Laser absorption spectroscopy (LAS) is a useful technique for sensitive quantitative measurement of plasma parameters. We used LAS to obtain plasma profiles inside the μ1 miniature ion thruster developed by the Institute of Space and Astronautical Science of the Japan Aerospace Exploration Agency; this thruster is intended for installation on small spacecraft weighing up to 50 kg. It operates at low microwave power (1 W) and has been developed as a complete system, including a neutralizer. At present, the thrust efficiency of the μ1 thruster is not as high as that of standard ion thrusters and optimization is required. A detailed profile of plasma inside the discharge chamber is necessary for further improving performance. We developed an experimental LAS setup with spatial resolution of 0.1 mm for a modified μ1 thruster model. The number density distribution of neutral particles in a metastable state was measured and found to be about 10¹⁷ m^-3.