Sources and propagation of errors in quantitative phase imaging techniques using optical interferometry

Quantitative phase imaging (QPI) has many applications in a broad range of disciplines from astronomy to microbiology. QPI is often performed by optical interferometry, where two coherent beams of light are used to produce interference patterns at a detector plane. Many algorithms exist to calculate the phase of the incident light from these recorded interference patterns as well as enhance their quality by various de-noising methods. Many of these de-noising algorithms, however, corrupt the quantitative aspect of the measurement, resulting in phase contrast images. Among these phase calculation techniques and de-noising algorithms, none approach the optimization of phase measurements by theoretically addressing the various sources of error in its measurement, as well as how these errors propagate to the phase calculations. In this work, we investigate the various sources of error in the measurements required for QPI, as well as theoretically derive the influence of each source of error on the overall phase calculation for three common phase calculation techniques: the four bucket/step method, three bucket/step method, and the Carré method. The noise characteristics of each of these techniques are discussed and compared using error parameters of a readily available CCD sensor array. Additionally, experimental analysis is conducted on interferograms to investigate the influence of speckle noise on the phase measurements of the three algorithms discussed

Compact, lensless digital holographic microscope for remote microbiology

In situ investigation of microbial life in extreme environments can be carried out with microscopes capable of imaging 3-dimensional volumes and tracking particle motion. Here we present a lensless digital holographic microscope approach that provides roughly 1.5 micron resolution in a compact, robust package suitable for remote deployment. High resolution is achieved by generating high numerical-aperture input beams with radial gradient-index rod lenses. The ability to detect and track prokaryotes was explored using bacterial strains of two different sizes. In the larger strain, a variety of motions were seen, while the smaller strain was used to demonstrate a detection capability down to micron scales

Sources and propagation of errors in quantitative phase imaging techniques using optical interferometry

Quantitative phase imaging (QPI) has many applications in a broad range of disciplines from astronomy to microbiology. QPI is often performed by optical interferometry, where two coherent beams of light are used to produce interference patterns at a detector plane. Many algorithms exist to calculate the phase of the incident light from these recorded interference patterns as well as enhance their quality by various de-noising methods. Many of these de-noising algorithms, however, corrupt the quantitative aspect of the measurement, resulting in phase contrast images. Among these phase calculation techniques and de-noising algorithms, none approach the optimization of phase measurements by theoretically addressing the various sources of error in its measurement, as well as how these errors propagate to the phase calculations. In this work, we investigate the various sources of error in the measurements required for QPI, as well as theoretically derive the influence of each source of error on the overall phase calculation for three common phase calculation techniques: the four bucket/step method, three bucket/step method, and the Carré method. The noise characteristics of each of these techniques are discussed and compared using error parameters of a readily available CCD sensor array. Additionally, experimental analysis is conducted on interferograms to investigate the influence of speckle noise on the phase measurements of the three algorithms discussed

Microbial Morphology and Motility as Biosignatures for Outer Planet Missions

Meaningful motion is an unambiguous biosignature, but because life in the Solar System is most likely to be microbial, the question is whether such motion may be detected effectively on the micrometer scale. Recent results on microbial motility in various Earth environments have provided insight into the physics and biology that determine whether and how microorganisms as small as bacteria and archaea swim, under which conditions, and at which speeds. These discoveries have not yet been reviewed in an astrobiological context. This paper discusses these findings in the context of Earth analog environments and environments expected to be encountered in the outer Solar System, particularly the jovian and saturnian moons. We also review the imaging technologies capable of recording motility of submicrometer-sized organisms and discuss how an instrument would interface with several types of sample-collection strategies

