Optical probe with nosepiece and cooling system

An optical probe has an outer tube 30 made of a chemically inert material defining an internal channel and an opening. A nosepiece 2 mounted within the outer tube at the opening, has an aperture for an optical window 32 and is formed of a material having a coefficient of linear thermal expansion of 14.0 x 10-6 K-1 or less at 20oC and a thermal conductivity of 60 Wm-1 K -1 or more at 20oC, such as Molybdenum. The optical window 32 is bonded to the nosepiece 2 around the aperture and is made of diamond. An optical fibre 34 extends through the outer tube 30 and the aperture of the nosepiece 2 to a rear surface of the window. A coolant system has an inlet channel through the outer tube 30 to the nosepiece 2. An outlet channel runs through the internal channel from the nosepiece 2 and a linking channel link the inlet and outlet channels at the nosepiece 2.