Effects of increased acceptance angle for Mach-Zehnder interferometer and Dark-field Schlieren imaging systems using a lens-pair configuration for high density X-pinch plasmas

We present the development of a Mach-Zehnder interferometer imaging system and a Dark-field Schlieren imaging system, sharing the common line-of-sight, to obtain the 2D line-integrated electron density of X-pinch plasmas. The imaging systems utilize the second harmonic of an Nd:YAG pulsed laser (532nm, <5nsec) as the light source. X-pinch plasmas typically have high electron densities (>10¹⁸ cm^-3), with the wire core region reaching to higher densities (>10²¹ cm^-3) comparable to solid density [1]. Due to such a high-density region within sub-millimeter scales, a stiff electron density gradient causes significant refraction losses. To overcome these challenges, light sources with wavelengths beyond the second harmonic of the Nd:YAG laser can be used, as refraction is proportional to the square of the wavelength [2]. However, the use of non-visual wavelengths introduces difficulties in aligning the optical system and selecting appropriate optics and filters for imaging. Therefore, rather than using a shorter wavelength system, we employ a lens-pair configuration to detect the high electron density gradient region by increasing the acceptance angle of our imaging systems. We present the measurements obtained with and without the lens-pair configuration to discuss its efficiency and practicality.