Bisero, D.

Ernst, G.J.

van Oerle, B.M.

Verschuur, J.W.J.

Witteman, W.J.

English

We report on a highly efficient frequency-doubling set-up of two BBO crystals in which the second crystal compensates the walk-off in the first. This yields a maximum conversion efficiency of 50% from 527nm to 263nm

University of Twente Research Information

Proceedings 1996 Symposium of the IEEE/LEOS Benelux Chapter, Enschede, The Netherlands High efficient harmonic generation in two 880 crystals by means of walk-off compensation B.M. van Oerle 1, D. Bisero 1, G.J. Ernst 2, J.W.J. Verschuur 2, W.J. Witteman 1• 2 1Nederlands Centrum voor Laser Research; P.O. Box 2662; 7500 CR Enschede 2 University ofTwente; Faculty of Applied Physics; Quantum Electronics Group; P.O. Box 217; 7500 AE Enschede We report on a highly efficient frequency-doubling set-up of two BBO crystals in which the second crystal compensates the walk-off in the first. This yields a maximum conversion efficiency of 50% from 527nm to 263nm. Introduction An efficiency-limiting factor in second harmonic generation in critically phase-matched crystals is the occurence of walk-off between the fundamental and second hannonic beam [1]. It is possible to compensate for the walk-off, by using a second crystal in which the walk-off is in the opposite direction. Such a method has been used to enhance the perfonnance of optical parametric oscillators [2]. We will show that it can also be used to increase the efficiency of second harmonic generation processes. This contribution will start with some physics of birefringent crystals and the origin of walk-off. Then the walk-off compensation scheme will be discussed, and it will be applied to a frequency doubling experiment, in which the fourth harmonic of a Nd:YLF laser system is produced. Walk-off in birefringent crystals The walk-off effect was already described by Christiaan Huygens in 1690, who observed a beam of sunlight passing through what he called Islandic crystal (CaC03) [4]. Even though the incident beam was perpendicular to the crystal surface, Huygens observed that it split in two beams that propagated at an angle of 6.6°. One beam was called the ordinary ray, and the other was called the extraordinary ray since it did not seem to obey Snell's law of refraction. Many optical crystals exhibit birefringence. The physical origin of this effect is the anisotropy of the crystal, that expresses itself in the direction dependence of the dielectric constant. This results in a different refractive index for the two directions of polarization. Z Moreover, the refractive index depends on the s propagation direction through the crystal. The ordinary beam is the optical beam with its electric field perpendicular to the plane fonned by the propagation direction and the optical axis. The extraordinary beam has its electric field in the same plane as the propagation vector and the optical axis. If an optical beam propagates along the optical axis Z, the extraordinary and ordinary beam are interchangeable (see figure 1). Due to the direction dependence of the dielectric Figure 1: Walk-off in a negative uniaxial czystal. constant, the electric displacement D is in general - 25 -

High efficient harmonic generation in two BBO crystals by means of walk-off compensation

https://ris.utwente.nl/ws/files/129960446/VanOerle1996high.pdf

High efficient harmonic generation in two BBO crystals by means of walk-off compensation

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