1 July 1998 Ž . Optics Communications 152 1998 319–323 Theoretical and experimental studies of single-mode operation in diode pumped Nd:YVO rKTP green laser: 4 influence of KTP length Y.F. Chen ) , T.M. Huang, C.L. Wang, L.J. Lee, S.C. Wang Precision Instrument DeÕelopment Center, National Science Council, 20 R & D Road VI, Hsinchu Science-Based Industrial Park, Hsinchu, Taiwan, ROC Received 26 January 1998; revised 17 March 1998; accepted 18 March 1998 Abstract We present a theoretical study of the single-mode operation in a diode pumped Nd:YVO rKTP green laser by 4 considering the combined action of the anisotropic emission cross-section of Nd:YVO and the KTP crystal acting as a 4 birefringent filter. The influence of the KTP length on the performance of single-mode operation was investigated. Comparison between theoretical predictions and experimental results is presented. q 1998 Elsevier Science B.V. All rights reserved. Keywords: KTP; Single-mode operation; Green laser; Nd:YVO laser 4 1. Introduction Compact multiwatt intracavity-doubled lasers are at- tractive for applications such as display, spectroscopy, material processing, biomedical, and pumping sources for tunable Ti:sapphire lasers. Such lasers may also become critical components of an all-solid-state compact UV source. However, chaotic fluctuation of the doubled output wx power, called ‘‘green problem’’ 1 , may exist in such intracavity-doubled lasers due to longitudinal-mode cou- pling and sum frequency generation. Some methods for avoiding the green problem have been proposed. A useful and practical method for eliminat- ing the instability is to operate the laser in a linear polarized single longitudinal mode. Unidirectional ring- cavity lasers are often used to produce several multiwatt wx intracavity-doubled green lasers 2 . However, designs that incorporate multiple intracavity elements, which frequently require very careful alignment for optimum performance, are not favoured for rugged, reliable, particularly space- ) E-mail: yfchen@pidc.gov.tw borne applications. Accordingly, there is need of a solid- state laser and a method which reduce the complexity of the alignment mechanisms in obtaining single-frequency fundamental lasers and single-frequency intracavity-dou- bled lasers. Several authors recently reported the single-mode oper- ation of a diode-pumped Nd:YVO rKTP green laser with 4 w x wx a linear cavity 3,4 . Helmfrid and Tatsuno 5 have theo- retically investigated single-mode operation of an intracav- ity doubled Nd:YVO laser. However, to the best of our 4 knowledge, the influence of the KTP length on the perfor- mance of single-mode operation has never been studied. In this work, we present a theoretical study of the single-mode operation in a diode pumped Nd:YVO rKTP 4 green laser by considering the property that Nd:YVO has 4 a large difference in emission cross-sections for light polarized parallel and orthogonal to the optical axis. The analysis reveals that a longer KTP crystal can increase the multi-mode threshold and enhance the single-mode opera- tion. The practical example of a Nd:YVO rKTP green 4 laser pumped by a 15-W fibre-coupled laser diode is considered to confirm our physical analysis. Experimental results show that the optimum KTP length for the highest 0030-4018r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. Ž . PII S0030-4018 98 00165-5