An autofocusing method using correlation coefficient (CC) is proposed for dual-wavelength off-axis digital holography. The complex amplitudes of the object wave relative to the two wavelengths are first retrieved at different reconstruction distances, and the correlation degrees are then calculated between the two complex amplitudes. Considered the diffraction independency between the two wavelengths, the maximum CC is employed to automatically determine the focus plane. Our method can be applicable for the amplitude, phase, or both mixed sample. The experimental results demonstrate that the proposed method can enable automatically autofocusing with higher resolution in contrast to the state-of-the-art method.
Based on the mode equations of the core mode LP01 and the cladding mode LP0M, combining with the phase matching condition, a method for simultaneous measurement of liquid refractive index and temperature using a single resonance
peak of long-period fiber grating's transmission spectrum is proposed. The operational principle is analyzed; experiments
are conducted. The theoretical results are compared with those of the experiments. The results show that they are in accordance with each other.
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