Abstract

We present both a computational and an experimental approach to the problem of biological aerosol characterization, joining the expertises reached in the field of theoretical optical scattering by complex, arbitrary shaped particles (multipole expansion of the electromagnetic fields and Transition Matrix), and a novel experimental technique based on two-dimensional angular optical scattering (TAOS). The good agreement between experimental and computational results, together with the possibility for a laboratory single-particle angle-resolved investigation, opens a new scenario in biological particle modelling, and might have major implications for a rapid discrimination of airborne particles.

© 2006 Optical Society of America

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  1. K. P. Gurton, D. Ligon, and R. Kvavilashvili, "Measured infrared spectral extinction for aerosolized Bacillus subtilis var. niger endospores from 3 to 13 μm," Appl. Opt. 40,4443-4448 (2001)
    [CrossRef]
  2. R. G. Pinnick, S. C. Hill, P. Machman, J. D. Pendleton, G. L. Fernandez, M. W. Mayo, and J. G. Bruno, "Fluorescence particle counter for detecting airborne bacteria amd other biological particles," Aerosol Sci. Technol. 23,653-664 (1995)
    [CrossRef]
  3. P. P. Hairstone, J. Ho, and F. R. Quant, "Design of an instrument for real-time detection of bioaerosols using simultaneous measurement of particle aerodynamic size and intrinsic fluorescence," J. Aerosol Sci. 28,471-482 (1997)
    [CrossRef]
  4. M. J. Seaver, D. Eversole, J. J. Hardgrove, W. K. Cary, Jr., and D. C. Roselle, "Size and fluorescence measurements for field detection of biological aerosols," Aerosol Sci. Technol. 30,174-185 (1999)
    [CrossRef]
  5. W. D. Dick, P. J. Ziemann, P.-F. Huang, and P. H. McMurray. "Optical shape fraction measurements of submicrometre laboratory and atmospheric aerosols," Meas. Sci. Technol. 9,183-196 (1998)
    [CrossRef]
  6. B. Sachweh, H. Barthel, R. Polke, H. Umhauer, and H. Buttner, "Particle shape and structure analysis from the spatial intensity pattern of scattered light using different measuring devices," J. Aerosol Sci. 30,1257-1270 (1999)
    [CrossRef]
  7. P. H. Kaye, J. E. Barton, E. Hirst, and J. M. Clark, "Simultaneous light scattering and intrinsic fluorescence measurement for the classification of airborne particles," Appl. Opt. 39,3738-3745 (2000)
    [CrossRef]
  8. S. Holler, Y. Pan, R. K. Chang, J. R. Bottiger, S. C. Hill, and D. B. Hillis, "Two-dimensional angular optical scattering for the characterization of airborne microparticles," Opt. Lett. 23,1489-1491 (1998)
    [CrossRef]
  9. Y. L. Pan, K. B. Aptowicz, R. K. Chang, M. Hart, J. D. Eversole, "Characterizing and nonitoring respiratory aerosols by light scattering," Opt. Lett. 28,589-591 (2003)
    [CrossRef] [PubMed]
  10. S. A. Burke, J. D. Wright, M. K. Robinson, B. V. Bronk and R. L. Warren, "Detection of molecular diversity in Bacillus Atrophaeus by amplified fragment length polymorphism analysis," Appl. Env. Microbiology,  70, 2786-2790 (2004)
    [CrossRef]
  11. F. Borghese, P. Denti, R. Saija, Scattering by model nonspherical particles (Springer, Heildelberg, 2002)
  12. C. Li, G. W. Kattawar, and P. Yang, "Identification of aerosols by their backscattered Mueller images," Opt. Express 14,3616-3621 (2006)
    [CrossRef] [PubMed]
  13. J. R. Bottinger, P. J. Deluca, E. W. Stuebing, and D. R. Van Reenen, "An Ink jet aerosol generator," J. Aerosol Sci. 29,Suppl. 1965-966 (1998)
    [CrossRef]
  14. P. S. Tuminello, E. T. Arakawa, B. N. Khare, J. M. Wrobel, M. R. Querry, and M. E. Milham, "Optical properties of Bacillus subtilis spores from 0.2 to 2.5 μm," Appl. Opt. 36,2818-2824 (1997)
    [CrossRef] [PubMed]
  15. A. Katz, A. Alimova, M. Xu, P. Gottlieb, E. Rudolph, J. C. Steiner, and R. R. Alfano, "In situ determination of refractive index and size of Bacillus spores by light transmission," Opt. Lett. 30,589-591 (2005)
    [CrossRef] [PubMed]
  16. M. I. Mishchenko, L. D. Travis, and A. A. Lacis, in Scattering, Absorption, and Emission of Light by Small Particles (Cambridge University Press, Cambridge, 2002)
  17. M. I. Mishchenko, D.W. Mackowski, "Electromagnetic scattering by randomly oriented bispheres: Comparison of theory and experiment and benchmark calculations," J. Quant. Spectrosc. Radiat. Transfer 55,683-694 (1996)
    [CrossRef]
  18. P. H. Kaye, K. Alexander Buckley, E. Hirst, S. Saunders and J. M. Clark, "A real-time monitoring system for airborne particle shape and size analysis," J. Geophys. Res.-Atmospheres 101, 19215-19221 (1996)
    [CrossRef]

