Patent ID: 7782463

Claim:
A particle density measuring probe for measuring the density of atoms or molecules in a plasma atmosphere by absorption spectroscopy, the particle density measuring probe comprising: a cylindrical light guiding member provided in the plasma atmosphere, the light guiding member including: a reflection plate for reflecting light that has propagated through the light guiding member, the reflection plate is provided at the front end of the light guiding member; and a plasma introducing portion in which, in a cross section perpendicular to the longitudinal direction of the light guiding member, a part devoid of a portion of wall surface is provided behind the reflection plate by a predetermined length in the longitudinal direction, and which allows mutual contact between the light passing through the part and atoms or molecules in the plasma atmosphere; and a main body that guides light in an axial direction by total reflection by a side wall, the main body being located behind the plasma introducing portion.