Measurements of size and absorption coefficient of a single moving particle by using dual burst Doppler signal

• Modified LDV method is proposed for measuring absorption coefficient of a particle.
• The proposed method employs only a single photodetector.
• The optimum conditions of an optical system are estimated theoretically.
• Experimental results show the feasibility of the proposed method.

Modified LDV method is proposed for measuring the diameter and absorption coefficient of a single moving particle by applying the Lambert–Beer’s law to dual burst Doppler signal. The diameter and absorption coefficient of a particle are determined simultaneously from the time difference and intensity ratio between burst components of reflected and refracted rays in a dual burst Doppler signal, using only a single photodetector. This method can be applied to a particle larger than the cross-sectional area of an illuminating beam. The optimum conditions of an optical system were estimated theoretically. Experiments were performed with polystyrene particles in water, water droplets, and water-black ink droplets to confirm usefulness of the proposed method.