2006

2005

2004

S. A. Burke, J. D. Wright, M. K. Robinson, B. V. Bronk and R. L. Warren, "Detection of molecular diversity in Bacillus Atrophaeus by amplified fragment length polymorphism analysis," Appl. Env. Microbiology,  70, 2786-2790 (2004)
[CrossRef]

2003

2001

2000

1999

B. Sachweh, H. Barthel, R. Polke, H. Umhauer, and H. Buttner, "Particle shape and structure analysis from the spatial intensity pattern of scattered light using different measuring devices," J. Aerosol Sci. 30,1257-1270 (1999)
[CrossRef]

M. J. Seaver, D. Eversole, J. J. Hardgrove, W. K. Cary, Jr., and D. C. Roselle, "Size and fluorescence measurements for field detection of biological aerosols," Aerosol Sci. Technol. 30,174-185 (1999)
[CrossRef]

1998

W. D. Dick, P. J. Ziemann, P.-F. Huang, and P. H. McMurray. "Optical shape fraction measurements of submicrometre laboratory and atmospheric aerosols," Meas. Sci. Technol. 9,183-196 (1998)
[CrossRef]

J. R. Bottinger, P. J. Deluca, E. W. Stuebing, and D. R. Van Reenen, "An Ink jet aerosol generator," J. Aerosol Sci. 29,Suppl. 1965-966 (1998)
[CrossRef]

S. Holler, Y. Pan, R. K. Chang, J. R. Bottiger, S. C. Hill, and D. B. Hillis, "Two-dimensional angular optical scattering for the characterization of airborne microparticles," Opt. Lett. 23,1489-1491 (1998)
[CrossRef]

1997

P. S. Tuminello, E. T. Arakawa, B. N. Khare, J. M. Wrobel, M. R. Querry, and M. E. Milham, "Optical properties of Bacillus subtilis spores from 0.2 to 2.5 μm," Appl. Opt. 36,2818-2824 (1997)
[CrossRef] [PubMed]

P. P. Hairstone, J. Ho, and F. R. Quant, "Design of an instrument for real-time detection of bioaerosols using simultaneous measurement of particle aerodynamic size and intrinsic fluorescence," J. Aerosol Sci. 28,471-482 (1997)
[CrossRef]

1996

M. I. Mishchenko, D.W. Mackowski, "Electromagnetic scattering by randomly oriented bispheres: Comparison of theory and experiment and benchmark calculations," J. Quant. Spectrosc. Radiat. Transfer 55,683-694 (1996)
[CrossRef]

