Tunable Single-Frequency Laser in Co2+:KZnF3

We have operated a tunable single frequency infrared laser based on the 4T2 to 4T1 transition in Co++ The laser cavity and diagnostics used in the experiment are shown in Fig. l. The cavity is a folded, three-mirror, astigmatically compensated design similar to the lasers used in earlier studies of the Co++ system.1–2 The crystal host is the cubic Perovskite KZnF3 which is clamped to a copper cold finger that is cooled by liquid nitrogen. The cavity is colinearly pumped by an Argon ion laser, but the pump beam is introduced by means of a dichroic beamsplitter, instead of the more conventional way employing transmission through a dichroic coating on an end mirror. The beamsplitter approach has an advantage for weakly absorbing crystals in that it permits a second pass of the pump beam through the crystal. With this design, net absorptions as high as 80% have been achieved in a crystal only 2mm thick.