Selective reflection from a potassium atomic layer with a thickness as small as lambda/13

We demonstrate that a method using the derivative of the selective reflection (SR) signal from a nanocell is a convenient and robust tool for atomic laser spectroscopy, achieving a nearly Doppler-free spectral resolution. The recorded linewidth of the signal from a potassium-filled cell, whose thickness l lies in the range 350-500 nm, is 18 times smaller than the Doppler linewidth (similar to 900 MHz full width at half maximum) of potassium atoms. We also show experimentally a sign oscillation of the reflected signal's derivative with a periodicity of lambda/2 when l varies from 190 to 1200 nm confirming the theoretical prediction. We report the first measurement of the van der Waals atom-surface interaction coefficient C-3 = 1.9 +/- 0.3 kHz x mu m(3) of potassium 4S(1/2) -> 4P(3/2) transitions with the nanocell's sapphire windows, demonstrating the usefulness and convenience of the derivative of SR technique for cell thicknesses in the range 60-120 nm.