Litron offers five distinct resonator configurations. This is more than any other manufacturer and this article sets out to help customers identify which one is best for their needs.
A. Conventional Stable
This multimode resonator has been around the longest time and is the simplest in terms of design. Typical characteristics are excellent energy extraction (measured as the amount of stored energy in the rod emerging in the pulse) and beam uniformity but somewhat high divergence and M2 values. Conventional stable resonators allow the user to vary parameters such as input energy (flashlamp voltage) and repetition rate with very little variation in beam quality.
B. Telescopic Stable
This variation on the multimode stable design places an intracavity telescope in the rear of the resonator. This has the two effects of compensating the thermal lensing in the laser rods and making the resonator appear considerably longer, without making it significantly more so, so reasonably short pulses are still obtained. The outcome is a laser beam with still very good spatial uniformity and efficient energy extraction but with much better divergence and M2 characteristics than a conventional stable resonator. The resonator is still flexible in terms of input energy and repetition rate and can be made even more so by means of adjustments to the telescope.
C. Gaussian-Coupled Unstable
This resonator comprises a P-branch confocal unstable resonator with a graded reflectivity mirror (GRM) for the output coupler. The rear mirror curvature is chosen so as to compensate the thermal lens in the rod and provide a more or less collimated output. The GRM unstable resonator provides lower values still for divergence and M2, with reasonable extraction efficiency but the downside is less uniform near field uniformity and much less flexibility in varying the input energy and repetition frequency.
D. Telescopic Stable TEM00
This is a variation on the telescopic stable resonator that additionally employs an intracavity aperture to suppress higher order transverse modes to allow the laser to give a beam with near diffraction limited, single mode TEM00 quality, with a uniform Gaussian profile. Input energy and repetition rate flexibility are similar for the telescopic stable resonator but extraction efficiency is relatively low, being between a third and a quarter of the multimode telescopic stable resonator. As an option, Litron offers a suite of apertures to allow a user to obtain a range of beam quality and energy trade offs from TEM00 to multimode.
E. Conventional Stable TEM00
Compared to a telescopic stable TEM00 laser, a smaller footprint, shorter pulse duration and greater input energy flexibility are the main benefits. However, lacking the telescope, the extraction efficiency is lower still.
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