Spectroscopic characterization of Nd:Y_2O_3: application toward a differential absorption lidar system for remote sensing of ozone

Abstract

Neodymium-doped yttria (Nd:Y2O3) is investigated as a solid-state laser material for frequency-tripled generation of ultraviolet laser wavelengths for use in remote sensing of ozone. Emphasis is placed both on the spectroscopy of the fundamental wavelengths at ∼0.914 µm and ∼0.946 µm to assess their feasibility for laser oscillation and on the absorption spectroscopy in the 0.8-µm wavelength region for determination of suitable pump sources. The temperature dependence of the emission and absorption characteristics of Nd:Y2O3 are examined, since aggressive cooling may be required for efficient ∼0.914-µm lasing due to its quasi four-level nature. Data for flash-lamp-pumped laser performance on the 4F3/2→4I11/2 is presented for Nd:Y2O3 and compared with Nd:YAG. Diode-pumped threshold-fluence and threshold-pump energy estimates for Nd:Y2O3 lasing on the 4F3/2→4I9/2 at 0.914 µm and 0.946 µm are calculated based on the data presented here. The measurements presented here for the Nd:Y2O3 indicate favorable absorption and emission properties. Favorable absorption properties in the ∼0.8-µm pump wavelength are compatible with a variety of potential pump sources. Favorable emission properties at reduced temperatures near 150 K indicate that Nd:Y2O3 operating at 0.914 µm and 0.946 µm will have normal-mode laser thresholds similar to that of room-temperature Nd:YAG operating at 0.946 µm. In Q-switched operation, however, Nd:Y2O3 is predicted to exceed the performance of Nd:YAG due to the lower 1.06/0.94 cross-section ratio, which helps to limit amplified spontaneous-emission effects. Although Nd:Y2O3 is not a new material, it has not been the topic of study due to growth problems associated with its high melting point. New advances in growth techniques and the favorable spectroscopic features of Nd:Y2O3 have inspired a new examination of this material.