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Optical filters can be designed to transmit, block, or reflect light at any wavelength range from the UV to the IR. Learn how to specify optical filters for your specific application and about the advantages of manufacturing optical filters using an advanced plasma deposition process.

Ultra-Narrowband Optical Filters Pushing Boundaries from the UV to the LWIR

Alluxa Engineering Team

Developments in ultra-narrow manufacturing capabilities enable transformative, world-changing, technology.

Advances in optical sensors and imaging technologies are ever more rapidly assimilated into how humans interact, understand themselves, and explore the world around them. The scope of inquiry for optical devices is broad and they enable technologies within, such as implanted transdermal bioMEMS devices, and beyond, or as space-flight surveyors deployed as near and deep space instruments. Central to the functionality of modern optical devices, ultra-narrow bandpass (UNBP) thin-film optical filters enable discrimination of sub-nanometer bands inside broad spectra. These filters, pioneered as NIR DWDM filters for the telecommunications industry, are now essential in extracting meaningful signal from imaging and sensing devices operating anywhere between the deep ultraviolet and the mid infra-red bands. (more…)
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COVID-19 Prevention and Testing

Solutions from Optics and Imaging

This webcast was originally broadcast on July 23, 2020 and is now available for on demand viewing.

The rise of the novel coronavirus, and the spread of the COVID-19 sickness, are central challenges facing the world today. Preventing the spread of and testing for COVID-19 are the focus of a massive worldwide research, development, and deployment effort -- and some of the first, and subsequently most widely, used approaches have been based on prevention and testing using optical imaging. This webcast consists of short presentations by three leading precision optics and imaging companies: specialists from Ophir, FLIR, and Alluxa will provide an overview of how optical technology is being used to help contain, and to hopefully help diminish, the COVID-19 pandemic. You will leave this webcast with an increased understanding of how our industry is providing solutions to this crisis.

 

Cost:

Register to attend.

Presented by: Dr. Rance Fortenberry, Director of Technology, Alluxa and others
Sponsored by: Alluxa, FLIR, Ophir

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The role of thin film optics in qPCR and Covid-19 detection

Rance Fortenberry, PhD

Filter features such as high transmission, steep edges, low ripple and deep blocking are important when testing many samples, says Dr. Rance Fortenberry, director of technology at Alluxa

  The current Covid-19 pandemic has highlighted the need for rapid and accurate quantitative analysis of dangerous pathogens, particularly Sars-Cov-2. Fortunately, our ability to determine the structure of new and dangerous viruses has continued to improve since the invention of polymerase chain reaction (PCR), which enables the production of billions of copies of a single DNA sample. (more…)
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Angle of Incidence (AOI) and Polarization

 

AOI and Snell’s Law

Angle of incidence (AOI) refers to the tilt of an optical filter with respect to the incident light (Figures 1a-1c). The simplest case is 0° AOI, where the incident light is normal to the filter.
Figures 1a-1c: Diagrams showing (a) normal AOI for an optical filter, (b) 45° AOI for a dichroic filter, and (c) 45° AOI for a high-reflectivity mirror.

Figures 1a-1c: Diagrams showing (a) normal AOI for an optical filter, (b) 45° AOI for a dichroic filter, and (c) 45° AOI for a high-reflectivity mirror.

Whenever non-normal incident light hits an interface between two different media, such as air and glass, Snell’s law shows that the angle of incident light will change as the light passes into the second medium (Figure 2). The degree of change is dependent on the respective indices of refraction: (more…)
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Cone Half Angle (CHA)

 

CHA and F-Number

Cone half angle (CHA) describes the extent to which an incident beam is converging or diverging. It is defined as the angle between the AOI of the incident beam and the most oblique marginal ray (Figures 1a-1c). Therefore, a 0˚ CHA is synonymous with collimated light, and larger cone half angles designate a pronounced convergent or divergent beam.
 
dichroic filters reflect specific wavelength ranges while transmitting others.

Figures 1a-1c: Diagrams showing uncollimated light and cone half angle for (a) an optical filter at 0° AOI (b) a dichroic filter at 45° AOI, and (c) a high-reflectivity mirror at 45° AOI.

(more…)
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Spectral Features

 

Cut-On and Cut-Off Wavelength

Cut-on wavelength describes an optical filter edge transition where transmission increases sharply over an increasing wavelength range, such as seen with a longpass filter. Conversely, cut-off wavelength describes an edge transition that decreases over a wavelength range, as seen with a shortpass filter. They are defined as the point on each respective edge where transmission reaches 50% of the peak (Figure 1), and are also known as 50% edge points and half-power wavelengths.
Cut-on and cut-off wavelengths, center wavelength (CWL), and full-width at half-maximum (FWHM) for a bandpass filter.

Figure 1: Cut-on and cut-off wavelengths, center wavelength (CWL), and full-width at half-maximum (FWHM) for a bandpass filter.

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Surface Flatness and Wavefront Error

 

Surface Flatness Interferograms

Surface flatness describes the deviation between the surface of an optical component and a perfectly flat reference plano surface. Optical filter surface flatness is measured using an interferometer (typically a laser Fizeau interferometer) that represents this deviation as a pattern of light and dark bands known as interference fringes. Interference fringes are a visual representation of the destructive interference that results from the difference in phase between light reflected off the optical filter and the reference flat. Once the interferogram is obtained, post-processing software can be used to create a 3D model of the surface. (more…)
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Temperature Dependence

  Interference filter spectra are temperature dependent. Extreme temperatures result in the expansion or contraction of the thin-film layers, resulting in a red shift with increasing temperature and a blue shift with decreasing temperature. This shift can be dramatic unless the filter has been specified and designed to operate in harsh environments, and is an especially important consideration for ultra-narrowband interference filters. (more…)
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Surface Quality

  Surface quality specifications refer to the type and amount of allowable imperfections on each of the coated or uncoated surfaces of an optical component. Although some surface imperfections are purely cosmetic, many can introduce unwanted scattering or make the optical filter more susceptible to laser induced damage, resulting in decreased system performance. (more…)
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Mechanical Dimensions

 

Clear Aperture (CA)

Clear aperture (CA) is defined as the dimensional area of an optical component over which the specifications must be met (Figure 1). It is usually specified in terms of diameter for round parts or length and width for square or rectangular parts.
Diagram showing wedge angle and parallelism.

Figure 1: Diagram showing the clear aperture (CA) of an optical filter.

(more…)
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