Enhanced conversion efficiency for harmonic generation with double resonance
Z. Y. Ou, H. J. Kimble
1993
Optics Letters
Conversion efficiency for cw harmonic generation is calculated for the situation in which both fundamental and harmonic waves are resonant. Compared with the situation of a singly resonant cavity at the fundamental, the doubly resonant geometry can lead to an increase efficiency can thus be achieved with nonlinear crystals pump power for the fundamental input. The idea of using a resonant cavity to enhance conversion efficiency in cw second-harmonic generation was first discussed by Ashkin et
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... .,' who found that the conversion efficiency can be greatly increased by resonating either the fundamental or the harmonic field. Because of its simplicity, the scheme of employing a resonator to build up the fundamental power is the one most widely used in practice and has recently led to the achievement of high cw conversion efficiency. 2 -7 For such a scheme, the conversion efficiency Y7 for the ratio of generated second-harmonic power P 2 ,out to the injected fundamental power P 1 ,j 1 n is found from the relation 2 ' 4 ' 7 where T 1 is the transmission coefficient for the input coupler of the buildup cavity for the fundamental field and L 1 is the total round-trip linear loss exclusive of T 1 for this field and where we have assumed that (T 1 ,Ll) << 1. ENL is the single-pass nonlinear conversion efficiency. Given the values of L 1 , P 1 ,in, and ENL, one can optimize the transmission of the input coupler T 1 for impedance matching of the input 2 ' 4 to find the optimum conversion efficiency 77P, with (1 + E +4,6NLmP,m )' where eNL ENL/L 1 2 provides a figure of merit for singly resonant intracavity harmonic generation. From this expression, it is clear that high conversion efficiency requires that 4 ENLP1im >> 1 or ENLP1,h. >> (L 1 /2) 2 , i.e., that the nonlinear conversion be much bigger than the linear loss. For fixed linear loss L 1 , we can achieve this end by increasing either ENL or P in. Unfortunately, the latter option is usually accompanied by unwanted thermal effects that degrade the performance of the buildup cavity so that Eq. (2) breaks down before 770P is reached. 4 6 Alternatively, the available fundamental power P 1 ii may be too small for efficient harmonic generation in some applications. Of course, the option of increasing the material nonlinearity as expressed by ENL (relative to L 1 ) is clearly the pathway of choice and has been followed of the effective nonlinear coefficient. High conversion of relatively low nonlinear coefficients and with modest in the experiments that have achieved high conversion efficiency with crystals with large nonlinear coefficients, such as LiNbO 3 , KNbO 3 , and KTP. 2 7 However, not withstanding some promising new methods, 6 crystals with large ENL are available only for limited regions in wavelength. Faced with this state of affairs, we describe in this Letter a technique for enhancing ENL by resonating the harmonic as well as the fundamental field. Although Ashkin et al.
doi:10.1364/ol.18.001053
pmid:19823287
fatcat:atdmfxwp5fdp3nmtzzp6th6tci