P. H. Kaye, K. Alexander Buckley, E. Hirst, S. Saunders and J. M. Clark, "A real-time monitoring system for airborne particle shape and size analysis," J. Geophys. Res.-Atmospheres 101, 19215-19221 (1996)
[CrossRef]

1995

R. G. Pinnick, S. C. Hill, P. Machman, J. D. Pendleton, G. L. Fernandez, M. W. Mayo, and J. G. Bruno, "Fluorescence particle counter for detecting airborne bacteria amd other biological particles," Aerosol Sci. Technol. 23,653-664 (1995)
[CrossRef]

Alexander Buckley, K.

P. H. Kaye, K. Alexander Buckley, E. Hirst, S. Saunders and J. M. Clark, "A real-time monitoring system for airborne particle shape and size analysis," J. Geophys. Res.-Atmospheres 101, 19215-19221 (1996)
[CrossRef]

Alfano, R. R.

Alimova, A.

Aptowicz, K. B.

Arakawa, E. T.

Barthel, H.

B. Sachweh, H. Barthel, R. Polke, H. Umhauer, and H. Buttner, "Particle shape and structure analysis from the spatial intensity pattern of scattered light using different measuring devices," J. Aerosol Sci. 30,1257-1270 (1999)
[CrossRef]

Barton, J. E.

Bottiger, J. R.

Bottinger, J. R.

J. R. Bottinger, P. J. Deluca, E. W. Stuebing, and D. R. Van Reenen, "An Ink jet aerosol generator," J. Aerosol Sci. 29,Suppl. 1965-966 (1998)
[CrossRef]

Bronk, B. V.

S. A. Burke, J. D. Wright, M. K. Robinson, B. V. Bronk and R. L. Warren, "Detection of molecular diversity in Bacillus Atrophaeus by amplified fragment length polymorphism analysis," Appl. Env. Microbiology,  70, 2786-2790 (2004)
[CrossRef]

Bruno, J. G.

R. G. Pinnick, S. C. Hill, P. Machman, J. D. Pendleton, G. L. Fernandez, M. W. Mayo, and J. G. Bruno, "Fluorescence particle counter for detecting airborne bacteria amd other biological particles," Aerosol Sci. Technol. 23,653-664 (1995)
[CrossRef]

Burke, S. A.

S. A. Burke, J. D. Wright, M. K. Robinson, B. V. Bronk and R. L. Warren, "Detection of molecular diversity in Bacillus Atrophaeus by amplified fragment length polymorphism analysis," Appl. Env. Microbiology,  70, 2786-2790 (2004)
[CrossRef]

Buttner, H.

B. Sachweh, H. Barthel, R. Polke, H. Umhauer, and H. Buttner, "Particle shape and structure analysis from the spatial intensity pattern of scattered light using different measuring devices," J. Aerosol Sci. 30,1257-1270 (1999)
[CrossRef]

Cary, W. K.

M. J. Seaver, D. Eversole, J. J. Hardgrove, W. K. Cary, Jr., and D. C. Roselle, "Size and fluorescence measurements for field detection of biological aerosols," Aerosol Sci. Technol. 30,174-185 (1999)
[CrossRef]

Chang, R. K.

Clark, J. M.

P. H. Kaye, J. E. Barton, E. Hirst, and J. M. Clark, "Simultaneous light scattering and intrinsic fluorescence measurement for the classification of airborne particles," Appl. Opt. 39,3738-3745 (2000)
[CrossRef]

P. H. Kaye, K. Alexander Buckley, E. Hirst, S. Saunders and J. M. Clark, "A real-time monitoring system for airborne particle shape and size analysis," J. Geophys. Res.-Atmospheres 101, 19215-19221 (1996)
[CrossRef]

Deluca, P. J.

