Physical properties of sapphire fibretips for laser angioplasty

The physical properties of sapphire contact probes were examined with respect to their use in laser angioplasty. The rounded and bullet-shaped probes are mechanically atraumatic and provide tactile feedback during laser angioplasty. The optical transmission characteristics of the flat, rounded and bullet-shaped probes were measured and the propagated laser beam profiles photographed in air and water. These properties are largely wavelenght independent in the small part of the spectrum currently used for laser angioplasty. Sapphire contact probes may heat up from direct absorption of laser light at the interfaces, but they probably also heat up by conduction from the heated tissue with which they are in contact. The rounded and bullet shaped probes focus light to a rather diffuse waist in air, but in water this focusing effect is lost. The divergence angle of the bare fibre is reduced in water. Transmittance characteristics depend on surface reflection, absorption, probe shape and surface smoothness. The flat probes transmitted 85% of the incident light, but the rounded and bullet probes absorbed and scattered almost half of the light.