Experiment and simulation of hole-coupled resonator modes with a CW HeNe laser

摘要

The Infrared Free Electron Laser (IRFEL) for the proposed Chemical Dynamics Laboratory at Lawrence Berkeley Laboratory will operate from 3 - 50 (mu)m and use all-metal optics. This choice of optics allows for broad tuning and has excellent power-handling capabilities. A hole-coupling approach for the optical resonator was adopted after extensive computer simulations verified that it fully met the design requirements. To bench-test the simulations we have carried out a scaled cavity experiment utilizing a visible (632.8 nm) continuous wave (CW) HeNe laser. Two cases have been studied: (a) a Gaussian near-concentric symmetric resonator and (b) a hole-coupled resonator with degenerate higher order modes. The simple geometry of the former case allows for a direct comparison with analytical theory and is useful for bench marking the diagnostic equipment. Since mode degeneracy should be avoided for good operation of an FEL, gaining an understanding of the latter case is important. Furthermore, it provides a good test case for evaluating the code performance. After discussing the theoretical model used in the simulations, we describe the cavity parameters and the experimental set-up. We proceed by comparing, for both case (a) and (b), the experimental results with theoretical predictions and simulations. This is followed by the summary and conclusions of these experiments.