Ensuring Precision with Optical Parallelism: A Deep Dive

Optical parallelism is a critical parameter in the design and application of optical components, particularly optical windows or parallel window. At Shape Optics, we specialize in producing high-precision optical components tailored to meet the stringent requirements of various industries, including aerospace, medical, and industrial inspection.

What is Optical Parallelism?

Optical parallelism refers to the alignment of the two surfaces of an optical window. For a window to be effective in its application, its surfaces must be parallel to prevent light distortion and ensure accurate transmission. This is particularly important in high-precision applications where even minor deviations can lead to significant performance issues.

Defining and Measuring Optical Parallelism

Optical parallelism is defined by the degree to which the surfaces of an optical window are parallel. This is typically measured in arc minutes or arc seconds. At Shape Optics, we employ state-of-the-art interferometry techniques to measure and ensure the parallelism of our optical windows. Interferometry allows us to detect even the slightest deviations by analyzing the interference patterns produced when light waves reflect off the surfaces of the window.

Applications of Parallel Windows

Our optical parallel windows are used across various industries:

  • Optical Instruments: Protecting sensitive components while maintaining the integrity of the light path.
  • Laser Systems: Ensuring laser beams pass through without distortion, critical for both medical and industrial applications.
  • Aerospace: Providing clear visibility in aircraft and spacecraft windows, designed to withstand extreme environmental conditions.
  • Medical Devices: Facilitating precise light transmission in imaging systems.
  • Industrial Inspection: Enabling accurate light passage in quality control machines.

Standards and Specifications

At Shape Optics, we adhere to stringent standards to ensure the highest quality of our optical components. Our typical specifications include:

  • Parallelism: Measured in arc minutes or arc seconds, with high precision applications requiring parallelism within a few arc seconds.
  • Surface Quality: Defined by scratch-dig standards such as 60-40 or 40-20.
  • Flatness: Ensured to be within fractions of a wavelength of light (e.g., λ/10).

Below is a table showcasing the typical specifications that can be reached when manufacturing optical windows:

SpecificationUsualSpecific
SizeDiameter up to 500mmDiameter from 0.5mm up to 1.5m
TransmissionVisible rangeUV to far infrared
Scratch & Dig20-1010-5
Surface Irregularityλ/10λ/20; λ/100 may be achieved with IBF (Ion Beam Figuring)
Surface Roughness5 to 15 Å RMSDown to 1 Å RMS (superpolishing)
Dimensional Tolerance+/- 0.1mm+/- 0.05mm
Thickness Tolerance+/- 0.05mm+/- 0.01mm
Parallelism≤ 10 arcsec≤ 1 arcsec
Clear Aperture85-90%95%
Damage Threshold5J/cm²20J/cm²
CoatingARCustom filtering, mirror, masks, ITO coatings

Size and Transmission: Our optical windows are available in a wide range of sizes, from as small as 0.5mm in diameter to as large as 1.5m. They are designed to transmit light across a broad spectrum, from UV to far infrared, making them suitable for a variety of applications.

Surface Quality: We achieve superior surface quality with scratch and dig specifications as high as 10-5. Our advanced polishing techniques, including Ion Beam Figuring (IBF), allow us to reach surface irregularity levels up to λ/100, ensuring exceptional optical performance.

Surface Roughness and Tolerances: Our superpolishing capabilities reduce surface roughness to as low as 1 Å RMS. We maintain strict dimensional and thickness tolerances, with specific tolerances as tight as +/- 0.05mm and +/- 0.01mm, respectively.

Parallelism and Clear Aperture: We offer unparalleled parallelism in our optical windows, with specifications up to ≤ 1 arcsec. Our windows also feature clear apertures of up to 95%, ensuring maximum usable optical area.

Damage Threshold and Coatings: Our optical windows can withstand high energy levels, with damage thresholds up to 20J/cm². We provide a variety of custom coatings, including anti-reflective (AR), custom filtering, mirrors, masks, and ITO coatings, tailored to meet specific application requirements.

Optical parallelism is essential for the performance of optical components in various high-precision applications. At Shape Optics, we are committed to providing the highest quality optical windows with precise parallelism, ensuring reliable performance and customer satisfaction. For more information on our products and capabilities, visit our website at Shape Optics or contact us directly.


Shape Optics is dedicated to advancing the field of optical engineering, and we look forward to serving your optical component needs with unparalleled precision and expertise.

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