Off-axis multispectral digital holographic microscope with partially coherent illumination

Abstract

We developed a new off-axis digital holographic microscope (DHM), working in transmission with a RGB LED illumination. This partially coherent multi-wavenlenght source gives a low noise holograms and the intensity image quality is fully exploitable for microscopy purposes. We implemented a full off-axis configuration enables the recording of the holographic data in one shot. As we used for the first tests a monochromatic CCD camera, the holograms are recorded separately in each spectral channel. The holograms are individually processed by the Fourier method to obtain, in each color, the complex amplitudes and the corresponding intensities and optical phases. The color intensities are recombined to obtain a composite RGB color image. The digital holographic refocusing and the optical phase map computation are successfully demonstrated. The multi-wavelengths operation provides a significant improvement of the collected information for colored samples. The full one-shot color hologram recording should be available with a color camera.

Heterodyne Near Field Speckles: from laser light to X-rays

“…We can therefore interpret Equation 11 as the low-pass filtered hologram of the scattering particle. In this regard, applications to digital holographic microscopy are worth mentioning, where partially coherent illumination effectively suppresses the coherent speckled noise inherent in laser sources, as well as multiple reflection fringes [143][144][145][146][147][148][149][150][151][152]. This is definitely an asset for applications such as improved three-dimensional imaging [143], pattern recognition [144], three-dimensional particle flow analysis [146], characterization of deformable objects [147] and studies of vesicle suspensions in shear flow [150], to name a few.…”

Optical Investigation of Individual Red Blood Cells for Determining Cell Count and Cellular Hemoglobin Concentration in a Microfluidic Channel

“…Another dichroic mirror splits the light beam again into two separate paths. The blue path is captured directly by a monochromatic CCD-sensor (Grasshopper3 USB3, FLIR) (Figure 1a, camera 1), while the green light beam enters a patented [19,20] differential digital holographic module. In this module a diffraction grating, placed at the input plane, generates different diffraction orders, where the zero-order diffraction is referred to as the reference wave, while the first order diffraction carries the phase information of the sample.…”

An off-axis digital holographic microscope with quasimonochromatic partially spatially coherent illumination in transmission

“…In DHM the reconstruction of the complex coherence function can be performed through phase-shifting [9,10] or off-axis approaches [1][2][3][4][5][6][11][12][13]. The phase-shifting approach allows for more effective utilization of the sensor sampling capabilities; however, it requires several interference patterns to be recorded for the reconstruction of a single complex coherence function distribution.…”

“…This results in oversampling of the distribution of interest, but allows for the reconstruction from a single interference pattern. Along with the absence of additional elements for creating variable phase delay (which are required for phase-shifting) this opportunity makes the off-axis imaging approach very convenient for real-time applications and thus widely used [1][2][3][4][5][6][11][12][13][14].…”

“…To overcome these difficulties, several schemes of DHM with partially coherent illumination in transmission have been proposed in phase-shifting [10] and off-axis [11][12][13] modalities, and the possibility of holographic imaging with suppressed coherent noise has been demonstrated. In the proposed off-axis DHM schemes [11][12][13] the off-axis modality has been achieved by introducing a diffraction grating into the setup and enlargement of the optical system [11] or even more complicated designs of the optical scheme [12,13] in comparison to the phase-shifting DHM with partially coherent illumination [10].…”