Lasing at 602-620 nm from a red algae-derived phycobiliprotein

Lasing in the 602-620 nm (orange-red) spectral region has been observed from R-phycoerythrin (RPE), a phycobiliprotein responsible for the >80% quantum yield of red algae. Photoexcitation of 8 μM RPE solutions in a Fabry-Pérot resonator with frequency-doubled Nd:YAG laser pulses (λ_p = 532 nm) yields >26 nJ of energy in ∼2.5 ns (FWHM) pulses, which corresponds to >10 W of peak power. Maximum laser emission occurs at ∼610 nm, the threshold pump energy fluence is measured to be 260 ± 15 μJ/mm², and more than 100 longitudinal laser modes are generated when the cavity free spectral range and mirror separation are Δλ = 0.18 nm and L = 777 ± 1 μm, respectively. In combination with the known versatility of the phycobiliproteins as fluorescent tags, the biomolecular RPE laser reported here suggests its applicability to clinical assays and in situ laser imaging.