Coherent spectroscopy in Potassium vapor with amplitude modulated light

We present the first experimental observation of Coherent Population Trapping (CPT) in Potassium, obtained with kHz-frequency modulation of the laser light amplitude. It is performed by acousto-optical amplitude modulation of the radiation from an external cavity diode laser, matching the D(1) line of K. The CPT resonances are detected both through K absorption and fluorescence. The resonances are studied in three kinds of K cells: i) pure-evacuated, ii) polydimethylsiloxane (PDMS)-coated-evacuated and iii) Ne-gas buffered. In all cases CPT-resonance narrowing with cell temperature is observed.. In the pure-evacuated cell we registered the lowest contrast and the highest width of the resonance, while in buffered/coated cells a strong enhancement of the CPT resonance contrast up to 15% is observed. This behavior is the opposite to the one exhibited by Cs and Rb. The observed contrast enhancement in K is accompanied by more than two orders of magnitude reduction of the resonance width. The results here presented prove the advantage of using Potassium in CPT-based applications.