A fiber-coupled heterodyne laser interferometer for plasma density measurements

This article describes a fiber-coupled setup for a heterodyne laser interferometer. The interferometer consists of a 561 nm continuous-wave laser in a Mach-Zehnder configuration. The diagnostic contains one reference beam and five probe beams (chords). The probe beams are created by splitting the unmodulated laser beam into five separate beams using a series of beamsplitters. The probe beams are then transmitted through fiber optic cable using fiber optic coupling optics. The reference beam is created using an acousto-optical modulator and is split into five beams in fiber optic cable to be recombined with the probe beams to measure phase angle to calculate line-integrated electron density. The setup has a fiber-coupled design that uses fiber optic splitters and polarization controllers to optimize interference pattern signals. The probe and reference beams are recombined using multiple fiber-optic splitters. This setup allows for a faster setup and reduced time spent aligning optics and components during plasma experiments.