Robust, compact implementation of an off-axis digital holographic microscope

Recent advances in digital technologies, such as high-speed computers and large-format digital imagers, have led to a burgeoning interest in the science and engineering of digital holographic microscopy (DHM). Here we report on a novel off-axis DHM, based on a twin-beam optical design, which avoids the limitations of prior systems, and provides many advantages, including compactness, intrinsic stability, robustness against misalignment, ease of use, and cost. These advantages are traded for a physically constrained sample volume, as well as a fixed fringe spacing. The first trade is not overly restrictive for most applications, and the latter provides for a pre-set assembly alignment that optimizes the spatial frequency sampling. Moreover, our new design supports use in both routine laboratory settings as well as extreme environments without any sacrifice in performance, enabling ready observation of microbial species in the field. The instrument design is presented in detail here, along with a demonstration of bacterial video imaging at sub-micrometer resolution at temperatures down to –15 °C

A Multi-Modal Volumetric Microscope with Automated Sample Handling for Surveying Microbial Life in Liquid Samples

In the study of microbial life, microscopy plays a unique role due to its ability to detect ordered structure, motility, and fluorescence signals. As such it has also recently gained attention in the context of searching for extant life on distant Solar System bodies bearing liquid water. In this paper we introduce a multimodal volumetric microscopy system for potential future spaceflight missions that combines digital holographic microscopy (DHM) and volume fluorescence imager (VFI), which are volumetric imaging methods that provide highresolution, high-throughput examination of liquid samples. DHM provides information on the absorption, morphology, and motility of imaged objects without requiring the use of contrast agents. On the other hand, VFI based on light field microscopy focuses on the fluorescence signals from the sample to observe specific structures dyed with targeted contrast agents or providing unique autofluorescence signals. We also present an autonomous sample handling and data acquisition system to allow for an autonomous mission to distant planets or moons, or for autonomous use in bodies of water on Earth. The full system, named ELVIS, or Extant Life Volumetric Imaging System, is capable of autonomously surveying a liquid sample to extract morphology, motility, and fluorescence signals of extant microbial life

Onboard Science Instrument Autonomy for the Detection of Microscopy Biosignatures on the Ocean Worlds Life Surveyor

The quest to find extraterrestrial life is a critical scientific endeavor with civilization-level implications. Icy moons in our solar system are promising targets for exploration because their liquid oceans make them potential habitats for microscopic life. However, the lack of a precise definition of life poses a fundamental challenge to formulating detection strategies. To increase the chances of unambiguous detection, a suite of complementary instruments must sample multiple independent biosignatures (e.g., composition, motility/behavior, and visible structure). Such an instrument suite could generate 10,000x more raw data than is possible to transmit from distant ocean worlds like Enceladus or Europa. To address this bandwidth limitation, Onboard Science Instrument Autonomy (OSIA) is an emerging discipline of flight systems capable of evaluating, summarizing, and prioritizing observational instrument data to maximize science return. We describe two OSIA implementations developed as part of the Ocean Worlds Life Surveyor (OWLS) prototype instrument suite at the Jet Propulsion Laboratory. The first identifies life-like motion in digital holographic microscopy videos, and the second identifies cellular structure and composition via innate and dye-induced fluorescence. Flight-like requirements and computational constraints were used to lower barriers to infusion, similar to those available on the Mars helicopter, "Ingenuity." We evaluated the OSIA's performance using simulated and laboratory data and conducted a live field test at the hypersaline Mono Lake planetary analog site. Our study demonstrates the potential of OSIA for enabling biosignature detection and provides insights and lessons learned for future mission concepts aimed at exploring the outer solar system.Comment: 49 pages, 18 figures, submitted to The Planetary Science Journal on 2023-04-2

Terrestrial Planet Finder: Technology Development Plans

One of humanity's oldest questions is whether life exists elsewhere in the universe. The Terrestrial Planet Finder (TPF) mission will survey stars in our stellar neighborhood to search for planets and perform spectroscopic measurements to identify potential biomarkers in their atmospheres. In response to the recently published President's Plan for Space Exploration, TPF has plans to launch a visible-light coronagraph in 2014, and a separated-spacecraft infrared interferometer in 2016. Substantial funding has been committed to the development of the key technologies that are required to meet these goals for launch in the next decade. Efforts underway through industry and university contracts and at JPL include a number of system and subsystem testbeds, as well as components and numerical modeling capabilities. The science, technology, and design efforts are closely coupled to ensure that requirements and capabilities will be consistent and meet the science goals