Abstract
We measure the absolute absorption cross section of molecules using a matter-wave interferometer. A nanostructured density distribution is imprinted onto a dilute molecular beam through quantum interference. As the beam crosses the light field of a probe laser some molecules will absorb a single photon. These absorption events impart a momentum recoil which shifts the position of the molecule relative to the unperturbed beam. Averaging over the shifted and unshifted components within the beam leads to a reduction of the fringe visibility, enabling the absolute absorption cross section to be extracted with high accuracy. This technique is independent of the molecular density, it is minimally invasive and successfully eliminates many problems related to photon cycling, state mixing, photobleaching, photoinduced heating, fragmentation, and ionization. It can therefore be extended to a wide variety of neutral molecules, clusters, and nanoparticles.
Highlights
We measure the absolute absorption cross section of molecules using a matter-wave interferometer
Gas-phase spectroscopy has been established in various systems, ranging from gas cells to free molecular beams or ion traps
Gas phase data are lacking because the number densities are too weak
Summary
We measure the absolute absorption cross section of molecules using a matter-wave interferometer. In this Letter we present a method to measure absolute absorption cross sections which circumvents repeated photon cycling and which can be applied to extremely dilute beams. We exploit photon recoil in a Kapitza-DiracTalbot-Lau (KDTL) matter-wave interferometer [10] to measure the reduction in quantum interference contrast as a function of the position and intensity of a recoil laser.
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