Role of phase in second-harmonic generation within an optical cavity (A)

Paul Mandel, Thomas Erneux

C. Sibilia, Alessandro Re, E. Fazio +1 more

Recently the cubic behavior of nonlinear second-order materials (the so-called cascading effect) was discussed and demonstrated. Here we discuss the bistability and the chaotic behavior of an optical ring cavity containing a second-order nonlinear material when second-harmonic generation occurs, focusing on the role of the cascading effect. The role in instability played by the phase mismatch Δk for second-harmonic generation is also considered.

Ling-An Wu, Harry J. Kimble

An experiment is described that investigates certain interference effects for second-harmonic generation within a resonant cavity. By employing a noncollinear geometry, the phases of two fundamental beams from a frequency-stabilized dye laser can be controlled unrestricted by the boundary conditions imposed in an optical cavity containing a KDP crystal and resonant at the second harmonic. The fundamental beams are either traveling or standing waves and generate either one or two coherent sources of ultraviolet radiation within the cavity. The experiment demonstrates explicitly the dependence of second-harmonic phase on the fundamental phases and the dependence of coupling efficiency on the overlap of the harmonic polarization wave with the cavity-mode function. The measurements agree well with a simple theory.

K. Lahti, Ilkka Juhani Tittonen

B. K. Mohanty

Taro Hasegawa

The nonlinear absorption process and associated phase shift in coupled optical cavities are studied experimentally by observing optical resonance properties. In the coupled cavity configuration, two optical cavities, one for a fundamental beam and the other for a second-harmonic (SH) beam, are coupled by a nonlinear crystal for the second-harmonic generation (SHG). The cavity for the SH beam effectively extends the nonlinear crystal length so that the frequency-conversion efficiency of the SHG, which is proportional to the square of the crystal length, is enhanced. In the observation, power reduction of the fundamental beam at resonance is observed as a small dip in the resonance curve. According to a model calculation, it is found that this power reduction is caused by blue-induced infrared absorption.