  We study the Neveu-Schwarz-Ramond (NSR) open super-string theory in the
proper-time gauge. The string field action is obtained by evaluating the
Polyakov string path integral. In this study, we focus on the open-string
free-field action, which corresponds to the string path integral on a strip.
Depending on the periodicity of the fermion fields, the open super-string has
two sectors: The Neveu-Schwarz (NS) and Ramond (R) sectors. We can impose the
gauge conditions to fix the (super-) reparametrization invariance on the
two-dimensional metric and its super-partner on the string world sheet to
secure the covariance, in contrast to the light-cone gauge condition.
Accordingly, the proper-time emerges in the NS sector and both proper-time and
its super-partner appear in the R-sector. Integration leads to free-string
field actions in both sectors.
