When customers come to us to design & manufacture a custom component, the conversation usually begins with the substrate. There is a lot to consider beyond just glass, paper, or film. Imaging on each has its advantages, are there are plenty of variations within each substrate category that might not be immediately obvious. We compiled some of the properties of our most common substrates to serve as a jumping off point for your next project.

Paper with Photo Emulsion:

Positives:

-Lowest cost option
– Large sizes available compared to glass substrates
– Good diffuse reflectance
– Image resolution to ~20 cy/mm
– Ability to produce a true gray scale
– Glossy,  Semi-gloss, and Matte finishes available: Glossy paper can hold a better line edge and slightly higher resolution (Though  it also has a higher specular reflectivity and can be too reflective in some applications). Matte (or semi-matte) will offer a more diffuse surface with a lower specular reflection, but the sharpness of the image is slightly lower than the Glossy paper
– Can be mounted to various backing materials (Kydex, Sintra) for added rigidity and protection
– Typ. reflectance ~82%R

Negatives:

-Large size change with temperature and humidity (~1 or 2%)
-Can be scratched, bent or otherwise easily damaged.

Paper with Photo Emulsion is an excellent low cost option that provides flexibility within the finish and size of the finished product. It can satisfy a large number of needs very effectively such as systems where specular reflectivity cannot be controlled.

Film with Photo Emulsion:

Positives:

– Moderate cost
– Large sizes available for Macro applications
– Image Resolution from ~50 cy/mm to ~120 cy/mm can be achieved
– Ability to produce a true gray scale (continuous tone)
– Can be mounted between glass for added rigidity/protection

Negatives:
– Moderate size change with temperature and humidity ( ~0.0012 %/% RH,   ~0.001%/degree F)
– Base not completely clear (typically 0.02-0.05 OD)
– Can be scratched

Film with Photo Emulsion is another cost effective solution that can satisfy a number  of imaging needs. Its ability to hold very sharp images, even at high resolutions make it well suited for many applications.  A major benefit of film is the capability to image a true grayscale, especially for applications where a half tone would be ineffective.

Sodalime Glass with Evaporated Chromium:

Positives:  
– No humidity size change
– The pattern is very durable  and more resistant to moisture, and thermal expansion than Film and paper
– Very sharp image with resolution of ~500 cy/mm or better (depending on the pattern)
–  Good wavelength transmission range
– Sometimes used for reflection images

Negatives:
Small size change with temperature  (  (~5x10^-6 /degree F)  )
No true grayscale (but can be mimicked with halftones)

The primary chrome on glass alternative and the industry standard for decades.  Providing very good optical clarity across a wide range of wavelengths available in many sizes and thicknesses for Bio medical, Aerospace, Industrial automation, and other precision imaging applications at a reasonable price.

Fused Silica (wrongly called quartz) with Evaporated Chromium:

Positives:

–  No humidity size change
– Higher durability
– Lower chance for edge chipping
– Very stable transmission through the visible wavelengths (91%).
– Better clarity and better wavelength transmission range than float glasses
– Smaller size change with temperature  (~0.33x10^-6 /degree F)

Negatives:
-Much more expensive than float glasses  to purchase and machine.

Fused silica is the Cadillac of optical materials providing excellent clarity, thermal stability , in a more durable material useful in any extreme environment applications such as aerospace, and other sciences utilizing applications where temperature changes and consistency across a broader wavelength is required.

*Both glass and Fused Silica can have other coatings (aluminum, gold, etc.) which have better wavelength blocking or reflection than chrome but are much more fragile and therefore require special care and handling, and can limit some of the imaging capabilities.  If considering specialized coatings call to discuss with one of our sales team.

Ceramic (alumina) with evaporated chromium:

Positives: 

– Could be very white (70% to 85% R typ.)
– Matte surface provides more diffuse, less specular reflection
– Good thermal stability

Negatives:
-Surface is formed from micro particles- can make image edge irregular
-Limited thickness availability, as well as limited overall size.
-Rather fragile

Opal/White Ivory Glass with evaporated chromium:

Positives:

– Very diffuse
– Glossy surface
– Reflectance 60%R
– Opacity varies with thickness

Negatives:

  • Being very diffuse, Opal has back illumination undercutting the image, sometimes causing problems
  • Material has been adapted for optical use, but not as much data on the material available

Opal is your choice as a high resolution “paper” giving a strong reflectivity and high contrast when paired with Blue chrome.  Useful whenever higher precision imaging is required in a reflective application such as vision systems, robotic surgery calibration, microscopy.

Other Substrates

Flashed Opal:

-This is clear glass with a  thin powdered white glass coating which has been melted onto the clear glass. It is not very even or flat which makes for poor imaging. It is a lower cost solution, however.

Flashed opal  has been replaced by Opal or ceramic that provide much better capabilities for durability and image quality.

 

Ground Glass with evaporated chromium:

-This is clear glass which has been abraded to form a frosted surface. It has many hills and valleys. Many spots and voids are seen in images. An image can be projected onto the ground surface- often used as a focusing screen.  An image on the ground surface can be used as a size reference to the optical image projected onto the ground glass. It is helpful when some diffusion or contrast is needed for locating a front side pattern.  The frosting process provides minor diffusion helping  avoid hot spots in backlit applications when diffuse lighting is not available.

 

Of all the variables you have to consider when designing a component for your photonics based system, substrate type is a great starting point. We hope this guide will serve to help highlight the advantages and drawbacks of substrates typically used in photonics based applications. As always, get in touch with our experienced engineers should you have any questions about how to proceed with your next project.