  Quantum optical techniques may yield immersion fluids with high indices of
refraction without absorption. We describe one such technique in which a probe
field experiences a large index of refraction with amplification rather than
absorption, and examine its practicality for an immersion lithography
application. Enhanced index can be observed in a three-level system with a
tunable, near-resonant, coherent probe and incoherent pump field that inverts
population of the probe transition. This observation contradicts the common
belief that large indices of refraction are impossible without absorption,
however it is well in accord with existing electromagnetic theory and practice.
Calculations show that a refractive index >> 2 is possible with practical
experimental parameters. A scheme with an incoherent mixture of pumped and
unpumped atoms is also examined, and is seen to have a lower refractive index
(~2) accompanied by neither gain nor loss.
