Pattern recognition with a digital holographic microscope working in partially coherent illumination

Abstract

We describe the implementation of the automatic spatial-frequency-selection filter for recognition of patterns obtained with a digital holographic microscope working with a partially coherent source. The microscope provides the complex-optical-amplitude field that allows a refocusing plane-by-plane of the sample under investigation by numerical computation of the optical propagation. By inserting a correlation filter in the propagation equation, the correlation between the filter and the propagated optical field is obtained. In this way, the pattern is located in the direction of the optical axis. Owing to the very weak noise level generated by the partially coherent source, the correlation process is shift invariant. Therefore the samples can be located in the three dimensions. To have a robust recognition process, a generalized version of the automatic spatial-frequency-selection filters has been implemented. The method is experimentally demonstrated in a two-class problem for the recognition of protein crystals.

Characterisation of laser marks using digital holographic microscopy

“…5 shows the unwrapped phase contrast image. The quantitative value of the phase is converted to a length scale using equation (12). It can be directly used for 3D profile measurement of the laser mark.…”

“…Various digital approaches have been presented to correct the curvature of the MO by using a digital phase mask [7][8][9]. It has been demonstrated that quantitative phase contrast images are possible and can be used directly for applications in optical metrology [10][11][12].…”

Off-axis multispectral digital holographic microscope with partially coherent illumination

“…DHM provides a numerical investigation of the third dimension by performing a plane-by-plane refocusing that overcomes the small depths of focus due to the high numerical apertures of the microscope lenses and the high magnification ratios. Due to the knowledge of the full complex amplitude provided by DHM, advanced hologram processing techniques were successfully developed, as for few examples, for automated pattern recognition [14,15], the control of the parameters and aberrations of DHM [16,17] and automated refocusing [18][19][20][21][22]. To counter the coherent noise, several configurations were proposed with optical sources of partial coherence [2,12,13,23,24].…”

Three-dimensional image fusion using computational holographic imaging

“…In Digital Holography (DH) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15], direct recording of a hologram by means of a solid-state sensor is possible in alternative to the use of film or plate. The recorded digital hologram can be numerically processed to calculate the complex wave front originally scattered or diffusively transmitted by the object under investigation.…”

“…From the complex wave front it is possible to extract separately the amplitude and the phase. Numerous applications have been exploited in the recent years for the DH in various contexts like image encryption [2], 3D imaging and object comparison [3], metrology for mechanics of materials [4] recognition of three-dimensional objects and patterns [5][6], and microscopy [7]. One of the advantages offered by DH is the possibility to use multiple wavelengths.…”