Linewidth of collimated wavelength-converted emission in Rb vapour

Abstract

Abstract. We present a study of the spectral linewidth of collimated blue light (CBL) that results from wave mixing of low-power cw laser radiation at 780 nm and 776 nm and an internally-generated mid-IR field at 5.23 µm in Rb vapour. Using a highfinesse Fabry-Perot interferometer the spectral width of the CBL is found to be less than 1.3 MHz for a wide range of experimental conditions. We demonstrate that the CBL linewidth is mainly limited by the temporal coherence of the applied laser fields rather than the atom-light interaction itself. Results obtained with frequency modulated laser light allow an upper limit of several hundred kHz to be set for the linewidth of the collimated mid-IR radiation at 5.23 µm, which has not been directly detected.

Cavity-enhanced frequency up-conversion in rubidium vapor

“…We find that a low finesse cavity more than doubles the output power and greatly reduces the linewidth of the blue light produced. In previous single pass FWM experiments, for low output powers (around 10 µW), the linewidth of the coherent blue light has been reported to be ≤ 3 MHz [2,20]. However, in our single pass setup, up to 340 µW of coherent emission can be generated.…”

Parametric wave mixing enhanced by velocity-insensitive two-photon excitation in Rb vapor

“…To date, studies of the FWM process in diamond-type energy-level systems in alkali atoms, mostly in Rb, have focused almost exclusively on detecting the CBL and inferring details of the generation process from the blue light properties [1][2][3][4][5][6][7][8][9][10][11][12][13]. The primary reason for this is that the mid-IR radiation at 5.23 µm generated by the process of amplified spontaneous emission (ASE) is completely absorbed by the glass windows of vapour cells usually used in such experiments.…”

Collimated blue and infrared beams generated by two-photon excitation in Rb vapor

“…Recent experiments achieved first 40 μW of 420 nm light through the additional coupling of both 5S 1∕2 hyperfine ground-state levels [1], and subsequently 1.1 mW by further optimization of input laser polarizations and frequencies [3]. The generated blue beam exhibits a high degree of spatial coherence [2], with a spectral linewidth typically limited by the linewidths of the applied laser fields [7]. The absolute frequency of the blue light has been found to be centered on the 6P 3∕2 → 5S 1∕2 transition, with tunability of ≥100 MHz possible by adjustment of the input laser frequencies [5].…”