CARS detection with diode lasers in digital holographic microscopy

The subject of this paper is coherent anti-Stokes Raman scattering (CARS) detection of different groups at molecular level in cells with low-energy CW diode lasers in parallel and simultaneously with holographic recording. This is essential for the non-invasive 3D reconstruction and markers free labeling of biological objects. A laboratory version of the diode lasers microscopic system with attachment for spectral detection is presented. Experimental results for parallel holographic recording of fixed cells and detection of CARS signals from different groups at molecular level, including — (S-H), (C-H) and (=(CH)) are obtained. They shows an advantage of the used phase-stepping algorithm (PSA) over a Fast Fourier Transform (FFT) algorithm for phase retrieval. The sensitivity of the CARS detection with diode lasers is estimated and compared for the same objects with a standard Raman micro spectrometer. The developed system is compact, suitable to perform measurement in real-time operation mode, and promising for markers free labeling of holographical reconstructed 3D images of the cells with parallel recorded 2D pictures of the CARS signals.