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Ventanas ópticas

September 1, 2020

Ventanas ópticas

 

An optical window is a transparent, optically flat substrate that is used to separate two different environments while still allowing light to pass through. They may be either parallel (used to minimize the distortion of a transmitted beam of light of a specific wavelength) or wedged (used to direct transmitted light at a specific angle and reduce back reflection) and come either uncoated or with an anti-reflective coating used to reduce reflectance and improve transmission.

Las ventanas ópticas están diseñadas para funcionar en todas las áreas del espectro UV-VIS-IR y, por lo tanto, están hechas de una variedad de sustratos. La elección del sustrato depende de múltiples factores, como la transmisión de materiales., índice de refracción, dureza, expansión térmica y resistencia química. Sherlan Optics focuses on optical windows made of glass substrates such as N-BK7®, sílice fundida, BOROFLOAT®33, B270 y material infrarrojo CaF2, dar, znse, Si así como una amplia gama de vidrios de alto índice.

Como otras ópticas planas, optical windows are used in many industries including aerospace, military and commercial avionics, scientific and medical instrumentation, academics and research, as well as industrial applications. Optical windows come in various sizes and shapes including round, square and rectangular and range in flatness from commercial grade to precision polished. Sherlan Optics offers a broad range of in-stock optical windows and provides free engineering consultation services and custom fabrication from prototype to production or anywhere in between.

 

Factors to consider when selecting an optical window.

There are many factors to consider when designing an optical window. Careful consideration of each of the factors below will determine how effectively an optical window will perform in a given application as well as the impact to cost and delivery.

 

Seleccione el material correcto: Dado que las ventanas ópticas pueden estar hechas de varios materiales, especificar el material correcto es esencial. Los factores a considerar incluyen la cantidad de transmisión requerida en un área particular del espectro., el índice de refracción, el número de Abbe, el coeficiente de expansión térmica, Dureza Knoop, y la densidad del material. Para obtener más información sobre cada uno de estos, click here.

 

Determine la forma y el tamaño: Como ocurre con los planos ópticos y los espejos, optical windows can be made into almost any shape to fit a specific application. sin embargo, if surface accuracy is critical, a round shape will yield a higher degree of surface flatness than a square or rectangular shape. Aspect ratio also plays a role. The closer the aspect ratio is to 6:1 (size to thickness) the easier it will be to achieve a higher degree of surface flatness and the less the part may flex or bend, causing a change in figure. sin embargo, if a 6:1 aspect ratio does not meet your requirements, Sherlan Optics manufactures optical windows with non-standard aspect ratios.

 

Establish the Correct Accuracy for your Application: Optical windows come in a wide range of accuracies from commercial grade to precision polished. Optical windows used as view ports, for example, do not require a high degree of flatness as they are typically viewed using with the naked eye. sin embargo, precision applications that require an optical window to pass light through with little to no distortion require both surfaces to be precision polished to a high degree of flatness. Sherlan Optics fabricates optical windows with surface flatnesses of λ/4, λ/10 and λ/20 measured peak to valley at 632.8nm and can maintain parallelism ≤ 2 segundos de arco.

 

Refine los Tolerances: As with all optics, optical windows may require tight tolerances. The tighter the tolerance in diameter, length and width or thickness, the more Sherlan techniques and longer manufacturing times are required to produce the window which both dictate an increase in price. The most difficult tolerance to hold is thickness. Tighter thickness tolerances require special blocking techniques and have the potential to increase the scrap rate as any scratch may be unable to be removed to stay within tolerance. Properly defining your tolerances can save you manufacturing time and reduce your costs.

 

Specify the Correct Scratch and Dig: Scratch and dig specifications are typically expressed using MIL-PRF-13830B and are used to classify any cosmetic flaws in an optical surface or coating. A scratch is defined as any marking or tearing of the surface; a dig is defined as any rough spot or pit on the surface of an optic. Scratch and dig is expressed as two numbers separated by dash. The first number indicates the allowable size and width of a scratch and the second number indicates the allowable size and number of pits over a defined area of an optic.

As with accuracy, imperfections in the surface of an optical window can distort the light traveling through the window. Commercial grade windows typically have a high scratch and dig number such as 80-50 whereas precision grade windows have a lower scratch and dig number such as 40-20. Extremely high precision laser optics require a very low scratch and dig such as 10-5. Understanding your application well enough to choose the correct scratch and dig number can save you time and money.

 

Define the Wedge: Optical windows can be specified by how much wedge, or variation in thickness, is allowed over the surface of a part. It is defined in arc minutes (an angular measurement that is 1/60th of a degree) or arc seconds where 60 segundos de arco es igual a 1 minuto de arco.

Wedge can be induced into an optical window to reduce the interference of reflections between the front and back surfaces or to separate and direct transmitted light at a particular angle.

Por el contrario, parallel optical windows are manufactured using special blocking techniques to ensure very little variation in thickness between the front and back of the window across its entire surface. This ensures that a beam of light traveling through the window is straight and not distorted due to angular deviation of the optical surfaces. A high degree of parallelism makes an optical window more expensive due to the amount of labor and scrap rate in the fabrication process.

 

Elija el revestimiento: Optical windows may come either uncoated or with an anti-reflective coating. Los recubrimientos antirreflejos estándar incluyen MgF2 o BBAR (antirreflejos de banda ancha) revestimiento para el espectro visible. Anti-reflective coatings help to improve transmission and eliminate ghost images.

Si el requisito es tener una reflectividad baja en una sola longitud de onda, Los abrigos en V son la mejor opción. V-coats can be designed to provide low reflectivity at several specific wavelengths as opposed to higher reflectivity over a broad wavelength range.

Las ventanas ópticas para usar con láseres requieren revestimientos duraderos (revestimientos dieléctricos) diseñado para usar en longitudes de onda específicas. Al elegir un revestimiento antirreflectante, es importante especificar el porcentaje de reflectividad que necesita en una longitud de onda específica.(s) así como el AOI (Ángulo de incidencia) usarás la ventana óptica. Sherlan Optics can provide MgF2, BBar, Abrigos en V, Recubrimientos dieléctricos y recubrimientos personalizados diseñados para satisfacer sus requisitos específicos..

 

Tomando la decisión final.

A good understanding of your application will help to choose the correct optical window. Determining the best optical window for your project will require you to:

Considere el entorno en el que se utilizará la ventana óptica. Los factores ambientales pueden influir en el tipo de material, selección de cosméticos y recubrimientos que mejor se adapte a su aplicación.

 

Defina sus requisitos y expectativas para especificaciones críticas como la precisión., tolerancias mecánicas, rayar y cavar y acuñar.

 

Seleccione el recubrimiento óptico correcto (si es requerido) para maximizar el rendimiento de su ventana. Identifique en qué ángulo de incidencia utilizará su ventana óptica, así como qué porcentaje de reflectividad necesita en una longitud de onda específica(s). Si usa la ventana óptica con un láser, proporcionar información sobre la potencia de su láser, el tamaño del punto y si el láser será pulsado o continuo durante un período de tiempo específico.

 

Definir cuidadosamente sus requisitos puede ahorrar tiempo de fabricación, lo que se traduce en costos reducidos. Si tiene alguna pregunta o necesita ayuda para perfeccionar sus requisitos, Sherlan Optics offers free engineering services.

 

 

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