OPTICAL 2ND-HARMONIC GENERATION IN LOSSY MEDIA - APPLICATION TO GASE AND INSE

The paper deals with optical second-harmonic generation in a medium ab sorbing the second-harmonic radiation, and where phase matching betwee n the fundamental and second-harmonic radiation is not necessarily ach ieved. We first take the waves to be in the form of traveling waves, a nd describe the damping of the fundamental beam due to harmonic creati on. It is found that both second-harmonic absorption and phase mismatc h enhance the depletion length of the pump wave. Before depletion, the second-harmonic output power is independent of the traversed thicknes s if it exceeds the second-harmonic attenuation length. When depletion occurs, the second-harmonic output power is constant, instead of quad ratic, in the input power. Next, second-harmonic generation in a plane -parallel plate of lossy material is envisaged in the case of normal i ncidence, including the multiple reflections expected in high-reflecta nce materials. The expressions of the harmonic output intensity, trans mitted or reflected, of this paper and from the conventional treatment , are compared. The deviation is noticeable in the case of the transmi tted harmonic power, and may be considerable in the case of the reflec ted power. Last, measurements of the second-harmonic output intensity in GaSe and InSe are reported at a fundamental wavelength of 1.06 mum. The sample dependence is in good agreement with our theory, which in tum is applied to derive new values of the nonlinear optical susceptib ilities in the layered-structured III-VI materials. The treatment is f ully analytical and may be applied to a wealth of materials.