Optical properties of Bromothymol Blue/PVA Composite: Development of flexible high performance laser filter

The present work reports the development of bromothymol blue (BTB) dye incorporated PVA composite films for flexible laser filter applications. The flexible films are prepared via simple solution casting technique. Different weight percentages (0.1%, 1.0% and 4.0%) of BTB are incorporated in the polymer matrix. The structural, morphological and ductility properties of the films are studied by using XRD, FESEM and stress-strain measurement techniques, confirming the successful inclusion of the dye in PVA matrix. The band gap of the BTB/PVA samples is decreased to ~2eV from 4.7eV, the band gap of pure PVA, which indicates the change in optical properties of the system due to the introduction of the dye. The 1.0% BTB/PVA composite films show almost zero transmittance in the 200-550nm wavelength range, but remain transparent in the rest of the visible-NIR range. 1.0% BTB/PVA film based laser filter shows excellent performance to block light from a high power laser (~5mW) of the wavelength ~540nm even when the filter is exposed continuously for 36 minutes. A figure of merit (FOM) parameter is introduced in this work to estimate the efficiency and applicability of polymer based laser filters. 1.0% BTB/PVA film based laser filter shows fairly high FOM proving its ability as a strong candidate for flexible laser filter applications.