Multiwavelength phase unwrapping and aberration correction using depth filtered digital holography

Abstract

In this Letter, we present a new approach to processing data from a standard spectral domain optical coherence tomography (OCT) system using depth filtered digital holography (DFDH). Intensity-based OCT processing has an axial resolution of the order of a few micrometers. When the phase information is used to obtain optical path length differences, subwavelength accuracy can be achieved, but this limits the resolvable step heights to half of the wavelength of the system. Thus there is a metrology gap between phase- and intensity-based methods. Our concept addresses this metrology gap by combining DFHD with multiwavelength phase unwrapping. Additionally, the measurements are corrected for aberrations. Here, we present proof of concept measurements of a structured semiconductor sample.

Two-wavelength digital holographic interferometry for unambiguous range extended measurements in fluid mechanics

“…This implies that, if the two lasers have a smaller difference in wavelengths, then the new range of unambiguous measurement will increase. [5,9] For the case of multiple-wavelength interferometry, the synthetic wavelength can be defined as [15,6]:…”

“…Off-axis configuration spatially separates the holographic images away from the undiffracted zero order. [5,6] EPJ Web of Conferences 264, 01009 (2022) https://doi.org/10.1051/epjconf/202226401009 EFM 2021 and Two-wavelength interferometry can be used in many areas of optical metrology, such as for the measurement of the thickness and surface profile/inspections of objects [3]. It can be used in research dealing with samples having large topographical changes and biological samples [7].…”

Optical field data compression by opto-digital means

“…We now perform the FT of the registered hologram, The first two terms are the autocorrelations of the FT of the object and reference beams corresponding to the central order. The last two terms are the FT of the object field and its complex conjugate, spatially separated due to the convolution with the Dirac delta function resulting from the FT of the plane wave given by equation (2). Taking advantage of this spatial separation, we select the order corresponding to the FT of the third term of equation 3, filtering the remaining terms.…”

“…This technique has given rise to the development of sophisticated opto-digital methods that profit from both the properties of optical systems and the flexibility of digital data processing algorithms. Among the applications of digital holography, we find metrology, microscopy, medical imaging, and optical security [1][2][3][4][5][6][7][8][9][10], to name a few. Specifically, digital holography allows for recording information from 2D and 3D objects [11,12], providing additional degrees of freedom for optical processing [13][14][15], and consequently making possible the reconstruction of scenes with depth [16].…”

Experimental Fresnel and Fourier digital holography using a digital micro-mirror device

“…Digital holography is an extremely valuable technique, enabling important applications like holographic microscopy [1], metrology [2], optical security [3,4], to name a few. In particular, digital holography enables the digital recording of an optical field, which can then be processed using a broad range of computational techniques [5][6][7][8].…”