Simple annular-beam generator with a laser-diode-pumped axially off-set power build-up cavity

We have developed a novel, compact-mode selective annular-beam generator that employs a laser-diode (LD)-pumped, passively locked power build-up cavity (PBC). The PBC functions as a flexible and compact light source that is capable of producing TEM0n high-order Hermite-Gaussian (HG) beams. The generated HG beams can then be converted to LG modes, particularly to annular-beams, using two cylindrical lenses. The system was theoretically studied and a mode-matching condition was derived. The tailoring position of the active semiconductor laser medium relative to the external cavity of the PBC enabled the production of single high-order HG modes. The optimum position was calculated by model calculations of the mode-coupling efficiency. The desired TEM0n modes of HG beams were generated by translating the axial position of the external cavity of the PBC in increments of ∼100μm relative to the LD emission surface. High quality TEM01 to TEM015 of the HG beams and their conversion to the desired LG modes having powers of the order of 1mW was successfully demonstrated. This system is suitable for optical tweezers.