Enhancement of stimulated Raman scattering in Nd³⁺-doped terrace-microspheres

Abstract

Terrace-microspheres of high-index multi-component glasses (BaO-SiO 2 -TiO 2 , n D =1.93; BaO-ZnO-TiO 2 , n D =2.2) containing various Nd 3+ contents were used for pumping experiments to investigate the influence of Nd 3+ content and matrix of glasses on the SRS enhancement effect. Pumping the terrace-microspheres containing low content of Nd 3+ (0.3ppm and 0.9 ppm) at 800-830nm wavelengths, Raman scattering due to glass matrix and Nd 3+ fluorescence were overlapped spectrally in the wavelength region of 860~940nm. Under such conditions, Nd 3+ works as a seeding and an amplifier of SRS, resulting in SRS enhancement at 840~940nm wavelengths. The terrace-microspheres of both highindex glasses showed SRS gain enhancement of 4 times (Normalized SRS gain = [SRS peak intensities at various pumping wavelength] / [SRS peak intensity at 790nm pumping wavelength]) and decrease in SRS thresholds from 2.5mW (λ pump ≈790nm) to 0.3mW (λ pump ≈810~830nm). On the other hand at high-content Nd 3+ (15, 120 and 16000ppm), Nd 3+ fluorescence intensity was far stronger than that of Raman scattering and SRS was not observed clearly. The reason why SRS decreased in the high-Nd 3+ -content glass spheres was discussed: Nd 3+ absorption in the region of 890~900nm wavelengths is one of the plausible explanations. Terrace-microsphere of Nd 3+ (0.9ppm) BaO-ZnO-TiO 2 glass was also used for pumping experiment, which glass shows 30 times stronger spontaneous Raman scattering than that of silica glass, and result in strongest SRS emission was performed. The high-index multi-component terrace-microspheres containing Nd 3+ of relatively low content have a potential application to a low-threshold spherical Raman laser for multiwavelength emission in the near-infrared region (λ=840~940nm).