Near-infrared distributed feedback laser emission based on cascade Förster resonance energy transfer to Nile Blue aggregates

• Utilization of dye aggregates allow to obtain higher redshift of stimulated emission.
• Spectral shift between excitation and emission is enlarged by FRET processes cascade.
• Tunable near-infrared DFB lasing is achieved on Nile Blue aggregate emission band.

We present the real time tunable distributed feedback lasing in the region of near-infrared light obtained in a dye doped polymeric layer via cascade energy transfer based on Förster resonance (FRET). The Rhodamine 6G and Rhodamine B laser dyes were used as a donor for FRET effect, while the Nile Blue dye served as an acceptor. The shift of the emission from visible to near-infrared region was possible due to the formation of the dyes aggregates of lower than for molecules energy levels. Therefore, through the sequence of energy transfers between molecules and aggregates, the shift between excitation and stimulated emission spectra of about 200 nm can be achieved. The use of the periodically modulated pumping beam from pulsed Nd:YAG laser allows to select and amplify particular wavelength from the gain profile according to Bragg conditions, what can be easily tuned by changing the period of the interference pattern. The reported tunability of distributed feedback emission from 725 nm to 745 nm confirmed that only Nile Blue aggregates were involved in the laser action, while donor molecules and aggregates, as well as acceptor in non-aggregated form, acted as a canal for energy transfer.

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