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 um in Rb vapour. Using a high-finesse Fabr
y-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 um, which has not been directly detected.
An evaluation of the absolute frequency and tunability of collimated blue light (CBL) generated in warm Rb vapour excited by low-power cw laser radiation at 780 nm and 776 nm, has been performed using a Fabry-Perot interferometer and a blue diode las
er. For the conditions of our experiments the CBL tuning range is more than 100 MHz around the resonant frequency of the 85Rb 5S1/2 (F=3) to 6P3/2 (F=4) transition. A simple technique for stabilizing the power and frequency of the CBL to within a few percent and 10 MHz, respectively, is suggested and demonstrated.
We are able to clearly distinguish the processes responsible for enhanced low-intensity atomic Kerr nonlinearity, namely coherent population trapping and coherent population oscillations in experiments performed on the Rb D1 line, where one or the ot
her process dominates under appropriate conditions. The potential of this new approach based on wave mixing for probing coherent atomic media is discussed. It allows the new spectral components to be detected with sub-kHz resolution, which is well below the laser linewidth limit. Spatial selectivity and enhanced sensitivity make this method useful for testing dilute cold atomic samples.
We analyze how light-induced coherent population oscillations and ground-state Zeeman coherence in an atomic medium with degenerate two-level transitions can modify spectra of applied cw resonant radiation at the sub-mW power level. The use of mutual
ly coherent optical fields and heterodyne detection schemes allows spectral resolution at kHz level, well below the laser linewidth. We find that ground-state Zeeman coherence may facilitate nonlinear wave mixing while coherent population oscillations are responsible for phase and amplitude modulation of the applied fields. Conditions for the generation of new optical fields by nonlinear wave mixing in degenerate two-level atomic media are formulated.
We present results of a study of four-wave mixing in Rb vapour with highly nonlinear susceptibility, using both homodyne and heterodyne detection. We demonstrate that the spectra have different appearances for media possessing electromagnetically ind
uced transparency and electromagnetically induced absorption, and for different relative polarizations of the drive and probe fields. We show that these differences allow the contributions of different processes responsible for the enhanced Kerr nonlinearity of the media to be distinguished.
We have observed the propagation of an approximately 35 ns long light pulse with a negative group velocity through a laser-cooled 85Rb atomic medium. The anomalous dispersion results from linear atom-light interaction, and is unrelated to long-lived
ground state coherences often associated with fast light in atomic media. The observed negative group velocity (-c/360) in the Rb magneto-optical trap for a pulse attenuated by less than 50% is in good agreement with the value of dispersion measured independently by an RF heterodyne method. The spectral region of anomalous dispersion is between 15 and 40 MHz, which is an order of magnitude wider than that typically associated with ground-state coherences.
