Dual-wavelength image-plane digital holography for dynamic measurement

Abstract

a b s t r a c tA dual-wavelength image-plane digital holography, combined with a windowed Fourier analysis, is presented for dynamic measurement of a vibrating object. In order to expand the range of the velocity measurement, the object is simultaneously illuminated by two lasers with different wavelengths. A sequence of digital holograms of a vibrating object is captured by a CCD camera and two wrapped phase maps are retrieved from each digital hologram. At each instant, a new phase distribution with a synthetic wavelength is obtained by subtracting these two wrapped phase maps. A windowed Fourier analysis is then applied spatially and temporally to retrieve the high-precision displacement and velocity of the tested object. Experimental results show the requirement on the camera capture frequency is reduced by the proposed method.

Applications of Digital Holography in Biomedical Microscopy

“…14, No. 2, June 2010 80 Other methods of numerical diffraction include wavelet or Fresnelet approach [53], fractional Fourier transform for highly astigmatic systems [54], and windowed Fourier analysis [55]. The Wigner space diagram is utilized for spacebandwidth analysis of holographic image formation [41].…”

Three-dimensional Information and Refractive Index Measurement Using a Dual-wavelength Digital Holographic

“…The concept of recording two holograms at different wavelength has been demonstrated and is proposed to solve 2π ambiguities in digital holography [15][16][17][18]. We can calculate the distribution of refractive indices of the sample simultaneously using dual-wavelength digital holography.…”

“…Its refractive index was 1.526 at the 632-nm wavelength and 1.535 at the 532-nm wavelength. We used index matching oil to resolve the 2π ambiguity, because the height of the sample was greater than that of the wavelength [17,18]. If the height of the sample had been less than the wavelength, the matching oil would not have been necessary.…”

Single Shot Dual-Wavelength Digital Holography: Calibration Based on Speckle Displacements

“…However, these methods fail when a single shot measurement is used for online quality control purposes as the frequency components of each wavelength are embedded in different places of the image spectrum. [17][18][19] Different laser sources in the single shot measurements, induce extra aberration and pseudo phase changes that can be suppressed by applying the modified flat fielding method. [9,11,20] In the flat fielding method they use a single dark frame and a flat frame captured from the system containing dual wavelengths to calibrate the measured data.…”