Self-induced high-speed modulation in microchip solid-state lasers with asymmetric end pumping

Abstract

We applied laser-diode sheetlike end pumping to a multimode Nd:YVO(4) laser and observed high-speed (>400-MHz) modulation of the intensity of chaotic pulsation near 1 MHz. The frequencies of modulation were the beat frequencies for pairs of closely spaced lasing modes. Asymmetric optical confinement and the resultant modal interference are shown to lead to oval-hollow-mode operation in which modal beat notes induce high-speed modulation, the frequency range of which is 2 orders of magnitude higher than the intrinsic relaxation oscillation frequency. Good numerical reproduction of the observed chaotic pulsations and their high-speed modulation was obtained with model equations in which such effects as nonlinear gain coupling among modes and field interference between pairs of modes were included. High-speed pulsations in nonchaotic lasers were also demonstrated.

Self-acousto-optic modulation and orthogonality violation in the transverse modes of a broad-area Nd-doped yttrium-aluminum-garnet single-shot laser

“…The appearance of nonorthogonal modes has been explained in cw lasers by an asymmetric thermal lens effect induced by the asymmetry of the spatial pump profile. The laser-induced temperature change modifies the refractive index with a spatial profile that matches that of the pump beam, therefore leading to an asymmetric index confinement [9]. However, in our pulsed, single-shot laser, YAG-matrix device, thermal effects are not expected to play a significant role in the dynamics [18].…”

“…Therefore, a system of ordinary differential equations for the amplitudes of those modes must be integrated [19]. The theoretical analysis performed in previous works on NOMs [9,20] relies on this approach. However, although useful to reproduce the temporal dynamics found in the lasers studied (such as chaotic relaxation oscillations or breathing modes), it imposes the modal-beat-mediated modulation of the output intensity from the beginning.…”

“…Attention to the breaking of the orthogonality condition that characterizes the empty cavity modes, usually employed to describe laser dynamics, is surprisingly recent. Otsuka et al [9,10] found experimental evidence of NOMs in sheetlike end-pumped Nd:YAG and LiNdP 4 O 12 solid state lasers in 2002, and they explained their presence as the result of a deformed thermal lens effect due to asymmetric pumping. They reported a high-speed modulation in the total output intensity (∼500 MHz) and energy level repulsion with increasing power as well.…”