Vittorio Bianco

Imaging live humans through smoke and flames using far-infrared digital holography

The ability to see behind flames is a key challenge for the industrial field and particularly for the safety field. Development of new technologies to detect live people through smoke and flames in fire scenes is an extremely desirable goal since it can save human lives. The latest technologies, including equipment adopted by fire departments, use infrared bolometers for infrared digital cameras that allow users to see through smoke. However, such detectors are blinded by flame-emitted radiation. Here we show a completely different approach that makes use of lensless digital holography technology in the infrared range for successful imaging through smoke and flames. Notably, we demonstrate that digital holography with a cw laser allows the recording of dynamic human-size targets. In this work, easy detection of live, moving people is achieved through both smoke and flames, thus demonstrating the capability of digital holography at 10.6 μm.

Random resampling masks: a non-Bayesian one-shot strategy for noise reduction in digital holography

Holographic imaging may become severely degraded by a mixture of speckle and incoherent additive noise. Bayesian approaches reduce the incoherent noise, but prior information is needed on the noise statistics. With no prior knowledge, one-shot reduction of noise is a highly desirable goal, as the recording process is simplified and made faster. Indeed, neither multiple acquisitions nor a complex setup are needed. So far, this result has been achieved at the cost of a deterministic resolution loss. Here we propose a fast non-Bayesian denoising method that avoids this trade-off by means of a numerical synthesis of a moving diffuser. In this way, only one single hologram is required as multiple uncorrelated reconstructions are provided by random complementary resampling masks. Experiments show a significant incoherent noise reduction, close to the theoretical improvement bound, resulting in image-contrast improvement. At the same time, we preserve the resolution of the unprocessed image.

Diagnostic Tools for Lab-on-Chip Applications Based on Coherent Imaging Microscopy

Today, fast and accurate diagnosis through portable and cheap devices is in high demand for the general healthcare. Lab-on-chips (LoCs) have undergone a great growth in this direction, supported by optical imaging techniques more and more refined. Here we present recent progresses in developing imaging tools based on coherent imaging microscopy that can be very useful when applied into biomicrofluidics. In some cases, the optical tweezers (OT) technique is combined with digital holography (DH), thus offering the possibility to manipulate, analyze, and measure fundamental parameters of different kinds of cells. This approach can open the route for rapid and high-throughput analysis in label-free microfluidic devices and for prognostic based on cell examination, thus allowing advancements in biomedical science.

Encoding multiple holograms for speckle-noise reduction in optical display

In digital holography (DH) a mixture of speckle and incoherent additive noise, which appears in numerical as well as in optical reconstruction, typically degrades the information of the object wavefront. Several methods have been proposed in order to suppress the noise contributions during recording or even during the reconstruction steps. Many of them are based on the incoherent combination of multiple holographic reconstructions achieving remarkable improvement, but only in the numerical reconstruction i.e. visualization on a pc monitor. So far, it has not been shown the direct synthesis of a digital hologram which provides the denoised optical reconstruction. Here, we propose a new effective method for encoding in a single complex wavefront the contribution of multiple incoherent reconstructions, thus allowing to obtain a single synthetic digital hologram that show significant speckle-reduction when optically projected by a Spatial Light Modulator (SLM).

Clear coherent imaging in turbid microfluidics by multiple holographic acquisitions

Recently it has been demonstrated that digital holography is a powerful means allowing imaging of both amplitude and phase objects in turbid flowing media. However, in quasi-static turbid microfluidics, multiple scattering contributions through the colloids superimpose coherently to the recording device, resulting in speckle noise and hindering a clear vision of the objects. In this Letter we exploit the Brownian motion of the colloidal particles to get multiple uncorrelated holograms, and we combine them to reduce the speckle contrast. In this way we get a multi-look gain without losing image resolution.

Quasi noise-free digital holography

One of the main drawbacks of Digital Holography (DH) is the coherent nature of the light source, which severely corrupts the quality of holographic reconstructions. Although numerous techniques to reduce noise in DH have provided good results, holographic noise suppression remains a challenging task. We propose a novel framework that combines the concepts of encoding multiple uncorrelated digital holograms, block grouping and collaborative filtering to achieve quasi noise-free DH reconstructions. The optimized joint action of these different image-denoising methods permits the removal of up to 98% of the noise while preserving the image contrast. The resulting quality of the hologram reconstructions is comparable to the quality achievable with non-coherent techniques and far beyond the current state of art in DH. Experimental validation is provided for both single-wavelength and multi-wavelength DH, and a comparison with the most used holographic denoising methods is performed.

Imaging through scattering microfluidic channels by digital holography for information recovery in lab on chip

We tackle the problem of information recovery and imaging through scattering microfluidic chips by means of digital holography (DH). In many cases the chip can become opalescent due to residual deposits settling down the inner channel faces, biofilm formation, scattering particle uptake by the channel cladding or its damaging by corrosive substances, or even by condensing effect on the exterior channels walls. In these cases white-light imaging is severely degraded and no information is obtainable at all about the flowing samples. Here we investigate the problem of counting and estimating velocity of cells flowing inside a scattering chip. Moreover we propose and test a method based on the recording of multiple digital holograms to retrieve improved phase-contrast images despite the strong scattering effect. This method helps, thanks to DH, to recover information which, otherwise, would be completely lost.

Self-propelling bacteria mimic coherent light decorrelation

We show here that live e-coli bacterial culture, thanks to the self-propelling feature, can significantly reduce the coherent noise. In fact, the typical self-propelled drive of such microorganisms provides enough time diversity in speckle patterns. Optical properties of a bacteria suspension have been investigated and analyzed thus showing that it behaves as a quite good optical speckle decorrelation device. Samples with different bacteria densities have been studied. The decorrelation effect has been demonstrated by probing the imaging performance in through transmission in coherent microscope configuration.

Spatio-temporal scanning modality for synthesizing interferograms and digital holograms

We investigate the spatio-temporal scanning of a single-pixel row for building up synthetic interferograms or digital holograms, shifted each other of a desired phase step. This unusual recording modality exploits the object movement to synthesize interferograms with extended Field of View and improved noise contrast. We report the theoretical formulation of the synthetizing recording process and experimental evidence of various cases demonstrating quantitative phase retrieval by adopting this intrinsic phase-shifting procedure. The proposed method could be particularly suited in all cases where the object shift is an intrinsic feature of the investigated system, as e.g. in microfluidics imaging.

Clear Microfluidics Imaging Through Flowing Blood by Digital Holography

Achieving a clear vision through turbid fluids is a highly desirable goal in microfluidics. In particular, observing particles dipped inside blood shows fascinating perspectives in all fields of bio-medical research. White-light microscopy cannot provide clear imaging due to the strong scattering of light by red blood cells. Here we solve the problem by Digital Holography microscopy. We show that, in cases where the blood flows along a microfluidic channel at sufficient speed, the hologram acts as a selective filter. This occurs due to the Doppler frequency shift experienced by the photons hitting the red blood cells, discarding the unwanted scattering. In cases where the blood flow is not quick enough to take advantage of the Doppler shift, multiple holograms can be processed to produce a clear image of the object. We show that the correlation coefficients between multiple acquisitions at different fluid speeds can be adopted to study the visibility of the fringes due to the moving colloidal particles in the medium. Hence, we estimate the threshold velocity required to completely discard all the scattered photons. In this way the object is seen as dipped in a transparent liquid thus completely eliminating the negative effect of turbidity on the imaging.