**4. Microscopic object analysis using DHM**

194 Advanced Holography – Metrology and Imaging

For comparison figure 12b shows the phase image calculated from the same hologram and

With the analysis of the intensity image reconstruction we demonstrate the ability of DPA to

Figure 13 shows a comparison between DPA (row A) and ASA (row B) in the reconstruction of several holograms where the best focus of the image is: *d'=0 mm*, *d'=10 mm*, *d'=30 mm* and

**d' 0 mm 10 mm 30 mm 70 mm** 

According to figure 13, as the reconstruction distance *d'* increases, the size of the reconstructed intensity image is constant for both algorithm until *d' = 10 mm*. For values of *d'* bigger than 20 mm, the size of the reconstructed intensity image is reduced when the ASA is used, whereas it remain constant when is used the DPA. The effect is most obvious for *d'* 

Summarizing, two main advantages can be attributed to the DPA algorithm: capability to maintain the size of a reconstructed image, independent of the reconstruction distance and wavelength for objects larger than a CCD and phase reconstruction with curvature compensation without the necessity of either a reference hologram or parameter adjustment. For a hologram of 1024 x 768 pixels using a standard PC computer (Pentium IV, 3.2 GHz) the required time for the calculation of the phase image, the intensity image and the distance *D* is 2.3, 1.2 and 2.6 seconds respectively. The limitations are related to the two manual filtering stages that exist in the reconstruction process. After the first propagation, the manual selection of Fourier transform components at the back focal plane can introduce

Fig. 13. Comparison between DPA (row A) and ASA (row B) in the intensity image

reconstructed with the ASA, but using a reference hologram (Colomb et al., 2006).

**3.1.4 Refocusing at different reconstruction distances** 

refocus at different distances *d'*.

reconstruction for different distances *d'*.

others element that disturb the reconstructed plane.

*d'=70 mm*.

**A** 

**B** 

*= 70 mm*.

In this section we study microscopic objects with regular forms starting from their Fraunhofer diffraction patterns obtained with DHM. Two types of analysis are considered: (i) analysis of objects according to their spatial distribution and (ii) analysis of individual objects.
