Abstract
An intra-cavity phase element, combined with a passive Q-switch saturable absorber and a suitable intra-cavity aperture, can provide extremely high mode discrimination, so as to obtain laser operation with single, pure, very high order Laguerre-Gaussian mode. With a Nd:YAG laser setup, well controlled and extremely stable Q-switched operation in the degenerate Laguerre-Gaussian TEM04, TEM14, TEM24, TEM34, and TEM44 modes was obtained. The measured output energy per pulse for each of these modes was 5.2mJ, 7.5mJ, 10mJ, 12.5mJ, and 13.7mJ respectively, compared to 2.5mJ for the Gaussian mode without the phase element (more than a five fold increase in output energy). Correcting the phase for these modes, so that all transverse lobes have uniform phase, results in a very bright and narrow central lobe in the far field intensity distribution that can theoretically contain more than 90% of the output energy.
Highlights
Pure high order transverse mode operation in laser cavities has been originally suggested in the 1960’s, and since experimentally investigated in various types of laser configurations [1] - [7]
We further show that correcting the phase of these modes, so that they have transverse uniform phase, results in a bright central lobe in the far field
The results revealed that more than 5-fold increase in output energy as compared to T EM00 operation can be obtained
Summary
Pure high order transverse mode operation in laser cavities has been originally suggested in the 1960’s, and since experimentally investigated in various types of laser configurations [1] - [7]. A limiting aperture is used in the conventional manner to further discriminate against higher transverse modes With such phase elements, efficient selection of pure T EM01, T EM02, T EM03 and helical T EM01∗ Laguerre-Gaussian (LG) modes was experimentally demonstrated, leading to an increase up to a factor of 2 in output power with respect to the fundamental T EM00 mode. In this article we show how an intra-cavity phase element, combined with the properties of a passive Q-switch saturable absorber and with a suitable intra-cavity aperture, can provide extremely high modal discrimination, enabling extremely stable and controlled operation of very high order LG modes (with as much as 40 lobes) These modes have a significantly larger mode volume than that of the Gaussian mode, resulting in more than 5-fold increase in output power. We further show that correcting the phase of these modes, so that they have transverse uniform phase, results in a bright central lobe in the far field
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