J. R. Bottinger, P. J. Deluca, E. W. Stuebing, and D. R. Van Reenen, "An Ink jet aerosol generator," J. Aerosol Sci. 29,Suppl. 1965-966 (1998)
[CrossRef]

Dick, W. D.

W. D. Dick, P. J. Ziemann, P.-F. Huang, and P. H. McMurray. "Optical shape fraction measurements of submicrometre laboratory and atmospheric aerosols," Meas. Sci. Technol. 9,183-196 (1998)
[CrossRef]

Eversole, D.

M. J. Seaver, D. Eversole, J. J. Hardgrove, W. K. Cary, Jr., and D. C. Roselle, "Size and fluorescence measurements for field detection of biological aerosols," Aerosol Sci. Technol. 30,174-185 (1999)
[CrossRef]

Eversole, J. D.

Fernandez, G. L.

R. G. Pinnick, S. C. Hill, P. Machman, J. D. Pendleton, G. L. Fernandez, M. W. Mayo, and J. G. Bruno, "Fluorescence particle counter for detecting airborne bacteria amd other biological particles," Aerosol Sci. Technol. 23,653-664 (1995)
[CrossRef]

Gottlieb, P.

Gurton, K. P.

Hairstone, P. P.

P. P. Hairstone, J. Ho, and F. R. Quant, "Design of an instrument for real-time detection of bioaerosols using simultaneous measurement of particle aerodynamic size and intrinsic fluorescence," J. Aerosol Sci. 28,471-482 (1997)
[CrossRef]

Hardgrove, J. J.

M. J. Seaver, D. Eversole, J. J. Hardgrove, W. K. Cary, Jr., and D. C. Roselle, "Size and fluorescence measurements for field detection of biological aerosols," Aerosol Sci. Technol. 30,174-185 (1999)
[CrossRef]

Hart, M.

Hill, S. C.

S. Holler, Y. Pan, R. K. Chang, J. R. Bottiger, S. C. Hill, and D. B. Hillis, "Two-dimensional angular optical scattering for the characterization of airborne microparticles," Opt. Lett. 23,1489-1491 (1998)
[CrossRef]

R. G. Pinnick, S. C. Hill, P. Machman, J. D. Pendleton, G. L. Fernandez, M. W. Mayo, and J. G. Bruno, "Fluorescence particle counter for detecting airborne bacteria amd other biological particles," Aerosol Sci. Technol. 23,653-664 (1995)
[CrossRef]

Hillis, D. B.

Hirst, E.

P. H. Kaye, J. E. Barton, E. Hirst, and J. M. Clark, "Simultaneous light scattering and intrinsic fluorescence measurement for the classification of airborne particles," Appl. Opt. 39,3738-3745 (2000)
[CrossRef]

P. H. Kaye, K. Alexander Buckley, E. Hirst, S. Saunders and J. M. Clark, "A real-time monitoring system for airborne particle shape and size analysis," J. Geophys. Res.-Atmospheres 101, 19215-19221 (1996)
[CrossRef]

Ho, J.

P. P. Hairstone, J. Ho, and F. R. Quant, "Design of an instrument for real-time detection of bioaerosols using simultaneous measurement of particle aerodynamic size and intrinsic fluorescence," J. Aerosol Sci. 28,471-482 (1997)
[CrossRef]

Holler, S.

Huang, P.-F.

W. D. Dick, P. J. Ziemann, P.-F. Huang, and P. H. McMurray. "Optical shape fraction measurements of submicrometre laboratory and atmospheric aerosols," Meas. Sci. Technol. 9,183-196 (1998)
[CrossRef]

Kattawar, G. W.

Katz, A.

Kaye, P. H.

P. H. Kaye, J. E. Barton, E. Hirst, and J. M. Clark, "Simultaneous light scattering and intrinsic fluorescence measurement for the classification of airborne particles," Appl. Opt. 39,3738-3745 (2000)
[CrossRef]

P. H. Kaye, K. Alexander Buckley, E. Hirst, S. Saunders and J. M. Clark, "A real-time monitoring system for airborne particle shape and size analysis," J. Geophys. Res.-Atmospheres 101, 19215-19221 (1996)
[CrossRef]

Khare, B. N.

