Phonon engineering in Nd3+-doped garnet lasers: filling the yellow gap and boosting fluorochrome excitation

Yellow light sources, emitting at the wavelength of 570 to ∼590 nm, are indispensable for many applications in biological diagnosis and treatment. However, a compact yellow laser is very difficult to attain owing to the absence of efficient electronic transitions, referring to the long-standing “yellow gap” over 60 years in the solid-state laser field. Here, we proposed a phonon engineering strategy to create yellow lasers in Nd3+-doped garnet laser crystals, which combines thermally driven electron–phonon coupling and intracavity frequency-doubling simultaneously. Via an ingenious cavity design, continuous-wave yellow lasing at 575.5 to 583 nm is realized from Nd:YAG and Nd:GGG by coupling various phonon modes. Benefiting from the thermally enhanced lattice vibrations, these yellow lasers exhibit an anomalous temperature dependence with improved output powers at high temperatures. Moreover, using this high-photon-flux yellow laser as a pump source, the fluorescent intensity of the Alexa Fluor probe is boosted by 100 times compared with the traditional green laser excitation, indicating its great potential for flow cytometry applications. These findings not only open up the possibility of creating unprecedented laser emissions in the traditional crystals but also provide a light source for molecular labeling and biological detection.