A webinar presentation on the TechBriefs (SAE Media Group) platform. This presentation explains how optical thin film interference filters work and how modern, reactive-magnetron-sputtering manufacturing processes produce filters of the highest quality. The physical characteristics of these filters lend themselves to many performance benefits, which are outlined. Basic optical filtration terminology and concepts are introduced. Computational optimization as a optical design strategy is presented and examples provided of how this approach can greatly improve filter performance and cost.

1. C H R O M A T E C H N O L O G Y C O R P ® www.chroma.com/FISH
SPUTTERING OF OPTICAL COATINGS
How Reactive Magnetron Sputter Coating Enables
Complex Filter Design and Precision Manufacturing

2. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Sputtering Basics
Features
Sputter coating, like electron beam or thermal
evaporative (“soft”) coating, is a form of physical vapor
deposition (PVD) that occurs under high vacuum.
Material is ejected from a “target” via ionized gas
bombardment (ex. argon+) due to an electric field that
creates a plasma.
Magnetron Sputtering is one type of sputtering
technique where magnetic fields help contain the
plasma, thereby increasing efficiency.
A negative high voltage is applied to the
metal target and ionized argon gas is
accelerated toward the target thereby
dislodging metal material.

3. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Sputtering Basics
Features
With reactive sputtering, oxide coatings can be made
by introducing oxygen gas which reacts with the metal
during deposition.
Ion-assist is used to deliver energy to the growing
film in order to promote void-free growth and enhance
film durability.
The high energy of the sputtered material
produces a much denser coating than what
could be achieved using electron beam or
thermal evaporation processes.

4. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Sputtering of Optical Coatings: Features & Benefits
Benefit to
Application
Coating
Properties
Sputtering
Characteristics
close matching to CIE color functions
Raman edge/notch filter spectral acuity
multi band designs optimized to application
enables narrow-bands for multi-spectral imaging
repeatability of execution
complex designs, needle layers
tight spectral tolerances
high-precision layer thickness control
thickness proportional to sputter power
optical monitoring
reactive sputtering w/ ionized oxygen
Process characteristics
flat/image quality dichroic for structured illumination
environmental durability for remote sensing
high laser damage threshold for laser mirror
high throughput for telecom bandpass filter
deep blocking for multi-photon microscopy
reasonable coating stress
low inclusion of sputter gas
high density
hardness and adhesion
high transmission, low absorption
low scatter
high purity
increased throw/ large mean-free path
dense plasma, high energy
high vacuum, low pressure
Physical characteristics
high temperature
low ripple

5. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Vacuum chamber
Metal target
Silicon or metal target
Glass substrate
Optical monitoring system
(measures transmission of
light through coating
during deposition)
Vacuum
pump
low-index
sputter
cathode
high-index
sputter
cathode
Atmospheric
pressure
Sputtering
Characteristics
Physical
increased throw/ large mean-free path
dense plasma, high energy
high vacuum, low pressure
high temperature
high-precision layer thickness control
thickness proportional to sputter power
optical monitoring
Process
reactive sputtering w/ ionized oxygen

6. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Vacuum chamber
Metal target
Silicon or metal target
Glass substrate
Optical monitoring system
(measures transmission of
light through coating
during deposition)
Vacuum
pump
low-index
sputter
cathode
high-index
sputter
cathode
High vacuum
Sputtering
Characteristics
Physical
increased throw/ large mean-free path
dense plasma, high energy
high vacuum, low pressure
high temperature
high-precision layer thickness control
thickness proportional to sputter power
optical monitoring
Process
reactive sputtering w/ ionized oxygen

7. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Sputtering
Characteristics
Physical
increased throw/ large mean-free path
dense plasma, high energy
high vacuum, low pressure
high temperature
high-precision layer thickness control
thickness proportional to sputter power
optical monitoring
Process
reactive sputtering w/ ionized oxygen
Vacuum chamber
Metal target
Silicon or metal target
Glass substrate
Optical monitoring system
(measures transmission of
light through coating
during deposition)
Vacuum
pump
low-index
sputter
cathode
high-index
sputter
cathode
high-index
deposition
cloud
O2+
Ar+
Ar+
High vacuum
high-index
deposition
cloud

8. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Vacuum chamber
Metal target
Silicon or metal target
Glass substrate
Optical monitoring system
(measures transmission of
light through coating
during deposition)
Vacuum
pump
low-index
sputter
cathode
high-index
sputter
cathode
low-index
deposition
cloud
O2+
Ar+
High vacuum
Sputtering
Characteristics
Physical
increased throw/ large mean-free path
dense plasma, high energy
high vacuum, low pressure
high temperature
high-precision layer thickness control
thickness proportional to sputter power
optical monitoring
Process
reactive sputtering w/ ionized oxygen

9. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
R1 R2
Incident Wave
Glass
Air
Reflected Waves
Multi-layer stacks use
constructive interference
of the reflected waves (at
and off of the multiple
interfaces) in order to
“block” unwanted light.
Thin Film Stack – alternating
high and low index layers
(not to scale)
Transmission
Interference

10. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Sputtering of Optical Coatings
Benefit to
Application
Coating
Properties
Sputtering
Process
Characteristics
close matching to CIE color functions
Raman edge/notch filter spectral acuity
multi band designs optimized to application
enables narrow-bands for multi-spectral imaging
repeatability of execution
complex designs, needle layers
tight spectral tolerances
high-precision layer thickness control
thickness proportional to sputter power
optical monitoring
reactive sputtering w/ ionized oxygen
Process characteristics
flat/image quality dichroic for structured illumination
environmental durability for remote sensing
high laser damage threshold for laser mirror
high throughput for telecom bandpass filter
deep blocking for multi-photon microscopy
reasonable coating stress
low inclusion of sputter gas
high density
hardness and adhesion
high transmission, low absorption
low ripple
high purity
Physical characteristics
increased throw/ large mean-free path
dense plasma, high energy
high vacuum, low pressure
high temperature
low scatter

11. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
From Process to Production
Spectral Plots
Visualizing performance
Sputtered Coatings
Enabling complex designs
Precision:
Control & Optimization
Transmittance:
Transmission & Optical Density

12. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Reading Spectral Plots
Transmittance: fraction of incident light transmitted through sample: T = I ÷ I0
Transmission: transmittance expressed in percent: %T = (I ÷ I0) × 100
Transmission is typically used to describe transmittance of desired light
Optical Density (OD) = -log T = -log [(%T) / 100
Optical Density includes loss of transmittance due to absorbance, reflectance
and scattering
It’s a measure of the total impedance of light through a medium (filter)
Transmission
Transmittance expressed as: Transmittance expressed as:
Optical Density

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C H R O M A T E C H N O L O G Y C O R P ®
Transmission & Optical Density, plotted together
Slope: steepness of transition from transmission to optical density
Steeper slopes require more thin film layers
Steep slopes are necessary for applications such as Raman spectroscopy and fluorescence microscopy

14. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Transmission: theoretical & measured filter spectra
Accuracy and precision: good match of theoretical and actual %T data
5 independent production lots of each filter

15. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Optical Density: theoretical & measured filter spectra
Accuracy and precision: good match of theoretical and actual OD data
5 independent production lots of each filter
OD measurement is noise-limited

16. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Accuracy, precision, high %T, low ripple, steep slopes

17. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Blocking: A fundamental optical challenge in fluorescence microscopy
Ratio between the light intensity of a fluorescence microscopy light source and fluorescence signal is typically in the
range of 1e6 – 1e10: 1, with extremes in cases such as single-molecule TIRF as high as 1e15 : 1

18. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Classical Fabry-Perot type of optical coating design
Design approach: based on “quarter-wave stacks” composed of individual layers with thicknesses which are
factors of ¼ wavelength of light

19. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
%T spectra of one production lot
Sputtering enables computational optimization
multi band designs optimized to application

20. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
%T spectra of two independent production lots, overlaid
Sputtering enables computational optimization
multi band designs optimized to application

21. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
%T spectra of three independent production lots, overlaid
Sputtering enables computational optimization
multi band designs optimized to application

22. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
%T spectra of four independent production lots, overlaid
Sputtering enables computational optimization
multi band designs optimized to application

23. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
%T spectra of five independent production lots, overlaid
Sputtering enables computational optimization
multi band designs optimized to application

24. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
%T spectra of six independent production lots, overlaid
Sputtering enables computational optimization
multi band designs optimized to application

25. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
%T spectra of seven independent production lots, overlaid
Sputtering enables computational optimization
multi band designs optimized to application

26. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
%T spectra of eight independent production lots, overlaid
Sputtering enables computational optimization
multi band designs optimized to application

27. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
%T spectra of nine independent production lots, overlaid
Sputtering enables computational optimization
multi band designs optimized to application

28. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
%T spectra of ten independent production lots, overlaid
Sputtering enables computational optimization
multi band designs optimized to application

29. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Combined %T and OD spectra of ten independent production lots, overlaid
Sputtering enables computational optimization
multi band designs optimized to application

30. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Sputtering enables computational optimization
notch filters with narrow rejection band, deep & steep blocking, broad transmission
488nm narrow notch rejection filter with UV/VIS/SWIR transmission

31. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Sputtering enables computational optimization
notch filters with narrow rejection band, deep, steep blocking, broad transmission
488nm & 561nm narrow notch rejection filters with UV/VIS/SWIR transmission

32. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Sputtering enables computational optimization
notch filters with narrow rejection band, deep, steep blocking, broad transmission
488nm, 561nm, & 633nm narrow notch rejection filters with UV/VIS/SWIR transmission

33. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Sputtering enables computational optimization
notch filters with narrow rejection band, deep, steep blocking, broad transmission
488nm, 561nm 633nm & 785nm narrow notch rejection filters with UV/VIS/SWIR transmission

34. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Sputtering enables computational optimization
notch filters with narrow rejection band, deep, steep blocking, broad transmission
488nm, 561nm 633nm & 785nm narrow notch rejection filters with deep, steep & broad blocking (high OD over
range)

35. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Sputtering enables computational optimization
Examples of customized CIE- type Z, Y & X photometry filters
Extremely accurate, F1’ < 2%
Black trace = target Yellow trace = design theory Shaded traces = measured filter spectra
Z

36. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Sputtering enables computational optimization
Examples of customized CIE- type Z, Y & X photometry filters
Extremely accurate, F1’ < 2%
Black trace = target Yellow trace = design theory Shaded traces = measured filter spectra
Z Y

37. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Sputtering enables computational optimization
Examples of customized CIE- type Z, Y & X photometry filters
Extremely accurate, F1’ < 2%
Black trace = target Yellow trace = design theory Shaded traces = measured filter spectra
Z Y X

38. +1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
THANK YOU
Published in Bellows Falls, Vermont, US
Chroma optical filters and related products may be purchased online or
via phone. For more information, please e-mail sales@chroma.com,
visit www.chroma.com or call 800.824.7662.