Abstract
We experimentally demonstrate the conversion of a Gaussian beam to an approximate Bessel–Gauss mode by making use of a non-collinear four-wave mixing (4WM) process in hot atomic vapor. The presence of a strong, spatially non-Gaussian pump both converts the probe beam into a non-Gaussian mode, and generates a conjugate beam that is in a similar non-Gaussian mode. The resulting probe and conjugate modes are compared to the output of a Gaussian beam incident on an annular aperture that is then spatially filtered according to the phase-matching conditions imposed by the 4WM process. We find that the resulting experimental data agrees well with both numerical simulations, as well as analytical formulae describing the effects of annular apertures on Gaussian modes. These results show that spatially multimode gain platforms may be used as a new method of mode conversion.
Highlights
Light propagating in non-Gaussian spatial modes has gained significant interest in recent history, and has been shown to be a useful tool in a variety of classical, nonlinear, and quantum optics schemes [1, 2, 3, 4, 5, 6]
A weak (50 μW) Gaussian spatial-mode probe beam detuned by 3.024 GHz to the red of the pump beam is injected at an angle of ∼ 1o with respect to the pump
The inherently multi-spatial mode nature of the 4WM process used here allows for the amplification of, for example, images that are imparted on the input probe beam
Summary
Light propagating in non-Gaussian spatial modes has gained significant interest in recent history, and has been shown to be a useful tool in a variety of classical, nonlinear, and quantum optics schemes [1, 2, 3, 4, 5, 6]. Both Bessel-Gauss and Airy modes exhibit selfhealing and limited diffraction properties, which have straightforward applications in optical communications and imaging [13, 14, 15, 9] In this manuscript, we present experimental results in which nondegenerate four-wave mixing is used to both convert an input Gaussian probe mode to a Bessel-Gauss beam, while simultaneously generating a spatially-separate Bessel-Gauss conjugate beam. Nondegenerate four-wave mixing (4WM) in warm atomic vapor has proven to be a diverse tool in quantum optics [16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26] In this thirdorder nonlinear process, a pair of photons from a strong pump beam are annihilated, and a pair of photons are created at a small angle relative to the pump (one in the “probe” mode and one in the “conjugate” mode). Due to this multi-spatial-mode nature [20], the 4WM process has been shown to allow the simultaneous generation of multiple pairs of entangled beams, applicable to quantum communication protocols [35]
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