An Improved Thermal Gas Lens for Optical Beam Waveguides

Gravitational and spherical aberrations in thermal gas lenses are known to cause distortions of light beams with gaussian intensity distribution. 1-5 The eventual use of this lens in long distance optical communication links depends in part on our ability to improve its quality and to develop effective beam control devices which periodically free the distorted beam from higher order modes.6 By analyzing the severe aberrations of the thermal gas lens reported in an earlier paper in this journal,4 we found that the axial exhaust of the heated gas was primarily responsible for the low quality of that lens. We demonstrate that a significant improvement of the focusing properties of the thermal gas lens can be achieved if the heated gas is exhausted in the radial direction. I I . CRITICAL A P P R A I S A L OF AN E A R L I E R T H E R M A L GAS L E N S The thermal gas lens used in a recent experiment4 was highly aberrated and caused severe beam deformations already for small off-axis 137 138