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October 22, 2020 Optical Surface Radius of Curvature

Optical surface radius is a primary control parameter. It must be measured to confirm the optical element meets specification. Spectrally Controlled Interferometry promises a faster and more accurate method to measure surface radius. Multiple methods are presently used to measure radius. Test plates: A test plate has a pre-measured radius to which the test surface… read more »

October 20, 2020 Measuring Material Homogeneity with SCI

Material Homogeneity Optical index homogeneity is an important material parameter influencing lens performance. Laser interferometers have painstakingly measured this parameter which requires four separate measurements.  Laser interferometers have either required the use of contact plates with oft times poisonous index matching fluids. Or polishing a wedge into the test part to isolate the front from… read more »

October 9, 2019 Measuring Optical Domes: Faster and More Accurate with SCI

Optical domes are an important component in environmentally challenging imaging environments. Accurate metrology is required to achieve good imaging system performance.  Applications of Dome Optics Dome optics are the last component in a growing number of imaging and guidance applications. Domes protect the imaging optics from the surrounding environment without degrading optical performance. Therefore the… read more »

July 17, 2019 Measuring Prisms: Multiple Wavefront Channels In One Setup

Prism Stacks Produce Multiple Wavefronts Prism stacks are difficult or even impossible to measure with a laser interferometer, yet are easy to measure with Spectrally Controlled Interferometry (SCI).  Examples of prism stacks for projector imaging systems, displacement measuring, monolithic or assembled component interferometers, and RGB combiners.  Laser Interferometer Back Reflections A laser light source interferometers… read more »

June 18, 2019 Measuring Prisms: S1, S2, Wavefront + Relative Angle

Prisms are complex optical components. Transmitted wavefront performance is controlled by multiple surfaces, the angle between them, and the material homogeneity.  SCI makes interferometric prism measurement fast, easy and more accurate than conventional methods. Conventional Approach: Multiple Instruments, Delayed Shipments Prisms are typically measured on multiple instruments and in several setups. A goniometer measures angles,… read more »

April 11, 2019 Total Thickness Variation (TTV)

Thickness variation (TTV), and often wedge, is specified in optical windows and substrates. There are two methods for measuring TTV: Front-to-Back and Direct. Front-to-Back TTV can only be calculated if the front and back measurements are performed without translating or moving the part. While this restriction poses challenges for traditional laser Fizeau systems, this is… read more »

April 2, 2019 Measuring Plane-Parallel Substrates

Plane-Parallel Substrates What could be easier than measuring a plate of glass? Actually, almost all interferometric measurements are easier! Measuring a plate of glass, or a substrate, is one of the most difficult interferometric measurements. In a laser interferometer, the two surfaces of the plate simultaneously interfere with the reference surface and each other creating… read more »

March 26, 2019 Spectrally Controlled Interferometry Photonics Spectra Article

Äpre Instruments has teamed with Zack Hobbs of Sydor Optics to bring an article describing SCI and some of its emerging uses. Read the article in the Photonics Spectra on-line journal. Please send us your comments and questions to inquire@apre-inst.com 

June 23, 2018 Failing Good Parts? Maybe the Problem is Retrace Error

Failing Good Parts? Maybe the Problem is Retrace Error Retrace error is rarely specified for an interferometer, often ignored and can cause good parts to fail. Knowing how to minimize, decreases scrap, saves time, and lowers manufacturing cost. Transmitted Wavefront Measurements Recently an ÄPRE upgrade customer using a 6X zoom interferometer noticed unexplained user-to-user variations…. read more »

June 14, 2018 Spectrally Controlled Interferometry – Wins Prestigious Award

ÄPRE’s Spectrally Controlled Interferometry was awarded one of Laser Focus World’s highest awards for innovation in photonics, a Gold-Level Honoree. We are proud to be recognized by this leading industry journal for the innovation that SCI brings to optical testing. Even more exciting is hearing from our customers how SCI saves time and money as… read more »

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