Removing unwanted light from high-power optical systems

An apparatus for removing unwanted cladding light from a high-power optical system, the optical system comprising an optical fiber, the optical fiber comprising a fiber cladding, the fiber cladding having a refractive index of n1, the apparatus comprising:

• a fluid to surround the fiber, the fluid having a refractive index of n2 such that n2≧n1, the fluid having an internal transmittance of τfluid such that τfluid≧0.999 over a distance of approximately 100 micrometers (μm);
• a glass block comprising a channel for the optical fiber, the fluid being interposed between the glass block and the fiber cladding, the glass block having a refractive index of n3 such that n3≧n2, the glass block having a transmittance of τglass such that τglass≧0.999 over a distance of approximately 1 centimeter (cm);
• a thermal compound in contact with the glass block, the thermal compound to absorb light, a heat flux at the thermal compound being less than approximately 200 Watts per square inch (W/in2);
• and
• a cold plate to remove heat from the apparatus, the cold plate exhibiting a thermal resistance that is less than approximately 0.15° C.-in2/W.