A novel system has been developed that can capture the wide- field interference pattern generated by interfering two independent and incoherent laser sources. The interferograms are captured using a custom CMOS modulated light camera (MLC) which is capable of demodulating light in the megahertz region. Two stabilised HeNe lasers were constructed in order to keep the optical frequency difference (beat frequency) between the beams within the operational range of the camera.
This system is based on previously reported work of an ultrastable heterodyne interferometer [Opt. Express 20, 17722 (2012)]. The system used an electronic feedback system to mix down the heterodyne signal captured at each pixel on the camera to cancel out the effects of time varying piston phase changes observed across the array. In this paper, a similar technique is used to track and negate the effects of beat frequency variations across the two laser pattern. This technique makes it possible to capture the full field interferogram caused by interfering two independent lasers even though the beat frequency is effectively random.
As a demonstration of the system’s widefield interferogram capture capability, an image of a phase shifting object is taken using a very simple two laser interferometer.
Patel, R., Achamfuo-Yeboah, S., Light, R. A., & Clark, M. (2014). Widefield two laser interferometry. Optics Express, 22(22), https://doi.org/10.1364/OE.22.027094