Kvavilashvili, R.

Li, C.

Ligon, D.

Machman, P.

R. G. Pinnick, S. C. Hill, P. Machman, J. D. Pendleton, G. L. Fernandez, M. W. Mayo, and J. G. Bruno, "Fluorescence particle counter for detecting airborne bacteria amd other biological particles," Aerosol Sci. Technol. 23,653-664 (1995)
[CrossRef]

Mackowski, D.W.

M. I. Mishchenko, D.W. Mackowski, "Electromagnetic scattering by randomly oriented bispheres: Comparison of theory and experiment and benchmark calculations," J. Quant. Spectrosc. Radiat. Transfer 55,683-694 (1996)
[CrossRef]

Mayo, M. W.

R. G. Pinnick, S. C. Hill, P. Machman, J. D. Pendleton, G. L. Fernandez, M. W. Mayo, and J. G. Bruno, "Fluorescence particle counter for detecting airborne bacteria amd other biological particles," Aerosol Sci. Technol. 23,653-664 (1995)
[CrossRef]

McMurray, P. H.

W. D. Dick, P. J. Ziemann, P.-F. Huang, and P. H. McMurray. "Optical shape fraction measurements of submicrometre laboratory and atmospheric aerosols," Meas. Sci. Technol. 9,183-196 (1998)
[CrossRef]

Milham, M. E.

Mishchenko, M. I.

M. I. Mishchenko, D.W. Mackowski, "Electromagnetic scattering by randomly oriented bispheres: Comparison of theory and experiment and benchmark calculations," J. Quant. Spectrosc. Radiat. Transfer 55,683-694 (1996)
[CrossRef]

Pan, Y.

Pan, Y. L.

Pendleton, J. D.

R. G. Pinnick, S. C. Hill, P. Machman, J. D. Pendleton, G. L. Fernandez, M. W. Mayo, and J. G. Bruno, "Fluorescence particle counter for detecting airborne bacteria amd other biological particles," Aerosol Sci. Technol. 23,653-664 (1995)
[CrossRef]

Pinnick, R. G.

R. G. Pinnick, S. C. Hill, P. Machman, J. D. Pendleton, G. L. Fernandez, M. W. Mayo, and J. G. Bruno, "Fluorescence particle counter for detecting airborne bacteria amd other biological particles," Aerosol Sci. Technol. 23,653-664 (1995)
[CrossRef]

Polke, R.

B. Sachweh, H. Barthel, R. Polke, H. Umhauer, and H. Buttner, "Particle shape and structure analysis from the spatial intensity pattern of scattered light using different measuring devices," J. Aerosol Sci. 30,1257-1270 (1999)
[CrossRef]

Quant, F. R.

P. P. Hairstone, J. Ho, and F. R. Quant, "Design of an instrument for real-time detection of bioaerosols using simultaneous measurement of particle aerodynamic size and intrinsic fluorescence," J. Aerosol Sci. 28,471-482 (1997)
[CrossRef]

Querry, M. R.

Robinson, M. K.

S. A. Burke, J. D. Wright, M. K. Robinson, B. V. Bronk and R. L. Warren, "Detection of molecular diversity in Bacillus Atrophaeus by amplified fragment length polymorphism analysis," Appl. Env. Microbiology,  70, 2786-2790 (2004)
[CrossRef]

Roselle, D. C.

M. J. Seaver, D. Eversole, J. J. Hardgrove, W. K. Cary, Jr., and D. C. Roselle, "Size and fluorescence measurements for field detection of biological aerosols," Aerosol Sci. Technol. 30,174-185 (1999)
[CrossRef]

Rudolph, E.

Sachweh, B.

