The wavefront coding imaging technology is a good approach of extending DOF (depth of field) of imaging
optical system with an identical exit pupil. A phase mask being introduced in the exit pupil of the optical system makes
the MTF of the system to be defocus-independent. As a result, the DOF of the system is extended without a loss of
resolution. How much this technique can extend the DOF of optical system? It was shown by experimental and
simulation results of some papers that a wavefront coding imaging system can make the DOF raise an order of
magnitude. However, there is no theoretical analysis of DOF extension of wavefront coding technique up to now. In this
paper, a special condition under which MTF of wavefront coding system is defocus-independent is discovered by
investigating the OTF of the wavefront coding imaging system with cubic phase mask. Based on the condition, an
expression of the DOF of wavefront coding imaging system is obtained. The conclusion is verified by the simulation
results.
Aluminium thin film is widely used for high reflectivity reflector. However, it is readily corroded in a variety of environments and in oxygen saturated water. Coatings deposition on it is considered as a way of increasing its corrosion resistance. Among all available deposition techniques, the use of plasma-assisted technologies has grown rapidly. Organosilicon monomers have been successfully used as precursors of Si-based films and among them hexamethyldisiloxane (HMDSO) has gained increasing interest owing to its lower cost and higher deposition rates comparing to similar silicon containing monomers. This work studies the effects of depositing parameters on the structure and composition of the coating and at last on the corrosion protection performance concerning their use as protective coatings on reflective aluminum metallisations. Therefore, we have done a serial of experiments and got corresponding samples with different parameters such as HMDSO glow discharge power and depositing time. In the experiments, the plasma polymerized HMDSO thin films have been obtained in a DC glow discharge from the monomer vapor. And then the corrosion protection performances are analyzed by environment experiments. To analyze the reason of the deposition parameters effect on protection performances, the chemical structure and composition of the films have been analyzed.
The coupling between two fibers with suitable microlens is more effective than directly coupling. The distance between two fibers can be enlarged eight times, but the coupling coefficient increases twenty to seventy times and the diameter of the focus facula decreases to 70%.
A highly accurate optical fiber liquid level sensor is presented. The single-chip microcomputer is used to process and control the signal. This kind of sensor is characterized by self-security and is explosion-proof, so it can be applied in any liquid level detecting areas, especially in the oil and chemical industries. The theories and experiments about how to improve the measurement accuracy are described. The relative error for detecting the measurement range 10 m is up to 0.01%.
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