Optical FlatsPRECISION OPTICAL FLATSAn optical flat is a precisely polished flat surface, used as a reference against which the flatness of an unknown surface may be compared. Edmund Optics offers both single surface and dual surface optical flats in either Zerodur or Fused Silica. he accuracy of an optical flat is measured in fractions of a reference wa!elength, "#$.%nm. A &'$( wa!e flat will ha!e a ma)imum peak to !alley de!iation of "#$.%'$( or #&."*nm. +e offer fi!e different le!els of accuracy for our single surface flats, &'* wa!e, &'&( wa!e, &'$( wa!e, &'"( wa!e and &'&((wa!e.For our dual surface flats, &'*, &'&( and &'$( accuracies are a!ailable.WHAT AN OPTICAL FLAT SHOWS+hen an optical flat-s polished surface is placed in contact with a surface to be tested, dark and light bands will be formed when !iewed with monochromatic light. hese bands are known as interference fringes and their shape gi!es a !isual representation of the flatness of the surface being tested. he surface accuracy is indicated by the amount of cur!e and spacing between the interference fringes. Straight, parallel, and e!enly spaced interference fringes indicate that the work surface flatness is e.ual to or higher than that of the reference surface. APPLICATIONS/easurement of the surface flatness of polished surfaces can be determined !isually by comparing the !ariations between a work surface and the surface of an optical flat. Optical flats are !ersatile optical components used in many applications, such as, inspection of gauge blocks for wear and accuracy, as well as the testing of !arious components including windows, prisms, filters, mirrors, etc. hey can also be used as e)tremely flat optical windows for demanding interferometry re.uirements. HOW AN OPTICAL FLAT WORKSAn optical flat utili0es the property of interference to e)hibit the flatness on a desired surface. +hen an optical flat, also known as a test plate, and a work surface are placed in contact, an air wedge is formed. Areas between the flat and the work surface that are not in contact form this airwedge. he change in thickness of the air wedge will dictate the shape and orientation of the interference bands. he amount of cur!ature that is shown by the interference bands can be used to determine the flatness of the surface. 1f the air wedge is too large, then many closely spaced lines can appear, making it difficult to analy0e the pattern formed. Simply applying pressure to the top of the optical flat alle!iates the problem. he determination of the flatness of any particular region of a surface is done by making two parallel imaginary lines2 one between the ends of any one fringe, and the other at the top of that same fringe. he number of fringes located between the lines can be used to determine the flatness. /onochromatic light is used to create sharp contrast for !iewing and in order to specify the flatness as a function of a single wa!elength. WHICH ACCURACY SHOULD BE USED - 1/4 WAE! 1/1" WAE! 1/#" WAE$his is a commonly asked .uestion and the answer is dependent on what is being tested. 1f the surface that is being tested is flatter than &'* wa!e, then a more precise flat will be re.uired to show a change in the interference pattern. 1n this case, a &'* wa!e flat would e)hibit straight parallel lines, but &'&( wa!e or &'$( wa!e flats would show enough cur!ature in the fringes to measure the surface accurately. WHAT %ATERIALS SHOULD BE USED - FUSED SILICA OR &ERODUR'$F(s)* Silica+ +e use a clear optical fused silica, which has a !ery low thermal e)pansion of (.33) &(4" per 56. 7eing highly durable and ha!ing good resistance to abrasion makes fused silica a good choice for applications that are high in wear and tear. Full mechanical, thermal, electrical, and chemical specifications are a!ailable. &),-*(,'+ 8ellow tinted Zerodur is a clear glass ceramic de!eloped by Schott 9esearch :abs. Zerodur e)hibits an e)tremely low thermal e)pansion of ;(.&( ) &( 4" per 56. 1n applications where temperature fluctuation is a concern, Zerodur offers a thermal stability that is unmatched. Full mechanical, thermal, electrical, and chemical specifications are a!ailable.OPTICAL FLAT CERTIFICATIONhe primary surface of all Edmund Optics optical flats is precision ground and polished to the stated accuracy and is tested and certified on our Zygo = 1nterferometer. he secondary surface of our single surface flats is pitch polished to window .uality only for !iewing the interference pattern. Each flat comes with a certificate of calibration, an instruction booklet, and its own storage case for permanent protection. I.-H-(s) I.t),/),-0)t,ic T)sti.1Each optical flat and plano precision mirror is tested for flatness error using our Zygo = 1nterferometer. +ith the aid of the interferometer and other precision testing e.uipment, EdmundOptics is able to pro!ide and ensure the highest .uality optics.RECALIBRATION=lease note that o!er time and with repeated use, optical flats can lose their degree of precision. Our Optical :ab can recalibrate and recertify our flats for a fee. For full details on our optical flatrecertification, please contact our Sales ?epartment.1nterested in learning e!en more about optical flats@ ?ownload our Optical Flat /anual.