A method of obtaining or maintaining optical transference into deaerated liquid in contact with a light transference medium is disclosed. The method comprises applying ultrasonic energy at a wavelength (λ) into deaerated liquid in contact with a light transference medium. The ultrasonic energy at wavelength (λ) originates at a distance (d) from an optical signal transmitted into the light transference medium. The distance (d) may be defined by a formula based on the wavelength (λ) of the ultrasonic energy.