Longitudinal pixel averaging for improved compensation in backscattering interferometry

Longitudinal averaging of the interference pattern in a compensated backscattering interferometer provides improved compensation for temperature induced refractive index perturbations. Fringe pattern likeness between two discrete detection regions of an off-the-shelf microfluidic chip illuminated by an inexpensive diode laser scales with interrogation length. Averaging the intensity distribution along a 2.75 mm length of the channel results in a 750-fold reduction in sensitivity to temperature and a baseline noise level of 3×10−8 refractive index units (RIU). These observations enable nanoliter-volume interferometric measurements at a level of 10−7 RIU in the presence of a 2°C temperature variation without the need for temperature control.