The study of optical forces exerted by off-axis Bessel beams on Rayleigh particles in the framework of generalized Lorenz-Mie theory demonstrated the existence of extra-forces named axicon forces, complementing the classical scattering and gradient forces already discussed extensively in the literature. The present paper revisits the same issue but in the more restricted case of on-axis beams. Results obtained in the case of off-axis beams are then confirmed but, computations being carried out in an easier framework, their meaning is displayed more clearly. Beside, we may easily distinguish between dark and non dark beams, a distinction which was not carried out in the off-axis study. A question at stake is to know whether the generalized Lorenz-Mie theory for Rayleigh particle identifies or not with the usual dipole theory.

在广义的Lorenz-Mie理论框架内对离轴贝塞尔光束对瑞利粒子施加的光学力的研究表明存在名为轴锥力的额外力，补充了文献中已广泛讨论的经典散射力和梯度力。本文重新讨论了相同的问题，但在同轴光束更受限制的情况下。然后确认了在离轴光束的情况下获得的结果，但是，在更简单的框架中进行计算时，其含义会更清楚地显示。此外，我们可以轻松地区分暗光束和非暗光束，这是离轴研究中未进行的区分。一个关键问题是要知道瑞利粒子的广义Lorenz-Mie理论是否与通常的偶极子理论相符。