Significance: Digital holographic microscopy is widely used to get the quantitative phase information of transparent cells.
Aim: However, the sample phase is superimposed with aberrations. To quantify the phase information, aberrations need to be fully compensated.
Approach: We propose a technique to obtain aberration-free phase imaging, using the derivative-based principal component analysis (dPCA).
Results: With dPCA, almost all aberrations can be extracted and compensated without requirements on background segmentation, making it efficient and convenient.
Conclusions: It solves the problem that the conventional principal component analysis (PCA) algorithm cannot compensate the common but intricate higher order cross-term aberrations, such as astigmatism and coma. Moreover, the dPCA strategy proposed here is not only suitable for aberration compensation but also applicable for other cases where there exist cross-terms that cannot be analyzed with the PCA algorithm.
Reflective liquid crystal spatial light modulator (SLM) is a widely used optical instrument because of its brilliant and high precision wavefront modulation ability. However, as mentioned by the producer and other researchers, the plane of SLM is not ideally flat but distorted during the manufacturing process. Here, we presented an automatic procedure for aberration correction based on interference. After the aberrations being measured with a wavefront sensor, the correction wavefront is automatically obtained by analyzing these aberrations. Then, the correction wavefront can be used to compensate the inherent distortion of SLM. This method is simple, user friendly and effective.
Over recent years, a research of wide-band light interference has led to new hope for three-dimensional fluorescence detecting without scanning. The research is the Fresnel incoherent correlation holography (FINCH) based on splitting light with a spatial light modulator (SLM). However, the conventional FINCH system is not that much effective to record weak fluorescent signal. It is mainly because the key parameter, optical path difference (OPD), that affects wideband light interference is not small enough. We note that the OPD can be decreased by adopting a spherical reference wave whose focal length is close to that of the object wave. And the hologram recordable area can be shifted from the area that is at a long distance from image plane to its neighborhood. This leads to the improvements of signal-to-noise ratio (SNR) of images and makes this method more suitable for recording weak fluorescent signal. In this investigation, we analyze the OPD character of this fluorescence holographic system and present how the OPD effects the choosing of experimental parameters to obtain high quality interference patterns. We also find that the central part of a wavefront is more likely to be decoded compared with the edge part.