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Summary form only given. A Bessel beam can have an extended focus compared to that of a Gaussian beam of the same spot size. Moreover, Bessel beams can be generated with a very small central spot, the profile of which regenerates if disrupted. These characteristics are favourable properties for the pump beam of a low threshold optical parametric oscillator (OPO). In particular, it has been predicted that pumping with a Bessel, rather than a Gaussian, beam will reduce the OPO threshold. Periodically poled lithium niobate (PPLN) is a nonlinear material that is particularly well suited to low threshold OPOs because of its high effective nonlinear coefficient and absence of walk-off This paper reports the study of a PPLN OPO pumped by a Bessel beam. Furthermore, unlike in previous studies, the experimental thresholds of an OPO under Bessel and Gaussian beam pumping are compared to each other and also to the standard theoretical model.