Liquid immersion is used in laser machining to cool and remove debris from samples.  The use of fluid media such as water, oils, or air for machining is well researched; however, the application of low-vapor-pressure fluids, such as ionic liquids, for laser micromachining has not been researched in depth.  Ionic liquids are electrically neutral salts that are liquid at room temperature.  These liquids tend to have low vapor pressure, which impacts a fluid’s ability to vaporize and cavitate during laser machining.  Fluids with high vapor pressures, on the other hand, can be considered volatile and easily vaporize with minimal added energy.  This paper discusses the effects of various immersion fluids on laser micromachining.   Different immersion media were tested on a borosilicate glass cover slip using ultrafast (300 fs) laser pulses focused by a high numerical aperture (NA 1.2) immersion lens.  For each immersion fluid, rectangular arrays of holes were machined with single, well-separated pulses, where the cover slip was translated laterally and stepped axially to change the focal position and bracketing the glass surface with positions both above (in the fluid) and below it (in the glass).  The machined samples were then replicated with polymer imprint lithography, and both the substrate and replica were imaged using optical and scanning electron microscopies.  The results suggest that fluids with lower vapor pressures, like ionic liquids, can expand the usable machining focal range, while also reducing the diameter of the holes and perhaps even mitigating collateral surface damage.