Single frequency and high power operation of diode-pumped solid-state lasers

Abstract

In recent years, advances made in semiconductor diode lasers have led to a resurgence in the development of solid-state lasers. Diode-pumped solid-state lasers (DPSSLs) are typically more compact, efficient, reliable and economical than alternative laser sources. In this thesis two areas of research in the field of DPSSLs have been investigated namely, single frequency ring lasers and high power diode bar pumped solid-state lasers.

Single frequency laser sources are important in a wide range of applications, and a number of methods are available for producing single frequency operation. In this work an acousto-optic modulator was used in a ring laser cavity to enforce unidirectional operation, which in turn can produce single frequency output. Acousto-optic devices can provide a simple, low-loss means of enforcing unidirectional operation in ring lasers, compared to other methods. Previously, the means by which this was accomplished was not understood. Here, two distinct mechanisms are described that can be used to enforce unidirectional operation, experimental verification is provided, and the implications that this has for the development of single frequency sources are discussed. Ring lasers were also constructed which operated at wavelengths of 1.3µm and 2µm, using acousto-optic modulators to produce unidirectional operation.

Diode bar lasers have recently emerged as one of the most economical pump sources for solid-state lasers, and are capable of producing high output powers in side-pumping geometries. In this thesis, the use of diode bars in end-pumping configurations is explored, as such systems potentially offer much higher efficiencies than side-pumping, and should be more suitable for output powers up to a few tens of watts. A significant problem with diode bar end-pumped systems is that the dimensions of the diode bar (10mm x 1µm) make it difficult to effectively couple their output into the lasing mode of a solid-state laser. In this thesis, initial attempts to end-pump lasers are described. Some degree of success was obtained. Also presented is a novel optical arrangement that manipulates the diode bar output to produce a beam with a much higher degree of symmetry, and hence, suitability for end-pumping. This system, using just two mirrors to chop up and rearrange the diode beam, has applications in a wide variety of situations involving laser beams with a large difference in dimensions and divergence properties in two orthogonal directions, and should allow diode bars to be effectively used for end-pumping solid-state lasers. Preliminary results for end-pumping a solid- state laser are presented, which offer great promise for optimised laser systems.

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