It’s all done with mirrors…” 

There is a joke in the optics community that the sole function of the glass is to support the coating.  While this might sound trite, there is a bit of truth to the comment.  Over the years I have had the pleasure of working on both sides of this humorous statement.  My early years with Spectra-Physics were in the Coating Department in Mt. View, CA.  Later involvements had me working on micro-optics the size of human hairs.  My current work has been on very large optics, some 6 meters in diameter weighing over 20,000 pounds. 

Coatings are the key:

Lasers function by providing feedback (reflecting) a very specific color at greater than 99%.  This is not your standard bathroom mirror (85%) which is just a single layer of metal .  The coatings used for making beams of light are quite specialized and require careful engineering to be functional.  The layers of material that are applied to establish such a high degree of reflectivity have a well-designed thickness and specific angle of incidence.   Inflection Point Mobiles uses the spectrally selective nature of these layered, dielectric coatings and then varies the angle of incidence by allowing the glass to drift with the wind.  As the angle varies, the effective thickness of the layers will shift.  This results in a color change – both in transmission and reflection.  I was allowed to retain any scrap coated glass from my early career years knowing that these specialized optics would make fabulous mobiles.  It took some time, but I have matured a design that I feel captures both the beauty of motion as well as enhancing the spectral shifts.  

Other industries utilize the ‘stack-layered’ coatings – in particular the microscopy field. Slides are illuminated with filtered light to enhance contrast of a stained sample. The technology has gone from using simple colored glass to highly sophisticated computer evaluation of the results.  The coatings made for this industry are known as ‘dichroics’ because they separate light. These filters are also very sensitive to any angular change – an artifact that is accentuated when used in a mobile.  This industry is another fabulous trove for artists as their mirrors are often quite spectacular.


If you have any questions please feel free to ask. 

Dave Head,
Oct 5, 2012, 12:24 AM