Radiation pressure force from optical cycling on a polyatomic molecule

We demonstrate multiple photon cycling and radiative force deflection on the triatomic free radical strontium monohydroxide (SrOH). Optical cycling is achieved on SrOH in a cryogenic buffer-gas beam by employing the rotationally closed $P(N^{\prime \prime }=1)$ branch of the vibronic transition ${\tilde{X}}^2{\Sigma }^{+}\left(000\right)\leftrightarrow {\tilde{A}}^2{\Pi }_{1/2}\left(000\right)$. A single repumping laser excites the Sr–O stretching vibrational mode, and photon cycling of the molecule deflects the SrOH beam by an angle of ${0.2}^{\circ }$ via scattering of ∼100 photons per molecule. This approach can be used for direct laser cooling of SrOH and more complex, isoelectronic species. (paper)