Phase signal of optical beam deflection from single microparticles: Theory and experiment

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Abstract
The optical beam deflection (OBD) signal from a single microparticulate sample was theoretically derived for the photothermal response to an intensity‐modulated excitation in the transverse experimental configuration. The dependencies of phase signal on the normal and transverse offsets of the probe beam were calculated and then experimentally verified. The OBD phase signal was chosen as a means of inspecting the particle interior, since it contains information about the heat source depth. The results showed that the phase signal was independent of the excitation beam power and that the surface absorbing layer thickness could be estimated from the phase variation using the modulation frequency. The possibility of correcting beam offsets by the phase signal was also considered.