Buried Nd: gadolinium garnet waveguide lasers grown by pulsed laser deposition

Description/Abstract

Pulsed laser deposition (PLD) has often been avoided as a preferred fabrication method due to the large number of particulates generated on the waveguides during growth. We have grown uncapped and buried Nd:GGG waveguide lasers, as before[1], to study the effect of particulates on the lasing power threshold. A comparison between the lasing power threshold of the waveguide and the particulate density is shown in fig.1. It can be seen that the effect of the particulates has a far more dramatic effect on those guides with increased confinement. An increase in particulate density from 3.5 x 10⁴ to 9.7 x 10⁵ particulates led to an increase in absorbed power threshold from 2.5mW to 167mW. A 4(greek mu)m thick guide with a particulate density of 3.2 x 10⁶ particulates cm^-2, however, lased easily at 19mW where a 2(greek mu)m thick waveguide would be unable to lase at the pump powers available. Even an increase up to 1 x 10⁷ particulates
cm^-2 (a very poor quality film) would still allow lasing at around 60mW. The 8(greek mu)m thick waveguide showed good waveguide performance regardless of particulate density, lasing at 2.2mW and 12.2mW with particulate densities of 5.5 x 10⁴ cm^-2 and 6.6 x 10⁶ respectively, a change in particulate density of over 2 orders of magnitude. The particulate density of the Capped layer is higher than that of the other 4(greek mu)m unclad waveguides at 1.5 x 10⁷ cm^-2. A film with such a high particulate density has been made in a 4pm unclad structure but was unable to lase at the incident laser powers available (~700mW @ 808nm). The buried laser had a lasing threshold of 14.8mW of absorbed power. For comparison lasing action in an uncapped layer with a particulate density 4 times lower was observed at 19mW absorbed power. Two new implementations to the traditional PLD apparatus of scanned CO₂ laser heating and off-centre multiple rotational targets have been used in the course of fabrication to increase the homogeneity of the films. These techniques will be discussed further.