Fluid Jet Polishing

Fluid Jet Polishing Technology 

LightMachinery's patented fluid jet polishing system uses a fine stream of slurry to accurately remove nanometers of material from an optical surface.  LightMachinery has spent many years refining this computer controlled polishing technology.  While 90%  of our optical fabrication is done using conventional techniques, most of our high accuracy etalons, VIPAS, interferometers and wafers are finished using the 'FJP'.

Fluid jet polishing enables LightMachinery to tackle some very complex and difficult optical fabrication tasks with confidence and is opening up a new era of optical device manufacturing.

• The adjustment of the shape and flatness of optical components such as etalon mirrors to within a few nanometers
• Very thin components, such as wafers and thin etalons, that are impossible to accurately polish using conventional technology
• The ability to measure the final performance of complex assemblies such as Michelson Interferometers and then to make arbitrary surface corrections to correct the overall performance
• Arbitrary optical surfaces such as phase plates, corrector plates, axicons and cylindrical axicons
• Materials that are compatible with our FJP process include; Fused Silica, all glasses, crystal quartz, Germanium,  Silicon, CaF2, MgF2, Salts
• Non compatible materials (so far) include metals and any material with grain structure or inhomogeneities

More information on the FJP process and some examples too

The fluid jet process is 100% computer controlled

Step 1 Measure the current surface profile, this is usually done using an interferometer. Step 2 Compare the current surface to the target surface profile. Step 3 Compute the required removal pattern

A conventionally polished 2" x 2" fused silica substrate (before fluid jet polishing) Measured with tunable laser mapping system in transmission there is a peak to valley slope of about 115nm

This same substrate after FJP Measured again with tunable laser mapping system in transmission there is a peak to valley error of about 3nm. Shown here in the same scale

Another 2" x 2" fused silica square This substrate was measured in reflection using a Zygo interferometer, the error is very large, about 1.8um of concave shap

After FJP Shown here at the same scale as the picture above the error is 10nm peak to valley

A Very Flat 4" Silicon Mirror Measured with a Zygo GPI after fluid jet polishing this silicon mirror has a surface variation matched to the zygo test flat to 1/100 wave peak to valley over a 95% clear aperture

Note the rms surface figure of lambda/1000! This is important for creating high finesse etalons

Before and after fluid jet polishing interferogram clearly demonstrates the FJP's ability to correct transmitted wavefront errors. This process was completed in a single pass, processing on only one side, based on transmitted wavefront data from a Zygo interferometer.

Created with FJP technology, this demonstrates our ability to make completely arbitrary shapes to very high precision. The fringes are caused by the air gap between the designed surface and a flat substrate

Axicons are optical components that are shaped like cones. They are not simple to make using conventional polishing technology but the fluid jet system seems to have no problem. This one has a 3mrad slope and is designed to flatten the top of a gaussian beam. Notice that, unlike a lens, the axicon has fringes with constant spacing.

This is the resulting interferogram from fluid jet polishing a grid of 3 x 3 micro lenses into the surface of a piece of fused silica.

Essentially these are 2D sine waves so there are 9 positive lenses and 4 negative lenses on the surface

The amplitude variation (sag) of the lenses is about 500nm over about 3mm but the radius of curvatures in the central regions of the lenses are about 120cm

Aspheric cylindrical lenses, acylinders, are useful in laser beam shaping applications and have become a bit of a specialty at LightMachinery. Designs such as the Powell lens can create a line focus with uniform intensity over long distances. Our unique fluid jet polishing capability makes polishing acylinders a routine process.

Axicons are optical components that are shaped like cones. They are not simple to make using conventional polishing technology but the fluid jet system seems to have no problem. This one has a 3mrad slope and is designed to flatten the top of a gaussian beam

Target surface A simple .jpg, 256 x 256 of ISO (we are still very pleased about our ISO 9001 certification). The depth was set to 250nm for the text.

Starting Surface This was already a pretty good surface, polished by our opticians to about 1/8 wave over the 2" x 2" square

After Fluid Jet Polishing This beautiful pattern was made using the fluid jet polishing machine in the usual raster mode.

After Fluid Jet Polishing The ISO image is polished (backwards) into the square optical component that has then been optically contacted to the lower 3" diameter holder. The visible fringes are from the air space between the surfaces.

Fluid Jet Polished And then Adhesive Free Bonded (optically contacted)

Target surface Another simple .jpg, 256 x 256. A constant change in color value between each segment

After Fluid Jet Polishing A stepped depth that gives rise to a phase mask matrix

Air Spaced Etalon Matrix This piece was then optically contacted to a flat piece of fused silica creating an array of air spaced etalons. Each one is has a gap that is 100nm wider than its neighbor

Conventional Flatness λ/10 Shown here a conventionally polished fused silica substrate. The wedge in the part is very good, about 50nm, less than lambda/10

An Early FJP result - Flatness of λ/100 After processing half of the part with fluid jet polishing. The surface flatness is reduced about 6nm peak to valley or lambda/100

Atomic force microscope analysis of a conventionally polished fused silica surface. The size of the area is 1.5 x 2.5 microns. Surface roughness is 1nm Rms

Atomic force microscope analysis of a fluid jet polished fused silica surface. The size of the area is 1.5 x 2.5 microns. Surface roughness is 1nm Rms

More strange surfaces A fluid jet polished image of a Canadian Penny in a 2" square of fused silica. The fused silica was then optically contacted to another piece of fused silica and the air space in between creates visible fringes that look a lot like an actual penny.

A depth map of the penny image

More strange surfaces Another optical element that would be impossible to make using conventional polishing, crossed cylindrical lenses

A top view of the crossed cylinders

Fluid Jet Polishing is crucial to making large aperture fabry perot etalons like the one shown above

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