Highly Efficient Lasing Action of Nd³⁺- and Cr³⁺-Doped Yttrium Aluminum Garnet Ceramics Based on Phonon-Assisted Cross-Relaxation Using Solar Light Source

Abstract

We constructed a theory to explain the mechanism of laser generation with a high optical–optical conversion efficiency for Nd3+- and Cr3+-doped yttrium aluminum ceramics when sunlight or lamplight sources are used for pumping. As a result, a unique mechanism of laser action was found where the solar or lamp-light power could be converted to laser power with a high efficiency close to 80%, which has not previously been observed. The high conversion efficiency was not only considered to be based on one-to-one photon conversion but on two-photon excitation by a single photon with phonon assistance. Thus, the mechanism of lasing action should include a process where thermal energy is converted to photon energy. The theoretical results we obtained were consistent with those of the experiments.

INCREASE IN EFFECTIVE FLUORESCENCE LIFETIME BY CROSS-RELAXATION EFFECT DEPENDING ON TEMPERATURE OF Nd/Cr:YAG CERAMIC USING WHITE-LIGHT PUMP SOURCE

“…12 A remarkable increase in laser gain and output laser power have already been observed. 12 Previously, some reports on the measurement of the fluorescence lifetime of the Nd/Cr:YAG ceramics excited with narrow-band light were published. 1À14 However, an increase in fluorescence lifetime was not observed as a function of temperature.…”

“…10 As a result of the analysis, we found that the integrated spectral intensity of the fluorescence components from T 2 level to 4 T 1 level occurs efficiently due to multi-phonon relaxation. 10,12,13 The first process is indicated in Fig. 7, which is independent of the temperature of the laser medium.…”

“…The effect of this phenomenon is marked when the temperatures of the laser materials are high. 12 Enhancing the cross-relaxation of the Nd ions enables us to realize a high conversion efficiency from solar light to laser. 12 A remarkable increase in laser gain and output laser power have already been observed.…”

“…12 Enhancing the cross-relaxation of the Nd ions enables us to realize a high conversion efficiency from solar light to laser. 12 A remarkable increase in laser gain and output laser power have already been observed. 12 Previously, some reports on the measurement of the fluorescence lifetime of the Nd/Cr:YAG ceramics excited with narrow-band light were published.…”

Float zone growth and spectral properties of Cr,Nd:CaYAlO4 single crystals

“…Cr,Nd:YAG is one of the most investigated media [11], and the transparent YAG ceramic is mainly used in recent studies [12]. However, absorption of Cr,Nd:YAG around 500 nm which corresponds to the wavelength of solar radiation peak and the absorption cross section are relatively small even at the absorption peak wavelength.…”