Atomic thermometry using 4S $$\rightarrow $$ 5P absorption spectroscopy in potassium vapor

Abstract We present a comprehensive study of the Doppler broadened $$4S \rightarrow 5P$$ transitions in natural abundance potassium vapor, focusing on both the $$\hbox {D}_1$$ and $$\hbox {D}_2$$ lines. Using a home-built 405 nm extended-cavity diode laser and a 10 cm heated vapor cell, we measure the transmission spectra across a wide range of probe intensities and vapor temperatures. Weak-probe measurements confirm the applicability of the ElecSus model, which accurately reproduces the observed absorption profiles and allows the quantitative extraction of atomic temperatures with high precision. The $$\hbox {D}_2$$ transition exhibits stronger absorption and greater sensitivity to temperature changes, while the $$\hbox {D}_1$$ line provides a robust test of the weak-probe regime. By fitting the Doppler broadened spectra with ElecSus , we demonstrate a spectroscopic thermometry technique capable of resolving small temperature variations, even in the presence of thermal gradients and electronic noise. Our results establish ElecSus as a reliable tool for the precise characterization of hot atomic vapors, demonstrating excellent agreement with models using experimentally determined 4S $$\rightarrow $$ 5P isotope-shift values.