The imaging properties of scattering particles in laser beams

Abstract

The scattering properties of spherical particles crossing a laser beam deviate from the Lorenz-Mie solution for particles both smaller and larger than the beam dimensions. For smaller particles the local beam properties at the position of the particle can be used in the Lorenz-Mie calculations, whereas for larger particles the varying beam properties over the surface of the particle must be accounted for. The Fourier Lorenz-Mie theory and the extended geometrical optics theory offer two methods for analysing such situations. These two methods are used to investigate the scattering fields of various scattering particles and to demonstrate the agreement of the results. The results are useful for understanding the signal origins in laser-Doppler and phase-Doppler techniques, especially the `trajectory effect' or `Gaussian beam effect'.

Optical particle sizing in backscatter

“…2 is illustrated in Fig. 3, computed using FLMT (Albrecht et al 1995) and the Debye decomposition of the FLMT (Albrecht et al 1999) and measured in the laboratory using a transient recorder to record the signal. For very small intersection angles ( , 2 2 sin Θ Θ ≈ ) and a planar system, Eq.…”

On the electromagnetic scattering of arbitrary shaped beams by arbitrary shaped particles: A review

“…FLMT was then used to provide benchmark results in a study of light scattering for a particle arbitrarily positioned in a laser beam using an extended geometrical optics (EGO) approach [62]. Both FLMT and EGO were then used to study the imaging properties of scattering particles in laser beams, including a discussion of the "trajectory effect" in the phase-Doppler method [63], which was previously studied in a GLMT framework [64], [65]. FLMT was also used to study optical particle sizing in backscattering with an emphasis on phase-Doppler instruments [66], particle sizing by a time-resolved approach in which microspheres are illuminated by short laser pulses [67], the time integrated detection of femtosecond laser pulses scattered by small droplets [68], and the feasibility of extending rainbow refractometry to small particles using femtosecond laser pulses [69].…”