In the present work the properties of laser-induced MW discharge was investigated experimentally. For these purpose both Slieren and interferometry techniques has been developed. Laser spark is created by impulse Ruby laser (6943 A, 0.22 J pulse energy and 25 ns-pulse duration) in focal point of short-focus lens (12 mm). This point is placed in the vicinity of the main maximum of MW-field in the focal area of parabolic mirror. The X-range impulse MW generator with output power 180 kW and pulse duration 1,2 μs via radiating system illuminates the focal area. Digital synchronous Schlieren system is used for visualisation of shock wave structures, exciting by laser spark and initiated MW discharge. The temporal evolution of optical density fields for breakdown plasma and thermal well, arising on this place are studied using the high-sensitive intro-chamber Fabry-Perot interferometer. Investigation area of supersonic flow is placed between the interferometer mirrors, which is installed inside the test chamber. In this case the chamber windows are not included in the optical path of the interferometer and it sensitivity for intro-cavity phase objects becomes very high. Intro-chamber plane interferometer Fabry-Perot has fineness about 14, light orifice diameter 86 mm and distance between mirrors 650 mm. Interferometer operates with single - frequency, stabilising (δλ/λ ≤10^-10) He-Ne laser with output power 1 mW. The interference picture is analysing by the high-sensitive gated (exposition time 1-500 μs) CCD camera.