Generation of Giant Pulses from a Neodymium Laser with an Organic-Dye Saturable Filter

Abstract

There has been much recent interest in the production of high-peak power laser pulses by regeneration switching. Organic dyes have been used as saturable filters for both the ruby (cyanine dyes) and neodymium (a polymethine dye) to produce single high-power spikes. The cyanine dye, in suitable concentration and path length, can also be used to produce a long train of slightly enhanced (gain about 10) regular Q-switched spikes from the ruby laser, but the neodymium laser can apparently only be operated in the single-pike mode. This paper reports the discovery of saturable filter action in a common dye, rose bengal, a derivative of fluorescein, which permits the production of an extremely regular sequence of enhanced spikes from the neodymium laser. Unlike the previous dyes, the transition corresponding to the saturable absorption occurs between two excited states, not between the ground state and an excited state. The population of the lower excited state is achieved by optical pumping of the dye solution, and, by varying the intensity of the pumping flash lamp, the optical density of the filter may be altered thus changing the spacing between light spikes as well as their height.