Abstract. Single-mode selection with Michelson selectors in cw standing-wave dye lasers is analyzed. The application of single and double Michelson mode selectors for compensation of spatial hole burning effects is described in detail. Upper limits for the pumping are considered. It is shown that with spatial hole burning compensation, even the single Michelson selector provides sufficient selectivity for high power single-mode operation in linear cavities.
PACS" 42.55To achieve high powers in the single-mode operation of standing-wave cw dye lasers one has to overcome the inherent complication connected with the spatially inhomogeneous saturation. The spatial pattern of the standing-wave field intensity inside the active medium creates a non-uniform distribution of the population inversion [1]. This effect, generally referred to as "spatial hole burning", leads to a waste of input power and is known to strongly favour multi-mode oscillation [2]. This problem is not present in the ring laser, where the travelling-wave mode gives the advantage of homogeneous saturation in the medium, with strong mode coupling and improved conversion efficiency as a result. However, with increasing single-mode field intensity the theoretical efficiency of the standing-wave laser approaches asymptotically that of a travelling-wave laser, as a consequence of broadening in the spatial hole burning structure [3J. In practice, though, the obtainable single-mode power in standing-wave cavities is ultimately limited by a second mode reaching threshold when the pump power is increased. Thus the common problem in conventional single-mode techniques involving Fabry-Perot (FP) etalons has been to introduce the selectivity required at high pump powers in spatial hole-burning conditions, without significant non-selective insertion losses reducing the efficiency. This paper considers the single-mode selection in a standing-wave cw dye laser using a Michelson mode selector for compensation of spatial hole burning effects. The Michelson selector was first applied in a single-mode dye laser by Liberman and Pinard [4]. The attractive properties of the Michelson device have been discussed in [5]: i) the operation as a retroreflector eliminates walk-off loss and yields a good geometrical purity of the beam; ii) the number of optical surfaces is reduced compared with air-spaced etalons; iii) the energy inside the selective element is divided instead of accumulated. Hence, insertion losses are lower than with FP etalons. Double and triple Michelson selectors with enhanced selectivity have recently been successfully applied in a standing-wave dye laser, and high single-mode powers have been obtained [5,6]. Previously, the exploitation of the spatial mode. structure for single-mode selection with FP etalons [7] and thin absorbing films [8] has been described. We have recently applied a single Michelson selector (SM) to compensate spatial hole burning effects in a cw dye laser [9]. The system was shown to be capable of single-mode operation at considerable...
