Small-Particle Imaging with Digital Holography

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1 Small-Particle Imaging with Digital Holography 6 July 2017

2 The ARL Patent Information Patent Number: US Methods and apparatuses for contact-free holographic imaging of aerosol particles Methods and apparatuses provide holographic contact-free imaging of aerosol particles in an efficient manner. An apparatus for holographic imaging of an aerosol particle comprising: a delivery device configured to generate a flow of air to deliver the particle to and from a region; a particle trap configured to trap and hold the particle in said flow of air substantially motionless in the region, and to later release the particle from said particle trap into said flow of air; a light source for outputting a first beam of light and a second beam of light, wherein the first beam travels into the region producing a first light wave which is unscattered by the trapped particle and a second light wave that is scattered by the trapped particle, and the second beam does not travel into the region; a beam splitter for combining the second beam with the scattered light of the first beam into combined interference light; an image sensor for sensing an interference pattern created by the combined interference light; and an image processor configured to generate an image of the aerosol particle based on the sensed interference pattern. Inventors: Matthew J. Berg and Gorden Videen

3 What our team is doing Determining the size and shape of small (micrometer) particles (like Pollen Spores) Imaging particles using advanced digital holography techniques Imaging in a way that does not require collection and/or immobilization of particle samples Generating quasi-3d representations of particle shapes from the images (to aid quick classification & characterization of aerosols) Useful for: Aerosol Science, Medicine, Cosmetics, Biology, Materials Synthesis... M. J. Berg et al. Small Particle Imaging with Digital Holography 2/8

4 Current Techniques Most imaging is done with optical microscopy (limiting) Particle images are formed directly, like digital photography, using high numerical aperture (NA) optics (expensive) Particles must be confined to small regions of space to yield in-focus images (drawback of high-na optics) Particle samples must be localized or collected (drain on time & materials) If out-of-focus images are obtained, images must be re-obtained, following adjustment for location and/or optics (further drain on time and materials) microscope New Methods Exist = Speed & Ease of Classification at Lower Cost M. J. Berg et al. Small Particle Imaging with Digital Holography 3/8

5 M. J. Berg et al. Small Particle Imaging with Digital Holography 4/8 Why are we better? Digital holography can image particles without lenses, using a single digital sensor, e.g., CCD/CMOS. Images are generated computationally from the recorded hologram. From a single hologram recording, images are focused after-the-fact. Thus, particles need not be confined as with conventional microscopy. Also, multiple particles in a diffuse group can be brought into focus one-by-one, from a single hologram of the group. There is evidence that partial 3D representations of the particle may also be possible (characterizations and classifications) digital hologram particle image

6 Implications of the Method Imaging may be done faster and on more particles (repeated measurements are not needed to generate focused images) This may enable more rapid characterization and classification Higher through-put particle characterization or detection in collections of unknown particles is now possible Easing of restrictions on the confinement or collection of particles The mechanical/optical complexity of conventional instruments may become simplified. Speed & Ease of Classification at Lower Cost M. J. Berg et al. Small Particle Imaging with Digital Holography 5/8

7 Risks Particles smaller than the pixel size of the sensor cannot be imaged (Image resolution is limited by the sensor hardware) Current limit on particle size is ~ 5 micrometers Through-put / imaging-rate is limited by the speed of the sensor (currently in seconds) The ability to resolve a particle s 3 rd -dimension is not fully understood (3D images are approximate) Dense, or crowded, collections of particles may not be imageable. Low Overall Risk & Solutions are forthcoming M. J. Berg et al. Small Particle Imaging with Digital Holography 6/8

8 Summary Low SWaP proof-of-principle system to demonstrate reliable continuous imaging of particle-sample stream is under development for 2018 demonstration DoD bio detection system slated for FY 19 identified for potential integration of this capability into that system R&D topics are being discussed with the customer for parallel development of data analysis capabilities Advancing State-of-the-Art to Prototype rapidly! M. J. Berg et al. Small Particle Imaging with Digital Holography 8/8