure-phase plate for realizing the smaller spot size than the usual Airy spot size. We have calculated 2,3,4,5 circulation zones for optimizing the highest energy compression (Strelratio) with the constraint of the Firstzero value <i>G</i>=0.8. Numerical results show that the 2-circular zone pure-phase plate can yield the highest Strelratio (<i>S</i>=0.59) with the constraint of <i>G</i>=0.8.The 3-circular zone pure-phase plate with the respective phases of <i>φ</i><sub>1</sub><i>φ</i><sub>2</sub><i>φ</i><sub>3</sub> has also been calculated. At the same time the 4,5 circular zone binary phase (0,π) plates are calculated to yield the result of <i>S</i> = 0.57 with <i>G</i>=0.8. The usage of the superresolution phase plate aims to realize the smaller spot size instead of the usage of the higher numerical aperture lens, which is the main advantage of this superresolution technology. Therefore, in this constraint of <i>G</i>=0.8, we have selected the 2-circular zone with binary phase for ease of fabrication. At last, we use a 50 nanometer fiber tip detector to scan the diffractive superresolution light spot in order to compare it with the Airy spot. Detailed experiments are presented.
In a traditional sense, Dammann grating can transfer the beam into one dimensional spots or two dimensional spots, which can be used for beam splitter or array illuminators. This paper presents a new kind Dammann grating that can realize the equal peak value intensity circular diffractive field. We call it circular Dammann grating. And the order of the grating is the number of the circular diffractive spectrums. We use the binary phase-only mask in our numerical simulation, we have obtained the optimized parameters, including the circular phase and radius of each ring. Our optimization algorithm is the simulated annealling algorithm. Different order circular Dammann grating can generate different circular diffractive field. We have calculated the number from 1 to 9 diffractive spectrums and found that with the increase of the encoding number of circular Danimann grating, more circular equal-intensity diffractive spectrums can be realized. Different order Dammann gratings have practical applications for different purposes. For example, the first order circular Dammann grating produce the smooth intensity in the central lobe, which can be used as the flat-top intensity for the wide applications of optical interference, such as producing optical fiber grating, optical detection, etc. The multi order Dammann grating can be used for beaming shaping and laser demonstration. In conclusion, circular Dammann grating is a novel diffractive optical element that has wide applications in optical information system.