B. Sachweh, H. Barthel, R. Polke, H. Umhauer, and H. Buttner, "Particle shape and structure analysis from the spatial intensity pattern of scattered light using different measuring devices," J. Aerosol Sci. 30,1257-1270 (1999)
[CrossRef]

Saunders, S.

P. H. Kaye, K. Alexander Buckley, E. Hirst, S. Saunders and J. M. Clark, "A real-time monitoring system for airborne particle shape and size analysis," J. Geophys. Res.-Atmospheres 101, 19215-19221 (1996)
[CrossRef]

Seaver, M. J.

M. J. Seaver, D. Eversole, J. J. Hardgrove, W. K. Cary, Jr., and D. C. Roselle, "Size and fluorescence measurements for field detection of biological aerosols," Aerosol Sci. Technol. 30,174-185 (1999)
[CrossRef]

Steiner, J. C.

Stuebing, E. W.

J. R. Bottinger, P. J. Deluca, E. W. Stuebing, and D. R. Van Reenen, "An Ink jet aerosol generator," J. Aerosol Sci. 29,Suppl. 1965-966 (1998)
[CrossRef]

Tuminello, P. S.

Umhauer, H.

B. Sachweh, H. Barthel, R. Polke, H. Umhauer, and H. Buttner, "Particle shape and structure analysis from the spatial intensity pattern of scattered light using different measuring devices," J. Aerosol Sci. 30,1257-1270 (1999)
[CrossRef]

Van Reenen, D. R.

J. R. Bottinger, P. J. Deluca, E. W. Stuebing, and D. R. Van Reenen, "An Ink jet aerosol generator," J. Aerosol Sci. 29,Suppl. 1965-966 (1998)
[CrossRef]

Warren, R. L.

S. A. Burke, J. D. Wright, M. K. Robinson, B. V. Bronk and R. L. Warren, "Detection of molecular diversity in Bacillus Atrophaeus by amplified fragment length polymorphism analysis," Appl. Env. Microbiology,  70, 2786-2790 (2004)
[CrossRef]

Wright, J. D.

S. A. Burke, J. D. Wright, M. K. Robinson, B. V. Bronk and R. L. Warren, "Detection of molecular diversity in Bacillus Atrophaeus by amplified fragment length polymorphism analysis," Appl. Env. Microbiology,  70, 2786-2790 (2004)
[CrossRef]

Wrobel, J. M.

Xu, M.

Yang, P.

Ziemann, P. J.

W. D. Dick, P. J. Ziemann, P.-F. Huang, and P. H. McMurray. "Optical shape fraction measurements of submicrometre laboratory and atmospheric aerosols," Meas. Sci. Technol. 9,183-196 (1998)
[CrossRef]

Aerosol Sci. Technol.

R. G. Pinnick, S. C. Hill, P. Machman, J. D. Pendleton, G. L. Fernandez, M. W. Mayo, and J. G. Bruno, "Fluorescence particle counter for detecting airborne bacteria amd other biological particles," Aerosol Sci. Technol. 23,653-664 (1995)
[CrossRef]

M. J. Seaver, D. Eversole, J. J. Hardgrove, W. K. Cary, Jr., and D. C. Roselle, "Size and fluorescence measurements for field detection of biological aerosols," Aerosol Sci. Technol. 30,174-185 (1999)
[CrossRef]

Appl. Env. Microbiology

S. A. Burke, J. D. Wright, M. K. Robinson, B. V. Bronk and R. L. Warren, "Detection of molecular diversity in Bacillus Atrophaeus by amplified fragment length polymorphism analysis," Appl. Env. Microbiology,  70, 2786-2790 (2004)
[CrossRef]

Appl. Opt.

