An improved technique for the measurement of low optical absorption losses in bulk glass

A thin rod sample is thermally clamped at both ends to provide a rigid mounting and a thermal short-circuit for heating effects associated with surface losses. The ends are index matched with liquid to minimize sample preparation. A laser beam is focused through the sample and the temperature rise due to the absorbed energy is monitored at its centre. Sensitivity is limited to a few dB km^–1 optical loss with a laser of 100 mW power. The theory is discussed in detail for this particular geometry and experimental verification presented.