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We utilize digital image-plane holographic microscopy (DIPHM) to achieve the real-time surface profile measurement of microstructure. The impulse response functions of DIPHM and traditional digital holographic microscopy (DHM) are both derived. The theoretical derivations indicate that the differences between the two techniques are caused by the diffraction effect of the recording plane with a finite size. The diffraction effect would introduce an unstable factor to the wavefront reconstruction. Therefore, the DIPHM has the characteristics of totally full field of view and low measuring noise compared to DHM. In addition, we take DIPHM and DHM in dual-wavelength mode as a special example to confirm the points above. From both experimental results and theoretical analysis, DIPHM is demonstrated to be an optimized technique with high-quality imaging, especially benefiting the situation where multi-wavelength measurement is required. This method is robust against environmental noise. SCANNING 38:288-296, 2016. © 2015 Wiley Periodicals, Inc.

A digital hologram-optimizing method was proposed to improve the imaging quality of dual-wavelength digital holographic microscopy (DDHM) by reducing the phase noise level. In our previous work, phase noise reduction was achieved by dual-wavelength digital image-plane holographic microscopy (DDIPHM). In the optimization method in this paper, the phase noise was further reduced by enhancing the real-image term and suppressing effects of the zero-order term in the frequency spectrum of a digital hologram. Practically, the carrier frequency of the real-image term has the correspondence with interference fringes in the hologram. Mathematically, the first order intrinsic mode function (IMF1) in bidimensional empirical mode decomposition (BEMD) has similar characteristics to the grayscale values of ideal interference fringes. Therefore, with the combination of DDIPHM and BEMD, by utilizing the characteristics of IMF1, the digital hologram was optimized with purified interference fringes, enhancing the real-image term simultaneously. Finally, the validity of the proposed method was verified by experimental results on a microstep.

We utilize digital image-plane holographic microscopy (DIPHM) to achieve the real-time surface profile measurement of microstructure. The impulse response functions of DIPHM and traditional digital holographic microscopy (DHM) are both derived. The theoretical derivations indicate that the differences between the two techniques are caused by the diffraction effect of the recording plane with a finite size. The diffraction effect would introduce an unstable factor to the wavefront reconstruction. Therefore, the DIPHM has the characteristics of totally full field of view and low measuring noise compared to DHM. In addition, we take DIPHM and DHM in dual-wavelength mode as a special example to confirm the points above. From both experimental results and theoretical analysis, DIPHM is demonstrated to be an optimized technique with high-quality imaging, especially benefiting the situation where multi-wavelength measurement is required. This method is robust against environmental noise. SCANNING 38:288-296, 2016. © 2015 Wiley Periodicals, Inc.