An optofluidic light detector based on the photoacoustic effect

An optofluidic light detector based on the photoacoustic effect is presented. The device performances are tested at 532 nm using a pulsed solid-state laser as light source and a potassium permanganate (KMnO4) water solution as active medium. As expected, the device shows linear response with respect to applied light irradiance. By changing flow rate the device sensitivity increases non-linearly. This change in sensitivity is mainly attributed to a rise in water temperature as the flow rate increases, leading to a higher thermal expansion coefficient. Changes of water temperature with applied flow rate are confirmed through independent fluorescence intensity experiments with Rhodamine B in water. Comparison of the photoacoustic and fluorescence data points out that the change in temperature inside the microfluidic device is not promoted by the absorbed laser light, but instead is mainly due to viscous friction.