Ensuring Optical Surface Accuracy: Key Techniques and Technologies

Optical surface accuracy is crucial for achieving the desired performance of optical components, marking the difference between the intended and actual shapes of surfaces.

This parameter, commonly quantified in terms of fringes or waves corresponding to the laser wavelength used in interferometry, is vital in preventing additional wavefront distortions. These distortions can lead to aberrations and compromise the efficacy of the system.

Measurement Techniques

Optical surface accuracy is measured using various methodologies, including different techniques such as test plates, laser interferometers, contact profilometers, laser interferometers integrated with computer-generated holograms (CGHs), and coordinate measuring instruments.

Traditionally, the test plate method predated interferometry, which involved placing a transparent plate next to a polished surface to assess its flatness. Using monochromatic light, interference fringes appear, and accuracy is determined by measuring the fringe count and irregularities.

The number of rings represents the difference in radius between the two surfaces, known as power, and the spacing between identically colored fringes represents a height deviation of half a wavelength of the light used, which indicates irregularities.

Computer-Generated Holograms (CGHs)

Computer-generated holograms (CGHs) act as null lenses, enhancing interferometric testing of intricate surfaces like aspheric and freeform shapes. CGHs are often combined with laser interferometers and serve an important role in monitoring the surface accuracy of aspheric lenses during the polishing process.

Typical CGH Test Configuration.

Typical CGH Test Configuration. Image Credit: Shanghai Optics

Contact Profilometry

Contact profilometry is a popular and economical method that includes measuring the sag values of the test surface (while a mechanical stylus traverses the element) and then comparing them to the nominal surface shape to determine accuracy.

Laser Interferometers

Laser interferometers use complex algorithms to precisely determine optical surface accuracy by splitting a light beam into two paths of unequal length, allowing for their subsequent interference.

Upon recombination, the resultant intensity modulation correlates with the amplitude and phase of the colliding beams, resulting in a pattern of light and dark bands known as interference fringes. These fringes aid in the detection of power errors and irregularities over the optical surface under consideration.

Zygo 6? Verifire XP Interferometer.

Zygo 6″ Verifire XP Interferometer. Image Credit: Shanghai Optics

Coordinate measuring tools reveal the topography of optical surfaces by point-wise scanning and detection. Surface accuracy is assessed using modern data analysis software by comparing the obtained surface data to the nominal surface profile.

This information has been sourced, reviewed and adapted from materials provided by Shanghai Optics.

For more information on this source, please visit Shanghai Optics.

Citations

Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Shanghai Optics. (2024, June 24). Ensuring Optical Surface Accuracy: Key Techniques and Technologies. AZoOptics. Retrieved on July 15, 2024 from https://www.azooptics.com/Article.aspx?ArticleID=2616.

  • MLA

    Shanghai Optics. "Ensuring Optical Surface Accuracy: Key Techniques and Technologies". AZoOptics. 15 July 2024. <https://www.azooptics.com/Article.aspx?ArticleID=2616>.

  • Chicago

    Shanghai Optics. "Ensuring Optical Surface Accuracy: Key Techniques and Technologies". AZoOptics. https://www.azooptics.com/Article.aspx?ArticleID=2616. (accessed July 15, 2024).

  • Harvard

    Shanghai Optics. 2024. Ensuring Optical Surface Accuracy: Key Techniques and Technologies. AZoOptics, viewed 15 July 2024, https://www.azooptics.com/Article.aspx?ArticleID=2616.

Ask A Question

Do you have a question you'd like to ask regarding this article?

Leave your feedback
Your comment type
Submit

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.