Atmospheres

P. H. Kaye, K. Alexander Buckley, E. Hirst, S. Saunders and J. M. Clark, "A real-time monitoring system for airborne particle shape and size analysis," J. Geophys. Res.-Atmospheres 101, 19215-19221 (1996)
[CrossRef]

J. Aerosol Sci.

B. Sachweh, H. Barthel, R. Polke, H. Umhauer, and H. Buttner, "Particle shape and structure analysis from the spatial intensity pattern of scattered light using different measuring devices," J. Aerosol Sci. 30,1257-1270 (1999)
[CrossRef]

P. P. Hairstone, J. Ho, and F. R. Quant, "Design of an instrument for real-time detection of bioaerosols using simultaneous measurement of particle aerodynamic size and intrinsic fluorescence," J. Aerosol Sci. 28,471-482 (1997)
[CrossRef]

J. Quant. Spectrosc. Radiat. Transfer

M. I. Mishchenko, D.W. Mackowski, "Electromagnetic scattering by randomly oriented bispheres: Comparison of theory and experiment and benchmark calculations," J. Quant. Spectrosc. Radiat. Transfer 55,683-694 (1996)
[CrossRef]

Meas. Sci. Technol.

W. D. Dick, P. J. Ziemann, P.-F. Huang, and P. H. McMurray. "Optical shape fraction measurements of submicrometre laboratory and atmospheric aerosols," Meas. Sci. Technol. 9,183-196 (1998)
[CrossRef]

Opt. Express

Opt. Lett.

Suppl.

J. R. Bottinger, P. J. Deluca, E. W. Stuebing, and D. R. Van Reenen, "An Ink jet aerosol generator," J. Aerosol Sci. 29,Suppl. 1965-966 (1998)
[CrossRef]

Other

M. I. Mishchenko, L. D. Travis, and A. A. Lacis, in Scattering, Absorption, and Emission of Light by Small Particles (Cambridge University Press, Cambridge, 2002)

F. Borghese, P. Denti, R. Saija, Scattering by model nonspherical particles (Springer, Heildelberg, 2002)

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Figures (9)

Fig. 1.
Fig. 1.

Spherical coordinate system as defined for the backward/forward TAOS experiment.

Fig. 2.
Fig. 2.

Simultaneously recorded forward and backward scattering patterns after processing for a single polystyrene microsphere (diameter: 1.44 μm), illuminated by a single shot of the second harmonic of a Nd:YAG laser.

Fig. 3.
Fig. 3.

Extinction σe and scattering σs cross sections for a dispersion of cluster of spores in a random orientation. Each spore is modelled as a cluster of two spheres, with radius 0.35 μm. The solid line is referred to a B. cereus spore; the dotted one to a B. subtilis spore.

Fig. 4.
Fig. 4.

Z 11(θ) in the forward (left part in figure) and backward (right part) regions for clusters of two spheres with different choices of the refractive indexes and fixed monomer radius (0.35 μm).

Fig. 5.
Fig. 5.

Experimental scattering pattern, in both the forward and backward hemispheres, for a cluster of two PSL microspheres (primary particle size is 1.44 μm in diameter) illuminated by a 532 nm pulsed laser.

Fig. 6.
Fig. 6.

Computational results for the same PSL spheres of Fig.5 in the forward (see left panel) and backward (right panel) regions. Both axes report cosθ according to the experimental setup (see Fig. 1)

Fig. 7.
Fig. 7.

Experimental TAOS patterns in the forward and backward hemispheres for a B. subtilis spore, illuminated by a 532 nm pulsed laser.

Fig. 8.
Fig. 8.

Computed patterns in the forward (see left panel) and backward (right panel) regions for a B. subtilis spore, modelled as a cluster of two spheres, each with a radius of 0.38 μm, illuminated by a 532 nm pulsed laser. Both axes report cosθ according to the experimental setup (see Fig. 1)

Fig. 9.
Fig. 9.

Intensity profiles as a function of cosθ along an arbitrary direction (indicated by the broken line in Fig. 8) extracted by the experimental (dotted line) and computational (solid line) scattering patterns for BG spores, both in the forward (left part in figure) and backward (right part) hemispheres.

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