Collimated blue light generation in rubidium vapor

Abstract

We describe an experiment for generating and characterizing a beam of collimated blue light (CBL) in a rubidium vapor. Two low-power, grating-feedback diode lasers, operating at 780.2 nm (5S1/2→5P3/2) and 776.0 nm (5P3/2→5D5/2), respectively, provide step-wise excitation to the 5D excited state in rubidium. Under the right experimental conditions, cascade decay through the 6P excited state will yield a collimated blue (420-nm) beam of light with high temporal and spatial coherence. We investigate the production of a blue beam under a variety of experimental conditions and characterize the spatial coherence and spectral characteristics. This experiment provides advanced undergraduate students with a unique opportunity to investigate nonlinear optical phenomena in the laboratory and uses equipment that is commonly available in laboratories equipped to investigate diode-laser-based absorption spectroscopy in rubidium.

Generation of coherent mid-IR light by parametric four-wave mixing in alkali vapor

“…4(b) that the 4WM process saturates after about 16 mW of total input power. The saturation of CBL was previously reported [22,25,27,36], and we find that this number corresponds to what was observed in Fig. 8 of Ref [25].…”

“…6 of Ref. [25], where the CBL was only observed around the 5S 1∕2 F 3 → 5P 3∕2 F 0 transition, in the case of zero detuning of the 776 nm laser. However, CBL was observed from the two ground states of Rb in the case of direct two-photon absorption, where the upper 5 2 D 5∕2 state is populated with two photons at 778 nm [23].…”

“…To date, experiments on CBL were focused on maximizing the efficiency of the nonlinear process by investigating the pump intensity and polarization dependence of the process, as well as its temperature dependence [22,23,[25][26][27]. A repumping beam was also added to maximize the generated CBL power [28], and an external cavity was used to enhance the output power and to narrow down the CBL linewidth [29,30].…”

Comparison of collimated blue-light generation in 85Rb atoms via the D1 and D2 lines

“…An excitation to the nD states of alkali metal atoms opens interesting possibilities for nonlinear optics, as the population inversion, guaranteed between certain excited levels with appropriate lifetimes and branching ratios, results in amplified spontaneous emission (ASE) and spontaneously-seeded fourwave mixing for the involved optical transitions. A lot of attention was recently given to the generation of the collimated blue light (CBL) at 420.3 nm via the 5S 1/2 → 5P 3/2 → 5D 5/2 transition in Rb vapor [9][10][11][12][13][14][15][16]. Such interacting systems have been successfully used to study the interplay of co-existing nonlinear processes [17,18], the effects of externally-seeded optical fields [19], and of optical resonators [20].…”

Linewidth of collimated wavelength-converted emission in Rb vapour

“…Since then it has become an active area of research of several groups [3,4,5,6,7] and has been even suggested for advanced undergraduate laboratories [8]. The technique is of interest because new optical field generation in atomic media can lead to important applications in quantuminformation science [9] and low atom number detection [10].…”