This paper deals with the development of an experimental method for measuring the electron density in a helium atmospheric pressure plasma jet (APPJ). The method is based on achieving a laser induced breakdown within the plasma jet by focusing a nanosecond infrared laser pulse. The laser pulse increases the electron density from the value in the jet n_0, which we want to find out, to the value n_f , which is easier to measure by standard methods. The idea of the method is to calculate the electron density n_0 from the electron density n_f. For this purpose, a model of laser plasma evolution that enables the connection of the electron densities n_0 and n_f via the laser pulse energy has been developed. Using this method, the time dependence of the electron density at one point of the helium APPJ was obtained. The values obtained fit well with the values from the literature. Using a stepper motor, the movement of the lens that focuses the laser pulse into the plasma jet is automated. The ability of precise automated focal spot translation opens up the possibility of spatially resolved measurement of electron density throughout the jet. In this paper, a qualitative electron density profile along the radial axis of the plasma jet is obtained. A characteristic donut shape was found in the primary discharge, but not in the secondary discharge.