Demystifying speckle field interference microscopy

Abstract

Dynamic speckle illumination (DSI) has recently attracted strong attention in the field of biomedical imaging as it pushes the limits of interference microscopy (IM) in terms of phase sensitivity, and spatial and temporal resolution compared to conventional light source illumination. To date, despite conspicuous advantages, it has not been extensively implemented in the field of phase imaging due to inadequate understanding of interference fringe formation, which is challenging to obtain in dynamic speckle illumination interference microscopy (DSI-IM). The present article provides the basic understanding of DSI through both simulation and experiments that is essential to build interference microscopy systems such as quantitative phase microscopy, digital holographic microscopy and optical coherence tomography. Using the developed understanding of DSI, we demonstrated its capabilities which enables the use of non-identical objective lenses in both arms of the interferometer and opens the flexibility to use user-defined microscope objective lens for scalable field of view and resolution phase imaging. It is contrary to the present understanding which forces us to use identical objective lenses in conventional IM system and limits the applicability of the system for fixed objective lens. In addition, it is also demonstrated that the interference fringes are not washed out over a large range of optical path difference (OPD) between the object and the reference arm providing competitive edge over low temporal coherence light source based IM system. The theory and explanation developed here would enable wider penetration of DSI-IM for applications in biology and material sciences.

High space–time bandwidth product imaging in low coherence quantitative phase microscopy

“…Recently, to address these issues in QPM systems, spatially low and temporally coherent light source also called pseudo-thermal light source (PTLS), have been employed in QPM 3 , 6 , 9 , 16 – 20 . PTLS is generated when a highly coherent laser beam is passed through a rotating diffuser, the output of the diffuser has high temporal and low spatial coherence properties 19 .…”

Highly sensitive quantitative phase microscopy and deep learning aided with whole genome sequencing for rapid detection of infection and antimicrobial resistance

“…These light sources either generate highly sensitive phase images at the cost of reduced temporal resolution (for white light and LEDs) or provide high temporal resolution at the expense of less phase sensitivity (for laser; Ahmad et al, 2021). The pros and cons of these light sources in QPM have been discussed in great detail in Ahmad et al (2021) and Ahmad et al (2022). Recently, a temporally high and spatially low coherent light source, also known as a pseudothermal light source (PTLS), has been proposed to resolve the issues associated with using the aforementioned light sources in QPM (Choi et al, 2011(Choi et al, , 2018Ahmad et al, 2015Ahmad et al, , 2016Ahmad et al, , 2021Ankit et al, 2020).…”

“…QPM encodes information about the specimens’ optical thickness (refractive index × geometrical thickness) in terms of modulated intensity patterns called interferograms. Various optical configurations of QPM exist, such as diffraction phase microscopy ( Bhaduri et al, 2014 ), spatial light interference microscopy ( Wang et al, 2011 ), Linnik interference microscopy ( Dubois et al, 2002 ; Ahmad et al, 2021 , 2022 ), Mirau interference microscopy ( Ahmad et al, 2015 , 2016 , 2019 ), and Mach-Zehnder interference microscopy ( Loehrer et al, 2014 ).…”

Highly sensitive quantitative phase microscopy and deep learning complement whole genome sequencing for rapid detection of infection and antimicrobial resistance

“…The pros and cons of these light sources in QPM have been discussed in great details in Refs. [23,24]. Recently, a temporally high and spatially low coherent light source, also known as a pseudo-thermal light source (PTLS), has been proposed to resolve the issues associated with the use of aforementioned light sources in QPM [23,25,26,[29][30][31].…”

“…QPM encodes information about the specimens' optical thickness (refractive index × geometrical thickness) in terms of modulated intensity patterns called interferograms. There exist various optical configurations of QPM, such as diffraction phase microscopy [20], spatial light interference microscopy [21], Linnik interference microscopy [22][23][24], Mirau interference microscopy [25][26][27], and Mach-Zehnder interference microscopy [28].…”