We demonstrate an all-optical thermo-plasmonic effect to switch/modulate the surface plasmon resonance signal intensity excited at the metal-air interface. This optically addressed thermo-plasmonic measurement scheme is suitable to amplify very small changes in the complex dielectric constant ( ${\epsilon }_m(T)$ ) of thin gold (Au) film, induced by the ${\mathrm{Ar}}^{+}$ laser. The predominant contributions due to small but highly repeatable transient photo-thermal effects in the complex metal dielectric constant is confirmed to be the reason behind the highly reproducible all-optical thermo-plasmonic device performance presented here.